Combined mode I - mode III fracture toughness of a high carbon steel

Self Cite

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 K~c, J,o 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 characterize 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. There has been a limited amount of experimental work done on mixed mode fracture. The observations on combined mode I -mode III fracture have been very scarce and there is no general agreement among authors on the effect of the addition of a mode III component to pure mode I loading. There has been some theoretical analyses of mixed mode I -mode II fracture under elastic plastic conditions. Shih [1] has analyzed the problem for small scale yielding under plane strain conditions. The difficulty is that under mixed mode conditions in the elastic-plastic range, the fields arising fom the various modes are nonlinear and not directly superimposable unlike under linear elastic conditions. The relationship between pure mode I and mode III fracture toughness values is also unclear. In view of all these factors there have been attempts made recently to delineate materials into different classes based on their shear susceptibility [2].The material chosen for study was commercial grade high density polyethylene used in packaging applications. The average thickness of the film was 3 mm. The combined mode I -mode III fracture toughness tests were performed using modified compact tension specimens [3]. In these modified compact tension specimens the crack inclination angle 0 is defined as the angle between the plane of the crack and the loading direction. The J-integral was chosen as the most appropriate parameter to analyze the fracture of the polyethylene since polyethylene is known to exhibit large crack tip plastic zones. Manoharan et al. [3] have pointed out the the modifications necessary to the ASTM E-813-87 standard in the case of mixed mode fracture. The J-integral tests were conducted using the multiple specimen method in general accordance with ASTM standards Int Journ of Fracture 71 (1995)

supporting

confidence: 78%

“…Ji =-ff~ P, dSt (5) fo f~lnPmd8 m = (6) where B is the crack front width, b is the remaining ligament width and f0 is a constant taken equal to the mode I value. The resolved critical mode I and mode III J-integral values were then calculated by constructing the resolved mode crack resistance curves using the procedure described elsewhere [3].…”

mentioning

confidence: 99%

On the combined mode I-mode III fracture toughness of high density polyethylene

Manoharan

1995

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“…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.…”

mentioning

confidence: 99%

A mixed mode fracture mechanism map

Manoharan

Kamat

1995

Self Cite

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)

“…In other materials, the local fracture micromechanism may be void initiation, growth and coalescence but the voids may be shallow and link up quickly leading to unstable crack propagation. This is the case, for example, in a 1.25% C steel [2]. In such materials, there is little possibility of shear localization influencing the growth of the voids and hence these materials are relatively shear insensitive.…”

mentioning

confidence: 94%

“…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.…”

mentioning

confidence: 99%

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

Monoharan¹,

Seow²,

Tio³

1996

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 K~o, J~c 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 stresss states so that the development of suitable parameters to characterize 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 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. 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. In addition to compact tension specimens, three point bend specimens with an inclined crack can also be used to determine the mixed-mode fracture behaviour of materials [13].The aim of the present study was to evaluate the feasibility of extending the mixed-mode fracture concept to impact testing using a Charpy type test specimen. The modified Charpy test specimen is shown in Fig. 1. The crack inclination angle can be varied to provide a range of mode I and mode In load combinations. Four angles 90°,75°,60 ° and 45 ° were used in the present study. This modified Charpy test specimen provides for a simple method to determine the mixed-mode impact resistance of materials. Apart from providing information on dynamic I n t J o u r n oF ~a~. t u r e 80 (199~)