The importance of stress analysis in failure investigations
Failure of a component is generally related to a combination of applied load (design and actual loads), operating environment, material properties, the geometry of the component and manufacturing techniques. In order to establish the underlying cause of a failure it is necessary to consider all these aspects.
At a micro level all components have flaws, defects and/or discontinuities which can be related to manufacturing/material defects that may, or may not, fall within acceptable limits of in-service inspection.
When the component is loaded, such flaws/discontinuities act as stress concentrations and in cyclic loading conditions may act as points of crack initiation. In the case of high load, failure occurs at the weakest point - often at a small material discontinuity or service induced flaw/fatigue crack. If the scope of the failure investigation is limited, for example only to a metallurgical investigation, it is likely that the findings will indicate that the failure is related to the metallurgical defects, whereas these metallurgical defects may only be a contributing factor.
It is therefore necessary to conduct a detailed analysis considering all aspects including - operational conditions at (and prior to) final failure, fractography, actual loading (current and historical), the stresses induced by such loading, material or operation induced defects as well as metallurgy in order to identify the underlying cause.
Neglecting any one of these aspects can lead to inappropriate remedial action and ongoing failure.
Published in Technical Tips by Origen Engineering Solutions on 1 August 2014