Research progress on high-temperature properties of carbon fiber reinforced polymer composites for cables

Abstract

Carbon fiber reinforced polymer composites (CFRP) cable has advantages of lightweight, high strength, and excellent durability, providing a new materials for cables and bringing out potential breakthrough in spanning capacity of structures. At present, CFRP cable has already been applied in some engineering bridges. The fire resistance performance of CFRP cable is critical for ensuring structure safety when suffering accidental fire disaster, and clarifying mechanical performance deterioration and failure mechanism of CFRP cable at elevated temperature is fundamental for research of its fire resistance. This paper summarizes current research progress on high-temperature properties of CFRP cable from two levels, including epoxy resin matrix and CFRP composites. Firstly, at resin matrix level, mechanical properties of epoxy resin and its degradation at elevated temperatures are reviewed and analysed, and potential ways to improve high-temperature performance of epoxy resin are suggested. Secondly, at CFRP composites level, high-temperature properties test methods and mechanical performance of CFRP composites in longitudinal direction and transverse direction at elevated temperatures are summarized and discussed. In addition, research shortage of high-temperature properties of CFRP cable is summarized, and corresponding further research is recommended.

Keywords

carbon fiber reinforced polymer composite cable epoxy resin high-temperature properties state-of-the-art review

Introduction

Currently, large-span structures with cables as major bearing element are becoming a construction boom. Carbon fiber reinforced polymer composites (CFRP) has advantages of light weight, high strength, corrosion resistance, fatigue resistance, and low-temperature deformation in material performance (Kong et al., 2023). Compared with traditional steel cables, CFRP cables can significantly reduce self-weight effect and bring out potential breakthrough in spanning capacity of structures (Liu et al., 2015).

CFRP cables generally include three categories, naming parallel rod cable, parallel plate cable, and stranded cable, which have different anchorage systems (Duo et al., 2022; Xie et al., 2022). A series of fundamental research work has been carried out regarding basic mechanical properties of CFRP composites for cables (Yang et al., 2020), as well as long-term service performance of CFRP cables (Wang et al., 2022). Besides, bridges are also potential to suffer risk of fire caused by traffic accidents, and correspondingly CFRP cable may expose to fire and suffer high temperature. At elevated temperature, the resin matrix of CFRP composites may exhibit softening, causing significant degradation of mechanical properties of CFRP cable. Especially, the softening will be more obvious after temperature exceeds glass transition temperature of resin matrix. It should be specially pointed out that transverse mechanical properties of unidirectional CFRP may exhibit more serious degradation at elevated temperature, and performance degradation in transverse direction of CFRP may be fatal because it can seriously influence anchoring performance since CFRP cable in anchorage system is subjected to significant transverse compression due to anchoring forces, which may even cause complete anchorage failure and result in collapse of cables or structures. Therefore, high-temperature properties of CFRP composites for cables need attention.

High-temperature properties of CFRP composites and its cable have been investigated in previous research. On level of basic materials for CFRP composites, including carbon fiber and epoxy resin matrix, previous research has investigated thermal properties of carbon fiber (Pradere et al., 2009; Sauder et al., 2002), thermo-mechanical performance of epoxy resin as well as its influencing factors and improving way (Moussa et al., 2012), and mechanical properties as well as constitutive model of epoxy resin at elevated temperature (Jahani et al., 2020). On level of CFRP composites for cables, previous research has investigated its mechanical properties at elevated temperature (Nguyen et al., 2019; Wang et al., 2011; Xu et al., 2020; Zhou et al., 2019; Zhuge et al., 2022), creep behaviour at elevated temperature (Jiang et al., 2022), strength degradation law after suffering elevated temperature (Zhou et al., 2022). In addition, influencing issues on failure mode of FRP composites have also been explored, including high-temperature test conditions (Nguyen et al., 2018), specimen dimensions and specimen processing technology (Rosa et al., 2022). At present, most of existing research mainly focuses on longitudinal mechanical properties of the CFRP composites at elevated temperature. However, it is also worth paying special attention to mechanical properties in the transverse direction of unidirectional CFRP composites for cables at elevated temperature, while CFPR composites inside the cable anchorage is subjected to significant compression and longitudinal shear force due to constraint force by anchorage (Wang et al., 2018).

Generally, unidirectional pultruded CFRP composites are most widely used for cables due to its high fiber volume content, which can achieve higher tensile strength and modulus and has economic advantage. In addition, epoxy resin is most widely used due to its comprehensive mechanical performance. Therefore, to further summarize current research state and shortages of the high-temperature properties of CFRP composites for cables, this paper summarizes and analyses existing work from two levels, including epoxy resin matrix and CFRP composites for cables. Review details include performance of resin matrix for CFRP composites, as well as mechanical properties and failure modes of unidirectional CFRP composites for cables in longitudinal direction and transverse direction. Eventually, recommendations for further research on high-temperature properties of CFRP composites for cables are proposed to address the shortage of the existing research.

High-temperature properties of epoxy resin

Typical CFRP composites for cables in engineering structures are comprised of unidirectional carbon fibers and epoxy resin matrix. Thus, clarifying the evolution of mechanical properties of epoxy resin matrix at elevated temperatures is the basis for investigating high-temperature properties of CFRP composites and cables. The influence of temperature on properties of epoxy resin includes two aspects. On one hand, the curing temperature influences the degree of crosslinking of epoxy resin, and thereby affects glass transition temperature and mechanical properties of resin matrix. On the other hand, the mechanical properties of cured resin matrix may significantly degrade at elevate temperature.

In this section, the main factors affecting mechanical properties and the effective ways for improving high-temperature properties of epoxy resin are summarized. Meanwhile, the main failure mode, failure mechanisms, and strength evolutions of epoxy resin at elevated temperatures are discussed as well. Correspondingly, specific recommendations are proposed for further research.

Curing and glass transition temperature of epoxy resin

The curing of epoxy resins is generally accompanied by the addition of curing agent and heating. In cuing process, cross-linking occurs between the molecules of epoxy resin system to form a stable molecules structure, and the epoxy resin will undergo three stages of transformation, including gel, three-dimensional grid, and fully cured (Li et al., 2004). The curing degree of epoxy resin can be used to evaluate whether epoxy resin is fully cured. The higher curing degree of epoxy resin, the more fully cross-linking of molecules, the more stable molecular networks, and the better high-temperatures properties. The properties of epoxy resin are dependent on its transition at elevated temperatures. With increasing of temperature, the performance of cured epoxy resin will exhibit two significant degradations, as shown in Figure 1. The first degradation is caused by the transition of epoxy resin from glassy state to rubbery state. In this process, weak bonds between molecular chains break (Mahieux and Reifsnider, 2001), and mobility of molecular chains increases. This process is also called glass transition, and the corresponding temperature is glass transition temperature T_g. With further increasing of temperature, primary bonds of molecular will break (Mahieux and Reifsnider, 2001), and the mobility of molecular chains dramatically increases, accompanied by large deformation of resin. In this process, the resin decomposes with gas produced and large amount of heat released. This process is also called resin decomposition, and the corresponding temperature is resin decomposition temperature T_d.

Figure 1.

The response of resin properties with elevating temperature (Moussa et al., 2012).

It is important to clarify that T_g of epoxy resins is an interval range, in which the mobility of molecular chains increases and the mechanical properties of resin degrade (Carbas et al., 2014). There are a variety of measurement methods of T_g, and therefore T_g measured by different methods is not entirely consistent (Startsev et al., 2020). Generally, dynamic mechanical analysis (DMA) is most widely used for investigating mechanical properties of resins at elevated temperatures (Stark, 2013). The measurement methods of T_g of using DMA include three types, naming the storage modulus method, the loss modulus method, and the loss factor method. T_g measured by the three methods increases gradually (Li et al., 2020). According to the mechanical properties transformation mechanism of epoxy resin at elevated temperatures, it is clear that the molecular chains of resin will gradually break at T_g. Correspondingly, the epoxy resin with higher curing degree has higher cross-linking of molecules and more stable molecular network, thus providing better restriction of molecular chains mobility. That is to say, the molecules unchaining needs higher temperature, resulting in better high-temperature properties of resin.

