Failure analysis of broken clamping shaft

Any interruption due to a component failure leads to unforeseen expenses and production interruptions. Most of the failures are linked to issues where the material is subject to specific loading and environmental conditions. OCAS is involved in analysing failures, proposing adequate repair methods and remedy actions to prevent failures from occurring again. We have assembled a multi-disciplinary task force to address the rising demand for services related to failure analysis, engineering critical assessment, fit-for-purpose analysis and asset integrity and reliability services. Discover this recent case.

Problem: Broken clamping shaft


In order to determine the cause of failure, the broken sample was investigated using optical and electron microscopy.


It is clear that failure initiated at the radius between shaft and thread, a location which typically shows high stress concentration. The presence of Ratchet marks and striations confirm the hypothesis of fatigue fracture. The two different spacings in striation (red and blue in figure below) indicate that the sample was subjected to different load levels.


The shaft was submitted to two-side bending. The failure could clearly be identified as a fatigue fracture, showing two distinct areas with different striation spacing, each corresponding to a different load level.


The concept should be re-evaluated. An alternative design with less sharp transition from shaft to thread would considerably reduce the risk for failure. Meanwhile, check similar shafts for cracking by means of penetrant examination.


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“Our dedicated OCAS team offers a versatile skill set in welding, corrosion, fatigue, wear and fracture. We are confident we can add value by supporting our customers in their asset reliability and structural integrity efforts.”

Annick Willems, Researcher Technical Support & Services Department, OCAS