Modeling the In-Plane Compression Response of As-Manufactured Steered Fiber Laminated Plates

Abstract

Robotic Automated Fiber Placement (RAFP) is a novel additive manufacturing modality for the production of laminated fiber reinforced composites. In addition to faster and precise manufacturing of composite structures, RAFP enables the designer to now use optimal steered fiber directions to maximize structural performance indices. The optimal solutions depend on loading and boundary conditions and are called “Variable Stiffness” (VS) laminates. Several studies have established that VS designs show significant benefits when compared to traditional laminates. A novel algorithm to derive optimal fiber paths to maximize uniaxial and biaxial buckling loads of 20 in ×20 in square VS laminates was introduced by the authors. The study utilized Bezier splines to represent the course center-lines, along with a “global manufacturing mesh” that would reduce the number of optimization variables. A surrogate model in conjunction with a multi-objective Genetic Algorithm (GA) was used to obtain a “Pareto front” of feasible solutions from which three feasible solutions were identified based on the criteria that the total gain in mass be less than 10%, the decrease in global stiffness capped at 10% and more than 25% increase in buckling load compared to a unidirectional laminate. These chosen designs were then manufactured and tested for uniaxial in-plane compression response. The proposed study presents the development of a numerical model using a pixelated FE mesh that captures manufacturing signatures like gaps and overlaps as well as the measured initial curvatures of the panels as manufactured. The load v/s load point displacement response of seven of the nine panels are well captured using the numerical model, with less than 5% error in initial stiffness and transition loads. A model with relaxed boundary conditions is used to correct for the deviation in the response curves for the rest two panels. Further, an optimization problem is introduced to examine the optimal straight fiber paths that maximizes the transition loads of the slightly curved panels and comparisons are drawn to establish that the steered fiber panels perform better than the straight fiber paths by up to 25% in terms of transition loads.