Determination of Unique Fracture Patterns in Glass and Glassy Polymers

The study of fractures of glass, glassy type materials, and plastic has long been of interest to the forensic community. The focus of this interest has been the use of glass and polymer fractures to reconstruct past events and to associate items of evidence. One example of this association is the matching of glass fragments from various locations where they can be shown to have come from a common origin. In the materials science community, fractography is the means and methods for characterization of fractured specimens or components in order to study or identify the mechanism of such failures, which is the focus on most of the literature on the subject. In the forensic science community, the focus is on the concept that assumes each fracture is unique. Generally, it is well-accepted that deviations exist; however, the emphasis has been on classifying and predicting fracture rather than determining that each and every fracture is, in fact, unique. In contrast, the basic premise that fractures are not likely to be reproducible is very relevant to the forensic science community. The issue arises when a given fracture pattern is restored or component pieces are physically fitted together and "matched" and the conclusion is drawn that this match is unlikely to be possible unless all the component pieces were derived from a single, original unit. This study documented the controlled fracture patterns of 60 glass panes, 60 glass bottles, and 60 plastic tail light lens covers. The pane and bottle specimens were fractured with three different types of fracture tips: sharp, round, and blunt. Two basic methods were used to initiate the fractures---dynamic impact from a dropping weight and static pressure from an InstronRTM 4204 Tensile Tester. The fracture patterns were then documented in such a manner that allowed the analyst to inter-compare the fracture patterns. Based on the limited specimens tested in this study, the results appear to indicate that the patterns could be unique. However, more studies under very controlled conditions would be needed to fully determine that each fracture forms a unique and non-reproducible fracture pattern.