Glass Fracture, Califirnia Glass ExpertPerforms Bottle Failure Analysis

California failure analysis expert witness was asked to perform a detailed failure analysis of a broken wine bottle. Glass fractography was used to determine the root cause failure mode. The failure originated at damage caused by the prop on the cork screw. The fact that there were two damage sites on opposite sides of the bottle and that the cork was only partially removed, indicates that the force to remove the cork was excessive. The donward force on the prongs crushed the top of the bottle at two places and initiated a crack that was driven by the force needed to move the cork. This failure was not the result of a bottle manufacturing defect; it was caused by the high forces needed to move the cork and the type of cork screw used. Upper left is a photograph of the two pieces of the bottle neck. Upper right is a 20X photomicrograph of the failure origin and the initial part of the crack. The arrows show the initial travel direction of the crack. Also, visible is the "crush point" at the beginning of the failure.

California Coating Expert Performs Failure Analysis of Epoxy Paint

A California coating expert was confronted with a municipal water tank with a rubbery epoxy coating. The complaint was that the epoxy paint was not properly mixed, and it had not cured properly. During the coating failure analysis, the study showed that the epoxy paint was aliphatic amine cured. In addition, the tank was painted in the winter, and it cured at 50°F. Prior to filling with water, the tank interior was given a final inspection. During the inspection the paint layer was found to be rubbery on the sunny side of the tank. Because epoxy is thought to be "cross linked" all were surprised that the paint was rubbery. and they were concerned that the paint adhesion had been compromised. Adhesion tests were positive. The fact is many epoxies 'soften' above their initial cure temperature. In this case, the epoxy paint had cured at or below 50°; thus, on a warm day (T> 70°F) the epoxy will initially be soft. However, over time, the paint will "re-cure" and harden at the higher temperature. The failure analysis demonstrated that there was no product defect.

Glass Expert Examines a Tempered Glass Window Failure

California failure analysis expert uses glass fractography to perform a glass failure analysis on a tempered glass window failure. The glass fracture analysis showed that the window failure was a result of heating the glass in the center. Due to the heat, the center of the window expanded. This created additional tensile stress on the window edges. Although the window edge was ground and chamfered, there was enough residual damage at the edge that the thermal stresses were able to cause window failure. Upper left shows the failure initiation site on the edge of the window. Upper right is a 40X photo micrograph of the origin on one of the fracture surfaces. The glass fracture analysis showed that the glass failure initiated on the window's edge face and propogated inward until the tensile center of the tempered glass window was reached. At this point the residual tempering stresses caused the entire window to self destruct into small "cubic" pieces. This may be a manufacturing defect because of the severity of the edge damage.