Li Chen

The needled/tufted interlocking fabric is a new fabric structure. At present, the mode II interlaminar shear behavior of needled/tufted interlocking composite has not been clarified. In this work, the needled/tufted interlocking fabrics and reinforced composites were fabricated, and the interlaminar shear behavior of mode II was studied experimentally and numerically, the mechanism of tufting effect on interlaminar shear properties of needled composites was revealed. The study found that the interlaminar shear properties of needled/tufted interlocking composites were greatly improved by tufted fiber bundles. The maximum failure load of the needled/tufted interlocking specimen increased 108.93%, and the interlaminar shear stress of the needled/tufted interlocking specimen improved by 89.39%. The interlaminar shear strength increased linearly with the increase of tufted fiber bundle implantation volume. The implantation pattern of tufted fibers had effected on interlaminar shear property. Under the same implantation volume, the thinner tufted fiber bundles and more implantation points were more beneficial to improve the interlaminar shear performance. The typical shear failure modes included matrix cracking, fibers pullout, and brittle fracture of tufted fiber bundles and needled fiber bundles. Moreover, a numerical simulation model of interlaminar shear behavior based on three cohesive zones (TCZMs) was proposed. The predicted displacement-load curves were highly in accord with the experiments. The error range was controlled within 1.08% - 3.76%. The simulation model could predict the mode II shear behavior of needled and tufted interlocking composites effectively, which was helpful to the early manufacturing process design of needled and tufted interlocking fabrics.

Increasing demand for high-performance applications of composite materials requires an integral forming process for complex components. As a composite reinforcement, 3D (three-dimensional) woven fabric has advantages in producing near-net-shaped preforms. However, previous studies focused on plates with uniform thickness, which are often variable thicknesses or special-shaped parts in practical applications. Some structures are prepared by stitching and then formed in the mold, but this increases the fiber damage. This study proposes a fabric design method based on yarn movement. By controlling the movement direction and distance of each yarn, the warp path in the fabric can be designed, which cause the change of fabric structure and achieve the integrated forming of special-shaped preforms. Based on this method, a software package for the preforms design and simulation is developed, which can be used for various woven and 3D textiles to illustrate its versatility.

This paper studies the ballistic impact performance of 3D woven composites (3DWCs) with hexagonal binding patterns. Para-aramid/polyurethane (PU) 3DWCs with three kinds of fiber volume fraction (V_f) were prepared by compression resin transfer molding (CRTM). The effect of V_f on the ballistic impact behavior of the 3DWCs was analyzed by characterizing the ballistic limit velocity (V50), the specific energy absorption (SEA), the energy absorption per thickness (E_h), the damage morphology and the damage area. 1.1 g fragment-simulating projectiles (FSPs) were used in the V50 tests. Based on the results, when the V_f increases from 63.4% to 76.2%, the V50, the SEA and the E_h increase by 3.5%, 18.5% and 28.8%, respectively. There are significant differences in damage morphology and damage area between partial penetration (PP) cases and complete penetration (CP) cases. In the PP cases, the back-face resin damage areas of the sample III composites were significantly increased to 213.4% of the sample I counterparts. The findings provide valuable information for the design of ballistic protection 3DWCs.

The deformations that occur during composite forming processes are governed by the friction between the fabrics and tooling material on the mesoscopic level. The effect of normal load and multi-plies on the frictional behavior of the carbon plain weave is investigated by simulating the friction between the fabric and metal semi-cylinder tool by using the experimental method. The periodic wavy friction-displacement curve between the metal tool and fabric is caused by the interwoven structure of the fabric. Both the increase in the normal load and the number of layers cause an increase in the real contact area during friction, leading to an increase in the friction force. The real contact area is calculated based on the Hertzian contact model and the self-designed testing method. The friction force values obtained from multiplying the real contact area with shear strength are closely aligned with the measured results.

