Damage analysis of carbon fabric-reinforced composites under dynamic bending

Fabric-reinforced polymer composites used in various applications can be subjected to dynamic loading such as impacts causing bending deformations. Under such loading scenarios, composite structures demonstrate multiple modes of damage and fracture if compared with more traditional, macroscopically homogeneous, structural materials such as metals and alloys. Among damage and fracture modes are fibre breaking, transverse matrix cracking, debonding between fibres and matrix and delamination. Damage evolution affects both their in-service properties and performance that can deteriorate with time. These failure modes need adequate means of analysis and investigation, the major approaches being experimental characterization and numerical simulations. This study deals with analysis of damage in carbon fabric-reinforced polymers (CFRP) under dynamic bending. The properties of, and damage evolution in, the composite laminates were analysed using a combination of mechanical testing and microstructural damage analysis using optical microscopy. Experimental tests are carried out to characterize the behavior of CFRP composites under large-deflection dynamic bending in Izod type impact tests using Resil Impactor. A series of impact tests is carried out at various energy levels to obtain the force-time diagrams and absorbed energy profiles for laminates. Three-dimensional finite element (FE) models are implemented in the commercial code Abaqus/Explicit to study the deformation behavior and damage in composites for cases of dynamic bending. In these models, multiple layers of bilinear cohesive-zone elements are placed at the damage locations identified in microscopic study. Initiation and progression of inter-ply delamination at the impact and bending locations is studied numerically by employing cohesive-zone elements between each ply of the composite. Stress-based criteria are used for damage initiation, and fracture-mechanics techniques to capture its progression in composite laminates. The developed numerical models are capable to simulate these damage mechanisms as well as their subsequent interaction observed in tests and microscopy. Simulations results showed a good agreement when compared to experimentally obtained transient response of the woven laminates.