The post failure behaviour of in-plane compression loaded sandwich panels is studied by considering the structural response of such panels with symmetrically located edge debonds. A parametric finite element model is used to determine the influence of different material and geometrical properties on the failure progression, i.e. after initiation of damage. The investigated failure modes are buckling of the debonded face sheets, debond propagation and face sheet failure. The postbuckling failure mode is mainly determined by the fracture toughness of the core and the bending stiffness and strength of the face sheets. The presented approach and results can be used to determine how sandwich panels should be constituted, or not, to promote damage progression favourable for efficient energy absorption during in-plane crushing. The prolonged damage propagation is very complex as it is strongly non-linear and depends on a combination of stiffness, strength and geometry of the constituent materials.

The influence of triggering topologies on the peak load and energy absorption of sandwich panels loaded in in-plane compression is investigated. Sandwich panels with different geometrical triggering features are manufactured and tested experimentally. The damage initiation in panels with grooves is investigated using finite element models. As expected the investigated triggering features reduce the extreme load peaks. A less expected result is that the plateau load following peak load tends to be higher for panels with triggering features. Both results are favourable for the crash performance of panels in vehicle applications. For panels containing no or few grooves the peak load seems to be governed by principles of fracture mechanics while initial failure in panels with a higher number of grooves appears to be controlled by the average stress.

Sandwich panels were designed for different collapse behaviour when compressed in the in-plane direction, by altering the material and geometrical properties. An approach previously developed by the authors was used in the design process of the sandwich panels. Panels with CSM glass fibre face sheets of two different thicknesses and two different core materials were studied both numerically and experimentally. The collapse mode of sandwich panels is mainly dependant on the relation between the fracture toughness of the core material and the bending stiffness and strength of the face sheets. By altering properties like the fracture toughness of the core material or the face sheet thickness, the failure mode could be altered. It was shown that the adopted approach can be used in design of sandwich panels for different failure behaviour.

Theenergy absorption mechanisms of sandwich panels subjected to in-plane compressionare studied. Quasi-static experiments are performed and analysed in orderto support the development of a modelling strategy for failureinitiation and propagation in sandwich panels. The test specimens consistof balsa wood cores and glass-fibre reinforced polyester faces. Duringcompression of a tested panel, the displacement field on oneouter face is measured using a digital speckle photography (DSP)equipment. The absorbed energy is related to debonding, delamination andcrushing of the face sheets and crushing of the core.At initial failure, the load drops dramatically and is thenrelatively constant during continued compression. The energy per unit lengthnecessary for propagation of the damage is considerably lower thanfor damage initiation. Assuming that the damage propagation is uniformthrough the thickness of the panels a simple model ofdamage growth is developed. Calibration of the model is howeverdubious due to the large scatter in the experimental results.The studied material shows damage mechanisms favourable for efficient energyabsorption but the behaviour is far from being optimal.