212 Stress Intensity Factor Estimation for a Crack Emanating from an Acme Threaded Bolt

Acme threads are widely used in power screws and screw jack applications. The mixed mode fracture behavior of 3D cracks in Acme threaded bolt depends on crack tip stress fields. Available solutions of Stress Intensity Factor (SIF) for threaded bolt are obtained by considering the bolt as a grooved round bar. This paper presents the SIF results of Acme threaded bolt taking into consideration of helix angle. Aspect ratios in the range of ($0.2<(a/c)<1$) and crack depth ratios in the range of ($0.1<(a/d)<1$) are considered along the crack plane for the SIF estimation. In the absence of helix angle, only mode-I fracture dominates along the crack front. With consideration of helix angle, mixed mode crack propagation occurs. The influence of mode-II and mode-III fracture is negligible in the crack front middle region. In the surface region, up to a diameter ratio of 0.2, significant influence of helix angle was observed.