Optimization of composite I-sections using fiber angles as design variables

A problem formulation and solution methodology for design optimization of laminated composite I-sections is presented. Objective functions and constraints are given in the form of beam stiffnesses. Two different objective functions are considered, maximum beam bending stiffness and maximum beam axial stiffness. Fiber directions in the beam walls are treated as design variables. It is assumed that the beam is constructed using unidirectional tape, and manufacturing issues associated with the use of unidirectional tape are discussed and included as constraints in the problem formulation and solution. The paper demonstrates that the design optimization of composite thin-walled beams is a complex global optimization problem that cannot be solved by means of traditional convex programming. Therefore, the solutions described are found using a global search algorithm, Improving Hit-and-Run, which allows the design variables to be either continuous or discrete with a user-specified discretization interval. Numerical results for two material systems and nine different design families for manufacturing composite I-sections are presented.