تسجيل الدخول

تسجيل

THE MECHANICAL FIT (FRACTURE MATCH)

المؤلف:  Max M. Houck، Jay A. Siegel

المصدر:  Fundamentals of Forensic Science

الجزء والصفحة:  p439-440

2026-08-18

24

THE MECHANICAL FIT (FRACTURE MATCH)

There is one set of circumstances where glass can be individualized to a particular object. This is called the mechanical fit or fracture match. This occurs where a piece of glass breaks into relatively large pieces that have at least one, good, intact edge that can be fitted to the edge of another piece from the same source. Since glass is hard and brittle, it doesn’t deform when broken. Since it is amorphous, there are no lattice points along which the glass would fracture when subjected to force; so fractures would be random events and no two pieces of glass would be expected to break in the same manner. Thus, if there is a good mechanical fit between two pieces of broken glass, one can conclude with certainty that they were once joined. This fit is often aided by the presence of stress marks along the broken edge. These marks are also randomly generated and are caused by the application of force at the breaking point. They can be seen only with the aid of a microscope. Even if a broken edge is relatively featureless, the stress marks will align where the break occurs. In Figure 1(a), a glass fracture match can be seen along with stress marks. Figure 1(b) shows stress marks that appear in glass where it is broken.

Figure 1 (a) A glass fracture match. The photomicrograph on the left is a piece of glass gouged out of a car windshield when the car struck a pedestrian. The photo on the right is the part of the windshield which showed the missing piece. (b) Stress marks produced when glass is broken. The piece at the top of the figure was found in a pair of glasses that were worn by the victim of a hit and run. The bottom piece was found at the scene. The detailed fracture match and stress mark match is strong evidence that the piece of glass at the scene came from the glasses.