Environmental factors affecting rapid shear in fibers from the passage of a bullet

In forensic casework, examination of garment damage can provide insight into the mechanism of the specific cause of fiber failure. Different methods of damage impart differing physical characteristics on individual fibers. These alterations are determined by a multitude of factors, among them increased temperature of affected fibers. The process of rapid shear occurs in thermoplastic materials following high-speed impact. It results in distinct features caused by excessive heat generated through the interaction, which is unable to dissipate at a rate that would leave the fibers unchanged. Rapid shear characteristics can be differentiated from other fracture patterns through non-destructive microscopical methods and with a minimal sample size. Fabric samples were shot under heated, chilled, and water-saturated conditions, using ammunition of varying velocities. Analyses performed on the defects were conducted using stereomicroscopy, polarized light microscopy and scanning electron microscopy. Globular-shaped fiber ends, characteristics attributed specifically to rapid shear, were observed in all nylon samples. Through this study, it was determined that the environmental conditions employed did not affect fiber end changes associated with rapid shear.