Session: 01-07: Nonlinear Problems in Aerospace Structures

Paper Number: 121550

121550 - Optimization of Variable Stiffness Composites Considering Gaps/Overlaps and Unified Structural Theories 

Composite materials offer the engineers to conceive structures with a lighter weight and higher stiffness. In addition, the mechanical performance can be tailored by modifying the orientations of the stacking sequence. In this manner, one can improve the buckling load, strength and/or stiffness of the original structure. These characteristics can be further enhanced if novel manufacturing techniques are involved in the design process. For instance, with the irruption of Automated Fiber Placement (AFP) the layup orientations are no longer forced to keep constant within the lamina, but can vary along pre-fixed directions. These composites in which the orientation is not constant anymore are known as Variable Angle Tow (VAT) or Variable Stiffness Composites (VSC).

Despite the improvements in the mechanical performance that VAT offer, there exist limitations due to the manufacturing process that limit their whole potential, and that may difficult the design process. In detail, such limitations are the fabrication defects. In the case of VSC manufactured by AFP, the main defects that arise are the gaps and overlaps that appear between two consecutive tow courses. The former leads to the presence of resin rich regions within the lamina, whereas the latter produces local thickness increments. As one can expect, these manufacturing signatures alter the mechanical performance of the structure if compared to the pristine numerical model.

To improve the prediction of the mechanical behavior of VAT structures, this work couples the Defect Layer Method (DLM) and the Carrera Unified Formulation (CUF) within a unique framework. DLM is used to map the defects due to the AFP process into the CUF-based Finite Element solver. In this manner, an efficient and cost-effective method is obtained to simulate both the manufacturing process and structural performance of VSC. Lately, this framework is wrapped into a script devoted to the optimization of tow-steered composites that takes into account the manufacturing signature. The purpose of this research is twofold: (i) study the effect of process-induced defects into the retrieve optimal design; (ii) investigate how the selection of the structural theory may influence the optimal solution.

Presenting Author: Alfonso Pagani Politecnico Di Torino

Presenting Author Biography: Alfonso Pagani serves as associate professor of spacecraft structures at the Department of Mechanical and Aerospace Engineering, Politecnico di Torino. Dr. Pagani is associate editor for Advances in Aircraft and Spacecraft Structures and the International Journal of Dynamics and Control. He conducts his research on structures, space mechanisms and advanced materials mechanics at the MUL2 Lab (www.mul2.com).