In summary, epoxy resin with higher curing degree and molecular cross-linking has higher T_g (Wang et al., 2017) as well as better high-temperature properties (Miao et al., 2020). For specific epoxy resin, the molecular cross-linking fully accomplishes when resin matrix is fully cured, and thus T_g reaches its ultimate capacity, namely completely cured glass transition temperature T_g∞ (Yang et al., 2021), wherein the resin performance reaches best. Therefore, obtaining higher curing degree of epoxy resins, or selecting specific epoxy resins with higher molecular cross-linking, are applicable way to achieve better high-temperature properties of CFRP composites for cables in engineering applications.

Curing degree improvement of epoxy resin

The curing degree of epoxy resin can be measured by Differential Scanning Calorimetry (DSC), which is obtained by measuring reaction heat of cured resin and uncured resin separately and calculating the ratio of them. Furthermore, secondary heating can be applied for resins not fully cured to achieve post-curing, thus inducing higher molecular cross-linking (Moussa et al., 2012) to achieve better performance of epoxy resin. It should be noted that the curing degree of epoxy resin is significantly affected by curing conditions (Wang et al., 2017).

To explore the relationship between curing degree and curing conditions (temperature, time) for initially cured epoxy resin under secondary heating, Moussa et al. (2012) conducted post-cured heating experiments on initially cured epoxy resin (at room temperature 20°C for 2 weeks, with initial curing degree of 94.3%), and obtained the relationship between secondary heating temperature, heating time and curing degree, as shown by the line in Figure 2. It should be noted that the secondary heating temperatures (60°C, 100°C, 150°C) were all greater than the initial-cured T_g (45.6°C). The results showed that secondary heating temperature and time had coupling effect on curing degree, meaning that resin with higher heat absorption obtained higher curing degree and reached fully cure faster.

Figure 2.

Curing degree and T_g versus post-curing temperature (Moussa et al., 2012).

Besides, Moussa et al. (2012) also found that T_g of resins all increased after experiencing secondary heating, as shown by the scatter in Figure 2, which was mainly due to two reasons. On one hand, the secondary heating will supply more heat to initially cured resin matrix, thus promoting the degree of molecules cross-linking in resin matrix and increasing T_g. On the other hand, the secondary heating reduces inner stress in resin caused by cooling and shrinkage during initial curing process (Nakamura et al., 1990), which is beneficial for stabilization of the molecular network in resin matrix and improved T_g.

Nevertheless, in Section “Curing and glass transition temperature of epoxy resin”, the performance transformation law of epoxy resin at elevated temperatures also indicates that the molecules will be unchained when temperature exceeds T_g, thus resulting in decrease of T_g. However, in the above tests, the decrease of T_g did not occur. The reason for this phenomenon is not identical, depending on the final curing degree and the molecule unchaining degree. Firstly, for incompletely cured resins, the occurrence of molecule unchaining not influence improvement of curing degree of resin matrix by secondary heating, and thus T_g will increase. Secondly, for fully cured resins, it is necessary to determine whether the molecular unchaining occurs, which may be determined by the secondary heating temperature as well as heating time. If the molecular unchaining occurs but not significantly, the degree of molecular cross-linking will be slight, and thus the decrease of T_g will be slight. Contrarily, if the secondary heating temperature or time is too high, molecular unchaining may be significant and T_g may be decreased. However, molecular chaining may also recover during the cooling process, making the final decrease of T_g also be slight. Till now, there is still not incontestable conclusion.

Based on the above analysis, it can be concluded that there may be an ideal value of heat input to get best molecular cross-linking and T_g of epoxy resin, which is determined by the heating temperature and time. Therefore, it is necessary to further investigate the relationship between curing degree and heating temperature and time, as well as their influences on mechanical performance of cured epoxy resin. To get higher curing degree and better performance of epoxy resin matrix, post-curing by secondary heating is a selection. Besides, direct high-temperature curing with proper time is also a selection. Yet, the two methods may have different influence on the performance of resin, which also deserve further investigation.

Curing conditions and properties of epoxy resin

Relevant investigations have been conducted to address the relationship between curing process and properties of resin. Jahani et al. (2020) investigated the effect of different curing methods and temperatures on T_g of epoxy resin. Two curing methods were adopted, and the curing temperatures were selected as 20°C, 50°C, and 70°C, respectively. The experimental specimens were divided into two groups comparatively. One group was cured directly at elevated temperature, corresponding to the black line in Figure 3(a). The other group was initially cured at room temperature, with secondary heating at elevated temperature, corresponding to the red line in Figure 3(a). While T_g was achieved as 54.9°C by just curing at room temperature, the results indicated that two curing methods had similar influences on T_g. Direct curing at 50°C or secondary heating at 50° after initial curing at room temperature both significantly improved T_g, which could theoretically be raised to T_g∞. However, when the temperature was raised to 70°C, T_g exhibited significant decrease after curing process. This phenomenon has also been proven by previous research (Carbas et al., 2014; Lahouar et al., 2017), which can be explained as follows. Curing temperature lower than T_g∞ of epoxy resin can effectively promote the molecules cross-linking and improve curing degree, and gradually increase T _g. Curing temperature at T_g∞ can accelerate the curing process, and T _g can be improved close to T_g∞. Curing temperature higher than T_g∞ may cause unchaining of molecular chains, decreasing T _g and making it lower than T_g∞, as well as degrading the properties of resin, such as modulus and strength. Therefore, T_g∞ of the epoxy resin used in the experiments by Jahani et al. (2020) in Figure 3(a) is theoretically between 50°C ∼ 70°C, and when the curing temperature rises to 70°C, significant molecular unchaining occurs and cannot recover just after the curing process (Moussa et al., 2012).

Figure 3.

The effect of curing temperature (Jahani et al., 2020). (a) Glass transition temperature versus different curing conditions; (b) tensile stress–strain relationship versus curing temperatures.

Combining the experimental results by Moussa et al. (2012) and Jahani et al. (2020), it can be found that during the cuing process at proper heating curing temperature, the molecules chaining of epoxy resin gradually develops until fully cured, when its glass transition temperature increases to T_g∞. Contrarily, molecular unchaining may occurs when temperature is higher than T_g∞. Therefore, according to the temperature differences that may induce molecular chaining or unchaining, the curing process of epoxy resin may exhibit the following status: (1) The curing temperature lower than T_g∞ can improve T_g regardless of curing time. (2) The curing temperature higher than T_g∞ may have different influence according to curing time and heat input limit. If the heat input or curing time is lower than the limit, the molecular chaining after curing will also be improved and thus T_g increases. Otherwise, if the heat input or curing time is higher than the limit, molecular chains of fully cured resin will be unchained, the molecular chaining will be decreased and thus T_g decreases.

