Application of the T-Scaling Method to Predict Fracture Toughness Under Compressive Residual Stress in the Transition Temperature Region

2018 ◽  
Author(s):  
Toshiyuki Meshii ◽  
Kenichi Ishihara
Keyword(s):  
Fracture Toughness ◽  
Residual Stress ◽  
Transition Temperature ◽  
Stress Distribution ◽  
Temperature Dependence ◽  
Temperature Region ◽  
Compressive Residual Stress ◽  
Crack Tip ◽  
Scaling Method ◽  
Crack Tip Stress

The fracture toughness Jc of a material in the ductile-to-brittle transition temperature region shows a test specimen thickness (TST) effect and temperature dependence, and apparently increases when a compressive residual stress is applied. Many models to explain these phenomena have been proposed that can also consider the large scatter of Jc. On the contrary, the authors have focused on the mean Jc and have demonstrated that the TST effect on Jc and temperature dependence of Jc are due to “the loss of the one-to-one correspondence between J and the crack-tip stress distribution” and that the “scaled” crack-tip stress distribution at fracture is independent of the TST effect on Jc or temperature. The T-scaling method was proposed and validated for this purpose. In this study, the fracture prediction of a specimen with compressive residual stress was performed using the T-scaling method, and its validity was confirmed for high-strength steel of 780-MPa class and 0.45 % carbon steel JIS S45C.

Prediction of the Temperature Dependence on Fracture Toughness by New Stress Distribution Scaling Method

2017 ◽  
Author(s):  
Kenichi Ishihara ◽  
Takeshi Hamada ◽  
Toshiyuki Meshii
Keyword(s):  
Fracture Toughness ◽  
Stress Distribution ◽  
Temperature Dependence ◽  
Temperature Region ◽  
Tensile Tests ◽  
Fracture Load ◽  
Small Scale ◽  
Scaling Method ◽  
Element Analysis ◽  
Scale Yielding

In this paper, a new method for scaling the crack tip stress distribution under small scale yielding condition was proposed and named as T-scaling method. This method enables to identify the different stress distributions for materials with different tensile properties but identical load in terms of stress intensity factor (K) or J-integral (J). Then, a method to predict the fracture load at an arbitrary temperature from the already known fracture load at a reference temperature was proposed by assuming that the temperature dependence of a material is represented as the stress-strain relationship temperature dependence. This method was combined with the T-scaling method and the knowledge “fracture stress for slip induced cleavage fracture is temperature independent.” Once the fracture load is predicted, fracture toughness Jc at the temperature under consideration can be evaluated by running elastic-plastic finite element analysis. Finally, the above-mentioned framework to predict the Jc temperature dependency of a material in the ductile-to-brittle temperature region was validated for 0.55 % carbon steel JIS S55C. The proposed framework seems to have a possibility to solve the problem the master curve is facing in the relatively higher temperature region, by requiring only tensile tests.

Shallow Flaws Under Biaxial Loading Conditions—Part I: The Effect of Specimen Size on Fracture Toughness Values Obtained From Large-Scale Cruciform Specimens1

2000 ◽  
Vol 123 (1) ◽  
pp. 10-24 ◽  
Author(s):  
Wallace J. McAfee ◽  
B. Richard Bass ◽  
Paul T. Williams
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Large Scale ◽  
Biaxial Loading ◽  
Crack Tip ◽  
Specimen Size ◽  
Biaxial Stress ◽  
Lower Transition ◽  
Crack Tip Constraint

