Mechanical properties of bifacial fabrics

Abstract

This study focuses on the qualitative evaluation of the mechanical properties of bifacial fabrics, which have a knitted structure on one face and a woven structure on the other. Woven, knitted, and bifacial fabrics were produced on a purpose-built machine, using wool/acrylic and polyester yarns. The bifacial fabric was manufactured with the woven structure being a plain weave and the knitted structure being a single jersey. The results of load–extension test showed unique tensile behavior, with two breakages in both the warp and weft directions, representing the woven and knitted structures. The bending length of the bifacial fabric in the weft direction with its knitted face up was smaller than that in the warp direction, and the bending length in the warp direction with its knitted face up was similar to that in two directions with the woven face up. The bifacial fabric demonstrated unique abrasion resistance on two faces, combining the performance of the knitted and woven fabrics in abrasion resistance. The abrasion resistance on the woven face was better than that on the knitted face. The knitted face of the bifacial fabric generally pilled less than the knitted fabric after abrasion over a certain number of cycles.

Keywords

bifacial fabric knitted structure mechanical properties woven structure

Skin, consisting of the epidermis and the dermis, is the largest organ in the human body. It is soft enough to allow movement, yet tough to withstand breaking and tearing.¹ Abrasions and incised wounds often occur to the skin in daily life, which may cause severe infection or bleeding. However, these injuries can be minimized or avoided by wearing suitable clothing as a protective barrier.

As a barrier to damage, clothing should absorb as much of the energy of the damage as possible, and the clothing usually endures the effects of punching, stretching, and abrasion on rough surfaces.² In this case, clothing is expected to have abilities such as suitable thickness to decrease the punching force, high toughness to absorb the stretching energy, good structural integrity even after some damage, and strong abrasion resistance.

The mechanical properties of traditional woven and weft knitted fabrics have been widely studied. Weft knitted fabrics are generally thicker and have better stretch and recovery properties than woven fabrics. The curved nature of the weft knitted loops allows knitted fabrics to endure high deformation.³ Woven fabrics are stronger, structurally more stable and have smoother surfaces than weft knitted fabrics.⁴ Hence combining these two structures in a single fabric might be a preferable approach to utilize the advantages of both fabrics.

Several methods to produce woven–knitted preforms have been reported, such as lamination and stitching.^5–7 These fabrics were very thick and heavy, and were used primarily in reinforced composites. Two outer layers of plain woven fabrics and two inner layers of weft knitted fabrics with four knitting structures were stitched together to produce the woven–knitted preforms.⁶ These preforms were impregnated with polyester resin prior to tests. It was found that the knitted structure inside had an outstanding impact on the mechanical properties of the composites, and the composite performed best on energy absorption and tensile strength when it was produced with interlock fabrics as its inner side.

Producing co-woven–knitted (CWK) fabrics with both woven and knitted structures has been previously achieved on a modified circular knitting machines⁸ and a modified flat knitting machine,^9–11 focusing on shielding properties^9,12 and reinforcement of composites.^13–16

In our previous study, bifacial fabric structures were developed for apparel applications using a purpose-built machine (Figure 1).¹⁷ Briefly, the needle bed was placed on a weaving machine with the needles’ tips close to the fell of the cloth and parallel to the lower layer of warp yarns.¹⁸ When weaving, the needles on the flat bed stayed at the rest position holding the old loops. When knitting, the needles were pushed forward by cams to catch the loop yarn in their hooks and then pull the loop yarn out of the warp yarns and old loops to shape new loops. During this procedure, there were no changes to the operation of the weaving machine.

Figure 1.

The purpose-built machine for bifacial fabric production: (1) heads, (2) reed, (3) weft yarn selector, (4) warp yarns, (5) knitting bed, (6) cam, (7) bifacial fabric.

