Investigation of Failure in Automotive Exhausts
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Initial investigation of some automotive exhausts that failed during operation in this study revealed that most of the fractures occurred at the position where the diameter of the exhausts changed. Light optical microscopy (OM) and scanning electron microscopy (SEM) examinations have shown that the aluminized coating in the failure area had become cracked during the manufacturing process. This situation led to substrate oxidation and cracking at the elevated temperatures and under cyclic load conditions. It is found that the failure is ultimately due to fatigue caused by the combination of mechanical vibrations and thermal cycles. In addition, oxidation of the crack tip may have accelerated the fatigue crack growth process. A design change mitigated the tendency for failure.