Prediction of ductile tearing of compact fracture specimens using the R-6 failure assessment diagram

Bloom, J. M.

doi:10.1016/0308-0161(80)90026-5

International Journal of Pressure Vessels and Piping

1980

DOI: 10.1016/0308-0161(80)90026-5

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Prediction of ductile tearing of compact fracture specimens using the R-6 failure assessment diagram

J. M. Bloom

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Cited by 14 publications

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“…The original concept of the R-6 approach came from the CEGB Dowling and Townley two-criterion approach [i] which states that structures will fail by either of two mechanisms: brittle fracture or plastic collapse. Harrison, Loosemore, and Milne of CEGB [2] reformulated the two-criterion approach into what is known today as R-6.The author used the R-6 failure assessment diagram to predict the ductile tearing behavior of compact fracture test specimens of HYI30 steel, A533B steel, and 7075-T651 aluminum [3]. While it is known that the R-6 assessment curve is based upon the elastic-perfectly plastic Dugdale strip yield model, the author used a simple approach [3] to account for strain hardening effects of the A533B steel.…”

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“…The author used the R-6 failure assessment diagram to predict the ductile tearing behavior of compact fracture test specimens of HYI30 steel, A533B steel, and 7075-T651 aluminum [3]. While it is known that the R-6 assessment curve is based upon the elastic-perfectly plastic Dugdale strip yield model, the author used a simple approach [3] to account for strain hardening effects of the A533B steel.…”

mentioning

confidence: 99%

“…While it is known that the R-6 assessment curve is based upon the elastic-perfectly plastic Dugdale strip yield model, the author used a simple approach [3] to account for strain hardening effects of the A533B steel. This approach was to take the average of the yield and ultimate strengths of the material for the flow stress.…”

mentioning

confidence: 99%

“…For HYI30, a material which exhibits very little strain hardening, the R-6 diagram predicted the behavior of the HYI30 compact specimens for the complete load history quite well. On the basis of this work [3], it was concluded that while the current R-6 curve could be used for materials with little or no strain hardening, prediction of specimen or structural behavior for materials with significant strain hardening would require an alternative assessment curve which accounts for these strain hardening effects.…”

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confidence: 99%

“…It can be seen from this figure that the data from the GE/EPRI 4T compact A533B specimens correlates well with this proposed strain hardening failure assessment curve. Now if the proposed strain hardening assessment curve is used to predict specimen behavior as was done in [3], plots of load versus slow stable crack growth (ductile tearing) can be produced. These are given in Figs.…”

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Prediction of ductile tearing using a proposed strain hardening failure assessment diagram

Bloom

1980

Int J Fract

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The author has recently completed an evaluation of an engineering failure assessment approach developed at the Central Electricity Generating Board (CEGB) of the United Kingdom and became aware of certain limitations of this approach. The CEGB failure assessment approach, referred to in the United Kingdom as R-6, is an engineering approach to the elastic-plastic fracture mechanics assessment of structural components.The use of the R-6 diagram allows a straightforward prediction of maximum load which a given structure can safely withstand.In addition, for a given load and either a postulated or actual defect size, the margin of safety of the structure can be directly determined from the diagram. The original concept of the R-6 approach came from the CEGB Dowling and Townley two-criterion approach [i] which states that structures will fail by either of two mechanisms: brittle fracture or plastic collapse. Harrison, Loosemore, and Milne of CEGB [2] reformulated the two-criterion approach into what is known today as R-6.The author used the R-6 failure assessment diagram to predict the ductile tearing behavior of compact fracture test specimens of HYI30 steel, A533B steel, and 7075-T651 aluminum [3]. While it is known that the R-6 assessment curve is based upon the elastic-perfectly plastic Dugdale strip yield model, the author used a simple approach [3] to account for strain hardening effects of the A533B steel. This approach was to take the average of the yield and ultimate strengths of the material for the flow stress. While this simple approach gave fairly accurate predictions of maximum load values for the displacement-controlled compact specimens, loads after maximum load were poorly predicted. Prediction of maximum load for load-controlled structures is adequate, as this corresponds to the instability point of the load-controlled structure. For displacement-controlled structures or specimens, the maximum load point does not correspond to the instability point, and therefore it is of interest to know the complete load history. For HYI30, a material which exhibits very little strain hardening, the R-6 diagram predicted the behavior of the HYI30 compact specimens for the complete load history quite well. On the basis of this work [3], it was concluded that while the current R-6 curve could be used for materials with little or no strain hardening, prediction of specimen or structural behavior for materials with significant strain hardening would require an alternative assessment curve which accounts for these strain hardening effects.(The 7075-T651 specimens responded in an essentially valid linear elastic manner.)The essence of the failure assessment diagram is that it is a w~iversal failure curve that has been normalized with respect to the linear elastic fracture mechanics (LEFM) behavior of the specific structural configuration at one extreme, and the limit load of the structure Int Journ of Fracture 16 (1980) R74 at the other extreme.In terms of the J-integral, the equation of the failure assessment curve can ...

