Typical unidirectional fiber-reinforced composite materials exhibit nonlinear longitudinal shear stress/strain (σ12 vs. ε12 and σ13 vs. ε13) behavior prior to matrix/composite failure. The source of this nonlinearity is assumed to result from the accumulation of sub-microcracks in the matrix constituent. It is further assumed that these sub-microcracks affect only the longitudinal shear modulus, while the remaining moduli are unaffected.
To reduce computation time, Helius PFA uses a series of three discrete reductions in the matrix and composite shear moduli to model the nonlinear longitudinal shear stress/strain behavior. These reductions occur prior to ultimate matrix failure and are optimized to fit the measured shear stress/strain curve for the given material. It should be noted that an experimentally measured longitudinal shear stress/strain curve is required to model the nonlinear behavior of the material. See the Material Manager User's Guide for instructions on how to include pre-fail nonlinearity in the material characterization process.
This example problem demonstrates the pre-failure nonlinearity feature on a single element model. Longitudinal shear stress/strain curves from models with pre-failure nonlinearity turned on and off are compared to the experimentally measured data used to generate the reduced shear modulus values. Then, results from a composite tube model are used to show how pre-failure nonlinearity influences model deformation.
For further information related to the pre-failure nonlinearity feature, refer to the Helius PFA User's Guide and the Theory Manual.
The input files used in this example problem are available for download here.