The bifacial structure is a newly developed fabric structure with a woven structure on one face and a knitted structure on the other, which is different from other fabrics, such as laid-in and so called co-woven–knitted fabrics.¹⁸ For example, in laid-in structures, warp or weft yarns were not woven or knitted with other yarns, and they were simply inlaid in the structures. Both the woven and knitted structures can be observed on two faces of the co-woven–knitted fabrics.

The bifacial fabric, as a hybrid textile, shows unique appearances, heat, and moisture transfer properties.^18,19 Briefly, water transfer on the woven face was much greater and faster than on the knitted face, and for a given fabric weight or thickness the thermal and evaporative resistances of the bifacial fabric were smaller than those of the woven and knitted fabrics. These unique properties can potentially be used to engineer or tune the performance of textiles. In this study, tensile strength, abrasion resistance, pilling properties, and bending stiffness of the bifacial fabric are investigated.

Experimental details

Fabrication

Table 1 shows the details of fabric samples. Though the warp and weft/loop yarns have the same fiber contents, their yarn parameters are normally different. Since warp yarns must withstand more load and abrasion than weft yarns during weaving, ring spun yarns with higher twist were selected as the warp yarns, and ring spun blended yarns with fewer twists were used as weft and loop yarns. The woven (plain weave) and knitted (single jersey) fabrics were produced on a weaving machine (CCI, Taiwan) and a knitting machine (Shima Seiki SES, Japan), respectively. The basic (Figure 2) bifacial fabrics were manufactured on a purpose-built machine, where the basic structure had only one weft yarn in one repetition (marked in red in Figure 2).¹⁷

Table 1.

Details of the fabrics used in this study

Fabric	Warp yarns			Weft/loop yarns
Fabric	Material	Count (tex)	Twist (/10 cm)	Material	Count (tex)	Twist (/10 cm)
Woven	100% polyester (white)	56	110 ± 9	35% acrylic/65% wool (red)	65	78 ± 5
Knitted	N/A			35% acrylic/65% wool (red)	65	78 ± 5
Bifacial	100% polyester (white)	56	110 ± 9	35% acrylic/65% wool (blue)	65	78 ± 5

Figure 2.

The basic bifacial fabric structure. (a) 2D sketch of the basic structure (1: warp yarn; 2: weft yarn; 3: loop yarn); (b) 3D sketch of the knitted face; (c) 3D sketch of the woven face (green: warp yarn; red: weft yarn; grey: loop yarn).¹⁸

Measurement of physical properties

All fabrics were conditioned at standard conditions (21 ± 2℃ and 65% ± 2% relative humidity)²⁰ prior to testing. The thickness (mm) of the fabrics was measured according to ASTM D1777-96(2011)²¹ using the Absolute Digimatic ID-C 1012PB thickness gauge (Mitutoyo Corp., Japan) with a foot diameter of 56.42 mm and a pressure of 1 kPa. Ten points on each sample were measured, and the average thickness was reported. Fabric weight was measured and mass/area (GSM: g/m²) was calculated for each sample. Volumetric density values (g/cm³) were calculated based on the GSM and fabric thickness.

Tensile strength tests were carried out using an Instron 30KN tensile tester (Instron Corp., USA) according to standard test method ASTM D5035-11.²² The distance between the surfaces of two jaws (gage length) was set at 75 ± 1 mm, and the selected testing range was 300 mm (this was quite close to the max range) under a loading rate of 300 ± 10 mm/min. Jaws with smooth metallic surfaces were selected according to the test standard, and no obvious jaw slippages were observed during tests of bifacial fabric samples. Five samples (25 mm × 150 mm) from the warp direction and eight samples (25 mm × 150 mm) from the weft direction of preconditioned fabrics were randomly taken, and they were measured under a uniform pretension (less than 0.5% of the full scale force). The typical load–extension curves of these specimens were reported.

Abrasion resistance was measured according to ASTM D4966-12e1 using a Martindale Abrasion and Pilling Tester (IDM, Australia),²³ with a specimen diameter of 38 mm and a pressure of 12 kPa. The knitted and woven faces of the bifacial fabrics were tested, while only the “outer” faces of the woven and knitted specimens were tested. The weights of specimens before and after specified cycles of abrasion were measured. The mass loss was then calculated and reported as a percentage of the mass before the abrasion.

