Fatigue crack constraint in plain-woven CFRP using newly-developed spread tows

This paper discusses the fatigue behavior of a new type plain-woven CF/epoxy composite (CFRP) using very thin and wide tows called as “spread tows”. Tension-tension fatigue tests were conducted and internal damage was observed by using an optical microscope. The experimental results showed that the fatigue lives of plain-woven CFRP using spread tows were longer than those of conventional plain-woven CFRP. As the fatigue tests were conducted at cyclic maximum stress of 600 MPa, we could not observe any crack in the new type plain-woven CFRP subjected to 106 cyclic loads. At cyclic maximum stress of 800 MPa, we could not observe any crack at the narrow weft part (about 0.05 mm thickness). It was found that fatigue crack formation and propagation criterion was affected by tow thickness. The cross-over point between the spread tows was regarded as (0/90)s cross-ply laminate and the ply failure strain was calculated. As a calculation result, it was clarified that fatigue crack formulation and propagation was constrained by using spread tows. Thereby, fatigue lives of the composites were improved compared with those of conventional plain-woven fabric composites.