Consideration of moving tooth load in gear crack propagation predictions

Effective gear designs balance strength, durability, reliability, size, weight, and cost. Even effective designs, however, can have the possibility of gear cracks due to fatigue. In addition, truly robust designs consider not only crack initiation, but also crack propagation trajectories. As an example, crack trajectories that propagate through the gear tooth are the preferred mode of failure compared to propagation through the gear rim. Rim failures will lead to catastrophic events and should be avoided. Analysis tools that predict crack propagation paths can be a valuable aid to the designer to prevent such catastrophic failures. The objective of the current work is to study the effect of moving gear tooth load on crack propagation predictions. Two-dimensional analysis of an involute spur gear using the finite element method is discussed. Also, three-dimensional analysis of a spiral-bevel pinion gear using the boundary element method is discussed. A quasistatic numerical simulation method is presented in which the gear tooth engagement is broken down into multiple load steps, with each step analyzed separately. Methods to analyze the steps are discussed, and predicted crack shapes are compared to experimental results.