Comparative study of delamination behavior of multidirectional carbon epoxy laminate

Abstract

Presence of delamination causes reduction in strength and stiffness of laminated composite structure and detrimental to the safety and stability of structures made of composite materials. Determination of the residual strength and stiffness with respect to a finite size of delamination would be helpful in assessment of structures fitness to usage whenever the defects are identified by non-destructive procedures. Experiments of in-plane compression testing of multidirectional laminate (150mm × 100mm × 4.4mm) with an artificial delamination (Ø30 and Ø40mm) at the center are carried out. For the purpose of reference, tests of an ideal laminate with identical ply sequence and without delamination are carried out. Each experiment is performed till failure measuring strains and displacements. Simulation of the experiment are carried out by finite element analysis using cohesive zone material model assuming bonded contact with bilinear material behavior. Simulation is carried out to establish cohesive zone material parameters for further usage in analyzing real structures for the structural integrity assessment when identified with defects and testing is not probable. Significant reduction in strength is observed due to the defect. It is observed that failure load and strain at failure are decreasing from ideal to larger defect size. Strain data comparison with FEA is carried out and % error is below 10% in the case of ideal laminate whereas it is above 20% for the cases of defective laminates.