Engineer Expert Witness Case Studies
These are a few of the cases that Steve has worked on.
Consumer Cart Split Rim Failure
The tires on a consumer cart were misread and overinflated. One rim failed catastrophically causing injuries to the person using the cart. Finite element models of the split rim design were used to estimate the stress levels and deflections in the rim at various inflation pressures. Hand calculations using readily-available formulas verified the magnitude of the finite element estimates. Opinions expressed included that the split rim design did not provide an adequate factor of safety at the labeled working pressure, and that overinflating the tire would highly overstress the rim.
Commercial Mowing Blade Fracture
The fracture of a commercial mowing blade allowed the blade to depart the mower and cause a fatal injury. The blade was analyzed to determine the stresses at various RPM levels with various crack depths. The stress information was used in a fracture mechanics analysis to determine the crack growth rate and failure mechanism.
Coal Processing Plant Fire
A coal processing plant experienced a major fire. The review of various exhibits cast suspicion on the design and manufacture of one piping section. Detailed finite element modeling analyzed this section subject to the thermal expansion and internal pressure of plant operation. Stress levels were compared to ASME standards. Low-cycle fatigue and overload analyses of the stressed piping sections were performed. Opinions expressed included a determination of the failure mechanism and a statement of the cause of failure.
Helicopter Landing Gear Assembly
A helicopter landing gear assembly was reviewed for stress concentrations. The design was compared to a competitive landing gear assembly. Significant differences in the design intent were identified.
Oil Field Equipment Failure
An oil field assembly failed, with the test plug departing the stripper bowl adapter and causing a fatal injury. Finite element models estimated the stress levels under internal pressure. Various adapter design improvements, which were readily-available to the manufacturer, were identified. Opinions expressed included the identification of design flaws and of readily-available strength calculations that had not been performed. The opinions indicated that this produced a foreseeable risk of adapter failure, and that had the flaws been corrected or the calculations been performed and honored, the fatal injury would in all likelihood not have occurred.
Gas Processing Plant Fire
A compressor valve cover failed in a gas processing plant. The resulting fire caused one fatality, multiple serious injuries and millions of dollars of damage. Finite element models were prepared and analyzed for the valve cover per the design print, per an exemplar cover and per the failed subject cover. Hand calculations using formulas available for up to 200 years were performed, with the results matching the modern finite element results. Opinions expressed included that the calculated stress levels did not provide an adequate safety margin, and identified two causes of failure: the designer’s choice of flange design and the presence of a manufacturing defect.
Pipeline Stepped Joint Weld
A detailed finite element model of a stepped joint in a pipeline was prepared and analyzed. It was found that the stresses in the thin wall portion of the pipe were larger than the stresses in the joint; the modeled weld joint did not contribute higher stresses.