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Note: Glass fractography is the most effective method for determining why a
glass object, such as a bottle, failed. This technique consists of examining the
fracture surfaces of the failure for artifacts such as Wallner lines and using
them to trace the crack back to its origin. Once the origin has been identified,
it can be examined in detail with a microscope to determine the cause of the
failure.
Jar FailureOverview: Figure
#1 is an overview of the failed jar. During opening, the jar separated into two
pieces and injured the person attempting to open it.
Failure Origin: Figure #’s 2 & 3 give two views of the
failure origin. This fracture originated from a blow to the side of the jar. The
force of this strike created a ‘star’ pattern of damage with numerous cracks
leaving the center point. One of these cracks was in the proper orientation to
complete the failure when an attempt was made to twist off the top. A portion of
the star pattern is shown in Figure #2. Figure #3 shows the origin as it appears
on the fracture surface.
Lid damage: Figure #4 is a macro-photograph of the origin that also shows the
condition of the lid in the same locality. This photograph demonstrates clearly
that the lid was hit in the same region as the fracture origin.
Conclusion
The jar failed as a result of a blow to its side. Damage to the lid indicates
that it was being hit in order to loosen it. Jars that contain jams, jellies and
other contents high in sugar often have the lids stuck after re-sealing. The
liquid sugar solidifies and tends to ‘glue’ the lid in place. Hitting the lid is
neither an effective way to loosen it, nor is this a safe technique. As
demonstrated above one can hit the glass and initiate a crack that can cause the
jar to fail when the lid is being twisted off. Often the person removing the lid
can be injured by the sharp glass created by the failure. A better method is to
immerse the jar in warm water to soften the ‘glue’ before trying to twist the
lid off.
Figure #1: Overview of a failed jam jar. The top section came
off during an attempt to remove the lid by twisting.
Figure #2: Photomicrograph of the side view of the fracture
origin. This failure resulted from a blow to the side of the jar. This is
demonstrated by the cracks radiating from the point where the blow struck the
side of the jar. (Mag. 8X)
Figure #3: Origin of the failure as it appears on the fracture
surface. This crack originated from a blow to the outside of the jar. The
fracture originated on the outer surface of the jar and worked its way inward
and laterally. (Mag. 40X)
Figure #4: Macro-photograph of the top of the jar. It clearly
shows the failure origin. In addition, it also shows damage to the lid. The lid
damage indicates that it has been hit with a hard object. Often a person will
bang a stuck lid to free it so it can be removed. In this case one of the
strikes missed the lid and hit the outer surface of the jar; in addition, it was
severe enough to crack the glass. |
