Failure analysis of a fastener system and its analytical prediction

This paper describes the failure analysis performed for a fastener system commonly used in civil construction. This system was manufactured using AISI-SAE 1045 steel and showed unusual sudden cracking while a preload was applied under normal working conditions. An exhaustive study aiming to find the cause or causes of this unusual cracking, including experimental work and analytical prediction, is the main objective of this work. Experimental techniques like fractography, metallographic inspection and spectrometry revealed defective manufacture and processing techniques of the elements. Furthermore, microstructural analysis revealed the presence of Widmanstatten ferrite which induces a fragile behaviour of the material. An analysis of the applied stresses on the fastener during preloading using a proposed analytical method demonstrated the presence of elevated loads that caused the initiation of cracks along the length of the fastener. This premature failure could be avoided if a proper heat treatment was applied to the fasteners. The analytical model, based on Lamé's theory, is considered an easy to use tool in order to predict the failure of similar fasteners and mechanical elements