Date of Award

Summer 8-2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department/Program

Forensic Science

Language

English

First Advisor

John Reffner

Second Reader

Nicholas Petraco

Third Advisor

Peter Diaczuk

Abstract

Evaluation of fabric defects may provide insight on the specific cause of fiber fracture. In forensic casework, fabric defects may provide a determination of previous occurrences connected to a case. Different methods of fabric breakage impart differing physical characteristics on individual fibers. These alterations to otherwise highly ordered fibers are determined by a multitude of factors, among them temperature. 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.

Due to the importance of temperature in the rapid shear process, temperature altering environmental factors could affect observable fiber characteristics after projectile-fabric interaction. This study aimed to discern how environmental conditions could influence those detectable features. 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 sample types through the microscopical methods noted. Furthermore, loss of birefringence and changes in retardation were noted in these fibers under crossed polarized light. Through this study, it was discovered that the environmental conditions employed did not affect fiber end changes associated with rapid shear.

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