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GLASS FRACTURES
3
Transcript
GLASS FRACTURES
Lesson Objectives:
- Identify the properties of glass;
- Explain the theories related to glass fracture.
GLASS FRACTURES
Properties of Glasses:
The main character of glass are transparency,hit resistance,pressure and breakage resistance, and chemical resistance
Glass Fracture:
The glass bends in response to any force that is exerted on anyone of its surfaces ;when the limit of its elasticity is reached , the glass fractures. Frequently, fractured window glass will reveal information that can be related to the force and direction of an impact; such knowledge may be useful for reconstructing events at a crime scene investigation.
Types of Glass Fractures:
- LOW VELOCITY IMPACT FRACTURES
Low velocity projectiles produce cracks in the glass,which radiate outward from the point of impact(radial cracks)
- HIGH VELOCITY IMPACT FRACTURES
A high speed projectile striking a piece of glass will produce a cone or crater. If the projectile passes through the glass , the opening on the exit side will be larger than the opening on the entry side.The size of a hole and the diameter of the crater cannot be used to reliably predict the size of the projectile.
- THERMAL FRACTURES
In non tempered glass is typical heat crack is curved , has a smooth edge , and has no indication of the point of origin of the crack. If a pane of glass has been cracked by the action of heat it shows characteristic long wavy fractures.
Direction and Sequence of force determination:
- The direction of force determination determines which direction a projectile went through the glass by evaluating radial fractures in the glass fractures first concentric ring.
- The sequence of force determination establish the sequence of the shots by considering the radial fractures termination points.
COLLECTING AND HANDLING GLASS AND GLASS FRAGMENTS
The gathering of glass evidence at the crime scene and from the suspect must be thorough if the examiner is to have any chance to individualize, the fragments to a common source. If even the remotest possibility exists that fragments may be piece together, every effort must be made to collect all the glass found.
GLASS ANALYSIS
Forensic analysis of glass consist 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.
Thank You!
Presentor: Barrios,Rubie Ann T.
3CR-A2-1
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