Micromechanical model for off-axis creep rupture in unidirectional composites undergoing finite strains

A microscale numerical framework for modeling creep rupture in unidirectional composites under off-axis loading is presented, building on recent work on imposing off-axis loading on a representative volume element. Creep deformation of the thermoplastic polymer matrix is accounted for by means of the Eindhoven Glassy Polymer material model. Creep rupture is represented with cohesive cracks, combining an energy-based initiation criterion with a time-dependent cohesive law and a global failure criterion based on the minimum in homogenized creep strain-rate. The model is compared against experiments on carbon/PEEK composite material tested at different off-axis angles, stress levels and temperatures. Creep deformation is accurately reproduced by the model, except for small off-axis angles, where the observed difference is ascribed to macroscopic variations in the experiment. Trends in rupture time are also reproduced although quantitative rupture time predictions are not for all test cases accurate.</p

Microscale modeling of rate-dependent failure in thermoplastic composites under off-axis loading

In this paper we develop a finite deformation micromechanical framework for modeling rate-dependent failure in unidirectional composites under off-axis loading. The model performance is compared with original experiments on thermoplastic carbon/PEEK composites tested at different strain-rates and off-axis angles. To achieve quantitative agreement with the experiments, a microcrack initiation criterion based on the local stress and the local rate of deformation state in the polymer matrix is proposed. Microcracking is represented by a cohesive zone model, with special attention to the inclusion of geometric nonlinearity in the formulation. In this regard, the cohesive geometric nonlinearity is based on extension of an existing formulation to three-dimensional space. Beside microcracking, the Representative Volume Element (RVE) also accounts for viscoplasticity in the polymer matrix. A recently introduced dedicated arclength control method is utilized to impose a strain-rate on the micromodel. Accordingly, kinematic relations governing the RVE deformation allow for the change in orientation of the micromodel in the loading process. This change in orientation of the microstructure has an important implication on the apparent material strength.Applied Mechanic