Thermomechanical behavior and experimental testing of flexible matrix composite box-beams with extension-twist coupling

Flexible Matrix Composites (FMC), are shown to exhibit large failure strains and high anisotropic properties with excellent potential for elastic tailoring. A box-beam analytical model exhibiting extension-twist coupling is extended to include thermomechanical effects. Using this model, a detailed parametric study is conducted on various FMC and carbonepoxy (CE) designs. Thermal analyses performed on FMC designs showed that some designs are highly sensitive to temperature variations whereas certain others are more thermally curvature stable than the baseline CE. A design procedure involving stiffness, deflections and strength is employed to derive candidate designs for FMC from a wide spectrum of laminates. Detailed quantitative analyses are performed on FMC candidate designs and compared with that of a CE baseline design. It is showed that FMC can be tailored to obtain thermally curvature stable laminates while satisfying certain design constraints. For example, the design [45, 75, 15] _s generates nearly 5 times twist under axial load when compared with the CE baseline. This design exhibits only 0.5° twist at the tip due to a change in temperature of -200°F whereas the baseline generates 6.5°. Validation studies on analytical predictions are performed by conducting experiments on FMC specimens. Wet filament winding technique is employed to fabricate several FMC box-beam specimens exhibiting extension-twist coupling. The specimens are tested for axial deformation, twist, and bending under various loading conditions. Excellent correlation between analytical predictions and experimental results is observed. For [45, 45] specimen, experimental data fall within 6% of the theoretical results for twist and bending under axial and bending loads respectively. The present investigation demonstrates the potential of FMC for structural tailoring and shows that it is a viable candidate for applications involving large elastic deformations.