Analyzing Lifting Eyes

Lifting eye mechanical failure
Notice the different gaps. These are indicators of failure modes.

Stress concentrations are everywhere and often a misunderstood phenomena. When we are brought in to analyze any compromises to a structure or part, the failure mode is different than most people think.

A lifting eye, for example, can fail in a few ways. Similar to an earring pulling through an ear, one failure point is the gap created from the bearing cross-section area.

In this situation, traditionally we analyze the shear planes. But that is only one contributing factor that requires further analysis.

However, another mode might be from hoop stress. This is a more likely failure where stress is distributed to the circumference of the hoop. The pull through applies stress. Typically the gap is less than the diameter of the pin hole. This is from snapback.

When we design, we treat the smallest area as a beam. We look at the bending stress and point load on the beam. We take a conservative approach to see how to limit the bending stress.

Once our analysis is done, we recommend a shackle that will have appropriate thickness to accommodate the maximum stress failure points.

Of course every situation is different and we work through the complexities with our clients. If you find such engineering challenges, let’s dialogue around it.

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