Evidence Examinations
Metallurgy Examinations
Comparison
Comparison examinations can determine
whether two metals or metallic objects came from the same source or from
each other. Metal comparisons can identify surface and micro-structural
characteristics such as fractured areas and accidental, damage, and
fabrication marks to determine whether the object was cast, forged, hot-
or cold-rolled, extruded, drawn, swaged, milled, spun, or blanked.
Examinations can determine mechanical properties such as the response of a
metal to an applied force or load. Examinations can also determine
chemical composition including alloying and trace elements.
Broken or Mechanically Damaged Metal
The causes of failure or damage such as
stress exceeding the strength or yield limit of the metal, a material or
manufacturing defect, corrosion, cracking, or excessive service usage
(fatigue) can be determined. The magnitude of the force or load that
caused the failure, how the force or load was transmitted to the metal,
and the direction it was transmitted can also be determined.
Burned, Heated, or Melted Metal
Examinations can determine the
temperature at which a metal was exposed, the nature of the heat
source, and whether a metal was in an electrical short-circuit
situation. |
Thermally damaged
box
springs.
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Cut or Severed
Metal
Examinations can determine the method by
which a metal was severed, such as sawing, shearing, milling, turning, arc
cutting, or flame cutting. The skill of the person who made the cut and
the length of time it took to make the cut can also be
determined.
Metal
Fragments
Examinations can determine how fragments
were formed. If fragments were formed by high-velocity forces, it can be
determined whether an explosive was detonated and the magnitude of the
detonation velocity. The identification of the object that was the source
of the fragments can also be determined.
Watches, Clocks, and Timers
The conditions causing a watch, clock,
timer, or other mechanism to stop or malfunction, and whether the time
displayed represents a.m. or p.m. (calendar-type timing mechanisms only)
can be determined.
Lamp Bulbs
Examinations can determine whether a lamp
bulb was incandescent at the time the glass was broken and whether an
unbroken lamp bulb was incandescent at the time it was subjected to an
impact force such as a vehicular collision.
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Radiograph of a cog
made of cocaine-containing polymer.
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Objects Unidentified as to Use or Source
Examinations can determine the
possible use for which an object was designed, formed, or
manufactured on the basis of the construction and the type of metal.
The possible identification of the manufacturer and specific
fabricating equipment used to form the object can be determined.
Identification of the source of the object if an unusual metal or
alloy is involved can be determined. |
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Objects With Questioned Internal
Components
X-ray radiography can
nondestructively reveal the interior construction and the presence
or absence of defects, cavities, or foreign
materials. |
Submitting Metallurgy Evidence
Questions concerning
metallurgy evidence should be directed to 03-9702366. Follow the Evidence
Submission directions including Requesting
Evidence Examinations and Packaging
and Shipping Evidence.
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