Abstract
Understanding of damage tolerance for aircraft interior sandwich structures is critical for design and certification purposes. This study investigates the effect of dynamic loading on the damage tolerance behavior of sandwich materials used in aircraft interiors, comprised of glass fibre phenolic resin face sheets and Nomex honeycomb core. These materials demonstrate strain dependent effects at loading rates relevant to aircraft design standards. A dynamic edgewise compression test method for residual strength testing of sandwich materials has been developed using a modified compressive Hopkinson pressure bar apparatus. Dynamic edgewise compression at strain rates of approximately 50 s for undamaged specimens showed an average increase in compression strength of 28 %, compared to equivalent edgewise compression tests at a quasi-static loading rate of 7.3e-5 s. Low velocity impact damage was replicated using a quasi-static indentation method to create damage in the sandwich material normal to the face sheet with a 25.4 mm hemispherical indentor. For low levels of indentation damage (0.22 mm residual dent) there was a significant reduction in residual dynamic compressive strength of 31 %. Static edgewise compression caused only a 15 % reduction in compressive strength for equivalent predamage. Common failure modes observed for dynamic failure of the sandwich structure were branching of cracks in the face sheet and fibre and matrix interface failure. This gives insights into the dynamic response of composite sandwich structures for the manufacture of future aeronautical structures with improved dynamic load considerations.
Published Version
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