A technology to determine shallow-flaw fracture toughness of reactor pressure vessel (RPV) steels is being developed. This technology is for application to the safety assessment of RPVs containing postulated shallow-surface flaws. It has been shown that relaxation of crack-tip constraint causes shallow-flaw fracture toughness of RPV material to have a higher mean value than that for deep flaws in the lower transition temperature region. Cruciform beam specimens developed at Oak Ridge National Laboratory (ORNL) introduce far-field, out-of-plane biaxial stress components in the test section that approximates the nonlinear stresses resulting from pressurized-thermal-shock (PTS) loading of an RPV. The biaxial stress component has been shown to increase stress triaxiality (constraint) at the crack tip, and thereby reduce the shallow-flaw fracture toughness enhancement. The cruciform specimen permits controlled application of biaxial loading ratios, resulting in controlled variation of crack-tip constraint. An extensive matrix of intermediate-scale cruciform specimens with a uniform depth surface flaw was previously tested and demonstrated a continued decrease in shallow-flaw fracture toughness with increasing biaxial loading. This paper describes the test results for a series of large-scale cruciform specimens with a uniform depth surface flaw. These specimens were all of the same size with the same depth flaw and were tested at the same temperature and biaxial load ratio (1:1). The configuration is the same as the previous set of intermediate-scale tests, but has been scaled upward in size by 150 percent. These tests demonstrated the effect of biaxial loading and specimen size on shallow-flaw fracture toughness in the lower transition temperature region for RPV materials. For specimens tested under full biaxial (1:1) loading at test temperatures in the range of 23°F (−5°C) to 34°F (1°C), toughness was reduced by approximately 15 percent for a 150-percent increase in specimen size. This decrease was slightly greater than the predicted reduction for this increase in specimen size. The size corrections for 1/2T C(T) specimens did not predict the experimentally determined mean toughness values for larger size shallow-flaw specimens tested under biaxial (1:1) loading in the lower transition temperature region.

Framework to Correlate Test Specimen Thickness Effect on Fracture Toughness With T33-Stress

2011 ◽  
Author(s):  
Toshiyuki Meshii ◽  
Tomohiro Tanaka
Keyword(s):  
Fracture Toughness ◽  
Transition Temperature ◽  
Temperature Region ◽  
Test Specimen ◽  
Crack Tip ◽  
Thickness Effect ◽  
Specimen Thickness ◽  
Out Of Plane ◽  
Elastic Crack ◽  
Crack Tip Constraint

This paper considered the test specimen thickness effect on the fracture toughness of a material Jc, in the transition temperature region, for CT and 3PB specimen. Framework to correlate test specimen thickness effect on fracture toughness with T33-stress, which is the out-of-plane elastic crack tip constraint parameter, was proposed. The results seemed to indicate a possibility of improving the existing methods to correlate the fracture toughness obtained by test specimen with the toughness of actual cracks found in the structure, in use of T33–stress.

scholarly journals Spreadsheet-based method for predicting temperature dependence of fracture toughness in ductile-to-brittle temperature region

2019 ◽  
Vol 11 (8) ◽  
pp. 168781401987089 ◽  
Author(s):  
Toshiyuki Meshii
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Yield Stress ◽  
High Temperatures ◽  
Test Data ◽  
Temperature Region ◽  
Master Curve ◽  
Fracture Toughness Test ◽  
Scaling Method ◽  
Japan Industrial Standard

A spreadsheet-based simplified and direct toughness scaling method to predict the temperature dependence of fracture toughness Jc in the ductile-to-brittle transition temperature region is proposed. This method uses fracture toughness test data and the Ramberg–Osgood exponent and yield stress at the reference temperature, and yield stress at the temperature in interest to predict Jc. The physical basis of the simplified and direct toughness scaling method is the strong correlation between Jc and yield stress. The simplified and direct toughness scaling method was validated for Cr–Mo steel Japan Industrial Standard SCM440 and 0.55% carbon steel Japan Industrial Standard S55C by comparing the simplified and direct toughness scaling prediction results with the median results of an experiment performed at four temperatures ranging from −55°C to 100°C and at three temperatures ranging from −85°C to 20°C, respectively. The simplified and direct toughness scaling method can predict Jc from both low to high temperatures, and vice versa. Thus, 12 and 6 predictions were made for each material. The prediction discrepancy for these 18 cases ranged from −50.4% to +25.8% and the average absolute discrepancy was 22.1%. These results were acceptable considering the large scatter generally observed with Jc. In particular, in case of predicting Jc at temperatures higher than the lowest temperature of −55°C for SCM440, the simplified and direct toughness scaling method predicted Jc more realistically than the American Society for Testing and Materials E1921 master curve approach. Although the simplified and direct toughness scaling method requires additional tensile test data compared with the master curve approach, the acceptable prediction accuracy at high temperatures seems beneficial because the mass and time required for tensile tests are admissible.

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