Low hardness on bearing race

An interesting paper in « Case studies in Engineering Failure Analysis » published on ScienceDirect.com.

Presence of decarburization on rolled bar coupled with out of square forging can lead to the presence of decarburized layer on one of the faces of a bearing race. This decarburized layer gives rise to low hardness on the face of the race. A series of examinations including micro-structural and macroscopic examinations on the defective samples revealed out of square forging as a root cause for the presence of the decarburized layer on a part of the one of the faces of a bearing outer race. This paper brings out the detail of investigation carried out.

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Design and failure modes of automotive suspension springs

An interesting publication in « Engineering Failure Analysis » of Decembre 2008. This paper is a discussion about automotive suspension coil springs, their fundamental stress distribution, materials characteristic, manufacturing and common failures. An in depth discussion on the parameters influencing the quality of coil springs is also presented.

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Design and failure modes of automotive suspension springs

Abstract

This paper is a discussion about automotive suspension coil springs, their fundamental stress distribution, materials characteristic, manufacturing and common failures. An in depth discussion on the parameters influencing the quality of coil springs is also presented.

Following the trend of the auto industry to continuously achieve weight reduction, coil springs are not exempt. A consequence of the weight reduction effort is the need to employ spring materials with significantly larger stresses compared to similar designs decades ago. Utilizing a higher strength of steel possesses both advantages and disadvantages. The advantages include the freedom to design coil springs at higher levels of stress and more complex stresses. Disadvantages of employing materials with higher levels of stress come from the stresses themselves. A coil’s failure to perform its function properly can be more catastrophic than if the coil springs are used in lower stress. As the stress level is increased, material and manufacturing quality becomes more critical. Material cleanliness that was not a major issue decades ago now becomes significant. Decarburization that was not a major issue in the past now becomes essential.

To assure that a coil spring serves its design, failure analysis of broken coil springs is valuable both for the short and long term agenda of car manufacturer and parts suppliers. This paper discusses several case studies of suspension spring failures. The failures presented range from the very basic including insufficient load carrying capacity, raw material defects such as excessive inclusion levels, and manufacturing defects such as delayed quench cracking, to failures due to complex stress usage and chemically induced failure. FEA of stress distributions around typical failure initiation sites are also presented.

Voir la source : ScienceDirect – Engineering Failure Analysis : Design and failure modes of automotive suspension springs.