Failure Analysis of Broken Tempered Glass Window

Failure analysis of tempered glass windows is normally impossible because the failed window falls apart into a large number of similar pieces, and locating the origin is impossible. However, there are cases when the window remains intact, and root cause failure analysis is possible. In this case the glass expert was able to preserve the origin and perform the failure analysis. Three failed windows were analyzed. In all cases the cause of failures were caused by a nickel sulfide contaminant particle (NiS). In one case, the NiS particle was visible in a macro-photograph. This is seen in the top left photograph. The other two images are photomicrographs of the NiS particle as it appears on the fracture surface at the origin. it is rare to be able to see the particle with the naked eye, but this is an exaple of such an event. The composition of the particle was determined to be Ni and S using energy dispersion spectroscopy. Failures of this nature are well understood and documented

Failure Analysis Expert Examines a Corrosion Failure

Corrosion engineer performed a metallurgy failure analysis to determine the cause of prematurely failing burners in a particular brand of gas grill. The burners in question would fail completely after two or three years of service. The failure analysis of the burner revealed that the grill manufacturer made the subject gas burners from an inferior grade of stainless steel. They used a relatively obscure alloy (J1). This alloy is a variation on 304 stainless steel. The 304 alloy contains 18% chromium (Cr), 8% nickel (Ni) and 2% maximum manganese (Mn), and it allows a maximum of 0.08% carbon (C). The J1 alloy allows the same amount of C but contains only 15% Cr; it also has 4% Ni and 8% Mn. Because the Cr is the active ingredient for the corrosion resistence of stainless steel, the J1 alloy will perform poorly in a corrosive environment. A by-product of burning propane in a gas grill is water. In addition, the burner is hot with other contaminants on it; a corrosion expert would state that this is a corrsive environment. Upper left is a photograph of a burner that failed prematurely. Upper right is an unetched metallugraphic sample of a piece of this burner. One can clearly see that the burner surface shows grain bounbary corrosion. It is believed that the low level of Cr and the presence of water and carbon makes the J1 alloy susceptable to stainless steel corrosion and unsuitable for gas grill burners. This product defect analysis indicates that this is a not a manufacturing defect but design defect.

Failure Analysis of Broken Drinking Glass

Glass expert performs a failure analysis on a broken drinking glass from a restaurant. As the glass was being filled with cold water, the drinking glass split into two equal halves. The failed drinking glass was made of thick glass, and its rim was tempered. A failure analysis was performed by a glass failure analysis expert, and he discovered that the failure had initiated at a minor damage site on the interior wall of the tumbler. It is hypothesized that the failure was caused by thermal shock. The cold water was poured into a glass recently removed from the dish washer; in this case, the glass had not cooled sufficiently before the interior wall was chilled by the cold water. The cold water rapidly cooled the interior wall and put it into tension. The tensile stresses caused by surface chilling caused the glass to crack. The damage on the interior is believed to have been caused by normal restaurant handling. Tumblers made from thicker glass cool more slowly, and these are more likely to exhibit this type of failure during rush periods in a restaurant. Curiously, this particular glass split perfectly in half.

The upper left photograph is an overview of the failed glass. Upper right is a 40X photomicrograph of 1/2 of the failure origin.

Failure Analysis Expert Examines Bottle Failure

Glass failure analysis expert witness prepared numerous bottle failures of "off the shelf" 12 oz beer bottles by over pressuring them with a hydraulic pump. These tests were needed to generate bottle failures of a known origin in order to examine the crack patterns, the fracture surfaces and the failure origins. Numerous bottles were broken, and even though the locations of the failure origins varied (i.e. some were on the body and others on the heel), they all had identical characteristics. They initiated as a single crack parallel to the bottle axis. Also, the origin was always on the outer surface of the bottle and located at a minor external glass defect. In addition, the failure initiated as a fracture mirror. The fracture mirror was surrounded by mist hackle. The failure shown here initiated at the heel of the bottle. an overview of the failed bottle is shown in the two upper left photographs. The initial crack is parallel to the bottle axis, and it wraps around the heel. At both ends of the initial straight crack the crack fans out. On the upper right is a 40X photomicrograph of the failure origin. The mirror fracture and mist hackle border are clearly visible. The minor defect at the origin is just the weakest part of thisstandard bottle. This bottle failed at 410 psi. This was not a defective bottle. This would not be a product liability case.

Failure Analysis of Failed Plastic Chair

Plastic Failure Analysis Expert performs a failure analysis on a plastic "lawn chair" that collapsed when someone sat in it. The right arm separated from the seat. Upper left is a photograph of the subject chair with the separated leg. Fractography, top center photograph, indicates that the failure was progressive (i.e. a fatigue failure). Examination of exemplar chairs at the site showed identical small cracks where the leg joins the side of the seat. All the chairs examined had this manufacturing defect, and these will eventually show fatigue faikure. This is a product defect (design defect) that must be corrected to improve the performance of the chair. Otherwise, this is a product liability that exposes the manufacturer.