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Repeated loading

Posted by admin on July 25th, 2012

When parts are subject to conditions of repeated loading, you need to consider the number of loads that part will be expected to withstand over its life span. The table below gives examples of types of repeated loads. The corresponding numbers are the expected number of times the loading may occur.

Read through the following suggestions if the part you’re designing will need to withstand repeated loadings, like the ones given above.

Cyclic loadings

The cyclical loading application is relatively infrequent and there is a long time between applications. If the loading is cyclical, use the Proportional limit for design calculations.

Repeated loadings

If the loading is repeated at short intervals and for long periods, use the S-N (stress vs. number of cycles) curves as the design criterion.

Avoid micro cracks

Smooth surfaces, as produced by highly polished mold surfaces, reduce the tendency for micro cracks to form.

Avoid stress concentration

To avoid stress concentration, use a smooth, generous radius in areas like corners where the width and thickness changes.

Enhance heat dissipation

At higher frequency or amplitudes with repeated loads, plastic parts tend to run hotter and fail sooner. Designing with thin walls and fatigue-resistant conductive materials is generally recommended to maximize heat transfer.


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