RESIDUAL PLASTIC STRAIN STATE AND DELAMINATION PATTERN OF COMPOSITE LAMINATES WITH AUTOMATED INDUCED-GAP SUBJECTED TO HEMI-SPHERICAL IMPACT LOADING

Abstract

Automated manufacturing defects are types of composite structure defects that occur during fiber deposition by advanced robots. The induced gap is the most probable type of defect in the Automated Fiber Placement (AFP) technique. This defect can affect the mechanical performance of the composite structures at both material level by inducing the material inhomogeneity and the structural level by introducing the consolidation effect in the structure during the curing process. The current study investigates the effect of induced-gaps on the damage assessment of thin composite plates under Low-Velocity Impact (LVI) loading. The paper focuses on the delamination initiation and propagation and the residual plastic strain state of the impacted plates. The primary application of this study is to understand the interaction of induced gaps on the delamination pattern of composite samples subjected to LVI. For this purpose, a series of LVI tests are performed. Ultrasonic C-scan analysis and microscopic observation are implied to evaluate the internal damage due to impact loading. Finite Element (FE) analyses are then performed to evaluate the residual strain of the composite plates under Impact Energy (IE) loading less than 15 J. Then, the residual plastic strain in the impact zone is evaluated using a meso-macro method, and the effect of the local plasticity that occurs in the gap zones on the delamination initiation and propagation is studied. Results show that the stress relaxation due to the resin plasticity at the gap areas can affect the delamination pattern of the impacted composite plates. It is also shown that the residual strain of the impacted plates at the gap areas are new sources of the damages that need to be considered in the LVI analysis of the composite plates manufactured by the AFP technique.