But my expert has hand calculations
Hand calculations are good.
It is very important that design engineers do hand calculations.
It is very important that engineering expert witnesses do hand
Hand calculations are good.|
But they aren't good enough in a
high stakes courtroom battle.
For everything but the simplest of part geometries, hand
calculations of stress are generally rough estimates.
Often they are only in the ballpark of the true maximum stress
levels. Sometimes they are only in the ballpark of the average
stress levels, and miss the highest stresses entirely.
In the span of 50 years, finite element analysis has gone from
esoteric research topic to widely available, widely applied mature
technology. In the 1980's, FEA required extremely expensive
mainframe computers, very expensive FEA codes and highly trained
analysts, and was still implemented at many large corporations.
In the 1990's, Unix workstations provided distributed FEA processing
and FEA packages went mainstream, lowering entry costs. A seat of
hardware and software still cost many tens of thousands of dollars,
and highly trained analysts were still required, and still FEA spread
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 needed to
consistently obtain accurate results, a fact unfortunately ignored
by too many in the industry.
Why does FEA usage continue to grow when all of these companies
already have hand calculations? Because, when applied correctly,
FEA works. It delivers accurate stress estimates for parts with
geometry too complicated for hand calculations alone, which describes
most of today's parts. Accuracy means that localized stress
concentrations can be removed. Accuracy means one less uncertainty,
meaning that a lower factor of safety can be considered--resulting
in lower weight, lower cost parts that are still stronger and have
longer life cycles. Accuracy means that an expert witness can
pinpoint areas of concern, and can often nail down the why's and
how's of a part failure. As discussed in
of Courtroom FEA,
this will often point the finger at the responsible
party, be it designer, manufacturer or end user. Accuracy can mean
reduced lab testing by concentrating the investigation on the suspect
areas. Accuracy means credibility.
FEA has internal checks that a good analyst needs 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, something is wrong with one or both of them,
and 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 aren't good enough in a high stakes courtroom battle.
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