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.

scholarly journals Influence of Vacuum Heat Treatments on Microstructure and Mechanical Properties of M35 High Speed Steel

Metals ◽  
2020 ◽  
Vol 10 (5) ◽  
pp. 643
Author(s):  
Chiara Soffritti ◽  
Annalisa Fortini ◽  
Ramona Sola ◽  
Elettra Fabbri ◽  
Mattia Merlin ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Grain Size ◽  
Vickers Hardness ◽  
High Speed ◽  
High Speed Steel ◽  
Plane Strain Fracture Toughness ◽  
Secondary Carbides ◽  
Heat Treated ◽  
Strain Fracture

Towards the end of the last century, vacuum heat treatment of high speed steels was increasingly used in the fabrication of precision cutting tools. This study investigates the influence of vacuum heat treatments at different pressures of quenching gas on the microstructure and mechanical properties of taps made of M35 high speed steel. Taps were characterized by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction, apparent grain size and Vickers hardness measurements, and scratch tests. Failure analysis after tapping tests was also performed to determine the main fracture mechanisms. For all taps, the results showed that microstructures and the values of characteristics of secondary carbides, retained austenite, apparent grain size and Vickers hardness were comparable to previously reported ones for vacuum heat treated high speed steels. For taps vacuum heat treated at six bar, the highest plane strain fracture toughness was due to a higher content of finer small secondary carbides. In contrast, the lowest plane strain fracture toughness of taps vacuum heat treated at eight bar may be due to an excessive amount of finer small secondary carbides, which may provide a preferential path for crack propagation. Finally, the predominant fracture mechanism of taps was quasi-cleavage.

OS1427 Evaluation method of crack growth in reactor piping subjected to seismic loading beyond small scale yielding condition

2013 ◽  
Vol 2013 (0) ◽  
pp. _OS1427-1_-_OS1427-3_
Author(s):  
Yoshihito YAMAGUCHI ◽  
Makoto UDAGAWA ◽  
Yinsheng LI ◽  
Jinya KATSUYAMA ◽  
Kunio ONIZAWA
Keyword(s):  
Crack Growth ◽  
Evaluation Method ◽  
Seismic Loading ◽  
Small Scale ◽  
Small Scale Yielding ◽  
Yielding Condition ◽  
Scale Yielding

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.

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