A sensitivity study on cohesive elements parameters: Towards their effective use to predict delaminations in low-velocity impacts on composites

Low-velocity impacts (LVIs) can seriously harm composite laminates by causing extended delaminations that, while hardly detectable, may reduce the compressive strength of structures. The authors propose a sensitivity study to investigate the influence of the cohesive elements parameters in LVI simulations, namely: the inter-facial strengths and the cohesive mesh size.In order to have a complete control on the mixed-mode behavior a bi-linear traction-separation constitutive law was implemented into Abaqus cohesive elements via an UMAT routine. The resulting cohesive elements are firstly assessed in simulations of standard inter-laminar fracture toughness tests which also highlight the cohesive parameters influence on the simulation of pure and mixed-mode tests.Then, the study focuses on LVI simulations: the variation of the predicted delaminated areas is addressed and the computational costs compared. Experimental results of impactor force time histories, extension of delaminations, obtained by means of ultrasonic inspections, are used as a term of reference for the sensitivity study.The proposed sensitivity analysis wants to point out how the cohesive parameters affect both the accuracy and the computational cost of LVI simulations. The results would be a first contribution to a definition of guidelines for an effective use of cohesive elements in such analyses.