Behuuwb. Wheuienw uwb

1. REPORTER: GELLANGCANAO, PRINCESS N.

2. Glass is an inorganic substance in a condition which is
continuous with, and analogous to, the liquid state of that
substance, but which, as the result of reversible change in
viscosity as to be, for all practical purposes ,rigid.
Glass is normally a fused mixture of silica usually in the
form of natural sand and two or more alkaline bases such as
soda, lime, or potash. It also contains quantities of various
other elements and metals present either as incidental
impurities in the basic constituents or added to them for color,
degrees of hardness, heat resistance, and other specific
purposes.

3. 1. Glass is somewhat flexible, it tends to bend upon application of force.
2. Glass bends on the direction where force is applied causing the opposite
side to stretch.
3. Glass can withstand more bending rather than stretching causing the
opposite side to start breaking.
The significance of knowing the characteristics of glass, either as evidence
or in the development of investigative leads, lies mainly in its physical
properties. These properties make it possible to determine that glass fragments
did or did not originate from the same sources, or to determine the manner in
which a piece of glass was broken.

4. Glass fractures may be caused by excessive exposure to heat or caused
by impact of a blunt instrument or object, or caused by projectiles.
TYPES OF GLASS FRACTURE:
1. RADIAL FRACTURES- primary fracture resembles the spokes of a
wheel where the radiating rod originates at a common point. When glass
breaks, the lines that radiate from the hole are caused by the glass
bending away from the point of impact. The radial fractures originate on the
opposite side of the glass, because this is the surface which is the first to
feel the tension. As the front of the glass is pushed in, the opposite side is
bent backwards. When the limit of glad elasticity is reached, it breaks, with
cracking resulting along the radial lines.

5. 2. CONCENTRIC FRACTURE – secondary fracture having the appearance of
circles around the point of impact connecting one radiating crack to the order,
thus forming triangular pieces of glass. While the radial fractures are forming
triangles are created between the fractures. The newly formed triangle glass
between the radial fractures also bends away from the direction of force. When
the limit of elasticity for this triangles is reached , the glass breaks in concentric
lines. Concentric fractures originate on the front of the glass.
3. CONCHOIDAL FRACTURES- A characteristic of glad is that when it breaks,
the fracture edges appear shell-like in form – that is, having elevations or
depressions in the shape of a shell. The technical name for this condition is
“Conchoidal” fracture.

6. FRACTURES CAUSED BY HEAT
Fractures caused by excessive exposure to heat can be distinguished from those caused by
impact since those due to heat do not show a regular pattern of radial and concentric lines. Heat
fractures are characteristically wave-shaped.
FRACTURE CAUSED BY A BLUNT INSTRUMENT/OBJECT
Thorough examination of glass fractures caused by the impact of a blunt instrument/object
will reveal a pattern of radial and concentric fractures.
When glass fractures are caused by the impact of a blunt instrument/ object, stress lines on
the edges of both the radial and concentric fractures can be seen.
FRACTURES CAUSED BY PROJECTILES
A small dense object such as bullet, pebble, or steel ball may impact upon a pane of glass
with such a little force, or such a high speed, that there is no bulging of the glass, and therefore,
no radial cracks Penetration of high velocity projectiles will produce a coning or catering effect,
where opening is larger on the exit side.