Pilling tests were carried out on a Martindale Pilling Tester (James H Heal & Co., UK) according to ISO 12945-2.²⁴ Three pairs of circular specimens from each sample were cut with one of each pair of specimens being 100 mm in diameter for the top sample holder and the other 140 mm in diameter for the bottom sample holder. A weight of 155 ± 1 g was applied to the specimens when testing according to Category 3 of the ISO testing standard. Visual assessment of pilling was completed in the viewing cabinet after each assessment stage. Each specimen was graded in accordance with the standard pilling photographs (EMPA Standard©, SN 198525), and the average grades were reported as the pilling results of fabrics.

Bending stiffness tests were carried out on a fabric stiffness tester (SDL Atlas, USA) according to standard test method ASTM D1388-08(2012).²⁵ Briefly, four specimens (25 mm × 150 mm) from the warp direction and four specimens (25 mm × 150 mm) from the weft direction were tested. The knitted and woven faces of both ends of each specimen were tested and calculated separately. Measurements in the same direction on the same face of the samples were averaged and reported as the overhang length on each face of the fabric sample. Bending length was equal to half of the overhang length. Flexural rigidity of individual specimens was calculated using equation (1)²⁵ where G is flexural rigidity (µjoule/m); W is fabric mass per unit area (g/m²); and c is bending length (mm).

Statistical analysis

A one-way analysis of variance (ANOVA; SPSS Statistics 22, IBM) was applied to the mass/area (n = 5, sample number of one fabric), thickness (n = 10), and bending length (n = 4) to test the significance of differences between fabrics at the 0.05 level. Pilling grades (n = 3) were analyzed using nonparametric tests (Independent Samples with Kolmogorov–Smirnov Test) at the 0.05 level.

Results and discussion

Appearance of bifacial fabrics

The bifacial fabrics have a unique appearance, with a knitted structure on one face and a woven structure on the other.

Comparing with conventional knitted (single jersey, Figure 3(a) left) and woven (plain weave, Figure 3(a) right) fabrics, there are only the knitted structure on one face (Figure 3(b) left) and only the woven structure on the other (Figure 3(b) right) of the bifacial fabric.

Figure 3.

Appearance of (a) knitted (single jersey) and woven (plain weave) fabrics, and (b) bifacial fabric.¹⁸

Visual observation of the fabric surface implied that the surface on the woven fabric feels smoother than the woven face of the bifacial fabric. The vertical lines seen on the woven face of the bifacial fabric cannot be seen on the woven fabric. The reason is that in the bifacial structure some weft yarns were pulled out of the warp yarns by the needles to create new loops at the intersections, and these weft yarns cannot force the warp yarns to bend regularly at the intersections (e.g. the white warp yarn in Figure 4(b)) as those in the woven fabrics. The “free” warp yarns had to stay at the bottom of valleys on the woven face of the bifacial fabric, while those effectively controlled warp yarns were pulled to the peaks by weft yarns, due to the looseness of loops and the stiffness of the weft yarns.

Figure 4.

Cross-sections of the bifacial fabric: (a) view in the warp direction; (b) view in the weft direction.¹⁸

Figure 4 shows the appearances of cross-sections of the bifacial fabric. It is clear that there are only knitted loops or wales on the upside (Figure 4(a)), and they are looser than the woven structure under them. The distribution of the warp yarns in Figure 4(a) also confirms the explanation of the rougher woven surface mentioned above. It can be observed in Figure 4(b) that the knitted loops are rooted in the woven structure, and the direction of fibers in the knitted loops is from the knitted face to the woven face.

