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Highlights • The correlation of CTOD and J has been discussed using new CTOD calculation formula. • Current conversion factor in code include the a 0 / W term even in the SSY condition. • The conversion relationship is almost constant. • It is also independent of a 0 / W , YR and the deformation level. • Conversion factor m is a common variable as the coefficient for CTOD and K. • This is reasonable considering that the J is equivalent to G in SSY condition. Abstract The authors have already established a new CTOD calculation formula especially focusing the effect of strain hardening exponent. On the other hand, there is the demand of the conversion to J integral in order to assessment. The relationship between CTOD and J has been discussed for many years. It can be said that ISO 15653 and ASTM E1820 include the latest forms which express that relationship. These conversion equations include some coefficients calculated by numerical analyses where the validation to actual condition around the crack tip may still be insufficient. One problem is the fact that the current relationships include the a 0 / W term even in the SSY condition where mechanical field should be independent with the shape of the specimen. In this study, the CTOD- J relationship is redefined by using CTOD calculation results obtained by the authors' previous reports. As a conclusion, except under very small a 0 / W conditions, the relationship factor, m is simple, constant and independent of a 0 / W , YR and the deformation level. It was also found that same m can be applied with the coefficient for obtaining CTOD from K introduced by the authors. This is convincing considering that the J integral, by definition, corresponds to the energy release rate, G in the SSY condition. [ABSTRACT FROM AUTHOR]

In the previous report, the authors proposed a new CTOD calculation formula which shows good correspondence with actual CTOD in large thickness materials by introduction of a correction parameter for varied blunting shapes at the crack tip by a strain hardening exponent. However, this formula is limited to the standard range of the crack depth to width ratio, a 0 / W from 0.45 to 0.55, and hence did not satisfy strong demand for evaluation of a wider a 0 / W range. Actually, ISO15653 can cover a wider a 0 / W range from 0.01 to 0.70 in order to respond to this demand, considering the description in the Annex, which specifies a J -integral based CTOD calculation formula. In the context of this situation, the authors’ recent report revealed that the plastic hinge model can be applied to a 0 / W conditions other than the range from 0.45 to 0.55 based on detailed observation of plastic deformation for wider a 0 / W conditions. Coordination of the rotational center is steady regardless of the load level and strain hardening exponent. In this study, first, based on a B × 2 B configuration, expansion of the applicable a 0 / W range for the proposed CTOD calculation formula is investigated with some modification of the proposed formula. Second, application to the B × B type specimen is investigated. Finally, validation of the FEM analysis for B × B type specimens by the silicone rubber replica method is presented. [ABSTRACT FROM AUTHOR]

The authors have already proposed a new crack tip opening displacement (CTOD) calculation formula based on the plastic hinge model considering the unique crack tip blunting behavior due to strain hardening of the material. This formula is limited to the standard length-to-width ratio ( a 0 / W ) range of between 0.45 and 0.55. However, CTOD calculations are necessary for various other a 0 / W conditions when the critical CTOD for a specific microstructure must be evaluated in a welded joint. ISO15653, which prescribes CTOD test methods for welds, covers a wide range of a 0 / W between 0.10 and 0.7 by applying a J -integral based CTOD derived from ASTM E1290 for a 0 / W from 0.10 to 0.45 and a plastic hinge based CTOD for a 0 / W from 0.45 to 0.70. This procedure leads to a discontinuity in the evaluated CTOD at a 0 / W = 0.45. This problem results from the fact that the J -integral based CTOD is inconsistent with the conventional plastic hinge based CTOD, especially in low yield-to-tensile ratio materials. Thus, a single CTOD calculation method for the wide range of a 0 / W is required for rational evaluation. In this study, the plastic deformation behavior of SEB specimens was analytically examined in the a 0 / W range from 0.05 to 0.70, and the capacity of the plastic hinge based CTOD was discussed with the aim of establishing a unified CTOD calculation formula for SEB specimens with the wide range of a 0 / W. [ABSTRACT FROM AUTHOR]

A new CTOD calculation method is investigated in this work, considering the variation of crack tip blunting due to strain hardening. The calculation formula is constructed assuming that CTOD 45FEM based on three-dimensional elasto-plastic FEM is the target CTOD to be calibrated. A new factor f is introduced to correct the plastic term. In this factor, the blunted crack tip shape is considered to depend on the strain hardening exponent, and f is given as a function of the yield-to-tensile ratio ( YR ) of the material and the specimen thickness. The appropriateness of the investigated CTOD calculation is verified numerically and experimentally. [ABSTRACT FROM AUTHOR]

Crack opening profiles and crack tip opening displacement (CTOD) in single edge notch bend (SE(B)) specimens are investigated by the observation of unloaded crack tips and silicone rubber replication of loaded crack tips. Measurements in different yield-to-tensile ratio ( YR ) steels are performed, and CTODs in BS7448 and ASTM E1290 are compared with them. Although CTOD calculated in accordance with BS7448 agrees well with the measured CTOD for a high YR steel, CTOD with BS7448 overestimates the actual CTOD for a low YR steel. On the other hand, the relationship between CTOD calculated in accordance with ASTM E1290 and the measured CTOD is independent of YR , but CTOD with ASTM E1290 gives approximately 15% smaller values than the measured CTOD. The application of numerical simulation to the estimation of crack opening profiles is also investigated, and different crack openings are apparent in different YR steel models. The overestimation of CTOD with BS7448 results from the round shape crack tip blunting in the wide region behind the crack tip for a low YR steel, and this blunting is induced by the plastic strain localization depending on the strain hardening properties. [ABSTRACT FROM AUTHOR]

Crack opening profiles and crack tip opening displacement (CTOD) in single edge notch bend (SE(B)) specimens were investigated by the silicone rubber replication of loaded crack tips. Their measurements revealed that CTOD in BS7448 overestimated the actual CTOD for low yield-to-tensile ratio steel, and motivated to investigate a new CTOD calculation method, considering the variation of crack tip blunting behavior due to strain hardening. Supposing that CTOD45FEM, which was defined by the width between two intersections of ±45o lines from the crack tip and the numerical crack opening profile, was applied as CTOD, the calculation formula was then calibrated based on finite element analyses. The elastic term was decided with boundary layer model simulations. A geometric hinge rotation was examined, and a rotational factor, r p was newly calibrated. Furthermore, a new factor f , which was given as a function of the yield-to-tensile ratio of the material and the specimen thickness, was introduced to correct the plastic term. The appropriateness of the proposed CTOD calculation was verified numerically and [ABSTRACT FROM AUTHOR]