From the above experimental results, the relationship of heat input, curing temperature, curing time, and their coupled effect on resin properties can also be obtained. In the study of Moussa et al. (2012), secondary heating at 150°C for 4 h obtained the highest T_g while 0.5 h obtained the lowest T_g. Since the secondary curing temperature of 150°C was much greater than T_g of resin matrix, it indicated that the short curing time may also induced more molecular chaining than unchaining, which might be due to that the heat input not exceed its limit. Besides, the molecular chaining might also recover somewhat at room temperature, and resulting in higher T_g with recovery time (Moussa et al., 2012). From the experimental results of Jahani et al. (2020), it was found that the curing temperature higher than T_g∞ for 4 h also obtained higher molecular chaining degree and higher T_g than initial state (Moussa et al., 2012), while for 1 day obtained higher molecular unchaining degree and lower T_g than initial state (Jahani et al., 2020). This phenomenon indicated that with longer curing time at much higher temperature than T_g∞, the molecular unchaining would become more obvious and gradually become dominant, which could not be recovered at room temperature. Therefore, with increasing curing time at temperature higher than T_g∞, the excessive heat input may be disadvantageous. However, it is difficult to accurately determine the limit of the heat input because the influence of curing temperature and time couples and the molecular mobility of resin is complex. Besides, it has also been validated that the secondary heating curing can get better T_g and higher mechanical properties than direct heating curing. While the molecular chaining is irreversible at room temperature (Michel and Ferrier, 2020), the T_g of epoxy resin by proper heating curing can remains, and is higher than that by curing at room temperature.

Previous research has also validated that the curing temperature can influence basic mechanical properties of epoxy resins (Carbas et al., 2014; Jahani et al., 2020; Lahouar et al., 2017) and the influence law is similar to that of T_g, with T_g∞ as the demarcation point. As can be seen from Figure 3(b), curing temperature lower than T_g∞ has slight influence on modulus and some influence on tensile strength, but cold temperature (−15°C) has relatively significant influence on modulus. Curing temperature higher than T_g∞ can significantly decrease modulus.

Mechanical properties of epoxy resin at elevated temperature

Except for T_g, the mechanical properties (such as tensile strength, shear strength, compressive strength, and elastic modulus) at elevated temperature as well as its evolution law with temperature is also critical. It has been validated that the mechanical properties degrade significantly at temperatures higher than T_g of epoxy resins (Bascom and Cottington, 1976; Plecnik et al., 1980), and some scholars have conducted deeper investigation on its law. Firmo et al. (2019) found that the resins exhibit significant viscoelasticity with increasing temperature close to T_g, and the shear modulus and strength exhibit significant decreasing trend. Jahani et al. (2020) also found similar law before temperature of T_g. Besides, it is also found that the performance degrading accelerates after temperature exceeding T_g (around 54.9°C). Compressive strength of epoxy resin at 60°C degraded to 55% of that at room temperature (Figure 4(a)), while tensile strength and modulus degraded seriously to 25% and 8% of that at room temperature respectively (Figure 4(b)). Meanwhile, the tensile stress-strain relationship exhibits increasing non-linear behavior with increasing temperature, especially after temperature exceeding T_g. Li et al. (2020) investigated the tensile stress-strain relationship of four types of epoxy resin at elevated temperature and summarized their evolution process into four stages, which is detail as follows. (1) At temperatures much lower than T_g, the mobility of molecular chain is difficult, the stress–strain relationship remains almost linear and fractures at the ultimate strength (Figure 4(b), 20°C). (2) With increasing of temperature, the mobility of molecular chain gradually increases, the stress-strain relationship exhibits nonlinearity and the tensile strength exhibits significant degradation (Figure 4(b), 40°C or 50°C). (3) At temperature close to T_g, the mobility of molecular chain increases remarkably, the tensile strength degrades more significantly, and the stress-strain relationship exhibits an obvious platform (Figure 4(b), black dashed line). (4) At temperature exceeding T_g, the molecular chaining is unchained with active mobility of molecular, the tensile strength degrades seriously, and stress-strain relationship exhibits significantly viscoelasticity (Figure 4(b), 60°C, 70°C, 85°C). For some types of epoxy resins, the third stage may be not obvious or not occur (Jahani et al., 2020; Li et al., 2020), but it is definite that the strength degrades seriously at temperature exceeding T_g.

Figure 4.

The effect of temperature on basic mechanical properties of resin (Jahani et al., 2020). (a) Compressive strength (b) tensile stress–strain relationship.

To obtain higher T_g and improve high-temperature properties of epoxy resins, researchers also explored to introduce new molecular structures in the epoxy resin or the curing agent (Liu et al., 2013), such as polyfunctionality, benzene ring, imide, liquid crystal structures, etc. For example, by means of chemical modification, the epoxy resin used in construction engineering can achieve T_g around 200°C and tensile strength of 50 to 60 MPa (Jiang et al., 2022), while in aerospace application, T_g over 250°C and tensile strength over 110 MPa has also been achieved (Chen et al., 2006). Such research mainly focuses on the high-temperature properties and basic mechanical strength improvement (Li et al., 2018; Wu et al., 2014; Ye et al., 2022), but the mechanical properties evolution of chemically modified epoxy resin at elevated temperature is rarely addressed. Banea et al. (2011) experimentally investigated the tensile stress-strain relationship of XN1224 epoxy resin (T_g 155°C) for aerospace application at temperatures of room temperature, 100°C, 125°C, and 150°C, respectively, and found that tensile strength at 100°C, 125°C, and 150°C degraded 33.8%, 68.4%, and 90.5% with comparison to that at room temperature. In addition, the stress-strain curve exhibited stage three (Figure 4(b)) at 125°C.

Therefore, it is definite that temperatures around T_g may significantly degrade mechanical properties. In addition, to determine the mechanical properties degradation point more accurately, it is recommended to estimate T_g of epoxy resin using the storage modulus method, corresponding to the temperature when the storage modulus decreased significantly. However, the experimental results of Li et al. (2021, 2023) also indicated that the storage modulus method to evaluate T_g may be not rigorous enough in special cases, for example, epoxy resin with two types of curing agent. In their experiments, two curing agents was mixing used by a certain ratio to obtain better high-temperature properties, and T_g of the new epoxy resin, naming AB, was measured to be 71.0°C using storage modulus method (Wu et al., 2014). In addition, T_g of the epoxy resin with single curing agent, naming A and B respectively, was measured to be 56.3°C and 92.9°C respectively. During the tensile test at elevated temperature, the stress-strain relationship began exhibiting stage three (Figure 4(b)) from 55°C to 70°C, and exhibited stage four (Figure 4(b)) at 80°C. According to this phenomenon, it can be concluded that the T_g and temperature-dependent mechanical properties is influenced by both two curing agents, whose molecular chaining may not be completely consistent. Therefore, the mechanical properties of resin AB will begin exhibiting significant degradation when temperature is close to lower T_g of resin A.

Thus, it can be further concluded that for chemically modified high-performance epoxy resin, if the molecular chaining after chemical modification is consistent, T_g can be estimated by storage modulus method and mechanical properties of resin begin exhibiting significant degradation around T_g. Contrarily, if the molecular chaining after chemical modification is not consistent, the initial degradation temperature may be determined by the one with lowest high-temperature properties. The collected literature regarding the degradation law of epoxy resin at elevated temperature is summarized in Table 1. As can be seen, the research into high-temperature properties of chemically modified epoxy resin is still insufficient. Further research is necessary for analysing the degradation mechanism at elevated temperature, and the form of molecular chains as well as influencing factors on its composition needs to be paid attention.

Table 1.

The glass transition temperature of epoxy resin and the critical temperature of properties degradation.

