Hybrid Multi-Scale Modelling of Damage and Fatigue in Short Fiber Reinforced Composites

Ease of manufacturing and favorable performance properties at a low weight make short fiber reinforced composites (SFRC) an attractive material for industrial applications. A pre-requisite for industrial deployment is the proper understanding and simulation of damage and fatigue in SFRC, which is still a challenge today. Typically SFRC components have a variable local statistical distribution of fiber orientation leading to different material properties and mechanical and fatigue behavior at different points. For a component simulation, each element in the FE model corresponds to the center of a Representative Volume Element (RVE). The effective stiffness, damage and fatigue behavior must be modelled for every element. First, different approaches to the appropriate mean field homogenization scheme are compared. The predictive abilities for stresses in individual inclusions are compared against full FE model results. It is confirmed that the full Mori-Tanaka formulation is the adequate homogenization approach for damage modelling in SFRC. Next, a micromechanical model for modelling the non-linear stress-strain behavior of SFRC is developed. Particular attention is given to fiber-matrix debonding. Debonded fibers are treated by replacing them with equivalent bonded inclusion (EqBI) with modified stiffness. FE validation is used to confirm the mechanical equivalence of the debonded fiber and the EqBI. Apart from fiber-matrix debonding, matrix non-linearity is also modelled. A method to predict the ultimate tensile strength of the SFRC is proposed and experimentally validated. Furthermore, a hybrid multiscale method is presented to predict the local SN curves of SFRC. This method involves both multiscale mechanics and tests. Both the SN curve predictions and key assumptions of the scheme are validated with the help of extensive experiments. Apart from own experiments, the proposed models (for both static loading and fatigue) are validated using representative published datasets. Finally a framework for fatigue simulation of an SFRC component is proposed. Static and fatigue tests are performed on a representative industrial component and the framework for fatigue simulation is validated. Apart from elastic properties of the constituents (matrix and fiber) and strength of the matrix, the input for proposed fatigue simulation methodology is only one input SN-curve with no specific requirements to the fiber orientation of the test coupon. Test coupons could have either uniform fiber orientation in the thickness or a “skin core” orientation variation. The fact that limited test data is required could be a breakthrough in view of further industrial deployment of composites solutions in industry, since collection of experimental fatigue data is often a major bottleneck for industrial deployment.nrpages: 1-337status: publishe