13th International Conference on Fracture June 16-21, 2013, Beijing, China Fracture of anisotropic materials with plastic strain-gradient effects Brian Nyvang Legarth1,∗ 1 Department of Mechanical Engineering, Solid Mechanics, Technical University of Denmark, DK-2800, Denmark * Corresponding author: bnl@mek.dtu.dk Abstract A unit cell is adopted to numerically analyze the effect of plastic anisotropy on fracture evolution in a micro-reinforced fiber-composite. The matrix material exhibit size-effects and an anisotropic strain-gradient plasticity model accounting for such size-effects through a material length scale parameter is adopted. The fracture process along the fiber-matrix interface is modeled using a recently proposed cohesive law extension having an additional material length parameter. Due to the fiber-matrix fracture a sudden stress-drop is seen in the macroscopic stress-strain response which defines the failure strain of the composite. The effect of the two material length parameters on the failure strain of the composite is studied. For small values of the material length scale parameter conventional predictions are obtained. Larger values of the material length scale parameter result in corresponding larger failure strains, but only up to a material length scale parameter approximately equal to 15% of the reinforcement size. At this point, the failure strain becomes smaller again for further increasing values of the material length scale. It is shown that the cohesive length parameter monotonically affects the failure strain as a decreasing failure strain is predicted for smaller value of the material parameter. a lccc Keywords Composite Materials, Strain-gradient plasticity, Debonding, Failure strain 1. Introduction Failure mechanisms of fiber-reinforced composite materials are still a challenging topic due to the large number of failure modes compared to conventional homogeneous materials[1]. A unidirectional fiber-composite subjected to transverse tensile loading often fail by either matrix damage or microcracks evolving at the fiber-matrix interfaces. For longitudinal loading the most often seen failure modes are matrix and fiber cracking. For a composite reinforced at the micron scale, two competing mechanisms affect the overall behavior: (I) interfacial failure reduces the strength and (II) strain-gradient effects enhance the strength. When analyzing such composites in general a full 3D analysis is required in order to fully represent the geometry, the loading and the boundary conditions. Such analyses are complicated and the computations become very time consuming when anisotropic plasticity and progressive debonding is to be accounted for. Thus, assuming a periodical distribution of the reinforcement allows for greatly simplified approaches.
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