No abstract

Solid carbon fiber/epoxy laminates manufactured by liquid resin infusion of twill fabric reinforcement are recycled in a bath of boiling sulfuric acid to separate the fibers from the matrix. The recycled reinforcement consists of long fibers arranged in a random, entangled mat. Using the same epoxy matrix and infusion materials and process, the recycled fibers are reutilized to manufacture solid laminates. The physical properties of the recycled laminates are evaluated by means of pulse-echo ultrasound, visual microscopy, and fiber volume content. The average fiber volume content of the recycled laminates is 33%, compared to the 62% of the twill laminates. The mechanical properties of the recycled composite include tension modulus and strength, compression modulus and strength, three-point bend flexure strength, and short beam shear strength. The properties are compared against the values of the twill reinforcement with quasi-isotropic stacking sequence. Results show that the recycled material offers promising elastic properties and strength values, similar to those of advanced carbon fiber sheet molding compounds, and therefore can be used as structural material.

Damage is inflicted on carbon-fiber/epoxy composite plates using both simulated lightning strike and mechanical impact in the effort to understand the relative effect of the two damage mechanisms. A methodology is proposed to characterize the damage resistance and tolerance of unconfigured composite plates subjected to lightning strike in a fashion that is consistent with the extensive work previously done on low-velocity impact. Using current and voltage diagnostics, it is possible to extrapolate the amount of electromechanical energy absorbed by the plate during the strike and compare it to that absorbed during a mechanical impact. Damage resistance is characterized by means of ultrasonic C-scans and microscopy, whereas residual strength is measured by means of compression after impact testing. Results show that the energy dissipated in a specimen during the lightning strike is much greater than the strain energy introduced by mechanical impact, and hence a comparison based on energy is not recommended. However, based on the relative threat levels associated with the impact and the lightning strike events, the comparison yields insightful observations on both damage state and residual performance. In general, for the configurations tested, lightning strike damage seems to be less detrimental than the mechanical impact in terms of both damage area and residual strength.