Ply splicing design is a crucial technology to realize the precise manufacturing of woven composite components with various complex shapes. This paper reports two ways of splicing, inter-layer splicing, and in-plane splicing. Two factors affecting the tensile properties of carbon fiber/epoxy laminated woven composites with ply splicing are discussed, including the number of continuous fabric layers on the surface and in-plane splicing spacing. The deterioration of the composites induced during the tensile test is characterized by acoustic emission and digital image correlation. The results reveal that the damage of the laminated woven composites with ply splicing occurs mainly at the butt jointing location and leads to fracture failure. Ply splicing has little effect on the tensile modulus of the composites. The tensile modulus is slightly reduced between 2% and 5%. But ply splicing has a more significant effect on its tensile strength. The total number of continuous fabric layers at the splice position approximately determines the strength retention ratio. The more the number of continuous fabric layers on the surface are, the higher the tensile strength of the composites. When the number of continuous fabric layers on the surface is three layers, the tensile strength retention ratio reaches 69%. The larger the splicing spacing is, the better the tensile properties of the composites. When the splicing spacing is increased to 30 mm, the tensile strength retention ratio reaches 77%.

The mechanical properties of yarns have a decisive effect on the performance of fiber-reinforced composite materials. Predictive simulations of the mechanical response of yarns are, thus, necessary for damage evaluation and geometric reconstruction of textiles. This paper proposed a quasi-fiber scale virtual modeling method regard to the axial tensile and transverse compressive behaviors of the twisted yarns. A stochastic properties model of the yarn was established for characterizing the statistical distribution of tensile strength. The variation of modeling parameters, including coefficient of friction, the amounts of virtual fibers per yarn and element length, versus calculation accuracy has been determined based on axial tensile and transverse compressive behavior of quartz fibers. The relationship between modeling parameters and mechanical behavior of yarn was established within the scope of this study. Axial tensile and transverse compressive behavior of yarns with different twists were predicted. The results show that balance between the modeling precision and computational efficiency can be achieved using the parameters, the COF of 0.35, virtual fiber count of 122 and Le of 0.3. This efficient modeling method is meaningful to be developed in further virtual weaving research.

Wearable human–computer interaction equipment is a common technology, which can improve the comfort, convenience, and safety of the human body, and also can monitor human health. The flexible and wearable tensile sensor can be conveniently installed on clothes or directly connected to the body. This provides a convenient, timely, and portable solution for the detection of human motion. Therefore, wearable electronic equipment is gaining more attention. In this paper, a highly stretchable, flexible, and sensitive strain sensor which is based on multi‐walled carbon nanotubes/Ecoflex nanocomposites is reported. A monofilament tensile sensor obtains good linearity (10.77%), low hysteresis (1.63%), good stability (6000 cycles under 100% strain), and ultra‐high strain range (ε = 1300%). This ultra‐stretchable sensor has potential applications in human motion monitoring, medical rehabilitation, health monitoring, human–computer interaction, and soft robots.

The aim of this study executed on Silicon Nitride (Si₃N₄) yarn is to examine some bending damage behaviors and fracture mechanisms that occur during the 3D orthogonal fabric forming process. A three point bending experiment device has been developed in order to simulate the Z-binder yarn bending condition. The effects of weft density, fabric thickness, and yarn tension have been studied. The Weibull analysis of the tensile strength show that the bending damage increases with the increase of weft density, fabric thickness, and yarn tension. The resulting bending damage causes a reduction in yarn strength of between 2.5 and 17.2% depending on the bending parameters of yarn. The growth of the fibrillation area also reflects similar trends with tensile strength loss rate. The fibrillation length produced by the yarns is mostly distributed within the range of 0.3 to 0.9 mm. A comparison of the calculation result to experimental data shows the bending fracture probability of filaments inside yarn are less than that of monofilament. The tensile and bending fracture of Si₃N₄ filaments exhibit typical brittle fracture characteristics.

A new algorithm to rapidly create representative volume elements (RVE) with random fibers distribution of high volume fractional was proposed. Derived from the classical hard core algorithm, and the “molecular force” effect was introduced to eliminate the irreversibility of the generation process. The new algorithm can create fiber microstructures with constant or random radius, and the volume fraction can reach 80% and 85% respectively. The stochastic statistical analysis of the generated fiber distribution shows that the generated microstructure is completely consistent with the spatial random distribution. Micro‐flow analysis was performed using the generated RVE, predicting the transverse permeability of the fiber tow, and the predicted results were in good agreement with the experimental results. A simple method for creating RVE with random distribution of fibers was provided for the micro‐mechanical analysis of composite materials.