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Because of high stiffness and strength to weight ratios, composite sandwiches are being used increasingly, especially in aerospace applications. The main drawback of sandwich components is their relatively low resistance to impact damage and the extent to which their strength is reduced under compressive loading after impact. As part of a wider study aimed at increasing the impact resistance of sandwich panels, a continuum damage model is proposed. The model developed describes the compressive behaviour of honeycombs made from materials that are prone to elastic buckling. The material behaviour in compression is described by a combination of three distinct constitutive models, namely elastic, elastic continuum damage and an inelastic strain accumulation model. This has been interfaced with a commercial finite element package to model soft body impacts onto a minimum gauge honeycomb core sandwich. Results from analysis are compared to experimental data and the correlation is found to be very good.

Critical facesheet wrinkling stresses are determined for thin gauge sandwich structure constructed from thick, highly orthotropic, honeycomb-cored materials containing sub-surface damage due to soft-body impact. A closed-form, analytical expression is extended to account for regions of crushed core extending a uniform depth into the core material. The results show that sub-surface core damage can significantly decrease facesheet support, further reducing the critical wrinkling stress computed from classical formulae. The model accounts for shear traction at the core/facesheet interface and provides a means of assessing the fundamental parameters governing the initiation of facesheet wrinkling in initially flat panels constructed from thick orthotropic cores containing sub-surface damage. The results are discussed in terms of the damage tolerance of panels used in aerospace applications.

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