On the relationship between mode I fracture toughness and susceptibility to mixed-mode fracture

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)

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confidence: 98%

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confidence: 98%

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

Manoharan

1995

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“…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.…”

mentioning

confidence: 99%

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confidence: 99%

“…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%

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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~)

On the combined mode I-mode II fracture toughness of polyethylene film

Manoharan

1993

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~, 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 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 II fraclure have been very scarce and there is no general agreement among authors on the effect of the addition of a mode II 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 analysed 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 from the various modes are nonlinear and not directly superimposable unlike under linear elastic conditions. The relationship between pure mode I and mode II 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]. In [2] the primary emphasis is suceptibility to mixed mode I -mode III fracture, but the principles should be extendable to mode I -mode II fracture as well.The material chosen for study was commercial grade low density polyethylene film used in packaging applications. The average thickness of the film was 50 microns. The fracture tests were performed using single edge notched specimens schematically depicted in Fig. 1. 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 analyse the fracture of the polyethylene since polyethylene is known to exhibit large crack tip plastic zones. Manoharan et al. [3] have pointed out the modifications necessary to the ASTM E-813-87 standard in the case of mixed mode fracture. In the present investigation, the primary effect under consideration is the relative contributions Int Journ of Fracture 62 (1993)