Issue 38

D. Carrella-Payan et alii, Frattura ed Integrità Strutturale, 38 (2016) 184-190; DOI: 10.3221/IGF-ESIS.38.25 189 sided bending tests on the same five layups, but with only one load level for each layup, so only five configurations. The idea is to assess if the load distribution on this kind of specimen can provide enough information to feed the damage model, as a three-points-bending test results in progressive load levels along the same specimen, both in tension and compression. Peak data such as load, displacement, strains from extensometers and gauges, temperature are measured from these tests at several representative cycles. The stiffness degradation of each specimen can be estimated from these evolutions. Additionally, running-in and unloading raw data are extracted to analyse the initial stiffness drop of the specimens and their final permanent strain. Parameters identification protocol The parameters identification consists in an FE-based optimization of the fifteen fatigue parameters to fit simulated stiffness degradation with experimental results. A step-by-step methodology identifying the parameters one by one from specific experimental data has been setup. As illustrated by two examples in Fig. 4, each c i parameter has a specific contribution on the numerical stiffness degradation, and therefore can be adjusted to perfectly fit with experimental results. Figure 4 : Effect of c 2,12 (left) and c 4,12 (right) on numerical stiffness degradation Therefore, two volume finite elements models reproducing the two testing procedures have been created, and the nonlinear fatigue solver with N-Jump algorithm is used to efficiently correlate the stiffness degradation of each testing configuration by adjusting the fifteen c i,jk parameters (note that the N-Jump is herein used as tests are carried out under constant amplitude loading). An illustration of the resulting correlation between experimental and simulated stiffness evolutions is given in Fig. 5. Figure 5 : Correlation between experimental and simulated stiffness evolutions ([0]20 layup in 3Pts Bending). Finally, the parameter c 9 is estimated by crosschecking the raw data of the unloading of some of the specimens.