PSI - Issue 5

Yoichi Kayamori et al. / Procedia Structural Integrity 5 (2017) 286–293 Yoichi Kayamori et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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BS7448 (1991) and ISO 12135 (2002) do not employ any Eqs. from (2) to (5), but put a constant r p of 0.46 for C(T) specimens. Kolednik (1989) conducted quite complex r p calculations for different specimen sizes, loading stages and material strain hardening properties, and resultant r p was dependent on their conditions. For example, in an annealed structural steel, r p was 0.57 for a C(T) specimen, where  was almost equivalent to the critical CTOD.

3. Finite element analysis

3.1. Analytical methods

A quarter of a stepped notch 1T C(T) specimen was modeled considering the symmetry conditions, as shown in Fig.2. The ratio of a 0 to W was set at 0.5 in the specimen model. Eight-node isoparametric hexahedral solid elements were used for this modeling. The special mesh design developed by one of the authors (2015) was applied to the crack tip, in which element shape and size were considered to maintain a reasonable aspect ratio for  ≤ 0.2 mm. Two different structural steels were modeled for this analysis. Low and high Y/T ratios, 0.6 and 0.9, were presumed to have the identical ultimate tensile strength,  uts , of 520 MPa. Their responses of the equivalent stress,  , versus the equivalent plastic strain, p  , were represented by the following Swift relation, where  is the fitting parameter and N is the strain hardening exponent:

N



   

   

p

ys   1





(6)



The analysis was performed by applying the displacement controlled loading on the rigid hole surface using a finite element code, Abaqus 14.1. Strain distribution was investigated to estimate the rotational center in each model.  was calculated using the deformed crack profile on the mid-thickness plane by means of the 45º intercept method, and was shown as  FEM in this study.

Fig. 2 Modeling and meshing of a stepped notch 1T C(T) specimen for FEA.