• Composites Research
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• v.33 no.3
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• pp.147-152
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• 2020

In this study, void behavior of composite laminate by local internal pressure gradient due to structural geometry and surface film application condition was experimentally evaluated through fabrication of spar/skin integrated structure specimens. Viscosity comparison and thermal analysis for both carbon fiber prepreg and surface film were conducted and cure characteristic and rate difference were analyzed. 2 types of spar/skin integrated structural specimens were prepared based on different application condition of surface film. Subsequently, those specimens were evaluated through visual surface inspection, non-destructive and destructive inspection. In a specimen #1 with full application of surface film, low pressurized area of composite laminate created by pressure gradient of structural geometry had voids. It exhibited that voids could not be evacuated and were locked in cured laminate by the influence of pre-cured surface film with relatively faster cure rate. In a specimen #2 without surface film, it revealed that all internal voids disappeared in the cured laminate. Therefore, it is verified that surface film acts as barrier film preventing void movement and evacuation during autoclave cure.

• Composites Research
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• v.18 no.3
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• pp.38-46
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• 2005

In order to characterize the outstanding performance of three-dimensional (3D) composites, the low velocity impact test has been carried out. 3D fiber structures have been achieved by using the automated tape placement (ATP) process and a stitching method. Materials for the ATP and the stitching process were carbon/epoxy prepreg tapes and Kevlar fibers, respectively. Two-dimensional composites with the same stacking sequence as 3D counterparts have also been fabricated for the comparison of damage tolerance. For the assessment of damage after the impact loading, specimens were subjected to C-Scan nondestructive inspection. Compression after impact (CAI) tests were conducted to evaluate residual compressive strength. The damage area of 3D composites was greatly reduced $(30-40\%)$ compared with that of 2D composites. Although the CAI strength did not show drastic improvement for 3D composites, the ratio of retained strength was $5-10\%$ higher than 2D samples. The effect of stitching on the impact performance was negligible above the energy level of 35 Joules.