Failure Mechanisms Of Ballistic Resistant Material And Decay Of Its Fibers

Nowadays, it's of great interests to investigate the ballistic resistance and failure mechanisms of personal body armor (including bulletproof vest and helmet), which is mainly made up of high tenacity, high modulus and high performance fiber, and its composites in the personal protection area,This paper for the first time has extensively investigated the microscopic failure modes of the ballistic targets with various structural semi-products (laminated fabrics, orthogonally cross-ply unidirectional laminates and laminated composites reinforced by fabric), different fibers (including p-aramid fiber, UHMWPE fiber and high strength glass fiber) and different combinations (or hybridization) as above described, which were penetrated by China standard lead core bullet and 1.1g chisel-shaped fragment simulating projectile(FSP). For composite or fabric laminated targets, Most of the fibers were failed from shearing in the impacted side of the targets after FSP penetration, and other fibers were failed from compression, bending, twisting, and/or coupled stresses. After bullet penetration there were little fibers failed from shearing but most of the fibers were failed from compression and twisting. But the fibers in any kind of the targets were largely broken by tension at the middle and distal sides of the targets. For the failures of the UHMWPE fibers, the melting morphology of the fracture points were observed. On the basis of microscopic failure observations and the ballistic experiments, it is found that hybridization can effectively improve the ballistic resistance of the hybridized targets, and it is the best arrangement that the fibers with relative low modulus, breaking extension and high brittleness located at the impact side of the target, and the fibers with relative high modulus, high breaking extension and high ductility set at the distal side of the target.Considered that the high performance fibers in the targets were largely broken by tensile stress, and strain rate during the ballistic impact was very high, this paper has measured the tensile impact properties at about 900 s"1 strain rate of several kinds of p-aramid fibers, carbon fiber, glass fiber and UHMWPE fiber by the Split Hopkinson Tensile Bar (SHTB) instrument. It is found that except carbon fiber, other kinds of high performance fibers are sensitive of strain rate, that is, the tensile properties at high strain rate are different from those at low strain rate or quasi-static state. Under assuming that the strength distribution of the single fiber is Weibull distribution with different pairs of scale and shape parameters the dynamic stress-strain equations of the high performance fibers were obtained. The tensile properties of the fibers werenecessary for the subsequent finite element modeling, which were also obtained by the stress-strain curves measured from SHTB instrument.The penetration of FSP into die Twaron 2000 p-aramid fabric reinforced composite was analyzed by a explicit dynamic finite element analysis (FEA). After the analysis, the velocity and acceleration history of the projectile, the relation between striking velocities and residual velocities, the relation between the number of the fabric layers and the ballistic limit (V50), and the evolution of the damage of the target were obtained. The simulation on the hybridization of different fabric types along the through-thickness direction was fundamentally the same to the microscopic failure observations and ballistic impact experiments, and on the simulation basis, a suggestion was put forth that three different kinds of fibers should be used along the through-thickness direction in order to maximize the ballistic resistance of the target. The through-thickness hybridization principle was that the foremost side of the target away from the projectile should have high compression and shear strength, the middle part should have high tenacity, and the distal part should have high break extension.The influence of temperature on the ballistic property of the target cannot...