Finite element simulation and reliability assessment of mode-I and mode-II delamination testing of composite laminates

During recent decades, the use of composite laminates has been increasing due to their desirable characteristics such as high stiffness, high strength, low density, corrosion resistance, and fatigue life. Delamination, as the most common failure in composite laminates, occurs due to the degradation of stiffness and interlaminar strength of composite materials. In the present study, numerical simulation and analysis of the Double Cantilever Beam (DCB) and the End Notched Flexure (ENF) tests are carried out using the Cohesive Zone Modeling (CZM) approach and the Finite Element Modelling and Analysis using the software ANSYS®. The results obtained are verified using relevant works in the literature. There are certain sources of uncertainty in the ply material properties, manufacturing, property measurement, and testing of composite laminates, which should be considered in the delamination testing and the design process. To this end, first, a parametric study is carried out to determine the influences of material and geometric properties together with the stacking sequence of the composite laminate specimens for the DCB and ENF tests and their variabilities on the mode-I and mode-II fracture toughnesses and their variabilities. Second, a probabilistic study is conducted to determine the non-deterministic characteristics such as the second-moment information of the mode-I and mode-II energy release rates and the probability of delamination growth in mode-I and mode-II in the DCB and ENF tests, respectively. Next, the sensitivity analysis is conducted to specify a ranking of important random variables for both the DCB and ENF tests. The reliability assessment is conducted using the First-Order Second-Moment (FOSM) method, histogram sampling, First-Order Reliability Method (FORM), Second-Order Reliability Method (SORM), Monte Carlo Sampling (MCS), and importance sampling using associated software Rtx®. Based on the parametric analyses, it is established that the variabilities of the thickness, length, and longitudinal elastic modulus of the DCB and ENF test specimens have the most significant effects on the variabilities of the mode-I and mode-II fracture toughnesses. Based on the reliability analysis it is shown that the probabilities of mode-I delamination growth in the DCB test and mode-II delamination growth in the ENF test, are 50.27% and 49.51%, respectively