A strength optimization approach for manufacturable 3D printed variable stiffness laminates with a strain-based approximation

Abstract

The 3D printed continuous carbon fiber reinforced polymers (CFRP) are promising lightweight structures with outstanding mechanical performance. In this work, we propose a structure-manufacture integrated optimization approach for strength maximization of variable stiffness 3D printed CFRP composites by tailoring the steered printing paths. The rule of mixture is modified to evaluate material properties and strength of the printed laminates considering the effect of fiber volume fraction. To make this approach applicable to CFRP with asymmetric layups, a strain-based two-level convex approximation for the failure index based on the Tsai–Wu failure criterion is proposed, which can take the tension-bending coupling effect into consideration. The local failure indices are aggregated using the p-norm formula to reduce the size of the strength optimization model. In order to guarantee the manufacturability of the optimal design, the curvature of the steered printing fiber paths is constrained using a hybrid control method within the approach. The numerical cases show that the strength enhancement of the 3D printed variable stiffness laminates depends on the load, where an improvement between 35% and 46% can be achieved under the tension. Moreover, the proposed method can not only converge stably, but also be capable of optimizing structures with complex geometry.