C. Ruiz

Prediction of impact damage in composite plates

This paper gives details of the implementation of improved failure criteria for laminated composite structures into LS-DYNA3D. Out-of-plane stresses have been taken into consideration for damage initiation. It is suggested, for the first time, that delamination is constrained by through-thickness compression stress. Interactions between different damage mechanisms have been considered. Damage predictions in good agreement with experimental ones have been achieved.

A delamination criterion for laminated composites under low-velocity impact

Abstract This paper describes details of an improved delamination criterion for laminated composite structures and its implementation to LS-DYNA3D. Out-of-plane stresses have been taken into consideration for damage initiation. The new delamination criterion, verified by experimental results for low-velocity impact, takes into consideration both the interlaminar shear and through-thickness compression stresses. Improved from the criterion proposed previously [Hou JP, Petrinic N, Ruiz C. Prediction of impact damage in composite plates. Composites Science and Technology 2000; 60(2): 273–81], delamination is not fully constrained by the out-of-plane compression. The influences of high local interlaminar shear stress induced by matrix cracking and fibre failure on delamination have also been taken into account. Predicted results from different criteria have been discussed, in comparison with experiment work.

Measurement of the properties of woven CFRP T300/914 at different strain rates

Abstract Three types of test, i.e. tension, compression and in-plane shear, have been carried out to measure the in-plane mechanical properties of woven CFRP T300/914 laminates at three different strain rates. Specimens were waisted symmetrically in the thickness direction. Difficulties presented in testing specimens with 90° reinforcement in compression and [±45] in tension at high strain rate are discussed. To obtain the modulus in [90] compression and in [±45] tension at high strain rate, specimens with uniform thickness have to be used. Results show linear elastic properties in both of the [0] and [90] directions. Under tension, the specimens remain virtually linear elastic up to failure. Plastic deformation occurred before total failure in compression tests. Tensile tests on [±45] specimens give non-linear stress strain curves. Results show that properties dominated by matrix, i.e. compression strength, Poissons ratio and in-plane shear modulus and shear strength are strain rate dependent and properties dominated by the fibres, such as tensile modulus and strength in [0] and [90] directions are virtually rate independent.

The effect of strain rate on the interlaminar shear strength of a carbon/epoxy cross-ply laminate: comparison between experiment and numerical prediction

A previously developed design of single-lap interlaminar shear specimen suitable for tests under impact rates of loading is re-examined and used to determine the interlaminar shear strength of a cross-ply carbon/epoxy material with important applications in the aircraft industry. The test has been modelled dynamically with an explicit-finite element code. The results of this analysis have been used to examine the state of stress just prior to failure and, in terms of a quadratic stress-interaction failure criterion, to predict the onset of delamination. The numerical predictions are compared with the behaviour observed experimentally.