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Research Papers

Investigating Some Technical Issues on Cohesive Zone Modeling of Fracture

[+] Author and Article Information
John T. Wang

NASA Langley Research Center, Hampton,
VA, 23681
e-mail: john.t.wang@nasa.gov

Contributed by the Materials Division of ASME for publication in the Journal of Engineering Materials and Technology. Manuscript received May 2, 2012; final manuscript received August 28, 2012; published online December 21, 2012. Assoc. Editor: Joost Vlassak.

J. Eng. Mater. Technol 135(1), 011003 (Dec 21, 2012) (10 pages) Paper No: MATS-12-1083; doi: 10.1115/1.4007605 History: Received May 02, 2012; Revised August 28, 2012

This study investigates some technical issues related to the use of cohesive zone models (CZMs) in modeling the fracture of materials with negligible plasticity outside the fracture process zone. These issues include: (1) why cohesive laws of different shapes can produce similar fracture predictions, (2) under what conditions CZM predictions have a high degree of agreement with linear elastic fracture mechanics (LEFM) analysis results, (3) when the shape of cohesive laws becomes important in the fracture predictions, and (4) why the opening profile along the cohesive zone length (CZL) needs to be accurately predicted. Two cohesive models were used in this study to address these technical issues. They are the linear softening cohesive model and the Dugdale perfectly plastic cohesive model. Each cohesive model uses five cohesive laws of different maximum tractions. All cohesive laws have the same cohesive work rate (CWR) defined by the area under the traction–separation curve. The effects of the maximum traction on the cohesive zone length and the critical remote applied stress are investigated for both models. The following conclusions from this study may provide some guidelines for the prediction of fracture using CZM. For a CZM to predict a fracture load similar to that obtained by an LEFM analysis, the cohesive zone length needs to be much smaller than the crack length, which reflects the small-scale yielding condition requirement for LEFM analysis to be valid. For large-scale cohesive zone cases, the predicted critical remote applied stresses depend on the shape of the cohesive models used and can significantly deviate from LEFM results. Furthermore, this study also reveals the importance of accurately predicting the cohesive zone profile for determining the critical remote applied load.

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References

Figures

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Fig. 1

Fracture analysis of a cracked infinite plate using a cohesive zone model

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Fig. 2

Linear softening and Dugdale models

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Fig. 3

Cohesive zone fully developed at crack growth initiation and unchanged during growth for linear elastic material

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Fig. 4

Five cohesive laws with different maximum tractions but the same cohesive work rate for both the linear softening and the Dugdale models

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Fig. 5

J-integral paths around a cohesive zone

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Fig. 6

Iterative solution procedure

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Fig. 7

Cohesive zone opening displacements along the cohesive zone length for cohesive laws with different maximum tractions (a=1l¯ch)

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Fig. 8

Cohesive zone length as a function of maximum traction for different crack lengths

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Fig. 9

Cohesive zone length as a function of crack length for cohesive laws with different maximum tractions

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Fig. 10

Critical remote applied stress as a function of maximum traction for different crack lengths

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Fig. 11

Critical remote applied stress as a function of the scale of cohesive zone length

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Fig. 12

LEFM energy release rate as a function of maximum traction

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Fig. 13

LEFM energy release rate as a function of the scale of cohesive zone length

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Fig. 14

Changes of critical remote applied stress due to modifying the cohesive zone opening profile from a cusp shape to a triangular shape

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