T-scaling method for stress distribution scaling under small-scale yielding and its application to the prediction of fracture toughness temperature dependence

2017 ◽  
Vol 90 ◽  
pp. 182-192 ◽  
Author(s):  
Kenichi Ishihara ◽  
Takeshi Hamada ◽  
Toshiyuki Meshii
Keyword(s):  
Fracture Toughness ◽  
Stress Distribution ◽  
Temperature Dependence ◽  
Small Scale ◽  
Small Scale Yielding ◽  
Scaling Method ◽  
Scale Yielding

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.

Prediction of Initiation Toughness Under Small Scale Yielding (SSY) and J0.2BL vs. Q Fracture Locus Using Local Approach Methodologies in 304SS

2012 ◽  
Author(s):  
A. Wasylyk ◽  
A. H. Sherry ◽  
J. K. Sharples
Keyword(s):  
Fracture Toughness ◽  
Small Scale ◽  
Initiation Toughness ◽  
Single Edge ◽  
Small Scale Yielding ◽  
Local Approach ◽  
Three Point Bending ◽  
Fracture Locus ◽  
Scale Yielding ◽  
Cracked Specimens

Structural integrity assessments of structures containing defects require valid fracture toughness properties as defined in national and international test standards. However, for some materials and component geometries, the development of valid toughness values — particularly for ductile fracture — is difficult since sufficiently large specimens cannot be machined. As a consequence, the validity of fracture toughness properties is limited by the development of plasticity ahead of the crack tip and the deviation of crack tip conditions at failure from small scale yielding. This paper described the use of local approach models, calibrated against invalid test data, to define initiation toughness in 304 stainless steel pipe material. Three fracture toughness geometries were tested, shallow cracked single edge cracked specimens tested under three point bending, deep cracked single edge cracked specimens tested under three point bending, and deep cracked single edge cracked specimen tested under tension. Initiation toughness and J-Resistance curves were defined for each specimen using the multi-specimen technique. All initiation toughness values measured were above the specimen validity limits. The fracture conditions at initiation were analysed using three local approach models: the Generalised Rice & Tracey, High Constraint Rice & Tracey and the Work of Fracture. The adequacy of local approaches to define the fracture conditions under large strains in 304 stainless steels was demonstrated. A modified boundary layer analysis combined with the local approach models was used to predict the “valid” initiation toughness under small scale yielding condition in this material by defining a J-Q fracture locus. The analytically derived fracture locus was compared to the J-Q values obtained experimentally and shown to be consistent.

Constraint-Correction of Cleavage Fracture Data From Miniature Specimens and Improved Estimates of Lower Bound Fracture Toughness

2009 ◽  
Author(s):  
Colin J. Madew ◽  
David W. Beardsmore ◽  
Richard O. Howells
Keyword(s):  
Fracture Toughness ◽  
Lower Bound ◽  
Cleavage Fracture ◽  
Crack Tip ◽  
Small Scale ◽  
Small Scale Yielding ◽  
Fracture Data ◽  
Scale Yielding ◽  
Miniature Specimens ◽  
Constraint Correction

Current assessments of pressurised components use fracture data collected on conventional size, 25 mm and 10 mm thick fracture specimens. It would be advantageous to be able to measure fracture toughness on what has commonly been termed miniature specimens (i.e. smaller than 10mm) as this would allow a more economical use of available plant material. However, tests on miniature specimens generally produce values of fracture toughness which over-estimate the fracture toughness of the material (as evaluated from the 25 mm or 10 mm specimens). In particular, the measured scatter in the data exhibits lower-bound values that are higher than the values obtained with conventional size specimens. A study has thus been undertaken in order to examine a methodology to derive fracture toughness from miniature specimens and allow a better determination of the lower-bound values. When cleavage fracture toughness tests are carried out using miniature specimens, the values of critical J obtained do not directly determine the cleavage fracture toughness of the material. This is because a loss of crack-tip constraint will generally occur before fracture. In such cases, it is necessary to apply an appropriate constraint correction to map the measured values to their equivalent small-scale yielding values. This paper uses a method for carrying out constraint corrections in order to assess data obtained from a recent UK miniature fracture toughness specimen testing programme. The method is based on the notion of matching areas enclosed by a same-stress contour of maximum principal stress around the crack tip in the specimen and small-scale yielding geometries. In applying the method, two-dimensional, plane strain finite element models of the specimen geometries have been developed together with a boundary layer model of the reference small-scale yielding condition to determine the appropriate areas.

