Environmental failures of high strength bolts

Selecting the optimum clamp load for a high strength bolt may present a design conundrum when a variety of service environments need to be considered. It is known that high clamp loads are necessary to prevent bolt fatigue failures. However, a high clamp load or tensile stress in a bolt may contribute directly to environmental induced stress cracking (EIC) in a corrosive environment. There are numerous applications in the transportation environment where high static and dynamic stresses as well as corrosion can contribute to bolt failure. The appropriate clamp load can be determined using a fracture mechanics methodology and testing bolt materials to determine the threshold for environmental induced crack propagation.