As a result, the woven and knitted structures were woven or knitted together, and the loops are shaped by pulling out the weft yarns in the bifacial fabric structures. Both of the two structures are merged into one layer, with the sinker arcs of loops still knitted as the weft yarns of the woven structure, while the needle arcs and loop arms stand on the woven structure and are linked to each other in the warp (wale) direction.

Structural characteristics

As Table 2 shows, the bifacial fabric has the same warp density as the woven fabric, and its wale density is slightly lower than the knitted fabric. The GSM of the bifacial fabric is less than the sum of the GSM of the woven and knitted fabrics, and so is the thickness. The differences in GSM and thickness among the three fabrics are statistically significant (Table 3). The volumetric density of the bifacial fabric is slightly less than that of the woven fabrics.

Table 2.

The measured constructional properties of the woven, knitted, and bifacial fabric samples used in this study

Fabric	Woven face		Knitted face			Mass/area (g/m²)	Thickness (mm)	Volumetric density (g/cm³)
Fabric	Warp (threads/cm)	Weft (picks/cm)	Course (courses/cm)	Wale (wales/cm)	Loop length (mm)	Mass/area (g/m²)	Thickness (mm)	Volumetric density (g/cm³)
Woven	11	22	N/A	N/A	N/A	203 ± 2.3	0.86 ± 0.01	0.237 ± 0.003
Knitted	N/A	N/A	10	8	5.3 ± 0.2	246 ± 4.1	1.23 ± 0.03	0.199 ± 0.003
Bifacial	11	11	11	6	5.9 ± 0.3	400 ± 4.5	1.73 ± 0.03	0.231 ± 0.003

Table 3.

Analysis of variance results for mass/area and thickness of the woven, knitted, and bifacial fabrics

Factor	Sum of squares	Degree of freedom	f-value	p-value
Mass/area	0.002	2	5014.679	<0.001
Thickness	3.817	2	2798.853	<0.001

The woven structure of the bifacial fabric restricts the ability of the knitted loops to reach the relaxed state to the same extent as they do in the knitted fabric. Those loops in the bifacial fabric cannot relax and expand in the fabric surface direction but can in the fabric thickness direction, leading to greater thickness than the knitted fabric (Table 2). This also results in the denser knitted structure of the bifacial fabric, with more loops per unit volume than the knitted fabric in this study, as the loops lack relaxation and are fixed by the woven structure in the bifacial fabric. Since the woven structure of the bifacial fabric is the same as the woven fabric, volumetric density of the bifacial fabric with both the woven and knitted structures is higher than the knitted fabric, yet slightly lower than the woven fabric.

Tensile strength

Typical load–extension curves of the woven, knitted, and bifacial fabrics are collected from original results to find their differences. As illustrated in Figure 5(a) and (b), the load–extension curves of the bifacial fabric show two peaks along both the warp and weft directions of the fabric, which differs from the woven and knitted fabrics, with only one breakage. The differences of the curves are expected to be caused by the different fabric structures, and not by the materials, because the woven, knitted, and bifacial fabrics were manufactured with the same yarns (Table 1), and the curves of the bifacial fabric agreed with the peaks of the woven and knitted fabrics very well. The total energy (the area under the curves, calculated using the module of Mathematical Area in Origin 8.0 (OriginLab, USA)) absorbed by the bifacial fabrics (warp direction: 8.4 Joule, weft direction: 14.9 Joule) was apparently greater than that of the woven (warp direction: 2.4 Joule, weft direction: 7.2 Joule) and knitted fabrics (warp direction: 6.1 Joule, weft direction: 3.6 Joule).

Figure 5.

Load–extension curves of woven, knitted and bifacial fabrics; (a) warp direction; (b) weft direction.

When testing the bifacial fabric specimens in the warp direction, slight slippages of some warp yarns were observed before the first breakage, as shown in Figure 5(a). This was due to some of the warp yarns not being tightly fixed by weft yarns, as explained earlier, and the higher fabric thickness increased the slippage of the warp yarns. On the contrary, this did not occur on the woven fabric, which had tightly fixed yarns and lower fabric thickness. However, the slippage here had little influence on the completion of tests and qualitative evaluation of differences among the three fabrics.