Equivalent CTOD Ratio β for Engineering Assessment of CTOD Correction for Constraint Loss

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Shape Parameter ◽  
Tensile Load ◽  
Crack Size ◽  
Small Scale ◽  
Structural Components ◽  
Small Scale Yielding ◽  
Stress Criterion ◽  
Scale Yielding ◽  
Weibull Stress

The critical CTOD δWP for structural components associated with plastic constraint loss in case of the brittle fracture over small-scale yielding condition can be corrected from CTOD fracture toughness δ by means of the “equivalent CTOD ratio β” defined as δ/δWP, which is based on the Weibull stress criterion. In this study, taking the case of specific wide plate components subjected to uni-axial tensile load, the effect on β is analyzed taking account of Weibull shape parameter m, loading level, constraint effect that can be influenced by material work-hardening and crack type/size in structural components, etc., and volumetric effect. It is found that the β-value is almost constant beyond the applied CTOD level that is lower than CTOD of small-scale yielding limit (SSY-limit) for 25 mm thick toughness specimen. From an engineering point of view, the β-value at the CTOD level of 0.01 mm is used in the whole loading range beyond SSY-limit CTOD, which provides to some extent conservative measure of fracture toughness of structural components. The defined β is found to decrease with increasing Weibull shape parameter m and yield-to-tensile ratio YR of steel for all type of wide plates concerned. The crack length effect on β is quasi-theoretically formulated, which can convert the β for the wide plate with reference crack size to β for target crack size. These β and quasi-theoretical equations for the correction of crack size effect can be utilized for estimating the CTOD for wide plate in consideration of constraint loss effect without numerical calculation of the Weibull stress.

Equivalent CTOD Ratio β for Engineering Assessment of CTOD Correction for Constraint Loss

2008 ◽  
Author(s):  
Mitsuru Ohata ◽  
Fumiyoshi Minami
Keyword(s):  
Fracture Toughness ◽  
Shape Parameter ◽  
Tensile Load ◽  
Crack Size ◽  
Small Scale ◽  
Structural Components ◽  
Small Scale Yielding ◽  
Stress Criterion ◽  
Scale Yielding ◽  
Weibull Stress

The critical CTOD δWP for structural components associated with plastic constraint loss in case of the brittle fracture over small-scale yielding condition can be corrected from CTOD fracture toughness δ by means of the “equivalent CTOD ratio β” defined as δ/δWP, which is based on the Weibull stress criterion. In this study, taking the case of specific wide plate components subjected to uni-axial tensile load, the effect on β is analyzed taking account of Weibull shape parameter m, loading level, constraint effect that can be influenced by material work-hardening and crack type/size in structural components, etc., and volumetric effect. It is found that the β-value is almost constant beyond the applied CTOD level that is lower than CTOD of small-scale yielding limit (SSY-limit) for 25mm thick toughness specimen. From an engineering point of view, the β-value at the CTOD level of 0.01mm is used in the whole loading range beyond SSY-limit CTOD, which provides to some extent conservative measure of fracture toughness of structural components. The defined β is found to decrease with increasing Weibull shape parameter m and yield-to-tensile ratio YR of steel for all type of wide plates concerned. The crack length effect on β is quasi-theoretically formulated, which can convert the β for the wide plate with reference crack size to β for target crack size. These β and quasi-theoretical equations for correction of crack size effect can be utilized for estimating the CTOD for wide plate in consideration of constraint loss effect without numerical calculation of the Weibull stress.

Fracture Toughness in Ultra Fine-Grained Magnesium Alloy

2006 ◽  
Vol 503-504 ◽  
pp. 155-160 ◽  
Author(s):  
Hidetoshi Somekawa ◽  
Toshiji Mukai
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Magnesium Alloy ◽  
Small Scale ◽  
Plane Strain Fracture Toughness ◽  
Small Scale Yielding ◽  
Fine Grained ◽  
Yielding Condition ◽  
Strain Fracture ◽  
Scale Yielding

The fracture toughness was investigated using in an extruded AZ31 magnesium alloy with an initial grain size of 1.0 μm. Since the small scale yielding condition was not satisfied with the present thin thickness, the value of plane-strain fracture toughness, KIC = 27.9 MPam1/2, was measured from Stretched Zone analysis. The values of KIC in AZ31 magnesium alloys were dependent on the grain size. The grain refinement was found to be one of the improvement methods for fracture toughness in magnesium alloy.

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.

A Plastic Zone Equation Based on Mean Yield Criterion

2010 ◽  
Vol 97-101 ◽  
pp. 534-537 ◽  
Author(s):  
Wei Deng ◽  
De Wen Zhao ◽  
Xiao Mei Qin ◽  
Xiu Hua Gao ◽  
Chun Lin Qiu ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Analytical Solution ◽  
Plastic Zone ◽  
Yield Criterion ◽  
Small Scale ◽  
Mode I ◽  
Mode I Crack ◽  
Small Scale Yielding ◽  
Scale Yielding ◽  
My Criterion

Based on mean yield criterion, an analytical solution for the mode I crack tip plastic zone (CTPZ) under small scale yielding was derived. The results reveal that the size of CTPZ determined by MY criterion is between those by Mises’ yield criterion the smallest, and by Tresca’s criterion the largest; while the zone is almost coincide with that by Mises’ one. The size of CTPZ is related to the ratio of fracture toughness to yield strength; with increasing of the ratio, the size of the zone increases, meaning the better of fracture toughness.

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