Speaker
Description
The layered structure of composite laminates makes them susceptible to delamination. To counteract this, translaminar reinforcements can be introduced, which can slow down or stop crack propagation by bridging. Through-thickness reinforcements such as z-pins and stitching threads displace fibers of the laminate laterally during insertion. As a result, eye-shaped resin zones without fiber reinforcement form around the reinforcements. Also, the laminate is compacted locally, leading to a distortion of the fibers and locally increased fiber volume contents. The modelling of realistic resin zone geometries and laminate microstructure is important for accurate simulations of the in-plane behavior of through-thickness reinforced laminates. Also, numerical studies on the thermal eigenstresses in the pin-laminate interface due to the contrast of thermal expansion of the constituents require a detailed description of the microstructure. Existing models and microstructure definitions feature different non-physical assumptions like discontinuous fiber paths or yield unrealistically high fiber volume contents. Also, they are limited to circular and elliptical through-thickness reinforcement geometries and are often based on micrographs of specific configurations. Therefore, they cannot be easily applied parametrically to other geometric configurations. Experimental studies demonstrated an increased Mode I fracture toughness for composite laminates reinforced with rectangular z-pins compared to laminates with circular pins. Therefore, a microstructure definition also applicable to rectangular transversal reinforcements is important to investigate the underlying mechanisms of geometries’ influence on the bridging behavior. In this work a detailed modelling of the microstructure around stitched threads and z-pins of different geometries is proposed, that parametrically considers the reinforcements’ shape, dimensions and possible overlap of the distorted fiber zones caused by adjacent reinforcements. The definitions of the distorted zone’s width and locally increased fiber volume content and fiber angle are independent of the chosen resin zone contour definition. The resulting microstructures for different fiber volume declining approaches and resin zone functions are presented and compared to micrographs. The influence of the modelling parameters on effective in-plane mechanical properties are investigated in a representative unit cell finite element simulation.
