Experimental investigations have been made on the mode I interlaminar fracture toughness (G
IC) of stitched CFRP (carbon fiber reinforced plastic) laminates. The G
IC of stitched CFRP laminates fabricated by resin transfer molding (RTM) and stitching with five kinds of stitch thread thicknesses, 400d (denier), 600d, 800d, 1000d, and 1200d were experimentally obtained by double cantilever beam (DCB) tests. Interlaminar tension tests for stitched CFRP laminates for a specimen containing only one stitch thread were also carried out. The consumption energy of the single stitched CFRP laminates (W
t) and stitch threads broken modes were obtained by such interlaminar tension tests. DCB test results show that the G
IC of stitched CFRP laminates of several stitch thread thicknesses are governed by stitch density (SD). It is found that the relationship between ΔG
IC/ΔSD and W
t are linear function. In other words, the G
IC of Kevlar
® stitched CFRP laminates is not only governed by SD but also W
t obtained from the interlaminar tension tests. It is also suggested that the interlaminar tension test results exhibit the potential for G
IC estimation on the Kevlar
® stitched CFRP laminates instead of conducting the DCB tests.
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