What happened: A dump truck owner had installed a pintle hook at the back of his truck so he could attach a pup trailer. Eight months later, the pintle hook catastrophically failed as he was driving down the highway, causing his trailer to detach and roll off the road.

Our investigation: dfa performed a thorough metallurgical examination of the failed hook. Beach marks were noticed on the shear fracture surfaces, and plastic deformation was observed where bends in the steel were made during the fabrication process.

Our conclusion: It was determined that the part failed due to a combination of cyclic fatigue loading and structural weakening of the steel due to an improper bend radius.

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Our investigation: A detailed inspection of the fitting was performed by dfa. Corrosion deposits were observed on the copper alloy part, in addition to the fine axial crack that propagated through the tapered thread.

Our conclusion: The cause of this failure was determined to be stress-corrosion cracking. This condition occurs when a sustained tensile stress and a corrosive environment combine to accelerate the failure of a metal part.

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Our investigation: The pump was disassembled, and it was found that the plastic coupling between the electric motor's shaft and the impeller's shaft had cracked. We performed a failure analysis and fractography of the broken plastic coupling to identify the fracture origin, direction of crack propagation, failure mechanism and the nature of stresses.

Our conclusion: We determined that the moulded plastic coupling was defective. The fractography analysis indicated that the coupling failed due to fatigue stresses under normal operating conditions, indicating poor design and workmanship by the pump manufacturer.

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