A mixed mode fracture mechanism map

Abstract

As fracture mechanics has developed as a discipline, many parameters have been developed to characterize the instability condition. However, a majority of this work has been confined to the investigation of mode I fracture. Thus, we have standardized methods for experimentally determining KIo, J~, and J-resistance curves for mode I crack propagation. However, cracks in real materials can be subjected not just to tensile stresses but to complex stress states so that the development of suitable parameters to charactrterize mixed-mode crack initiation and propagation is important in the evolution of suitable design criteria. Further, observations indicate that initially flat cracks in some tough materials tend to reorient themselves to oblique planes during growth. For these materials, crack propagation can be said to occur under combined mode conditions.A considerable amount of work on mixed mode I/III fracture toughness of materials [1-26] is available. Of this work, a portion involves non-proportional loading which we do not consider here, focusing instead only on work involving modified compact tension specimens [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] . The superposition of mode III loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has liitfle effect or even results in an increase in the fracture toughness. Fracture mechanism maps delineating regions of susceptibility to tensile and shear loads have been proposed [27,28]. In this paper, data on a wider range of materials, including steels, aluminum alloys, metal matrix composites, ceramics and polymers have been used to extend and reinforce the fracture mechanism map concept.The data for the yield strength (o), mode I fracture toughness (J,) and 45 ° mixed mode fracture toughness (JTo) fofdifferent materials is enumerate~i in Table 1. The effect of the yield strength and mode I fracture toughness on the mixed mode fracture toughness can be represented by a plot of J.rJJic versus J J o . It can . . . . . Y , clearly be seen that materials which have a very low J,Jo rano exhibit a h~gher • Y .mixed-mode fracture toughness than the mode I fracture toughness. W~th an increase in the J J o ratio, the JTJJ,o ratio decreases and becomes significantly lower than unity indicating an increased susceptibility to mixed mode fracture. This trend, however, is reversed after a critical value of J J o is reached• An Int Journ of Fracture 73 (1995)

Effect of heat treatment on the mixed-mode impact behaviour of a low carbon steel

“…This behaviour is consistent with the concept of a fracture mechanism map proposed in a recent paper [14] where it was argued that as the mode I fracture toughness increases the susceptibility to mixed-mode fracture also increases. The differing susceptibilities of the various materials to mixed-mode loading is related to the microstructural fracture mechanisms operative in these materials.…”

“…Further, observations indicate that initially flat cracks in some tough materials tend to reorient themselves to oblique planes during growth. For these materials, crack propagation can be said to occur under combined mode conditions.A considerable amount of work on mixed mode I/III fracture toughness of materials is available using proportional loading methods [1-13] and all the work using such a loading method has recently been summarized [14]. The superposition of mode In loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness.…”

“…The superposition of mode In loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness. Fracture mechanism maps delineating regions of susceptibility to tensile and shear loads have been proposed to explain such differences [ 11,14].In the mixed-mode fracture toughness tests outlined above, the use of a modified compact tension specimen has enabled the testing of materials under a variety of combinations of mode I and mode III loadings. By using appropriate defined mixed-mode versions of the stress intensity factor K and J integral, the susceptibility of these materials to mixed-mode fracture can be quantified.…”

“…The superposition of mode In loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness. Fracture mechanism maps delineating regions of susceptibility to tensile and shear loads have been proposed to explain such differences [ 11,14].…”

“…A considerable amount of work on mixed mode I/III fracture toughness of materials is available using proportional loading methods [1][2][3][4][5][6][7][8][9][10][11][12][13] and all the work using such a loading method has recently been summarized [14]. The superposition of mode In loading results in drastic reduction in fracture toughness in some materials whereas in other materials it has little effect or even results in an increase in the fracture toughness.…”