Experimental investigations of interlaminar strength for Kevlar(R) stitched CFRP laminates were carried out. The used Kevlar(R) thread thicknesses are 400d (denier), 600d, 800d, 1, 000d and 1, 200d. The stitched carbon fiber (CF) preforms were cured with RTM (resin transfer molding) technique. Stitching types employed to CF dry preform (T300 and T700) are a modified lock stitch (MLS) which has the stitch inter-locking position on the CFRP laminate surface and a lock stitch (LS) which has the inter-locking position in the CFRP laminate where an industrial sewing machine was used. Test specimens containing a single stitching thread were cut from the stitched CFRP laminates. The test specimens were loaded to the out-of-plane direction by a screw driven testing machine. Load-displacement curves were obtained and sectional observations for broken test specimens were executed. Maximum tension load and consumption energy for the single stitchthread specimens were measured. A trend would be found that MLS cases show larger maximum load and consumption energy than those of LS cases for each stitch thread thickness. The maximum load of the test specimen increases with stitch thread thickness. On the other hand, the consumption energy of 1, 000d is the highest among all the stitch thread thickness specimens. The reason why the 1, 000d MLS case shows the highest energy is an intense pull-out phenomenon. It is revealed that the maximum load and consumption energy of the stitched CFRP laminates was governed by an inter-locking position of stitching in the CFRP laminates. It is also suggested that the allowable strength and load distribution along the stitch thread affects the breaking position of the stitch thread in the CFRP laminates. A similarity is unveiled in the relationship between the values of G1 by double cantilever beam (DCB) tests and failure modes of stitching threads and in the relationship between the value of consumption energy by the present tests and failure modes of stitching threads.
