Software for the Design and Certification of Unitized Airframe Components

摘要

This report presents the results of the investigation of two important subjects associated with the design and certification in unitized airframe components. The first subject is related to the effects of residual stresses on the structural stability of thin unitized components machined from aluminum plates, in particular 7050-T74 and 7050-T7451 plates. The findings indicate that residual stresses introduced in a plate during the rolling operation (bulk stresses) and residual stresses introduced into a part machined from the plate during high speed machining should be included as a modeling consideration when designing thin unitized components. The second subject is related to the computation of strain energy release rate in damaged laminate composite materials. Typical failure in the presence of an initial defect, such as delamination, appears under a mixed mode loading, therefore it is essential to have an efficient algorithm for the computation of the strain energy release associated with each loading mode for the construction a mixed mode failure criterion for the determination of residual strength of unitized components made of composite materials. The Virtual Crack Closure Technique (VCCT) was considered during the Phase I project. It was found that typical numerical implementations of the VCCT utilizing the h-version of the finite element method (FEM) are unreliable because the results are meshdependent. A modification of the method was investigated, involving a combination of numerical and analytical computations, which is well suited for its implementation with the p-version of the Finite Element Method.