Abstract:

Objective In order to reveal the influence of reinforcement parameters on the impact properties of three-dimensional angle interlock composites, angle interlock composites were designed and prepared with two levels of reinforcement tightness and three levels of weft density, and the influences of fabric structure parameters and layering methods on low-velocity impact properties of the composites are investigated.

Method Three-dimensional angle interlock fabric reinforcements were prepared using a three-dimensional loom and composites were prepared using vacuum assisted resin transfer molding process (VARTM). The low-velocity impact test was carried out by using the double-guide drop hammer impact tester. After the low-velocity impact test, the crack area of the matrix on the back of the samples was measured, the depth of the pit on the front of the sample was measured by a digital depth meter, and the damage morphology of the impact surface of the material was photographed by a camera.

Results When fabric tightness decreases from 46% to 37%, fiber binding to the matrix weakens. Under impact, the matrix deforms more, increasing the likelihood of shear failure between resin-rich weft points and adjacent buckling warp edges. This lowers the material's mean-failure energy. Cracking behavior in material matrices varies with impact energy and tightness. Under low impact, tighter materials form micro-cracks, reducing cracking area but facilitating crack growth with increasing energy. Looser materials show limited micro-crack expansion and only crack at higher impact due to their structure. Under high impact, tighter materials have deeper pit fronts but smaller cracking areas, with aramid fibers absorbing energy through deformation. Stronger matrix-fiber binding leads to greater deformation, deeper pits, and enhanced impact absorption. Raising weft density from 30 to 36 picks/cm boosts mean-failure energy from 20.2 J to 27.1 J. Higher weft density increases fiber volume in plastic deformation, potentially enhancing matrix brittleness due to compressive stress, but overall improves the material's energy absorption. As weft density increases, the cracking area of the matrix exhibits a first increasing then decreasing trend at lower impact energy. Initially, an increase in weft density from 30 to 33 picks/cm, enhances warp bending wave height at warp-weft overlaps, leading to a more pronounced stress concentration and increased matrix cracking under impact loads. However, as weft density rises to 36 picks/cm, yarns squeeze each other during weaving, reducing fiber gaps and altering warp turning angles due to yarn deformation, which stabilizes the cracking area. Additionally, the arc shape of warp and weft yarns dissipates impact load, further reducing cracking likelihood. At higher impact energy, matrix cracking decreases with increasing weft density, as aramid fibers absorb energy through plastic deformation, and a higher fiber volume content per unit area due to increased weft density further decreases cracking.

Conclusion Fabric tightness and weft density have significant influences on the impact resistance of the material, and the fabric with greater tightness shows better impact resistance. When the total tightness of the fabric increases from 37% to 46%, the mean-failure energy per unit weight of the composite increases from 5.48 J/kg to 8.08 J/kg, implying a weight reduction by about 1/3. With the increase of weft density, the impact resistance of the composite is improved. When the weft density increases from 30 to 36 picks/cm, the mean-failure energy of the material increases from 20.2 J to 27.1 J. In addition, the same direction laminated composite has better impact resistance. Under lower impact energy, the bearing body of the angle interlock composite is the matrix, and under higher impact energy, the bearing body is the reinforcement.

Key words: three-dimensional angle interlock composite, reinforcement, aramid fiber, tightness, weft density, lay-up angle, impact resistance