Generally speaking, the woven structure has straighter warp and weft yarns (Figure 4), resulting in higher break force and lower elongation, while the curved nature of loops allows the knitted structure to have lower break force and higher elongation. The slope of the first peak of the bifacial fabric in Figure 5 (24.24 in the warp direction and 31.50 in the weft direction) was similar to that of the woven fabric (32.84 in the warp direction and 35.47 in the weft direction), while the slope of the second peak (0.56 in the warp direction and 2.62 in the weft direction) approximately equaled that of the knitted fabric (0.71 in the warp direction and 3.17 in the weft direction). Along with the observation during tests, the warp or weft yarns in the woven structure were broken prior to the loop yarns in the knitted structure in both directions. Therefore, the first peak represents the tensile performance of the woven component, and the second peak corresponds to the knitted component in the bifacial fabric. The two peaks are similar to those of the woven and knitted fabrics, respectively.

In the warp direction, the second peak of the bifacial fabric is far away from the first one (Figure 5(a)). The remaining knitted loops were almost free in the broken area after all warp yarns were broken (first peak), which was shown by the load value (close to zero N) around the extension of 50 mm, because the loop arms had to bend heavily over the weft yarn to catch the next loop along the warp direction, and they released the bending parts when the warp yarns were broken. Moreover, fewer wales (6 wales/cm, Table 2) on the limited width of specimens caused reshaping and movement of the loops in the knitted structure.²⁶ After the first peak occurred, the broken area was so loose that loop yarns could slip and move over one another, leading to a higher elongation in the second peak. Actually, the width of the bifacial fabric specimen decreased sharply in this period, while the length of the bifacial fabric specimen increased substantially until breakage occurred.

In terms of the weft direction (Figure 5(b)), there were more loop yarns (11 courses/cm, Table 2) in the broken area of the bifacial fabric specimen after weft yarns in the woven structure broke. These loop yarns let the bifacial fabric perform well on the height of the second peak. However, the smaller wale density of the bifacial fabric (6 wales/cm, Table 2) resulted in a smaller elongation of the second peak along the weft direction (approximately 80 mm in Figure 5(b)). Specifically, lower wale density gave higher tension of loop yarns, due to less contraction than the knitted fabric (see wale density in Table 2), as knitted loops in the bifacial fabric were fixed by the woven structure. During tensile tests, the two ends of specimens (loop yarns) were held by the clamps of the tensile tester, and the loops were so tight that they could not supply extra yarns for the elongation of the specimen. In other words, loops could not be easily reshaped and pulled out from one to another, leading to a lower elongation of the second peak.

Abrasion resistance

In abrasion resistance tests, the unique structure of the bifacial fabric allowed the fabric to perform in different ways on each face (Figure 6).

Figure 6.

Mass loss percentage of woven, knitted, and bifacial fabrics under abrasion.

Generally, the knitted face of the bifacial fabric experienced less mass loss than the knitted fabric before 20,000 cycles. This can be explained using the four steps: fuzz formation, entanglement, growth, and wear-off.²⁷ The knitted face of the bifacial fabric and the knitted fabric were made from the same yarns (Table 1) and thus would have similar fuzz formation and entanglement at the very beginning. Since loop yarns in the bifacial fabric were tightly fixed by the woven structure, fibers in the loop yarns were not easy to pull out during abrasion, leading to less growth and wear-off when compared with the looser knitted fabric. However, a gradual increase of the mass loss percentage on the knitted face of the bifacial fabric was still observed, as some fibers under stretching or abrasion in the loop yarns broke with continuous abrasion.

