日本複合材料学会誌

A new fiber spreading technology (FUKUI method) to obtain the continuously wide and thin reinforcing fiber tow was developed. Thin prepreg sheet less than 0.05 mm in thickness can be prepared by using this method. In the previous study, the tensile tests were conducted on the Carbon/Epoxy quasi-isotropic laminates which were composed of stacking these prepreg sheets. As a result, the thin-ply effect was found, that is, the initial failure stress increases with decreasing ply thickness. This effect was previously predicted by Kageyama et al. In this work, the thin-ply effects on the compressive properties have been studied. As a result, the thin-ply effect was found not only in tensile tests but also in compression tests. This result implies that the design strength of composites can be improved by the use of thin prepreg sheets. In other words, this result means that the weight saving and reliability can be achieved using thin prepreg sheets as a composite materials.

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The present study investigated the improvement of low-velocity impact damage resistance of CFRP laminates due to the through-the-thickness stitching experimentally and numerically. First, we conducted drop-weight impact tests for stitched and unstitched laminates. The results of damage inspection confirmed that stitching did improve the impact damage resistance, and revealed that the improvement effect became greater as the impact energy increased. Moreover, the stitching affected the through-the-thickness damage distribution. Then we performed FEM analysis and calculated the energy release rate of the delamination by using Virtual Crack Closure Technique (VCCT). The numerical results revealed that the stitching affected the through-the-thickness damage distribution because the stitch threads particularly decreased the mode I energy release rate around the bottom of the laminate. Comparison of the results of models which contain delamination of various size revealed that the energy release rate became smaller as delamination size increased, therefore the stitching improved the impact resistance more effectively when the impact energy was larger.

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