An energy based damage mechanics approach to modelling impact onto woven composite materials-Part I: Numerical models

Abstract The increased use of composite materials in a wide spectrum of industries has led to the development of improved predictive techniques, which can aid in the detailed understanding of the behaviour of a composite component or structure to a range of potentially damaging threats. This paper presents an energy based damage mechanics model for woven carbon composites under high strain loading. This damage mechanics approach introduces five damage variables for in plane damage per ply layer. The damage variables are associated with warp and weft fibre damage in both tensile and compressive failure modes, with an additional damage variable to determine the deterioration of the fibre–matrix interface. The damage variables are directly related to the stiffness degradation within the composite laminae and ultimately within the laminate. The evolution of damage in each mode is controlled via a series of damage-strain equations, thus allowing the total energy dissipated for each damage mode to be set as a material parameter, which is mesh size independent. The damage mechanics approach has been implemented into both the LLNL and LS versions of DYNA3D for plane stress (shell) elements. This encompasses both the standard shell element and the solid-shell formulations available within these codes. In the present paper, validation examples are presented for this damage model. The tensile and the tensile-shear responses are modelled at a coupon level, including relevant strain rate effects and tabs, with the proposed damage model. The results show very good agreement with the available experimental data. Suggestions are also presented for additional non-standard experimental tests to derive all material model parameters directly, rather than an inverse modelling approach in which uniqueness may not be guarantee. This paper also presents an interface modelling technique for explicit FE codes. The formulation is again based on damage mechanics and uses only two constants for each delamination mode; firstly, a stress threshold for damage to commence, and secondly, a critical energy release rate for the particular delamination mode. The model has also been implemented into the LLNL DYNA3D Finite Element (FE) code and the LS-DYNA3D commercial FE code. The interface element modelling technique is applied to a series of common fracture toughness based delamination problems, typically the Double Cantilever Beam (DCB) test, and validated for the dynamic case via a simple analytical plate impact simulation. A subsequent part II paper describes the results of simulations using the proposed damage mechanics based models on a series of experimental CRAG plate impact tests.

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