Computational assessment of composite structure weaknesses in short-fiber reinforced MMCs: Fid-Bau Portal

Computational assessment of composite structure weaknesses in short-fiber reinforced MMCs

Li, Xu-Dong

Short-fiber composite samples, which contain a fairly large number of Voronoi grains and ellipsoidal short fibers, are generated by computer simulation to mimic real ones for investigating coherent interrelations of composite structure weaknesses (CSWs) with local microstructures. Mesoscopic stress response in a composite sample is modeled to be composed of matrix stress field disturbed by individual short fibers. An analytically numerically based approach is developed on the basis of Eshelby's equivalent inclusion method. Three crucial aspects constitute a kernel of the approach, i.e., (1) segmentation of short fibers; (2) establishment of geometric relation of short fiber with surrounding grains and (3) local nature of micromechanics. The approach allows numerical computation of mesoscopic stress and strain distributions in simulated short-fiber composite samples, which incorporates not only orientation-induced anisotropies but also geometry of composite constituents. A strong concern focuses on correlating CSWs with local microstructures. Software NACIW-MMCs is developed for performing composite simulations and executing proposed approach. The proposed analytically numerically based procedure is employed for numerical computation of mesoscopic stress distributions in short fibers. It is found that the defined 'synergetic interaction factor' and 'relevance parameter' are two adequate physical parameters, which account for synergetic interactions due to orientation-induced local anisotropies. By using the two defined physical quantities, CSWs can be correlated with local microstructure of simulated composite samples. Computational experiments confirm that not only stiffness mismatch between fiber and matrix materials but also orientation-induced local anisotropies exert decisive influence on distribution of CSWs in short-fiber composites. The mesoscopic stress and strain distributions within a short fiber are critically dependent on local evolution of elastic anisotropy of surrounding grains. Whether a CSW may become a failure origin must be evaluated in conjunction with local damage mechanism. Six instructions are proposed for discerning CSWs, which might inspire one to establish a methodology for designing and tailoring MMC materials.