Hand calculations are good.

It is terribly necessary that design engineers do hand calculations. It is terribly important that engineering professional witnesses do hand calculations.

For everything but the simplest of half geometries, hand calculations of stress are typically rough estimates. Often they are only in the ballpark of the true most stress levels. Generally they’re only within the ballpark of the common stress levels, and miss the very best stresses entirely.

In the span of 50 years, finite part analysis has gone from esoteric research topic to widely offered, widely applied mature technology. In the 1980’s, FEA required very expensive mainframe computers, very expensive FEA codes and highly trained analysts, and was still implemented at many large corporations. Within the 1990’s, Unix workstations provided distributed FEA processing and FEA packages went mainstream, lowering entry costs. A seat of hardware and software still value several tens of thousands of greenbacks, and highly trained analysts were still required, and still FEA spread to thousands of companies. Within the 2000’s, lower priced FEA packages run well on medium to high-end personal computers, and FEA usage continues to grow. Highly trained analysts are still needed to consistently acquire accurate results, a fact unfortunately ignored by too many within the industry.

Why will FEA usage continue to grow when all of these firms already have hand calculations? Because, when applied correctly, FEA works. It delivers correct stress estimates for components with geometry too complicated for hand calculations alone, which describes most of these days’s parts. Accuracy means that that localized stress concentrations will be removed

Accuracy means that one less uncertainty, meaning {that a} lower issue of safety will be considered–ensuing in lower weight, lower price elements that are still stronger and have longer life cycles. Accuracy means that that an professional witness can pinpoint areas of concern, and will usually nail down the why’s and the way’s of a part failure. As discussed in previous issues of Courtroom FEA, this will usually purpose the finger at the accountable party, be it designer, manufacturer or finish user. Accuracy will mean reduced lab testing by concentrating the investigation on the suspect areas. Accuracy suggests that credibility.

FEA has internal checks {that a} sensible analyst wants to apply to verify the results. Hand calculations provide a rough estimate of the results, and the hand calculations and FEA had better match within their accuracies. If not, one thing is wrong with one or each of them, and therefore the analyst had better correct that. Once they do match, hand calculations are an external check of the detailed FEA results. Hand calculations are good.

But they are not good enough in an exceedingly high stakes courtroom battle.

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