For a piece of glass that has been fractured radially, the lines will intersect the surface of the glass at right angles on the side of the glass OPPOSITE the side that received the force. Knowing the type of fracture (radial or concentric) allows the investigator to determine the direction of the impact on the glass. Using a hand lens or stereoscope you can observe lines of stress that intersect at right angles on one side of the glass and obliquely on the other side. Concentric fractures make circular patterns around the point of origin of the force.īy looking at the edge of a fractured piece of glass, you can observe the conchoidal pattern in the glass. Radial fractures extend outward in a line from the point on the glass where the force originated. The two types of conchoidal fractures are radial and concentric. The window can also be tested for gunshot residue or metal residue.Ĭonchoidal (shell-like) fracture patterns in the glass are the result of stress on the glass and breakage due to application of a force. Therefore, it is important to care fully search the area of the crime scene for other evidence in order to determine what caused the breakage. Sometimes stones at high speed (coming off of a tire) may cause damage to glass that mimic bullet fracture patterns. A low velocity bullet hole will exhibit more shattering around the hole and the hole may be irregular in shape. A bullet at high velocity produces a hole in the glass where the exit side is wider than the entry side. Examination of the hole (if there is one) will identify whether the object was a low velocity or high velocity projectile. The first task is to determine what type of object caused the damage to the glass. After the object has reached its elastic limit, the force will produce fractures and/or breaks in the glass. When a force is applied to a glass object it will bend until it reaches its elastic limit.
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