Rubber Failure Analysis Demonstrates Rubber Fatigue

California rubber failure analysis expert performs a failure analysis on a rubber paddle. This piece failed as a result of fatigue. The fatigue failure initiated on the outer surface at a stress riser and progressed inwards. This is damonstrated by the photomicrographs above. Upper left is taken at 10X. Upper right is taken at 40X. The fracture surface has all the aspects of a classic fatigue failure.

Cast Iron Metal Fatigue Failure

California failure analysis expert performs a failure analysis on a failed cast iron "latch lever" from a wood stove. This failure initiated as a fatigue crack at a casting defect. It progressed as a fatigue crack through most of the thickness until the final overload failure. Upper left is a photograph of the backside of the lever, and it shows the casting defect. Upper right is a 10X photo-micro-graph of the fracture surface. Cast iron fracture surfaces are "grainy". Fortunately, oblique lighting reveals the fatigue stria on the fracture surface. When latched, the surface with the casting defect is in compression; it is believed that this is why the crack progressed mostly as a fatigue failure.

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.

Product Liability, Chair Failure Analysis

Failure analysis expert witness examined a failed hospital chair. The chair failed during a breast X-ray examination. The chair had been altered 3 years prior to the failure, and the machine shop that had made the alterations was accused of causing the fatigue failure. Examination of the chair discovered hammer marks on a critical region of the chair. The chair owner had performed repairs two days prior to the accident. The nature of the repairs was such that the hammer marks would have been appropriate. Therefore, the failure was attributed to user error. This fatigue fracture was not the result of a product defect. Therefore, product liability was not in question.