Failure analysis pinpoints OEM engine flaw

The unnamed OEM appointed Ricardo to investigate why crankshafts were failing across one of its engine families, and Ricardo brought in Axiom to consult on the issue. Stockton-based Axiom sectioned the broken crankshafts to examine the actual machined radius profiles of the journals, which can be a factor in the initiation of fatigue issues.

“We examined the extent of the cracking, charted the position of the failures and the morphology of the cracks,” explained Axiom co-founder and metallurgist Dr Rene Hoyle.

“The crankshafts were sectioned so our experts could study the actual crack face. In some cases we will actually ‘break open’ a crack and examine it under a high-powered microscope; the peaks and troughs of the crack are like an open book to experts in failure analysis. Once the extent and type of failure was plotted it was a relatively simple matter to identify the cause, which in this case was due to metal fatigue.”

Although the engines were already operating on the road, the problem had not been identified during pre-production testing. Instead, it was discovered during on-going endurance tests carried out by Ricardo. Following extensive running on a test bench, the engines were examined and the crankshaft problem was revealed.

“No one wants to suffer a catastrophic engine failure, such as a snapped crankshaft, in the outside lane of the M1,” said Hoyle.

“Manufacturers go to great lengths to make sure their latest designs are suitable for the intended application, but if things go wrong and cracking is found, they need to understand what is causing the problem.”

While the engines in question were already fitted to thousands of vehicles, Axiom says the early identification of the problem has potentially saved the manufacturer tens of millions of pounds in recall and compensation costs.