The type of resin	Temperature of stage 3 or stage 4/°C	T_g measured by different methods/°C
		DMA			DSC
		Storage modulus method	Loss modulus method	Loss factor	DSC
E51+condensationamine epoxy curing agent 105+ amino-terminated polyoxypropylene D203 (Li et al., 2021;Li et al., 2023)	55	71	72.6	85.8	/
E51+ condensationamine epoxy curing agent 105 (Li et al., 2021)	>70	92.9	94.9	105.3	/
E51+amino-terminated polyoxypropylene D203 (Li et al., 2021)	<70	56.3	56.3	68.7	/
A2014 (Li et al., 2020)	70	56.3	58.4	68.3	/
A420 (Li et al., 2020)	40	31.6	32.6	43.6	/
S30 (Li et al., 2020)	55	32.8	33.7	47.8	/
C1 (Li et al., 2020)	55	49.9	53.9	63.2	/
S&P 220 HP (Firmo et al., 2019)	60	/	/	/	54.9
S&P Resin 220 (Firmo et al., 2019)	50	47	/	60	/
XN1244 (Li et al., 2023)	125	≈125	/	155	/

DMA: dynamic mechanical analysis; DSC: differential scanning calorimetry.

In summary, current research on basic mechanical properties of traditional epoxy resin at elevated temperatures is relatively comprehensive, and its strength evolution law is relatively clarified. However, for chemically modified epoxy resins to obtain better high-temperature properties, its temperature-dependent mechanical behavior and evolution mechanism is still not clear enough. Thus, further research is necessary, with attention on influence of the form of molecular chains.

Summary

During curing process, epoxy resin with higher curing degree and molecular cross-linking will have higher T_g, and proper heating curing temperature can improve T_g. In addition, secondary heating curing can achieve better mechanical properties than direct curing at high curing temperature. Increasing curing temperature can improve T_g as well as its mechanical properties at elevated temperature. Yet, if curing temperature exceeds T_g∞, the curing time should be proper. Otherwise, excessive heat input may cause molecular unchaining, resulting in decreasing of T_g and mechanical properties.

The research into high-temperature properties of epoxy resins has cleared the influencing law of temperature on status transition of resin, as well as its mechanical properties evolution law at elevated temperature. However, current research on high-temperature properties of chemically modified epoxy resin is still insufficient, especially when inconsistent types of molecular chains exist, which make the degradation mechanisms at elevated temperature complex and not easy to determinant the influencing factors. Thus, further research is needed.

High-temperature properties of unidirectional CFRP composites for cables

High-temperature properties of CFRP composites in longitudinal direction

Unidirectional CFRP is mostly used for cables, which is generally composed of carbon fibers and epoxy resin matrix and fabricated by pultrusion process. At elevated temperatures, the carbon fiber is little affected (Sauder et al., 2002), while CFRP is significantly affected owing to temperature-dependent performance of resin matrix. The interface between resin matrix and carbon fibers tends to fail at elevated temperatures, resulting in significant strength degradation and modulus softening of CFRP. In addition, unidirectional CFRP composites for cables has anisotropic mechanical properties in longitudinal (fiber) direction and transverse direction. For CFRP cables, the longitudinal properties are mainly the tensile performances, which dominate the performance of cable body. Correspondingly, the transverse properties include compressive and shearing performances, which dominate the performance of CFRP cable inside the anchorage. Therefore, this section summarizes the test methods and temperature-dependent performance of CFRP composites for cables in longitudinal and transverse direction respectively.

Test methods

The temperature-dependent tensile performance of unidirectional CFRP is usually conducted by tensile tests at elevated temperature, which can be divided into the steady-state test method and transient test method (Bisby, 2003), whose loading procedures are shown in Figure 5.

Figure 5.

Thermo-mechanical loading path. (a) Steady-state test (b) transient test.

The steady-state test starts applying tension after temperature elevated to target temperature, while the transient test starts temperature elevation after specimen loaded to target stress. Thus, the temperature field in specimens by steady-state test is relatively uniform, and relatively accurate performance of CFRP at specific elevated temperature can be obtained. In addition, the critical temperature obtained by steady-state test is relatively conservative. The transient test mainly reflects the thermo-mechanical response of CFRP after experiencing temperature elevation (Rosa et al., 2022). Additionally, the temperature field in specimens is not uniform in transient test due to incomplete heat conduction in short time. Thus, to obtain more accurate temperature-dependent performance of CFRP, which is critical for analysing the failure mechanism of CFRP at specific elevated temperature, this section summarizes the research by steady-state test.

Failure modes

In tensile test at elevated temperature, the state of CRRP changes with increasing temperature. According to Section “Curing and glass transition temperature of epoxy resin”, the mobility of molecular chains will increase at elevated temperature (Mahieux and Reifsnider, 2001). Especially, when temperature is close to T_g, epoxy resin matrix will significantly soften and CFRP will exhibit viscoelastic rubber state. With temperature continuously increasing to T_d of epoxy resin, the resin will gradually decompose, leaving only carbon fibers.

At elevated temperatures, CFRP may exhibit fiber fracture initialling from weak points with fatal defects, and further induce interlayer splitting in longitudinal direction at fiber-resin matrix interface. Especially, if the defects are distributed intensively, fracture of fibers will develop in transverse direction. By tensile tests at elevated temperature, Yu and Kodur (2014) found that the failure modes of CFRP laminates and bars were similar, indicating that cross-sectional form had little influence on damage modes. In addition, the tensile failure modes of CFRP at different elevated temperatures were summarized and categorised into three types. (1) Failure mode I: At room temperature, the damage begins with resin matrix cracking and final fails by fibers explosive fracture, exhibiting brittle fracture of specimens. (2) Failure mode II: With increasing temperature, the softening of epoxy resin matrix causes significant interfacial bonding degradation between fibers and resin matrix, resulting in interlayer splitting in longitudinal direction and final failure by fiber bundles fracture with part of resin wrapping them. (3) Failure mode III: With temperature continuously increasing, the resin completely decomposes, and the fiber bundle expands in transverse direction and finally fractures.

Xu et al. (2020) also investigated the mechanical performance of CFRP at elevated temperatures, and further classified failure mode II into two types, distinguished by resin softening (failure mode II-I) and resin beginning decomposition (failure mode II-II), as shown in Figure 6. In failure mode II-I, the resin softens at temperature close to T_g, and CFRP exhibits explosive rupture with partial fibers fracture. In failure mode II-II, after decomposition of resin matrix, CFRP exhibits fiber bundle fracture with residual resin wrapping it. According to the above research, failure mode of CFRP is related with the response of resin at different elevated temperatures. If the temperature is high enough to cause glass transition of resin, the fiber-resin interface would exhibit significant degradation, resulting in insufficient stress redistribution and collaboration of fibers, and causing tensile failure initiating from the weak point with fatal defects.

Figure 6.

Failure modes of CFRP (Xu et al., 2020). (a) Failure mode I (b) failure mode Ⅱ-I (c) c) failure mode Ⅱ-Ⅱ (d) failure mode ⅡI.

In addition, Hawileh et al. (2015) found that CFRP pre-preg had similar failure modes with CFRP plates and bars at elevated temperature (Yu and Kodur, 2014), although their manufacturing processes and amplitude of tensile stress–strain curve were significantly different. Li et al. (2022) found that the failure mode of fiber reinforced polymers with different resin also had similar failure mode at elevated temperature, but the temperatures corresponding to different failure modes were significantly different, which was determined by different T_g of resins.

Therefore, it can be concluded that the failure modes of different CFRP at elevated temperatures are similar, determined by the elevated temperature and the glass transition and decomposition temperature of CFRP, neglecting the manufacturing process and resin types. That is to say, the temperature-dependent performance of resin is dominant on failure modes of CFRP at elevated temperature.

