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Stability of terrestrial composite-material structures can be assessed for environmental effects.

A research project has yielded progress on several fronts toward the goal of minimizing thermal and aging distortions of composite-material (specifically, polymer- matrix/graphite-fiber) outer-space structures that are required to retain precise dimensions and shapes. The achievements of this project are also applicable to terrestrial composite-material structures to the extent to which various environmental effects can be properly taken into account. Examples include effects of expansion caused by absorption of atmospheric moisture (similar to effects of purely thermal expansion) and effects of outgassing of volatile constituents of polymers (effects of out-gassing are more pronounced in the outer-space vacuum).

This T-Joint Composite-Material Structure served as a model for computational-simulation demonstration and testing of the concept of anti-distortion appliqués as means of reducing thermal distortions.
One of two main approaches followed in this project involved the concept of using exterior material additions, called "anti-distortion appliqués," as means of deliberately introducing thermomechanical distortions to offset undesired thermomechanical distortions such that the magnitudes of the resulting net thermomechanical distortions are reduced as nearly as possible to zero. A composite Tjoint structure (see figure) was selected as the subject of a demonstration computational-simulation problem, and a finite-element model was developed to characterize the thermomechanical properties of the structure. (An experimental model of the structure was also constructed but the project ended before the structure could be tested.)

In the computational simulations, initially, some assumed thermal distortions were shown to be reduced by trial-and-error positioning of anti-distortion appliqués. Subsequently, optimization software was employed to automatically adjust the design parameters of the anti-distortion appliqués so as to minimize an objective function based on distortional displacements in the structure. It was found that an effective and practical way to effect the optimization was to introduce only a few appliqués and set their location coordinates as design parameters.