NCJ Number
241445
Date Published
2013
Length
99 pages
Agencies
NIJ-Sponsored
Annotation
This study tested the hypothesis that fracture patterns in glass and glassy polymers are unique and therefore unlikely to be reproducible due to distinctive matrix imperfections.
Abstract
The study found that although some similarities were found in a limited number of specific fracture lines, the overall patterns were not duplicated. The fracture patterns of plastic lenses exhibited some general similarities, such as the center of many of the lenses breaking completely out of the lens. They also had a tendency to fracture along the mold lines of the lens; however, there were no duplicates of overall fracture patterns. Thus, the report urges caution in evaluating the uniqueness of fracture in this type of material. In supporting the theory that coincidental duplication fracture patterns are highly unlikely, this research aids practitioners in substantiating court testimony about the significance of fracture matching of broken glass and polymers materials. This study documented the controlled fracture patterns of 60 class panes, 60 class bottles, and 60 plastic tail light lens covers. The pane and bottle specimens were fractured with three types of penetration tips: sharp tip, round tip, and blunt tip. Two basic methods were used to initiate the fractures: dynamic impact from a dropping weight and static pressure from an Instron 4204 Tensile Tester. The fracture patterns were than documented in detail in a manner that allowed the analyst to inter-compare the fracture patterns. 41 figures; 10 tables; 28 references; and appended fracture images, high speed fracture video, testing device design, and timing system
Date Created: March 27, 2013