Predicting low velocity impact damage and Compression-After-Impact (CAI) behaviour of composite laminates

Abstract

Low-velocity impact damage can drastically reduce the residual strength of a composite structure even when the damage is barely visible. The ability to computationally predict the extent of damage and Compression-After-Impact (CAI) strength of a composite structure can potentially lead to the exploration of a larger design space without incurring significant time and cost penalties. A high-fidelity three-dimensional composite damage model, to predict both low-velocity impact damage and CAI strength of composite laminates, has been developed and implemented as a user material subroutine in the commercial finite element package, ABAQUS/Explicit. The intralaminar damage model component accounts for physicallybased tensile and compressive failure mechanisms, of the fibres and matrix, when subjected to a threedimensional stress state. Cohesive behaviour was employed to model the interlaminar failure between plies with a bi-linear traction-separation law for capturing damage onset and subsequent damage evolution. The virtual tests set up in ABAQUS/Explicit were executed in three steps, one to capture the impact damage, the second to stabilize the specimen by imposing new boundary conditions required for compression testing and the third to predict the CAI strength. The observed intralaminar damage features, delamination damage area as well as residual strength are discussed. It is shown that the predicted results for impact damage and CAI strength correlated well with experimental testing without the need of model calibration which is often required with other damage models.

Predicting Impact Damage, Residual Strength and Crashworthiness of Composite Structures

“…Queen's University Belfast This paper will focus on recent developments in addressing the challenge of developing a mesoscale finite element based damage model, which builds on the work of Falzon's research group [5,6,7,8,9], for predicting impact damage, residual strength and energy absorption capacity of carbon fibre composites structures.…”

“…According to plastic-damage theories, the plastic strain represents all irreversible deformations including those caused by matrix microcracks. The shear strain γ ij was decomposed into the elastic part γ ij,el and the inelastic/plastic part γ ij,in , (4) The elastic strain is given by, (5) The stress-strain constitutive laws are represented by an exponential function, (6) where is the initial yield strength, determined by the 0.2% offset strain point.…”

“…g ij is the volumetric energy release rate associated with elastic fracture energy (red area in Figure 4). A quadratic interpolation function for the fracture energy in the mix-mode case was described in [6] to account for the multidirectional loading cases. An accurate measure of the characteristic length is the ratio of the elemental volume V and fracture plane area A, l * = V/A, described in [6].…”

“…An efficient strategy for determining when element deletion is likely to have to be invoked, due to element distortion, is to track the value of the determinant of the Jacobian operator (det J) [6] and delete the element if this value approaches zero. As J is not available directly from ABAQUS/ VUMAT, and adding this calculation to the subroutine would incur an additional computational cost, the strategy adopted was to interrogate the determinant of the deformation gradient (det F) which is available directly from ABAQUS.…”

Modelling the crush behaviour of thermoplastic composites

“…A composites damage model based on fracture and continuum damage mechanics, has been developed by Falzon's research group, initially for predicting low-velocity impact damage [15][16][17] and compression after impact strength [18] and was subsequently used to capture crushing behaviour, validated using experimental data from wedge-shape specimens [19]. This computational model assumed that the shear modulus remained constant under shear loading.…”