Improved Methods for Quantifying and Designing for Impact Damage Tolerance

摘要

Aerospace industry primes have indicated that improvements to current methods forcharacterizing damage tolerance of full-scale composite structures are needed. Amethodology to address this need is being developed that utilizes experimental resultscorrelated with analysis models to enable a reduction in time and funding resourcesrequired to demonstrate that damage tolerance requirements of a composite structurehave been met. The subject of the work outlined in this document was a scale-up effort,extending the scope of traditional coupon level experimental and analysis approachesto include larger representative structural elements. This effort is intended to lay thefoundation for designing a modified damage tolerance test procedure that more closelyreplicates loads and failure modes observed in composite airframe and nacellestructures. Once validated, this combined experimental/analysis approach willsignificantly reduce the number of tests required for airframe designers to demonstratedamage tolerance of composite structures. This paper outlines part of the validationeffort undertaken to correlate a finite element (FE) nonlinear buckling numericalsimulation to a set of coupon and scaled-up blade stiffened panel test results. Theexplicit FE analysis approach incorporates a user defined nonlinear material subroutine(VUMAT) to capture material softening behavior due to fiber and matrix failure modes.Two numerical models were evaluated, a 4”x6” test coupon, and a scaled up 10”x12”double blade stiffened panel, with both subjected to in-plane compression loads.