The mass loss percentage on the knitted face of the bifacial fabric increased rapidly after 20,000 cycles, which was much quicker than the knitted fabric. When all loops on the knitted face of the bifacial fabric were broken, although the remaining weft yarns were still woven with warp yarns, these weft yarns could not effectively fix the warp yarns, but only separate the warp yarns into two layers (Figure 7(b) left). At this moment, the woven structure could not hold the loop yarns any more. Hence the broken loops were very easy to remove, and weight loss occurred sharply with continuous abrasion. However, the overall trend of mass loss percentage on the knitted face of the bifacial fabric is similar to that of the knitted fabric, which differs from the woven fabric and the woven face of the bifacial fabric.

Figure 7.

Appearances of fabrics after abrasion: (a) knitted and woven fabrics, and (b) knitted and woven faces of the bifacial fabric. The white square in Figure 7(b) show some slight damage to the weft/loop yarns.

As explained earlier, the woven face of the bifacial fabric had more raised strips, and was thus rougher than the woven fabric (Figure 3), which reduced the abrasion resistance on the woven face. Although the mass loss percentage on the woven face of the bifacial fabric was slightly lower, due to higher GSM (Table 2), than that of the woven fabric after 20,000 cycles, its actual mass loss was greater. This was proved in the white square in Figure 7(b, right), where the weft yarns became much thinner after abrasion, as some fibers in these weft yarns were broken and removed. However, since the weft yarns in both the woven fabric and the woven face of the bifacial fabrics were tightly fixed, the woven face of the bifacial fabrics still maintained structural integrity and performed in almost the same manner (Figure 6) as the woven fabric throughout the abrasion testing process.

The left image in Figure 7(b) seems to show a negative abrasion result on the knitted face of the bifacial fabric. This is, as explained earlier, due to the unique bifacial fabric structure. The loop yarn was one of two weft yarns in one unit of the plain weave (Figure 2), so the fabric structure is thoroughly destroyed if one of the two weft yarns is taken away. At this moment, only the other weft yarns (blue) and warp yarns (white) are observed (left image in Figure 7 (b)) and weight lost rises sharply at about 30,000 cycles (Figure 6).

Since woven fabrics normally have less pilling, only the knitted fabric and the knitted face of the bifacial fabric were examined on the pill tester. The pilling performance of the knitted fabric and the knitted face of the bifacial fabric was assessed as shown in Figure 8, and their difference was not statistically significant (p = 0.1 at 2000, 3000, 4000, and 7000 cycles, p = 0.518 at 5000 cycles). However, bifacial fabrics seemed to perform better than the knitted fabrics.

Figure 8.

Visual assessment grades in pilling tests of knitted fabrics and the knitted face of bifacial fabrics. Error bars show standard deviations.

Even though the knitted face of the bifacial fabric has a similar surface structure to the knitted fabric, loops in the bifacial fabric are fixed much more tightly than those in the knitted fabric, leading to different performance in the four pilling steps: fuzz formation, entanglement, growth, and wear-off.²⁷ Before 500 cycles (Figure 8), fewer fibers were pulled out from the two fabrics, and protruding fibers (hairiness) were primarily responsible for the similar trend. With continuous abrasion, it was easier to pull fibers out from the looser knitted fabric, and the looser knitted fabric pilled more than the knitted face of the bifacial fabric, due to the loops in the bifacial fabric being fixed by the woven structure on the back, resulting in a lower pilling grade after 500 cycles. It was observed that the number and size of pills on the knitted and bifacial fabrics increased after 500 cycles, which also reflected the increasing number of free fibers pulled out. In addition, there were no pills obviously falling off, which might be due to the light loading (155 g) and tenacious wool/acrylic fibers.

Bending stiffness

The bifacial fabrics are generally stiffer than knitted and woven fabrics (Figure 9). However, the bending length on the knitted face along the weft direction of the bifacial fabric is smaller than that of the woven fabric, yet greater than that of the knitted fabric. The differences in bending length of the woven, knitted, and bifacial fabrics are statistically significant (Table 4). This is considered to be caused by the unique structure, particularly the thickness and the interaction between the knitted and woven structures of the bifacial fabric.

