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Disbond damage growth in honeycomb cored sandwich structures due to static and fatigue mixed mode loading is investigated numerically and experimentally. A two dimensional finite element model was generated using core homogenization and the Crack Surface Displacement Extrapolation mode separation method, integrated into a fracture mechanics based analysis sub-routine to predict face/core interface fatigue crack propagation. The Cycle Jump technique was furthermore applied to accelerate fatigue analysis. Mixed mode fatigue characterization testing was conducted using Double Cantilever Beam specimens loaded with Uneven Bending Moments, generating a relationship between crack propagation rates and energy release rate amplitudes as a modified Paris Law, measured at three mode-mixity phase angles. The measured Paris laws were subsequently used as input data for the numerical fatigue model. The numerical model was validated against CFRP/Nomex® Sandwich Tearing Test specimen tests with a propagating face/core interface crack yielding varying mode-mixities. The results from the validation showed good agreement between numerical predictions and experimental measurements. [ABSTRACT FROM AUTHOR]

• A theoretical model for service life analysis of auxetic honeycomb/substrate structures under thermal cycling is developed. • The auxetic structures have lower stress concentration than non-auxetic structures of the same density. • Lower relative density can increase the service life of the structures. • Auxetic structures possess much higher service life than non- auxetic structures. This paper studies the fatigue behavior of auxetic honeycomb layer/substrate structures due to interfacial delamination damage. First, the interfacial thermal stress and cyclic interfacial thermal stress intensity factor (ITSIF) at the free ends of the structure are determined in terms of the thermal shock time, relative density, aspect ratio, and internal cell angle of the honeycomb. Then, a theoretical model for the service life analysis of the structures is established based on Paris's law. The results show that the auxetic structures have a lower ITSIF level and a longer service life compared with those of the non-auxetic structures. Another interesting finding is that a reduction in the relative density of the honeycomb layer will increase the service life of the structures. This confirms the significance of applying auxetic materials in re-usable structures for thermal protection purposes. This research is the first attempt to evaluate the service life of the auxetic honeycomb layer/substrate structures under thermal cycling. [Display omitted] [ABSTRACT FROM AUTHOR]