Critical Plane Analysis of Fatigue Crack Nucleation Under Tension, Shear, and Compression

When fatigue cracks develop from microscopic precursors in rubber, they tend to do so on specific planes.  The orientation and loading experiences of such planes under the action of a given mechanical duty cycle directly govern the rate at which associated cracks develop, and ultimately the fatigue life.  Here we demonstrate the consequences of this principle for three loading scenarios that are common in elastomer components: simple tension, simple shear, and simple compression.  For each case, we first identify a prospective failure plane, we consider the associated local mechanical duty cycle, and we estimate the rate of damage accumulation for the prospective plane.  After considering all possible planes, we then identify the most critical plane(s) as the one (or several) plane(s) that has(ve) the maximum rate of damage accumulation.  The analysis illuminates how fatigue behavior can be expected to differ between tension, shear, and compression, and how these differences derive from the same fundamental material behaviors.