An improved delamination fatigue cohesive interface model for complex three-dimensional multi-interface cases

Abstract

This work presents a cohesive interface model for predicting interlaminar failure of composite laminates under tension-tension fatigue loading. The model features improvements on previous formulations and utilizes four-integration-point elements, which offer several new advantages, while maintaining the merits of the previous single-integration-point elements. An element-based crack tip tracking algorithm is incorporated to confine fatigue damage to crack-tip elements only. A new local rate approach is proposed to ensure accurate integration of strain energy release rate from local elements. Furthermore, a dynamic fatigue characteristic length is proposed to offer a more accurate estimation of fatigue characteristic length in complex threedimensional cases. Fatigue initiation is incorporated by using a strength reduction method, without changing the propagation characteristics. The numerical approach has been verified and validated using multiple cases and was then applied to fatigue damage development in open-hole laminates, where a good agreement between numerical analysis and experimental results was obtained.

Relationship Between Matrix Cracking and Delamination in CFRP Cross-Ply Laminates Subjected to Low Velocity Impact

“…However, for the elements in this region, the increases in their damage variables (SDEG) were inhibited by the stress release as detailed in Section 4.2.2, and these elements were still capable of bearing the stress (at least 20 MPa), even though their SDEG were larger than 0.9. Therefore, only the cohesive elements whose SDEG became 1.0 were considered as failure [50] and regarded as the delaminated region.…”

Composites fatigue delamination prediction using double load envelopes and twin cohesive models

“…Locally, cohesive elements follow a fatigue constitutive law that is usually an extension of a bilinear static cohesive law [11][12][13][14][15][16][17][18], taking into account an assumed number of fatigue cycles in a given time increment. The number of cycles elapsed in a fatigue model over one second is here defined as 'numerical fatigue frequency', which is usually much larger than the fatigue frequency of actual tests.…”

“…2b. Under fatigue loading, damage initiation is usually predicted by a failure criterion devised based on experimental S-N curves [16,19,20]; when the initiation criterion is satisfied, the mode I/II strength pair is scaled or reduced to zero [16,20]. Good agreement has been achieved in some cases, however, building up a thoroughly validated fatigue damage initiation approach is still a challenge, which becomes even more difficult due to the generally large scatter in experimental results [21,22].…”

A simulation method for fatigue-driven delamination in layered structures involving non-negligible fracture process zones and arbitrarily shaped crack fronts

“…The existing CZMs for fatigue delamination can be divided into two main groups [4]: the loadingunloading hysteresis models [20][21][22][23][24][25][26], which simulate the whole load cycle to compute the evolution of the damage variable, and the envelope load models [27][28][29][30][31][32][33], which only model the maximum cyclic load. One of the main advantages of the loading-unloading hysteresis models is that they are capable to model variable loading spectra.…”

“…Note that the use of fitting parameters that are not possible to be determined experimentally or need to be adjusted depending on the problem make the predictive character and accuracy of the methods questionable. Others [31,33], make use of the length associated to an integration point in the crack propagation direction, l e , instead. In this case, the propagation direction must be determined in advance.…”