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 Case Studies of Thread Non-Conformance
The following studies examine the effect of dimensionally non-conforming threads on fastener performance. In summary, a dimensionally non-conforming thread will not perform its intended design function.
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A properly formed bolt will not stretch and fail when torqued to its yield point whereas non-conforming bolts failed on average at 71 percent of their yield point. The author concludes, "Such reductions in yield strength and loss of pre-load are not acceptable for flight safety critical applications"
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This study sought to capture the different response of a dimensionally conforming versus non-conforming threads to shock. It determined that conforming threads took approximately 97 percent longer to loosen when subjected to an external shock than those threads that were out of tolerance.
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This study was designed to investigate the performance of bolts in an environment with vibration. It indicated that bolts with conforming pitch diameters failed in approximately 782 seconds, whereas bolts with non-conforming pitch diameters failed in 8 to 29 seconds.
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A similar study sought to compare the tensile strength of bolts with and without dimensionally conforming pitch diameters. This study indicates that the mean tensile strength for conforming product was 20 percent greater than those with threads identified as non-conforming.
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