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LESSON 7: GLASS FRACTURES
The glass bends in response to any forces that exerted on anyone of its surfaces.
When the limit of its elasticity is reached the glass fractures will occurs.
OBJECTIVES
1. IDENTIFY THE PROPERTIES OF GLASS FRACTURE
2. EXPLAIN THE THEORIES RELATED TO GLASS
TYPES OF GLASS FRACTURES
PROPERTIES OF GLASSES
GLASS FRACTURE
Low-velocity projectiles produce cracks in the glass, which radiate outward from the point of impact (Radial Cracks)
Transparency
Radial and Concentration Fracture
High-velocity impact fracture a high speed projectile striking a piece of glass will produce a cone or crater
Heat resistance
Conchoidal Fracture
Thermal Fracture in non-tempered glass a typical heat crack is curved, has smooth edge, and has no indication of the point of origin of the crack
Pressure, Breakage and Chemical Resistance
Direction of force determinations: This method determines which direction a projectile went through the glass by evaluating radial fractures in the glass fracture’s first concentric ring.
The determination of force direction is a process easily done by a crime scene technician. The purpose of this determination is to establish which direction the projectile went through the glass.
Glass fragments are pieces of larger glass items that cannot be identified, or are less than 50% of the original item. If glass fragments have been in the environment for long periods of time, they may become weathered and the edges may smooth out and they may have a frosty appearance
Place small glass fragments in paper bindles, then in coin envelopes, pill boxes, or film cans which can be marked and completely sealed. Place large glass fragments in boxes. Separate individual pieces with cotton or tissue to prevent breakage and damaged edges during shipment. Seal and mark the box containing them.
Forensic analysis of glass consists of the examination of two or more fragments to determine whether they have a common origin. Identifying broken glass fragments having a common source to the exclusion of all other sources may only be done if they can be physically matched together.