Strength degradation mechanism

Tensile tests of CFRP at elevated temperature also indicate significant strength degradation. Wang et al. (2007) and Xu et al. (2020) found that the tensile stress-strain curve of CFRP was almost linear at elevated temperature before resin decomposition, as shown in Figure 7. In addition, the tensile strength of CFRP exhibited little degradation at elevated temperature (20°C-150°C) much lower than T_g (220°C). With temperature (200°C-300°C) closing to and exceeding T_g, the tensile strength exhibited continuously significant degradation, indicating that the glass transition of resin could significantly influence tensile strength of CFRP. However, the strength retention rate at 300°C was still over 40% of that at room temperature. Besides, the modulus of CFRP just exhibited relatively small degradation, even at temperature exceeding T_g. With temperature increasing close to resin decomposition temperature (350°C), the tensile strength exhibited another significant degradation, with retention rate of about 37% of that at room temperature. It should be noted that the stress-strain curve at 350°C in Figure 7 is incomplete due to measurement technical problem. Besides, the modulus exhibited sharp degradation, with retention rate of 48% of that at room temperature.

Figure 7.

Tensile stress–strain curves of specimens at high temperature (Xu et al., 2020).

In addition, Yu and Kodur (2014) found that the tensile strength and modulus retention rate was still over 80% at temperature close to T_g by steady-state tensile test of CFRP bars and strips. Hamad et al. (2017) found that the tensile strength and modulus retention rate of BFRP, GFRP, and CFRP bars was about 50% and 70% respectively after resin began decomposition. Li et al. (2022) comparatively conducted tensile test of BFRP bars using different resins at elevated temperature, including phenolic resin (T_g = 375°C, T_d = 506°C), vinyl resin (T_g = 101°C, T_d = 338°C) and epoxy resin (T_g = 87°C, T_d = 326°C), and found that the tensile strength retention rate were 66%, 45% and 80% before resin decomposition, but the modulus retention rate were much higher, with 78%, 81% and 87% respectively. Rosa et al. (2022) conducted steady state tensile test of GFRP with vinyl resin at elevated temperature up to 715°C, and found that after complete decomposition of resin, the tensile strength retention rate decreased to 4%, but the modulus retention rate was still 66%.

In summary, the properties degradation and failure mode of different fiber reinforced polymers are similar, and can be divided into three stages (Xu et al., 2020). To better describe the degradation law, testing data by previous research (Hamad et al., 2017; Hawileh et al., 2015; Khaneghahi et al., 2018; Li et al., 2022; Nguyen et al., 2018; Rosa et al., 2022; Wang et al., 2007; Xu et al., 2020; Yu and Kodur, 2014) is collected and normalized to establish the relationship between properties degradation and failure mode, as shown in Figure 8. It can be seen that the degradation law exhibits similar trends, but the degradation path is not identical due to the differences of fiber volume ratio, fiber type, resin type, manufacturing process, and the form of composites. Generally, at temperatures much lower than T_g and before significant softening of resin (corresponding to failure mode I), the tensile properties gradually decreases with elevating temperature, with strength and modulus retention rate over 80% and 90% respectively. At temperatures around T_g and before decomposition of resin (corresponding to failure mode II-I), with gradual softening of resin, the tensile strength decreases significantly with retention rate of about 50%, but the modulus decreases relatively smaller with retention rate of about 85%. At temperature over T_d and after resin decomposition occurring (corresponding to failure mode II-II), the tensile strength also decreases relatively smooth with elevating temperature with retention rate of about 30%–40%, and the modules speedily decreases with retention rate still over 50%. At temperature over T_d and with continuous until complete decomposition of resin (corresponding to failure mode III), the tensile strength and modulus also decrease at a certain speed, with final retention rate around 10%–30% and 30%–50%, respectively.

Figure 8.

Residual properties of CFRP at high temperature. (a) Tensile strength versus temperature (b) elastic module versus temperature.

Based on the above analysis, it should be noted that the decreasing of tensile strength is earlier and more significant than modulus. In addition, the strength retention rate is strongly related with temperature-dependent performance of resin, and dominated by resin type and its T_g, exhibiting relatively different decreasing speed. Generally, after resin softening at elevated temperature, the fiber-resin interface will also softens, resulting in insufficient stress redistribution and collaboration of fibers (Cao et al., 2009; Hamad et al., 2017; Khaneghahi et al., 2018; Li et al., 2022; Wang et al., 2007), thus leads to significant strength degradation. Comparatively, the modulus retention rate is relatively much higher than strength before T_d, neglecting of fiber types, resin types and composites forms. This phenomenon is mainly due to the fact that contribution of modulus mainly comes from fibers (Li et al., 2022), which are not significantly influenced by temperature. Yet, the modulus retention rate also decreases speedily after T_d.

Furthermore, although the general trends of degradation law of mechanical properties of CFRP at elevated temperatures are consistent and widely accepted by different researchers, there is still obvious divergence in retention ratio at specific temperature, especially at temperature around T_g and exceeding T_d. The strength and modulus degradation speed and retention ratio are not fully consistent. From macro view, this may be attributed to fiber manufactory, resin type, manufacturing process etc. Yet, the macro view cannot clearly analyse the mechanism of these differences. From micro view, this may be attributed to quality of carbon fibers, temperature-dependent properties of resin and fiber-resin interface defects by manufacturing process. The dominant issue of fibers quality is the probabilistic defects distribution in fibers considering length effect, which can significantly influence strength retention ratio after softening and decomposition of fibers. In addition, the temperature-dependent properties of resin can also influence fiber-resin interface performance at elevated temperature, thus leading to different stress redistribution capacity around premature fracture fibers with fatal defects and resulting in different strength retention ratio. Furthermore, the modulus retention ratio around T_g and exceeding T_d can also be influenced by temperature-dependent properties of resin and manufacturing quality of CFRP. For example, different manufacturing defects such as fibers wrinkle can result in different modulus retention around T_g and exceeding T_d, due to softening or decomposition of resin. Yet, if the high-temperature properties of resin around T_g is better, the influence of manufacturing defects can be relieved. Anyway, after complete decomposition of resin, the modulus retention ratio will still be dominant by manufacturing defects, and the strength retention ratio will be dominant by probabilistic fiber defects and manufacturing defects. This is due to the fact that fiber defects can significantly decrease the strength of fibers, and manufacturing defects can decease collaborative working of fiber bundles after resin decomposition.

However, although the above mechanism is reasonable, the quantified influencing mechanism is still lacking due to technical restrictions, such as the effective testing and characterization tool for establishing model of probabilistic defects in fibers and manufacturing defects. Researchers such as Zhu et al. (2023) and Salem et al. (2021) investigated the damage evolution and failure mechanism of CFRP at elevated temperature using multi-scale FEA model, but the probabilistic defects are still not considered. Thus, this problem needs further research to clarity it.

Critical temperature

Except for temperatures of T_g and T_d, another critical temperature is also focused to assess high-temperature properties, which is the temperature corresponding to tensile strength with retention ratio of 50% (Yu and Kodur, 2014). Generally, it ranges around T_g to T_d. The measured critical temperature is dependent on the test method, and the value by transient test is somewhat higher than steady-state tests (Hajiloo et al., 2018; Xu et al., 2020). This phenomenon is due to that the temperature field in specimens is not uniform in transient test, with decreasing temperature gradient from surface to interior. Thus, the critical temperature by steady-state test is conservative, while that by transient test is suggested to be the upper limit (Hajiloo et al., 2018).

High-temperature properties of CFRP composites in transverse direction

Transverse mechanical properties of CFRP composites at room temperature

Typical unidirectional CFRP for engineering structures is usually manufactured by pultrusion, and has anisotropy mechanical properties. For example, its compressive strength in transverse direction is less than 10% of tensile strength in longitudinal direction (Zong, 2020). As shown in Figure 9, the compressive strength of unidirectional GFRP at room temperature is dominant with the angle θ between compressive force and fiber direction. At θ of 0°, naming the longitudinal direction, the strength is highest. At θ of 90°, naming the transverse direction, the strength is about 50% of the longitudinal compression. At θ of 45°, equivalent to be subjected to shear force, the strength is lowest, only about 40% of the longitudinal compression (Zhou et al., 2013). Therefore, the transverse compressive and fiber-resin interfacial shear strength of GFRP is poor with comparison to longitudinal tensile strength, which is similar to CFRP. However, the transverse compressive strength is necessary for improving anchoring efficiency in anchorage of CFRP cable, resisting clamping force in mechanical anchorage and circumferential extrusion pressure in mechanical-bonding composite anchorage. According to Section “Mechanical properties of epoxy resin at elevated temperature”, the softening of resin at elevated temperature will decrease transverse compressive strength, which may be more significantly than longitudinal tensile strength. Thus, it is necessary to clarify the degradation of transverse mechanical properties at elevated temperatures.

