Design of fiber-reinforced variable-stiffness composites for different open-hole geometries with fiber continuity and curvature constraints

Abstract In this study, the optimum design of fiber-reinforced composite plates with different hole geometries for various load conditions is investigated. Strain energy/compliance is optimized using three different design methodologies: constant-stiffness (CS), variable-stiffness (VS), and variable-stiffness with least-squares & continuity constraints (LSC). In all the cases, variable-stiffness and LSC designs both reveal better structural performance with reduced compliance and less stress concentrations around the hole in comparison to the optimum constant-stiffness designs. The compliance significantly decreases after optimization especially for the bi-axial loading case. Most importantly, the LSC method allows manufacturable fiber angle distributions that satisfy the maximum curvature limit, making the proposed LSC method applicable to well-established variable-stiffness manufacturing techniques such as 3-D printing and automated fiber placement. The benefits obtained by using variable-stiffness becomes less pronounced as the hole size decreases with respect to the area of the plate. The use of variable-stiffness is found to be more advantageous over shape-optimization methods of constant-stiffness composites. The comparison to the literature findings (Huang et al., 2016) reveals that 13% further reduction in structural compliance with the proposed LSC design method is possible. The proposed design method provides manufacturable variable-stiffness composites with significant improvements in structural performance.