Figure 9.

(a) Bending length, and (b) flexural rigidity of knitted, woven, and bifacial fabrics. Error bars show standard deviations.

Table 4.

Analysis of variance results for bending length of the woven, knitted and bifacial fabrics

Groups	Sum of squares	Degree of freedom	f-value	p-value
Warp direction and knitted face up	403.083	2	355.475	<0.001
Warp direction and woven face up	859.849	2	775.075	<0.001
Weft direction and knitted face up	310.630	2	804.407	<0.001
Weft direction and woven face up	456.891	2	899.064	<0.001

In the warp direction of the bifacial fabric, the interlinked structure (woven structure or wales in the knitted structure) prevents the specimen from bending (pulling the top face or pushing the bottom face), and the thickness of the fabric enhances this effect. This interaction results in a higher bending length in the warp direction.

In the weft direction with the knitted face (“outer” face for knitted and woven fabrics) placed up, the wales on the knitted face are separated, and they cannot push or pull the fabric on the surface. Therefore, the woven structure on the back side has a more important impact on the bending length. In the woven structure of the bifacial fabric, there are 11 weft yarns and 11 loop yarns per centimeter (Table 2). Because of the curved nature, the loop yarns (only sinker arcs of loops actually) are too weak to affect the bending length, which is also the reason for the lowest bending length of the knitted fabric. So the number of the weft yarns determines the bending length. In this way, the woven fabric with the highest weft density (22 picks/cm, Table 2) has the longest bending length. With a weft density of 11 picks/cm (Table 2), the bending length of the bifacial fabric in the weft direction with its knitted face placed up should be between the woven and knitted fabrics.

In the weft direction with the woven face up, the bending length of the bifacial fabric is explained by a schematic shown in Figure 10. The knitted wales on the knitted face of the bifacial fabric are closer to each other and push on each other when the fabric is bent towards the knitted face along the weft direction. Meanwhile, the woven structure (upside) will pull the bending part. The interaction of them increases the bending length in this situation.

Figure 10.

Bending model of bifacial fabrics in the weft direction with the woven face up.

Conclusion

Bifacial fabrics have a unique appearance, with a woven surface on one face and a knitted surface on the other. The bifacial fabric demonstrates unique abrasion resistance, combining the performances of knitted and woven fabrics compared in this study. The abrasion resistance of the woven face outperforms the knitted face of the bifacial fabric. The knitted face of the bifacial fabric generally pills less than the knitted fabric after abrasion over a certain number of cycles. The tensile behavior of the bifacial fabric is unique, with two tensile peaks and a relatively high toughness in the warp and weft directions due to the combination of the woven and knitted structures. This behavior is helpful in obtaining structural integrity after the first breakage, and it might be suitable for some special applications, such as protective clothing and reinforced composites. The bending length of the bifacial fabric in the weft direction with its knitted face up is smaller than that in the warp direction, and the bending length in the warp direction with its knitted face up is similar to that in both directions with the woven face up.

Since this study is an overall evaluation of the mechanical properties of bifacial fabrics, quantitative investigations on bifacial fabric structures and their properties are still required. The purpose-built machine should be improved as well, to enhance the quality of the bifacial fabrics in the future. More bifacial fabrics made from other fibers and patterns should be examined to verify the results in this study.

Footnotes

Acknowledgements

We would like to thank Andrew Jones, Doug Dower, and Peter Herwig from CSIRO Manufacturing for woven and knitted fabrication. Appreciation is also extended to Professor Wu Chen for facilitating the bifacial fabric sample production at Wuhan Textile University. We also acknowledge the MoE Innovation Team Project in Biological Fibers Advanced Textile Processing and Clean Production for supporting the construction of the purpose-built bifacial fabric production equipment.

Declaration of conflicting interests

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

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors received the support of the MoE Innovation Team Project in Biological Fibers Advanced Textile Processing and Clean Production for the construction of the purpose-built bifacial fabric production equipment.

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