Reliability Engineering Snapshot TM

Illustrated Case Studies in the Maintenance Reliability Engineering World of Failure Analysis, Predictive Maintenance, and Non Destructive Evaluation



Machine Design - Case Study No. 25: Using Finite Element Analysis in Failure Analysis and Redesign


FEA rendition of leafmount

Finite element analysis is not just a design tool. It can be used to do failure analysis. Even better, the failure analysis information can be used to redesign the problem out.

The component to the left is a 2nd generation design. It was designed by hand. It did better than its predessor, and lasted six years instead of only 8 months. Inspection of the failed 2nd generation component revealed some astounding information that didn't seem to make sense. Therefore a model was made and loaded in the manner that was suspected.


Finite Element Model - LoadedThe model revealed some high stresses where the two arms meet the flat plate (picture right). Those stresses were oriented in such a fashion that the model predicted what in reality actually happened.

FEA Model Cross Section Of Leafmount ArmThe model predicted that the cracks would start at the outside edges of the arms and travel inwards from both sides. The fractography of the failed arms revealed the same thing.

With this in mind a totally radical change was made in the design to accomodate the stresses that could not be minimized or eliminated. The model that was used to troubleshoot the existing design was used to redesign it.

FEA Shadow Model Of Leafmount RedesignFEA Model - Redesigned Leafmount - Loaded
The 3rd generation design increased the lateral strength necessary to improve the performance of the design. The one arm was used in pairs to simulate the one piece 2nd generation design. This design has been in for five years now and has shown no signs of fatigue (20 million cycles).


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Mr. Eric Adams - FEA Analyst Mr. Eric Adams - FEA Analyst Mr. Eric Adams - FEA Analyst