The propagation mechanism of stress waves Stress wave is the propagation form of stress and strain disturbance, and the mechanical disturbance in the deformable solid medium shows the change of mass speed and corresponding stress and strain state. In ballistic shock, the stress wave produced by the moment of contact between the bullet and the target plate travels in two directions, one is the axial transmission of the continuous pulse along the fiber, the affected fiber is transmitted through the interaction of the base resin and the interlacing point, the stress wave spreads over many fibers, and the other is the longitudinal propagation of the stress wave along the target plate.
Stress waves produce continuous reflections between the fabric and substrate interface of the target plate and the free face of the target plate, causing the pressure to become a pull stress. It is found that when stress waves travel in two different materials, the interface to the two materials produces incident waves and reflective waves, and the transfer of stress waves in materials that produce plastic deformation is much more common than in elastic deformation materials. The speed at which stress waves travel in fibers mainly depends on the Eyang modiform I5 of the fiber and its status in the composite material. In general, the higher the modulus of the material, the lower the mass, and the faster the stress wave travels. Regarding the effect of fiber form on the speed of stress wave propagation, Chen Limin 6 By studying Kevlar 129 and nylon 66 fabrics, it is believed that the presence of overlap points or shrinks of fibers in the fabric will cause the stress wave to react and affect the propagation of stress waves in it (Figure 1). Table 1 shows the propagation speed of stress waves in several free fibers (fibres with a crumpling rate of 0) and fabrics, and it can be seen from the table that the higher the fiber modulus, the faster the rate of stress wave propagation, and the higher the ability of free fibers to transmit stress waves is significantly higher than that of the ethnofibre and parallel fibers. Therefore, in the design of bulletproof composite materials, it is necessary to take into account the mechanical properties of fibers and the state of fibers in the fabric.