This presentation was made at the 2019 NAFEMS World Congress in Quebec Canada

Resource Abstract

Engineering for durability of rubber components often requires the consideration of multiple load cases. Using Endurica DT's incremental fatigue solver, we demonstrate here how such cases can be analyzed for 3 examples: a simple tension strip under cyclic increasing and cyclic decreasing loads, a transmission mount under a block cycle schedule, and a tire executing the FMVSS 119 durability testing schedule. Material properties for these examples include both crystallizing and noncrystallizing rubbers, all obeying a hyperelastic stress-strain law. In each case, damage from each step of loading history is accrued by integrating the fatigue crack growth rate law over a specified duration, for each potential critical plane. Critical plane analysis is used to identify the most critical plane for each finite element, at each increment of the analysis. At the end of each increment, the accrued damage state is written on a per element basis to a restart file. At the beginning of each new increment, the analysis initializes integration from the end-state of each element recorded previously in the restart file. Using this simple procedure, quite realistic compositions of loading history can be generated and analyzed, and – in addition – the residual / remaining life can be computed at the end of each increment. The simple tension strip example recreates experimental results previously reported by Gent, Sun and Marteny, showing that sequence effects in rubber can be successfully predicted. The transmission mount example demonstrates how block cycle schedules can be implemented, and how a single pass through the schedule can be used to extrapolate the number of schedule repeats required to reach end-of-life. The tire example shows how residual life calculations can be used to understand the damaging effects of each step of a durability schedule. Taken together, the three examples show the range of problems that can be solved using an incremental fatigue solver.