Figure 9.

Compressive strength of GFRP at different fiber orientations (Zhou et al., 2013).

However, there is limited research on transverse mechanical properties of unidirectional CFRP, especially at elevated temperatures. Therefore, transverse mechanical properties of CFRP at room temperatures are firstly reviewed and summarized. The method of testing transverse mechanical properties for CFRP plates or rods is shown in Figure 10, including transverse compressive tests, transverse shear tests, and three-point bending tests. Han et al. (2015) conducted transverse compressive tests on CFRP rods and plates, and found the major failure mode was longitudinal splitting, exhibiting significant cracking along longitudinal fiber direction and penetrating the transverse section, which indicated that fibers contributed little to transverse compressive strength. Besides, for CFRP plates, its strength was only 120 MPa.

Figure 10.

Schematic view of test equipment. (a) Transverse compressive test of CFRP rod (b) transverse compressive test of CFRP plate (c) transverse shear test of CFRP rod (d) flexural test of CFRP rod.

Han et al. (2016) also found that the failure mode of unidirectional CFRP plates under transverse compression was similar to that of matrix resin. In addition, by electron microscope scan of the fractured cross sections, the following phenomena were observed. Firstly, the resin was almost completely crushed with obvious longitudinal cracking, and part of the fibers in longitudinal cracking dispersed. Secondly, no transverse cracking was observed, indicating that the fibers hardly bear transverse forces. Thirdly, part of the fibers along the longitudinal cracking wrinkled or even fractured, with no resin or part of resin wrapping them, indicating that fiber-matrix debonding occurred. Therefore, the transverse compression failure of unidirectional CFRP includes four typical damages, namely longitudinal cracking of resin matrix, debonding of fiber-resin interface, wrinkle of fibers along cracking and fiber fracture (Han et al., 2016). Thus, it can be concluded that the failure initials with resin cracking in longitudinal direction, saying that strength of resin and fiber-resin interfacial bonding is dominant for transverse compressive strength of unidirectional CFRP.

To further investigate the coupling effect of transverse compression and longitudinal tension, Han et al. (2016) conducted tensile tests using mechanical anchorage, and firstly induced transverse compression damage on CFRP rods by over clamping the anchorage. During the tensile test, some longitudinal cracking in CFRP inside the anchorage firstly occurred, due to the coupling effect of transverse compression and the longitudinal interfacial shear caused by anchorage force. In addition, the longitudinal cracking gradually developed to the free end of the anchorage, and finally resulted in longitudinal splitting failure around the surface of CFRP rods, exhibiting almost no significant transverse cracking, as shown in Figure 11. The results indicates that transverse compressive strength should be carefully paid attention because excessive compression may damage anchorage performance due to its coupling effect with longitudinal interfacial shear when subjected to tension loads.

Figure 11.

Failure mechanism of transverse compression (Han et al., 2016).

At present, the basic failure mode and mechanism of CFRP under transverse compression is relatively clear. However, such research is relatively little, the influencing parameters are not quantified investigated, including strength of resin and fiber-resin interface, as well as manufacturing defects. In addition, a universal strength model is also lacking. Besides, the coupling effect of transverse compression and longitudinal fiber-resin interfacial shear capacity also needs further research for guiding more reasonable design of anchorage.

Transverse mechanical properties of CFRP composites at elevated temperature

Xu et al. (2023) found that elevated temperatures significantly decreased the transverse compressive strength, but not changed the damage initialling and development pattern. Zong (2020) compared the transverse compression properties of unidirectional CFRP laminates (T800 carbon fiber, epoxy resin, T_g>150°C) at room temperature and 150°C, and found their failure characteristic similar, except that separation of fibers from the resin matrix was more noticeable at elevated temperature. Additionally, their stress-strain relationship was also similar, and both of them were almost linear. Yet, the peak compressive strength at 150°C decreased by 32%, while the modulus decreased slightly. However, such research is still quite insufficient. The research by Zong (2020) just presents basic transverse compressive performance of CFRP at specific elevated temperature, but the strength degradation and evolution law at different elevated temperatures is not investigated, as well as the temperature-dependent compressive stress-strain relationship and its constitutive model.

Besides, the high-temperature transverse compression properties of CFRP inside the anchorage of cables may be also influenced by anchorage constraint. For example, the CFRP rods in bonding-mechanical composite anchorage have circumferential constraint, but CFRP plates in mechanical clamping anchorage have almost no lateral constraint, as illustrated in Figure 12. At elevated temperature that may cause significant softening of resin matrix, CFPR composites in anchorage with no lateral constraint will obviously exhibit more significant degradation in compression properties (Zhou and Zhao, 2019). Therefore, investigation on the transverse compression properties of CFPR at elevated temperature considering constraint of anchorage still needs further research.

Figure 12.

Influence of lateral support on compression failure modes (Zhou and Zhao, 2019).

Except for the transverse compression properties at elevated temperature, some scholars also investigated the mechanical properties of CFRP after suffering elevated temperature. Fang et al. (2021) conducted coupling tension-flexure tests on CFRP rods after suffering different elevated temperatures (100°C and 200°C), and found that the ultimate transverse (flexure) strength decreased with pre-elevated temperatures. Yet, the damage degree after elevated temperature, the degradation law of the residual mechanical properties and the relationship between them were not discussed or clarified. Besides, according to Sections “Curing degree improvement of epoxy resin” and “Curing conditions and properties of epoxy resin”, this conclusion may be not universal because mechanical properties may be improved due to post-curing effect of resin with pre-elevated temperatures, and this problem needs attention. For example, we found that the transverse compressive strength of unidirectional CFRP (T700 carbon fiber, epoxy resin, T_g 220°C) was improved from about 155 MPa to 170 MPa after suffering elevated temperature (135°C for 4 h and 165°C for 2 h).

In summary, the transverse mechanical properties of CFRP will degrade at elevated temperature due to softening of resin matrix, resulting in significant degradation in anchorage performance of CFRP cables. At present, the research on transverse compression properties of CFRP is relatively little, especially at elevated temperature, making it insufficient to support the investigation of CFRP anchorage degradation at elevated temperatures. Thus, further research is necessary on transverse properties of CFRP at both room and elevated temperatures, especially establishing the temperature-dependent stress-strain relationship, which is the basis for investigating anchorage performance degradation of CFRP cable at elevated temperature.

Summary

Currently, the investigation on longitudinal tensile properties of CFRP composites at room temperatures and elevated temperatures is relatively comprehensive, and the failure modes and mechanism is clarified. In addition, the tensile properties degradation law at elevated temperatures is also relatively clear. Generally, at elevated temperatures within or around T_g, both tensile strength and modulus degradation are primarily dominated by high-temperature properties of resin, while at temperatures exceeding T_d, the retention strength and modulus ratio are also closely related to probabilistic fiber defects and manufacturing defects. However, the quantified influencing mechanism of such issues is still not sufficient due to lacking effective testing and characterization tool for establishing the model of probabilistic defects.

