A diesel engine flywheel was failing around the bolt circle. Photo A shows a flywheel coated with PhotoStress plastic, and then bolted to the diesel engine for dynamic testing. When the bolts were tightened, very high stresses appeared, which were well above the design limit of the material as shown in Photo B. Superposition of forces due to dynamic testing caused premature fatigue failure. The major problem was thus defined by PhotoStress analysis as one of assembly-induced stresses. Redesign of the flywheel (where it mated to the shaft of the diesel engine) significantly reduced the initial assembly stresses as shown in Photo C.

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