Significance of Geometric Nonlinearity in the Design of Thermally Loaded Structures

Abstract

In reality, all structures exhibit some degree of nonlinearity; however, in many cases, its effects are negligible to the overall structural response and it is common to treat them as such in analysis and design optimization. Due in large part to this practice, severe consequences and structural failures may arise when this nonlinearity cannot be neglected. Currently, this occurs with increasing frequency as designers continue to explore innovative aircraft concepts that push the limits of existing design tools and industry standards. In this research, such a case is investigated where geometrically nonlinear effects result from an elevated temperature environment. The thermoelastic response of characteristic aerospace structures is investigated by comparison of linear and nonlinear analysis results. Results indicate that geometric nonlinearity, which manifests as stress stiffening behavior and deformation-dependent load contributions, plays a significant factor in properly predicting the structural response for structures found in modern military aircraft with embedded engines. In addition, parametric studies present the influence of geometry parameters and boundary fixivity, or how components are attached to adjoining structures, on the nonlinearity in order to identify features that make it critical. Based on these observations, some guidelines regarding when geometric nonlinearity should be included in the structural analysis of thermally loaded structures are provided. These guidelines are useful to the structural analyst or designer faced with the analysis of components in a thermal environment due to engine heat, aerodynamic effects, or other sources.