Geometric analysis and constrained optimization of woven z-pinned composites for maximization of elastic properties

In this study, an optimization problem is carried out for maximizing the out-of-plane elastic constants of woven z-pinned composites, subjected to some constraints on their in-plane elastic constants and geometric parameters. A unit-cell model is used to obtain the elastic constants as functions of geometric parameters including the pin radius and distribution density, the resin-rich zone length, the unit-cell length, the yarn thickness and width, and the yarn waviness created by z-pinning or weaving. A parametric study on the unit-cell geometry is conducted to evaluate the optimization variables and determine whether they are effective enough on the elastic properties or not. Using the key results of the parameter study, which are the equality of the yarn width and the unit-cell length as well as selecting the lowest practical yarn thickness, the constrained optimization problem is defined and solved using a modified artificial bee colony algorithm. Significant improvements in the out-of-plane constant against controlled reductions in the in-plane ones are observed. The more flexible the constraints on the in-plain constants, the better the out-of-plane constants. The optimum out-of-plane elastic modulus is greatly dependent on the pin distribution density and the ratio of the yarn width to the pin radius.