Nickel Sulfide Particles in Tempered Glass

Glass failure analysis expert witness performs a failure analysis on a tempered glass window. The failure was initiated by a nickel sulfide, NiS particle. The glass failure analysis expert was able to retrieve both halves of the failure origin. One side of the failure origin contained the protruding NiS particle. On the other side of the failure origin there was a hole out of which the NiS particle had pulled out when the two halves of the failure origin were separated. Above are two photographs of the two halves of the failure origin retrieved during the failure analysis. These photomicrographs were taken at 100X magnification using Nomarski interference contrast optics. This is a manufacturing defect. The NiS entered the glass during the melting operation.

Glass Expert Discusses Tempered Glass Fracture Surfaces

California glass expert witness discusses crack travel directions during tempered glass failure. During tempered glass failure the glass sheet "self destructs" because the internal residual stresses are tensile and drive the failure. Essentially the glass failure results in the glass breaking into tiny cubes. This means that the crack is constantly changing directions. The California failure analysis expert has observed that the crack breaks through and travels in two directions. This is shown in the 20X photomicrograph above. Even though the crack is spreading in two directions, this does not indicate that this piece contains a failure origin. This is an interesting special case where the crack is spreading from a point, but it is not exiting the origin.

Glass Expert Performs a Bottle Failure Analysis

A California Glass failure analysis expert witness was asked to examine a failed wine bottle. A portion of the bottle top broke off midway down the cork as the cork was being removed. The root cause failure analysis revealed that the bottle had received a impact to the side. The distinct Wallner lines (see the photomicrograph above) located near the origin demonstrate that the impact was severe. The interaction of the crack front with the vibrations generated by the impact caused very visible Wallner lines. There was no manufacturing defect associated with this failure. When and how the impact occured cannot be determined from this failure analysis.

Glass Bottle Damage; GLass Bottle Failure Analysis

Glass expert illustrates wine bottle damage that occured during corking. This product defect occured during cork insertion. The "push rod" was off center, and it impacted the top of the bottle. As a result, there was a crush point that would have resulted in a crack during cork removal by the user. Glass failure analysis of broken bottles would have shown the origin at the top of the bottle.

Product Liability Expert Asses Changing Part Suppliers

Product liability is strongly dependent on part quality. This is a big issue when changing part suppliers, and there are times a product liability expert must be hired to examine parts from the new supplier.

In this case the supplier of a molded nylon part was changed and plastic failure analysis tests showed that the thread strength of the replacement part was inadequate. The possibilities considered were a change in the poloymer, improper glass filling and incomplete thread geometry. The new supplier actually failed on all three counts. He substituted a different polymer, he used shorter glass fibers, and he did not properly mold the part. A failure analysis expert performed a root cause failure analysis which indicated that incomplete molding of the threads was the main cause of the decrease in strength. A failure analysis expert cross sectioned representative parts and found the female threads were incomplete, and these provided inadequate strength. The cross section photomicrograph on the upper left shows the representative threads of a part from the original supplier. Upper right is that of the alternate supplier. One can see that the alternate supplier had formed incomplete threads.