Comparatively, the investigation on transverse mechanical properties of CFRP composites at both room and elevated temperatures are insufficient. Generally, the failure mechanism under transverse compression is clear, and closely related with the properties of resin matrix and fiber-resin interface. Yet, the quantified influencing mechanism is still insufficient, and the temperature-dependent stress-strain relationship is also lacking. Besides, for more reasonable investigation of anchorage performance degradation of CFRP cable at elevated temperature, the coupling effect of transverse compression and longitudinal fiber-resin interfacial shear capacity also needs further research, and the enhancing effect of anchorage constraint to CFRP composites needs to be considered.

Conclusions

This paper summarizes current research status of high-temperature properties of CFRP composites for cables from two levels, including epoxy resin and CFRP composites. Firstly, the properties of epoxy resin matrix at elevated temperatures, the methods for improving high-temperature properties, as well as the mechanical properties degradation and evolution law at elevated temperatures, are summarized. Secondly, test methods for mechanical properties of CFRP composites in longitudinal and transverse directions at elevated temperatures are summarized, and the failure modes and mechanical properties degradation are discussed. Besides, the insufficiency of existing research is also summarized, and further research is recommended. Some conclusions can be drawn as follows:

(1) The curing degree influences the degree of molecules cross-linking of epoxy resin, thus influencing its T_g. Elevating curing temperature can improve molecules cross-linking and thus improve the mechanical properties of epoxy resin, but curing temperatures over T_g∞ with excessive time may cause molecules unchaining due to excessive heat input. Thus, curing temperature around T_g∞ can achieve relatively better performance of resin. In addition, secondary heating curing after initial curing can achieve better performance than direct curing at elevated temperature.

(2) The properties degradation law of conventional epoxy resin at elevated temperatures is relatively clear, becoming significant around T_g. The properties degradation law of different chemically modified epoxy resin at elevated temperatures may be different, and mechanical properties of epoxy resin with multiple chemically modification at elevated temperature are complex, especially when inconsistent types of molecular chains exist. Therefore, further research is necessary to clarify the degradation mechanisms and influencing factors of multiple chemically modified epoxy resin at elevated temperatures.

(3) The longitudinal tensile properties of CFRP composites at elevated temperatures is dominant by T_g and T_d due to glass transition and decomposition of resin. The failure modes and mechanism are clarified, and the tensile properties degradation law at elevated temperatures is also relatively clear. Generally, at elevated temperatures within or around T_g, both tensile strength and modulus degradation are primarily dominated by high-temperature properties of resin, with modulus degradation relatively little. However, at temperatures exceeding T_d, both strength and modulus degrades accelerating, with relatively larger retention ratio of modulus than strength. Such retention ratios after T_d by different research vary greatly, which are closely related to probabilistic fiber defects and manufacturing defects. However, the quantified influencing mechanism of such issues is still not sufficient due to lacking effective testing and characterization tool for establishing the model of probabilistic defects.

(4) The transverse mechanical properties of CFRP composites at room and elevated temperatures are closely related with the properties of resin matrix and fiber-resin interface. Generally, the failure mechanism is clear, but the quantified influencing mechanism of relative issues is still insufficient, and the temperature-dependent stress-strain relationship is also lacking. In addition, the transverse compression properties of CFRP inside the anchorage of cables may be also influenced by anchorage constraint, which may provide enhancing effect as well as inducing longitudinal fiber-resin interfacial shear stress having coupling effect with transverse compression. Thus, further research is needed for more reasonable investigation of anchorage performance degradation of CFRP cable at elevated temperature.

Footnotes

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work is financially supported by the National Key Research and Development Program of China (2022YFB3706505, 2021YFB3704403) and CSCEC Technology R&D Program (CSCEC-2022-Z-8).

ORCID iD

Xiaogang Liu

References

Banea

De Sousa

FSM

Da Silva

LFM

, et al. (2011) Effects of temperature and loading rate on the mechanical properties of a high temperature epoxy adhesive. Journal of Adhesion Science and Technology 25(18): 2461–2474.

Bascom

Cottington

(1976) Effect of temperature on the adhesive fracture behavior of an elastomer-epoxy resin. The Journal of Adhesion 7(4): 333–346.

Bisby

(2003) Fire Behaviour of Fibre-Reinforced Polymer (FRP) Reinforced or Confined Concrete. PhD Thesis. Canada: Queen’s University at Kingston.

Cao

Wang

(2009) Tensile properties of CFRP and hybrid FRP composites at elevated temperatures. Journal of Composite Materials 43(4): 315–330.

Carbas

RJC

Marques

EAS

DA Silva

LFM

, et al. (2014) Effect of cure temperature on the glass transition temperature and mechanical properties of epoxy adhesives. The Journal of Adhesion 90(1): 104–119.

Chen

Wang

Zhou

, et al. (2006) High-performance resin matrix for T800carbon fiber composites. Acta Materiae Compositae Sinica 23(04): 29–35.

Duo

Liu

Yue

, et al. (2022) A novel variable curvature clamping anchor for the multilayer CFRP plate cable: concept, numerical investigation, and design proposals. Structures 43: 164–177.

Fang

Huang

, et al. (2021) Experimental investigation on mechanical performance of carbon fiber reinforced polymer wire after exposure to elevated temperature. Composite Structures 274: 114388.

Firmo

Roquette

Correia

, et al. (2019) Influence of elevated temperatures on epoxy adhesive used in CFRP strengthening systems for civil engineering applications. International Journal of Adhesion and Adhesives 93: 102333.

10.

Hajiloo

Green

Gales

(2018) Mechanical properties of GFRP reinforcing bars at high temperatures. Construction and Building Materials 162: 142–154.

11.

Hamad

RJA

Megat Johari

Haddad

(2017) Mechanical properties and bond characteristics of different fiber reinforced polymer rebars at elevated temperatures. Construction and Building Materials 142: 521–535.

12.

Han

Wang

(2015) Experimental research on mechanical properties of transverse enhanced and high-temperature-resistant CFRP tendons for prestressed structure. Construction and Building Materials 98: 864–874.

13.

Han

Wang

(2016) Experimental research on fracture behaviors of damaged CFRP tendons: fracture mode and failure analysis. Construction and Building Materials 112: 1013–1024.

14.

Hawileh

Abu-obeidah

Abdalla

, et al. (2015) Temperature effect on the mechanical properties of carbon, glass and carbon–glass FRP laminates. Construction and Building Materials 75: 342–348.

15.

Jahani

Baena

Barris

, et al. (2020) Influence of curing, post-curing and testing temperatures on mechanical properties of a structural adhesive. Construction and Building Materials 324: 126698.

16.

Jiang

Fang

, et al. (2022) Experimental investigation on high-temperature creep behavior of carbon fiber reinforced polymer cable. Composite Structures 291: 115533.

17.

Khaneghahi

Najafabadi

Shoaei

, et al. (2018) Effect of intumescent paint coating on mechanical properties of FRP bars at elevated temperature. Polymer Testing 71: 72–86.

18.

Kong

Shi

Dong

, et al. (2023) Hygrothermal resistance of large tow carbon fiber and its reinforced polymer composites. Polymer Composites 44(10): 6913–6928.

19.

Lahouar

Caron

Pinoteau

, et al. (2017) Mechanical behavior of adhesive anchors under high temperature exposure: experimental investigation. International Journal of Adhesion and Adhesives 78: 200–211.

20.

Zhang

Sun

, et al. (2004) Curing characteristics of linear heating of an epoxy resin. Acta Materiae Compositae Sinica 21(03): 17–21.

21.

Liu

, et al. (2018) Preparation of high performance adhesives matrix based on epoxy resin modified by bis-hydroxy terminated polyphenylene oxide. Journal of Adhesion Science and Technology 32(11): 1224–1238.

22.

