Reliability-based design of composite sandwich plates with non-uniform boundary conditions

Abstract

A reliability-based design of a rectangular sandwich plate with anisotropic face sheets and edges elastically restrained against rotation is presented. The plate is optimized for minimum weight subject to a reliability requirement against axial and shear buckling. The influence of reliability requirement on the optimal design is captured by comparing the results of non- deterministic and deterministic optimization procedures. In addition, the calculated sensitivity coefficients show the face sheet and core thicknesses to have much higher influence on reliability than other random parameters such as material moduli and face sheet ply orientation angle. ~~ Introduction For a structure to perform its intended function with desired confidence, the uncertainties related to geometry, material, load, and boundary conditions must be considered in its design. The traditional method of dealing with uncertainties is to use either conservative values for the uncertain quantities or safety factors within the framework of deterministic design. However, the deterministic-based approach has been shown to frequently yield designs with inconsistent reliabilities for different components. In contrast the non-deterministic or probabilistic design offers a more efficient-and robust method for dealing with uncertainties. In this case the uncertain parameters are modeled as random variables with particular distributions, means, and standard deviations. If such statistical information is available, then the non- deterministic design approach could be used to arrive at an optimal design with proper balance between performance and reliability requirements. The reliability-based optimization has been an active area of research for a number of years. Wang ar~I Grandhi' have considered reliability-based structural optimization in a multidisciplinary environment. They calculated safety index by using intervening variables for limit function approximation and using the HL-RF or modified HL-RF algorithm for reaching the constraint boundary. Tomg and Yang' proposed an advanced mean value method (AMV) to efficiently calculate the reliability and identifying the most probable failure point (MPP). They developed an efficient reliability analysis by expanding the limit functions in terms of intermediate design variables. The design constraints were approximated using multi-point splines in searching foi- the optimum. Mahadevan and Liu' investigated the optimization of composite structures for reliability requirements. Two types of objective functions-, namely, the mmimization of tilt: sum of the component reliability indices and the minimization of the overall structural weight, ate investigated. In this paper we discuss our investigation regarding