Discrete Damage Modelling of Clamped Tapered Beam Specimen Under Fatigue Loading

Clamped Tapered Beam (CTB) sub-element, proposed by Advanced Composite Project Team at the NASA Langley Research Center was studied under monotonic fatigue loading. The specimen was designed to study matrix crack initiation from pristine condition, delamination initiation and propagation including migration from one interface to other. Regularized eXtended Finite Element Method (Rx-FEM), which allows modeling displacement discontinuities associated with matrix cracks independent of the mesh orientation was used for analysis. Previously developed fatigue Cohesive Zone Method (CZM) was modified to include the S-N information in the Newton-Rapson equilibrium loop. The analysis was conducted in two phases, before and after the experimental data was revealed. The blind predictions were conducted at R=0.1 load ratio for 80% and 70% values of the fatigue load amplitude with respect to static strength and overestimated the rate of delamination growth. The corrected predictions took into account the R=0.2 load ratio, thermal residual stresses and were based on the modified algorithm. The failure event sequence and the respective cycle counts were consistent with experimental data.