Low velocity impact response of hybrid and fibre-metal composites
Date of Issue2017-02-23
School of Mechanical and Aerospace Engineering
The present thesis covers detailed investigation on the quasi-static indentation and low-velocity impact response of Fibre Metal Laminates (FML) using experimental and finite element simulation study. The FML panels investigated were made from balanced woven GFRP fabric composite layer bonded with aluminium alloy Al 2024-O metal sheet. Indentation and low velocity impact experiments were conducted on FML panels of 1/1, 2/1, 3/2 and 4/3 configurations using hemispherical ended indenter/impactor. Static indentation test allows one to correlate the characteristic load-displacement curve with distinct failure stages of the respective material layer in the FML panel. It also provides corresponding energy magnitude required to induce particular failure mode in FML panel. Using these energy levels, impact velocities for impact tests were derived. Along with experimental observations, a robust and reliable finite element model was developed using ABAQUS, a commercially available finite element software. Adhesive bonding between metal and composite layers of FML was modelled using special purpose cohesive element. Three non-interactive material models were defined to simulate the behaviour of metal, composite and cohesive interface in finite element model. The damage response was defined using continuum damage mechanics (CDM) based damage model constituting 1) Johnson-cook (JC) failure criteria for metal layer 2) Interactive mode based failure model for composite layer and 3) Quadratic nominal stress based failure criteria for cohesive layer in progression with fracture mechanics based damage evolution formulation. High fidelity solutions were obtained through these robust finite element models. Variable parameters having interrelated influencing factors were studied to understand the role of the material layers to indentation and impact response of FML. The influence of initial contact surface (geometry related), impact velocity (event related) and metal composite interface (MCI) bonding (material related) were considered for the investigation. Both experiment and numerical results showed that the considered geometry and the material related parameters have strong influence on the threshold force to cause damage initiation in FML whereas the threshold influence of event related parameter is constant for all investigated FML configurations. From the absorbed energy perspective, FML panels absorb ~90% of impact energy in average through different dissipation modes; ~60% by plastic deformation of the metal layer, ~20% by residual elastic energy and ~10% by forming new damage surface. Finally, the influence of the clustering level of metal and composite layers towards the structural integrity of FML panel was analysed. Load carrying capability, plastic flow of metal layers and extent of damage in each material layers were found strongly dependent on level of clustering for a given FML panel thickness and metal volume fraction (MVF).