Cao

, et al. (2020) Effect of high temperature on mechanical properties of epoxy adhesives for structural strengthening. Journal of Building Material 23(3): 642–649.

23.

Zheng

, et al. (2021) Effect of curing agent mixing on interfacial bond behavior of glued CFRP plate-steel plate at elevated temperature. Acta Materiae Compositae Sinica 38(12): 4073–4089.

24.

Zhu

Shen

, et al. (2022) Thermophysical and thermomechanical properties of basalt-phenolic FRP rebars under high temperature. Construction and Building Materials 342: 127983.

25.

, et al. (2023) Effect of high temperature on mechanical properties of CFRP plate-steel plate lapping interface based on developed adhesive. Acta Materiae Compositae Sinica 40(12): 6596–6609.

26.

Liu

Wang

Hui

, et al. (2013) Progress in epoxy resin of high-temperature resistance. Composites Science and Engineering (3): 118–121.

27.

Liu

Zwingmann

Schlaich

(2015) Carbon fiber reinforced polymer for cable structures—a review. Polymers 7(10): 2078–2099.

28.

Mahieux

Reifsnider

(2001) Property modeling across transition temperatures in polymers: a robust stiffness–temperature model. Polymer 42(7): 3281–3291.

29.

Miao

, et al. (2020) Eugenol-derived reconfigurable high-performance epoxy resin for self-deployable smart 3D structures. European Polymer Journal 134: 109805.

30.

Michel

Ferrier

(2020) Effect of curing temperature conditions on glass transition temperature values of epoxy polymer used for wet lay-up applications. Construction and Building Materials 231: 117206.

31.

Moussa

Vassilopoulos

De Castro

, et al. (2012) Time–temperature dependence of thermomechanical recovery of cold-curing structural adhesives. International Journal of Adhesion and Adhesives 35: 94–101.

32.

Nakamura

Yamaguchi

Iko

, et al. (1990) Internal stress of epoxy resin modified with acrylic polymers having crosslinks produced byin situ UV radiation polymerization. Journal of Materials Science 25(6): 2711–2716.

33.

Nguyen

Ferrier

(2018) Elevated temperature behaviour of carbon fibre-reinforced polymer applied by hand lay-up (M-CFRP) under simultaneous thermal and mechanical loadings: experimental and analytical investigation. Fire Safety Journal 100: 103–117.

34.

Nguyen

Hong Vu

Ferrier

(2019) Thermo-mechanical performance of carbon fiber reinforced polymer (CFRP), with and without fire protection material, under combined elevated temperature and mechanical loading conditions. Composites Part B: Engineering 169: 164–173.

35.

Plecnik

Bresler

Cunningham

, et al. (1980) Temperature effects on epoxy adhesives. Journal of the Structural Division 106(1): 99–113.

36.

Pradere

Batsale

Goyhénèche

, et al. (2009) Thermal properties of carbon fibers at very high temperature. Carbon 47(3): 737–743.

37.

Rosa

Firmo

Correia

(2022) Experimental study of the tensile behaviour of GFRP reinforcing bars at elevated temperatures. Construction and Building Materials 324: 126676.

38.

Salem

Mkaddem

Rubaiee

SSSA

, et al. (2021) Numerical investigation of thermomechanical damage in CFRP composites. In: International Conference Design and Modeling of Mechanical Systems. Cham: Springer International Publishing, 59–66.

39.

Sauder

Lamon

Pailler

(2002) Thermomechanical properties of carbon fibres at high temperatures (up to 2000°C). Composites Science and Technology 62(4): 499–504.

40.

Stark

(2013) Investigation of the curing behaviour of carbon fibre epoxy prepreg by dynamic mechanical analysis DMA. Polymer Testing 32(2): 231–239.

41.

Startsev

Vapirov

Lebedev

, et al. (2020) Comparison of glass-transition temperatures for epoxy polymers obtained by methods of thermal analysis. Mechanics of Composite Materials 56(2): 227–240.

42.

Wang

Wong

PMH

Kodur

(2007) An experimental study of the mechanical properties of fibre reinforced polymer (FRP) and steel reinforcing bars at elevated temperatures. Composite Structures 80(1): 131–140.

43.

Wang

Young

Smith

(2011) Mechanical properties of pultruded carbon fibre-reinforced polymer (CFRP) plates at elevated temperatures. Engineering Structures 33(7): 2154–2161.

44.

Wang

, et al. (2017) Vanillin-Derived high-performance flame retardant epoxy resins: facile synthesis and properties. Macromolecules 50(5): 1892–1901.

45.

Wang

Zhang

, et al. (2018) Anchorage systems of CFRP cables in cable structures—a review. Construction and Building Materials 160: 82–99.

46.

Wang

Liu

Yue

(2022) Research progress of carbon fiber reinforced polymer composite cable: anchorage system and service performance. Journal of Building Structures 43(09): 45–54.

47.

Wang

Jiang

, et al. (2014) Improvements of heat resistance and adhesive property of condensed poly-nuclear aromatic resin via epoxy resin modification. Petroleum Science 11(4): 578–583.

48.

Xie

Tao

Sun

, et al. (2022) An investigation of hygrothermal effect on fatigue behavior of adhesively bonded anchorages for FRP tendon. Construction and Building Materials 316: 126044.

49.

Wang

Han

(2020) Mechanical properties of pultruded high-temperature-resistant carbon-fiber-reinforced polymer tendons at elevated temperatures. Construction and Building Materials 258: 119526.

50.

Chen

Zhu

, et al. (2023) Prediction of transverse mechanical performance of UD CFRP composite lamina considering high-temperature properties of epoxy. Mechanics of Advanced Materials and Structures 30(16): 3351–3364.

51.

Yang

Fahmy

MFM

Guan

, et al. (2020) Properties and applications of FRP cable on long-span cable-supported bridges: a review. Composites Part B: Engineering 190: 107934.

52.

Yang

Xie

Kainuma

, et al. (2021) Improvement in bond behavior and thermal properties of carbon fiber-reinforced polymer strengthened steel structures. Composite Structures 278: 114704.

53.

Yang

Liao

, et al. (2022) Preparation and property of EP with high temperature resistant and its prepreg. New Chemical Materials 50(2): 119–123.

54.

Kodur

(2014) Effect of temperature on strength and stiffness properties of near-surface mounted FRP reinforcement. Composites Part B: Engineering 58: 510–517.

55.

Zhou

Zhao

(2019) Failure mechanisms based degradation model of unidirectional fiber reinforced polymer composites. Acta Materiae Compositae Sinica 36(06): 1389–1397.

56.

Zhou

Gui

, et al. (2013) Compressive damage mechanism of GFRP composites under off-axis loading: experimental and numerical investigations. Composites Part B: Engineering 55: 119–127.

57.

Zhou

Zhang

Song

, et al. (2019) Effect of temperature on material properties of carbon fiber reinforced polymer (CFRP) tendons: experiments and model assessment. Materials 12(7): 1025.

58.

Zhou

Pang

Zhang

, et al. (2022) Experimental investigation of the mechanical properties of carbon fiber-reinforced polymer (CFRP) tendons during and after exposure to elevated temperatures. Materials and Structures 55(2): 82.

59.

Zhu

Ren

, et al. (2023) Damage evolution model and failure mechanism of continuous carbon fiber-reinforced thermoplastic resin matrix composite materials. Composites Science and Technology 244: 110300.

60.

Zhuge

Tao

Wang

, et al. (2022) Effects of high temperatures on the performance of carbon fiber reinforced polymer (CFRP) composite cables protected with fire-retardant materials. Materials 15(13): 4696.

61.

Zong

(2020) Research on Mechanical Behavior of Carbon Fiber Composite Laminates in Thermal Environment. Master Thesis. Habin, China: Harbin Institute of Technology.