Lugs and pins, rivets, bolts are the most essential joints used in structural components apart from the welds. These elements experience dynamic loading during their life, leading to failure by fatigue. Fatigue failure is due to the initiation of fatigue cracks from these joints, as they are the locations of stress concentration. Conventional continuum mechanics based analysis cannot predict the initiation and growth of fatigue cracks from these stress concentrators. Fracture mechanics based parameter, viz., stress intensity factor provides the basis for estimation of state of stress in the presence of the crack.

Theoretically, crack initiation from stress concentrators is assumed to be under open hole conditions, but real life structures contain rivets, bushes that have interference with the base metal; as a consequence, the stress profile in the absence of the fatigue crack is different for each of these conditions. It is a function of levels of interference at the pin-plate or bush plate interface and load transfer mechanism Many studies have been performed to estimate stress intensity factors (SIFs) and fatigue life at these joints. Although effects of geometric configuration, method of loading and interference levels on stress intensity factors were studied, many of the works do not deal with them comparatively or in combination and did not discuss the cumulative influence of all of them on the SIF due to unavailability of closed form solutions and  difficulty in experimental studies.

In an attempt to bridge this gap, the current study uses Finite Element Analysis to evaluate the cracks emanating from a circular hole in a finite width rectangular plate under different loading conditions such as open hole load, bearing load, pin load with and without interference and the effects of introducing a bush.

This study brings out the threshold crack lengths beyond which the type of loading starts losing the influence on stress intensity factor. This study also brings out the threshold interference levels beyond which there is no beneficial impact on the SIF and hence the life of component. It was observed that irrespective of type of loading, up to certain interference levels, there exists a crack length beyond which all the cases yield same stress intensity factors. Also, beyond certain interference levels, influence of geometric effects is higher than that of interference levels. Comparison of SIFs are also drawn between the cases of pin loaded plate, plate loaded by pin – bush combination and plate loaded by a pin with diameter equivalent to that of bush.


Combined Effect of Loading and Interference Level on Stress Intensity Factor for a Pin Loaded Joint

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Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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