Journal of Reinforced Plastics and Composites

Three basic mode-II test methods (ENF, JIS, and ASTM D7905M-14) are assessed using the material system AS4/8552 carbon/epoxy unidirectional composite laminate to understand similarities and differences. The modified JIS method uses a PTFE film coated stainless steel rod instead of the PTFE strip that was proposed in JIS. The ASTM D7905M-14 test method determines FEP film crack front (NPC) and shear precrack front (PC) fracture toughnesses. Alternately, wedge precracked specimens were also tested to assess the shear versus opening mode precracking on mode-II fracture toughness. The analysis and test results revealed that the JIS method is a mixed-mode I-II test and result in lower value of mode-II fracture toughness. The G_I loading is about 51 J/m² for the material tested and G_IIc measured by JIS is always less than pure mode-II fracture toughness. The G_IIc measured from the ASTM D7905M-14 NPC and the ENF tests are almost identical, but the ASTM test offers a compliance equation that may be beneficial in fatigue crack growth studies. As suggested in ASTM standard, shear precracked specimen is appropriate to measure mode-II fracture toughness.

Both in-plane shear modulus and in-plane shear strength of multiscale hybrid composites have been studied. Carbon fibre-based laminates have been fabricated including functionalized multiwall carbon nanotubes by means of solvent spraying method and hot compression process. Mechanical in-plane shear characterization has been carried out using off-axis three-point flexure test. Fibre volume fraction of multiscale hybrid composites has been determined through thermogravimetric analysis and fracture surfaces after testing have been imaged by scanning electron microscopy. Results reveal that the inclusion of functionalized multiwall carbon nanotubes on laminates has a small influence on in-plane shear modulus, although it increases up to 15% of the in-plane shear strength. Multiwall carbon nanotube functionalization improves shear stress transmission between matrix and carbon nanotubes, which represents a reinforcement effect responsible for the increase in in-plane shear strength. Scanning electron micrographs have confirmed in-plane shear tests results.

This paper investigates the effects of radial stresses induced by anchoring component at anchor zone on the tensile properties of basalt fiber-reinforced polymer tendons and proposes allowable radial stresses for design and application. The tensile experiments were first conducted to determine the tensile strength of basalt fiber-reinforced polymer tendons with different types of anchorage including bonding, friction, and compression with protective layer to achieve different levels of radial stresses. The longitudinal compressive strength, transverse compressive strength, and in-plane shear strength of basalt fiber-reinforced polymer tendons themselves were also measured for theoretical prediction. On the basis of experiments, the theoretical analysis by Hoffman strength criterion on ultimate tensile strength of basalt fiber-reinforced polymer tendon was conducted according to the above experimental results while the allowable axial stress for application was studied accordingly. The results show that the radial stress affects significantly on the ultimate strength of basalt fiber-reinforced polymer tendon. The mean values of ultimate strength of basalt fiber-reinforced polymer tendons anchored by friction and compression with different radial stresses are 5, 12, and 15% lower than that of the specimens by bonding anchor. Hoffman strength criterion is proven to be an effective model in predicting the ultimate strength with different anchorages. For 6 mm basalt fiber-reinforced polymer tendon, the radial stresses at the anchor zone are recommended to be below 50 MPa to assure no strength reduction and below 90 MPa with allowable 10% strength reduction. Radial stress is not allowed to exceed 130 MPa to avoid compression failure. The prediction method can guide the design of effective anchorage for the prestressing application of basalt fiber-reinforced polymer tendon.

This paper presents a study on the compressive and flexural strength of engineered cementitious composite (ECC) cubes and slabs, reinforced with various polymer fibres. The type of fibre, fibre content and aspect ratio were the parameters considered in this study. For all types of fibre, the compressive strength of the ECC decreased as the reinforcing index increased. For the ECC polypropylene fibre (PP) slabs, the first crack strength significantly decreased with an increase in the fibre content. For the ECC polyethylene fibre (PE) slabs, the first crack strength decreased as the reinforcing index increased. For the ECC PE slabs, the usage of PE 1600D fibres showed a substantial increase in flexural strength due to their higher tensile strength and E modulus. The ECC PP slabs behaved like plane concrete due to the zero value of flexural strength, which was attributed to the weak interfacial bonding with the cement matrix, low tensile strength and E modulus of the PP fibres. The highest ductility was observed for the ECC-PE slabs with the highest recorded deflection values; these values achieved many extended multiple cracks and an extensive area under the load–deflection curve indicating high energy absorption capacity.

Fiber-reinforced plastics are a cost efficient solution for many structural applications as they offer sufficient stiffness and a large freedom of shapes provided by injection molding. These materials are increasingly being used for making structural components, which are subjected to complex and repeated mechanical loads. Therefore, the need for a method to predict the mechanical behavior of such materials is important. In this work, a through process modeling methodology suitable for coupling the microstructure and the macroscopic response of composites considering plastic injection molding process for different injection modes is presented. The key tasks discussed in this work are (1) simulation of the whole manufacturing process in order to obtain the fiber orientation distribution at each point of the part; (2) estimation of local effective properties using the orientation tensor obtained by performing a two-step homogenization and (3) prediction of the mechanical response as a function of a local anisotropy using a mean-field homogenization technique which is based on assumed relationships between average values of strain and stress fields in each phase. The scheme suggested allows to analyze the influence of processing conditions on elastic properties of composites. By changing these conditions, for example, the injection mode (central or linear), the cavity thickness, the fiber volume fraction, the microstructure and hence the local elastic properties of the material can be tailored. Thus, for desired structural response of composites, the optimum filling parameters can be chosen even at the stage of design.

The word hybrid composite defines the composite containing more than one type of fiber material as reinforcing fillers or additives. It has become an attractive property of hybrid composite than single fiber containing composite. Natural fiber hybrid composites are providing “eco-materials” to the world which has gained key importance in preserving our environment. Due to excess availability of industrial, agricultural, mining, and domestic solid wastes from the primary process, the environmental and ecological storing and disposal problems are created. In order to safeguard the environment, solid waste materials are used as good fillers for making natural fiber polymeric composites to improve its mechanical and moisture properties.