Design optimization of thin-walled composite beams.

摘要

A design optimization tool for preliminary design of composite I-beams is developed. The design tool combines mechanics of laminated thin-walled composite beams with a global optimization algorithm in a search for an optimal design. In the optimization problem formulation, beam stiffnesses are used as the objective function and constraints. Two different objective functions are considered, maximal beam bending stiffness and maximal beam axial stiffness. Here, for the first time, fiber directions in the beam walls are treated as design variables. It is assumed that the beam is constructed using unidirectional tape, and associated manufacturing issues are discussed in detail and included as constraints in problem formulation and the solution procedure. It is demonstrated that the design optimization of composite thin-walled beams is a complex global optimization problem. Therefore the solution method is based on a global search algorithm, Improving Hit-and-Run, which allows the design variables to be continuous or discrete with a user specified discretization interval. Numerical results for two material systems and nine different design families showed that it is possible to design a composite I-beam which has higher axial, torsional and bending stiffnesses than an aluminum beam with the equivalent cross-section. Experimental procedures for measurement of beam principal and coupling stiffnesses are developed. Beam specimens are tested under pure bending, pure torsion and pure axial loading conditions. The results of the experimental study showed that the predicted beam stiffnesses agree well with the measured stiffnesses. Some discrepancies are believed to be due to some variations in material properties and possible small imperfections in beam cross-section and loading fixtures.