Y. Kagawa, K Goto/ Materials Science and Engineering 4250(1998)285-290 Static Crack growth Interface Debonding 2mm Crack Bowing Crack bridging 2mm 2mm Fig. 6. Crack growth process of the composite from direct observation. The white dotted-line indicates matrix crack front. fitting of the experimentally obtained F(c/r) for 0.5< r≤3.0 yields: where a is the applied stress, c is the crack length and the s) is the dimensionless shape factor. As F(c/r) for =1.0391-099331(c/r)+0. 27049(c/r)2 specimen used could not be obtained from the literature, it was obtained from the experiment of the +0.062984(c/r)3-0.041821(c/r)4 pure PMMA specimen, assuming that the applied in +0.0053704(c/r)3 tensity factor is equal to the critical stress intensity factor of pure PMMa ShinkoliteA, KcN The applied stress intensity of the composite, K, is 1.0 MPaym [8D). The fifth order polynomial curve obtained substituting Eq (2) into Eq (1).Fig11shows the change of the normalised K, i.e. K/Km with the nterface Circumference stress: o Crack Plane Crack Plane Stage II 020苏 2≈4MPa Radial stress: o StageⅢ 050010001500200025003000 Crack Plane CrackPlane Distance from interface /um 7. Schematic drawing of crack growth process of the composite ig. 8. Thermal stress distribution in the matrix and the fibre.Y. Kagawa, K. Goto / Materials Science and Engineering A250 (1998) 285–290 289 Fig. 6. Crack growth process of the composite from direct observation. The white dotted-line indicates matrix crack front. K=Fc r  sc 1 2 (1) where s is the applied stress, c is the crack length and F(c/r) is the dimensionless shape factor. As F(c/r) for the specimen used could not be obtained from the literature, it was obtained from the experiment of the pure PMMA specimen, assuming that the applied in￾tensity factor is equal to the critical stress intensity factor of pure PMMA (Shinkolite®A, Kc m: 1.0 MPa m [8]). The fifth order polynomial curve fitting of the experimentally obtained F(c/r) for 0.55 c/r53.0 yields: F(c/r) =1.0391−0.99331 (c/r)+0.27049 (c/r) 2 +0.062984 (c/r) 3−0.041821 (c/r) 4 +0.0053704 (c/r) 5 (2) The applied stress intensity of the composite, K, is obtained substituting Eq. (2) into Eq. (1). Fig. 11 shows the change of the normalised K, i.e. K/K m c with the Fig. 7. Schematic drawing of crack growth process of the composite. Fig. 8. Thermal stress distribution in the matrix and the fibre