Solving Nonlinear Composite Material Problems Using the Automated StructuralOptimization System (ASTROS)

摘要

Most advanced composite materials have nonlinear stress versus strain curves--grossly so in the laminas shear direction. If linear approximations are used, overly conservative design will result. This thesis expands the usefulness of the Automated Structural Optimization System (ASTROS) finite element (FE) program by incorporating a newly developed capability to include material nonlinearities. By dividing a FE problem into several intervals, and incorporating the changing nature of the nonlinear material properties within each element, a good approximation of the laminate's actual stresses and strains can be obtained without the undue experimentation involved in testing every individual configuration. Each material property is updated in terms of tension and compression as appropriate. Updating the material properties is possible in the material axes through comparison to cubic spline curves made from experimental data. The resulting piecewise linear analysis accurately captures the nonlinear nature of the properties. This research considered plane stress flat plates with and without holes. Graphite/Polyetheretherketone is an advanced composite material that has good high temperature strength properties and nonlinear material properties.