Applicability of the Modified Ritchie-Knott-Rice Failure Criterion to Examine the Feasibility of Miniaturized Charpy Type SE(B) Specimens

Toshiyuki Meshii,Teruhiro Yamaguchi,Yuma Higashino

doi:10.1155/2016/3728035

Toshiyuki Meshii, Teruhiro Yamaguchi + Show 1 more

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https://doi.org/10.1155/2016/3728035

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Abstract

This paper examined whether the modified Ritchie-Knott-Rice (RKR) failure criterion can be applied to examine the feasibility of miniaturized Charpy type SE(B) specimens of thickness-to-width ratio B/W=1. The modified RKR failure criterion considered in this paper is the (4δt,σ22c) criterion which predicts the onset of cleavage fracture when the midplane crack-opening stress measured at a distance equal to four times the crack-tip opening displacement, denoted as σ22d, exceeds a critical stress σ22c. Specimens with B values of 25, 10, 3, and 2 mm (denoted as 25t, 10t, 3t, and 2t specimens, resp.) manufactured with 0.55% carbon steel were tested at 20°C. The results showed that the modified RKR criterion could appropriately predict the occurrence of cleavage fracture accompanied by negligibly small stable crack extension (denoted as KJc fracture) naturally for the 25t and 10t specimens. The modified RKR criterion could also predict that KJc fracture does not occur for the 2t specimen. The σ22c obtained from specimens for the 25t and 10t specimens exhibited only a small difference, indicating that the Jc obtained from the 10t specimens can be used to predict the Jc that will be obtained with the 25t specimens.

Highlights

Test specimen size effects on the cleavage fracture toughness Jc of a material in the ductile-to-brittle transition temperature (DBTT) region are important when assessing aging steel structures and reactor pressure vessels
This paper is an extension of our previous works to examine whether the (4δt, σ22c) failure criterion can be applied to examine the feasibility of miniaturized Charpy type SE(B) specimens, that is, (1) whether the criterion could predict the occurrence of cleavage fracture accompanied by negligibly small stable crack extension and (2) whether σ22c is identical to that observed in full sized specimens in the case where KJc fracture occurred
The (4δt, σ22c) criterion could predict that KJc fracture does not occur for the 3t and 2t specimens if the necessary condition, that is, “the stress level of σ22d is maintained as σ22c for increasing load,” is explicitly considered

Summary

Introduction

Test specimen size effects on the cleavage fracture toughness Jc of a material in the ductile-to-brittle transition temperature (DBTT) region are important when assessing aging steel structures and reactor pressure vessels. The former is a definite parameter determined by the specimen geometry and yielding properties, and the latter is statistical behavior determined by the distribution of the weakest constituent” [26]; it was thought that the minimum toughness of a material, observed for a specific specimen and temperature, can be transferred by running an elastic-plastic finite element analysis (EP-FEA) with a given stress-strain relationship and a failure criterion For this failure criterion, one of the modified Ritchie-Knott-Rice failure criterion, that is, the (4δt, σ22c) criterion [3], which predicts the onset of cleavage fracture when the crack-opening stress σ22, measured at a distance from the crack-tip equal to four times the cracktip opening displacement (CTOD) δt (hereinafter denoted as σ22d), exceeds a critical value σ22c (Figure 1), was considered. 10t specimens exhibited only a small difference, indicating that the Jc obtained from the 10t specimens can be used to predict the Jc that will be obtained with the 25t specimens

Outline of This Work and Material Selection

VgASTM

Discussion

Findings

Conclusions

E: Young’s modulus