Courtroom FEA: But my expert has hand calculations
Hand calculations are good.
It's terribly vital that style engineers do hand calculations. It's very important that engineering professional witnesses do hand calculations.
For everything however the simplest of half geometries, hand calculations of stress are usually rough estimates. Usually they're only in the ballpark of the true maximum stress levels. Sometimes they are only within the ballpark of the typical stress levels, and miss the highest stresses entirely.
Within the span of 50 years, finite part analysis has gone from esoteric research topic to widely on the market, widely applied mature technology. In the 1980's, FEA needed extraordinarily expensive mainframe computers, very expensive FEA codes and highly trained analysts, and was still implemented at several massive 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 price several tens of thousands of bucks, and highly trained analysts were still required, and still FEA unfold to thousands of companies. In 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 required to consistently get correct results, a truth sadly ignored by too many in the industry.
Why does FEA usage continue to grow when all of these firms already have hand calculations? As a result of, when applied properly, FEA works. It delivers correct stress estimates for elements with geometry too complicated for hand calculations alone, that describes most of these days's parts. Accuracy means that localized stress concentrations can be removed. Accuracy suggests that one less uncertainty, that means {that a} lower issue of safety can be considered–resulting in lower weight, lower cost components that are still stronger and have longer life cycles. Accuracy means that that an expert witness will pinpoint areas of concern, and can typically nail down the why's and how's of a part failure. As discussed in previous problems of Courtroom FEA, this can usually point the finger at the responsible 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} smart analyst wants to use to verify the results. Hand calculations provide a rough estimate of the results, and the hand calculations and FEA had higher match within their accuracies. If not, something is wrong with one or both of them, and also the analyst had higher correct that. Once they do match, hand calculations are an external check of the detailed FEA results. Hand calculations are good.
But they don't seem to be sensible enough in a very high stakes courtroom battle.
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