value related to the strength of adhesion of base material and inclusion generally is different from the fracture toughness value for the crack occurrence in the base material. The fracture toughness in the debonding development expressed by the strain energy release rate is denoted by Gd0 and that in the crack occurrence is denoted by Gc0. When the restricting condition mentioned later is satisfied, according to the relative magnitude of the values of Gd and Gd0 and the values of Gc, and Gc0, the following matters for the fracture behavior can be stated: (A) Case of Gd < Gd0 and Gc. < Gc0: neither debonding develops nor cracking occurs. (B) Case of Gd < Gd0 and Gc > Gc0: debonding does not develop but cracking occurs. (C) Case of Gd > Gd0 and Gc < Gc0: debonding develops but cracking dose not occur. (D) Case of Gd > Gd0 and Gc > Gc0: there are both possibilities of debonding development and crack occurrence. In (A), (B) and (C) mentioned above, respective fracture behaviors can be specified, but in the case of (D), it becomes necessary to judge further which actually occurs, debonding or cracking. For this purpose, the ratio of the strain energy release rates of debonding and cracking Gd / Gc and the ratio of the fracture toughness values of debonding and cracking Gd0 / Gc0 are considered. According to the relation of the magnitude of the values of Gd / Gc and Gd0 / Gc0, the following matters can be stated: (a) Case of (Gd / Gc) < (Gd0 / Gc0), i.e. Gd / Gd0 < Gc / Gc0:cracking occurs. (b) Case of (Gd / Gc) > ( Gd0 / Gc0), i.e. Gd / Gd0 > Gc / Gc0:debonding develops. The analysis is carried out with the model that a crack occurs from one tip of debonding (see Fig.1c). Figure 6 : Nondimensional Mode I stress intensity factor under uniaxial tension in the y direction Figure 7 : Normal stress r V and tangential stress T W r near the debonding tip under uniaxial tension in the y direction
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