Delamination and fracture modeling techniques for shell composite structures in LS-DYNA

Over the last decade, increased demands of laminated composite in advanced structural applications have pushed forward the necessity to develop a broad range of modelling strategies. Cohesive zone modelling (CZM) is a powerful technique useful to characterize and reproduce the interlaminar & intralaminar behaviour of composite structures when subjected to static and dynamic loads. CZM efficiently replicates phenomenologies such as debonding, fracture propagation and delaminations between adherents or inside laminated components. Their use within numerical models is still limited due to the lack of guidelines about their appropriate implementation. Today industrial practices push forward the application of shell meshes to minimize the computational cost and to improve the realization of full and complex assemblies. For these purposes, the adoption of CZM with shell elements needs model techniques that allow the definition of the correct strength and stiffness comparable to the physical properties of the real specimen. Several approaches to predicting and simulate the initiation and propagation of delamination in shell composite laminates have been investigated. An appropriate methodology to establish and evaluate the cohesive constitutive stiffness parameters for the characterization of progressive delamination with shell adherents is proposed. Different shell-cohesive models were evaluated to outline the suitable methodology that defines the correct compliance and strength of a composite structure. Different practices were being analyzed with recent explicit and implicit LS-DYNA solvers. Particularly, modal analysis and quasi-static loading conditions were performed to evaluate and verify that the cohesive stiffness inserted in the model effectively describes the right compliance of the structural assembly. Furthermore, the results obtained and the procedures detailed were inspected through dynamic standard problems like DCB, ENF and LVI simulations to ensure that the refined proceeding describes the physical dynamical behaviour of the entire assembly. The methodology detailed tries to solve specific problems that arise with the adoption of cohesive elements in shell structure and support the application of CZM for the definition of damageable assembly. The techniques detailed demonstrates that shell-cohesive models with the correct compliance functionally reduce the computational cost associated and ensure accuracy of the results.