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Prediction of ductile tearing using a proposed strain hardening failure assessment diagram

Bloom

1980

Int J Fract

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Corrections: ?Prediction of Ductile Tearing Using A Proposed Strain Hardening Failure Assessment Diagram,? by J. M. Bloom

Bloom

1980

Int J Fract

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Recently, it was brought to the author's attention that the J-integral fully plastic solutions of Goldman and Hutchinson [i] for a finite center-cracked panel under plane strain conditions for large values of the strain hardening exponent (n > 7) and small crack length-to-width ratios (a/w < 1/4) could be as much as 37 percent in error on the high side when 7ompared to the more accurate solutions of Shih and Kumar [2] and others [3,4].It was noted in [i] that numerical difficulties occur for a/w + 0 and large n. On reexamining the expressions used to derive the strain hardening failure assessment curve for the infinite plane strain center-cracked panel, the author, in addition, found that the plane strain limit load correction of 2/J3 was inadvertently excluded. This correction is raised to the "(n + i) th'' power in the fully plastic solution and is, therefore, quite significant.The author has recalculated the proposed universal strain hardening curve using the estimation scheme of Shih and Kumar [2] and the expression for the fully plastic infinite plane stress center-cracked panel solution derived by Shih and Hutchinson [5]. This latter expression was corrected for the plane strain condition by the author using results obtained from [2] for a finite center-cracked panel with a small crack length-to-width ratio (a/w = 1/4) for both plane strain and plane stress conditions. The correction was based on the ratioing of the solution "h" functions. As reported in the earlier blue page report of April, 1980, the failure assessment curve in terms of the J-integral can be written aswhere Kr, S r are the elastic and plastic coordinates of the failure assessment diagram and o is the applied stress on the specimen or structure. The equation of the corrected proposed universal failure assessment diagram for plane strain conditions is n-l 1 2 n+l S 3a hlr~ ~tv,n) S r r J/Jelastic K 2 1 + 9 n-l 1 + S 2 + 4~(1_v2)r r ~International Journal of Fracture 16 (1980) R73-R77.Int Journ of Fracture 16 (1980)

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Fracture Mechanics Based Assessment of a Pressure Vessel Using R6 Procedure

Srinivasan,

Prakashan,

Anandavally Parameswaran

et al. 2023

Trans Indian Inst Met

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Prediction of ductile tearing of compact fracture specimens using the R-6 failure assessment diagram

Cited by 14 publications

References 4 publications

Prediction of ductile tearing using a proposed strain hardening failure assessment diagram

Prediction of ductile tearing using a proposed strain hardening failure assessment diagram

Corrections: ?Prediction of Ductile Tearing Using A Proposed Strain Hardening Failure Assessment Diagram,? by J. M. Bloom

Fracture Mechanics Based Assessment of a Pressure Vessel Using R6 Procedure

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