Application of a T-Stress Based Constraint Correction to A533B Steel Fracture Toughness Data

2008 ◽  
pp. 307-307-21 ◽  
Author(s):  
RL Tregoning ◽  
JA Joyce
Keyword(s):  
Fracture Toughness ◽  
T Stress ◽  
Constraint Correction

Investigation of Constraint Effects on Fracture Toughness for CC(T) Specimens

2004 ◽  
Author(s):  
Dieter Siegele ◽  
Igor Varfolomeyev ◽  
Kim Wallin ◽  
Gerhard Nagel
Keyword(s):  
Fracture Toughness ◽  
Crack Tip ◽  
Temperature Shift ◽  
Local Stress ◽  
Significant Loss ◽  
Reference Temperature ◽  
T Stress ◽  
Local Stress State ◽  
Constraint Effects ◽  
Crack Tip Constraint

Within the framework of the European research project VOCALIST, centre cracked tension, CC(T), specimens made of an RPV steel were tested and analysed to quantify the influence of local stress state on fracture toughness. The CC(T) specimens demonstrate a significant loss of crack tip constraint resulting in a considerable increase in fracture toughness as compared to standard fracture mechanics specimens. So, the master curve reference temperature, To, determined on the basis of CC(T) tests performed in this study is about 43°C lower than To obtained on standard C(T) specimens. Finite element analyses of the tests revealed that the above experimental finding is in a good agreement with the empirical correlations between the reference temperature shift and the crack tip constraint as characterised by the T-stress or Q parameter (Wallin, 2001; Wallin, 2004). The results of this work are consistent with a number of other tests performed within the VOCALIST project and contribute to the validation of engineering methods for the crack assessment in components taking account of constraint.

Constraint Based Assessments of Large-Scale Cracked Straight Pipes and Elbows

2015 ◽  
Author(s):  
Marius Gintalas ◽  
Robert A. Ainsworth
Keyword(s):  
Fracture Toughness ◽  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Large Scale ◽  
Initiation Point ◽  
T Stress ◽  
Advanced Analysis ◽  
Material Fracture ◽  
Fracture Toughness Specimen

The paper presents T-stress solutions developed to characterize constraint levels in large-scale cracked pipes and elbows. Stress intensity factor, KI, solutions for pipes and elbows are normalised by material fracture toughness to define the Kr parameter in fitness-for-service procedures, such as R6. Adding knowledge on levels of T-stress allows more advanced analysis through a normalised constraint parameter βT. The paper presents analyses for 6 pipes and 8 elbows. Values of the normalised constraint parameter βT are calculated for each pipe and elbow at the experimentally measured crack initiation point. Comparison of constraint levels in the pipes and elbows with those in various types of fracture toughness specimen are used to predict the initiation loads using the R6 method and to provide guidelines for transferability.

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.

Implementation of Ductile Damage Models to Determine Constraint Parameters for Ductile Materials: Phase 1 — Generic Constraint Conditions

2020 ◽  
Author(s):  
J. Beswick ◽  
P. James ◽  
J. Sharples
Keyword(s):  
Boundary Layer ◽  
Fracture Toughness ◽  
Yield Surface ◽  
Void Growth ◽  
Layer Model ◽  
Gtn Model ◽  
Ductile Materials ◽  
Damage Models ◽  
Boundary Layer Model ◽  
T Stress

Abstract It has been observed that steels which are operating in the ductile regime demonstrate greater resistance to tearing under conditions of reduced crack-tip constraint. Constraint is influenced by both geometry and load conditions. For example, fracture toughness specimens with shorter cracks relative to wall thickness, or those subjected to tension as opposed to bending, will demonstrate reduced constraint. Constraint may be quantified by an elastic T-Stress or the elastic-plastic Q parameter. R6, a set of structural integrity guidelines widely used in the nuclear industry, suggests that the effective fracture toughness of a material at reduced constraint may be calculated using a material-specific toughness locus. To define this locus, it is usually necessary to perform laboratory tests on the material at various levels of constraint, which are both expensive and time consuming. For cleavage (low-temperature) fracture, it is also possible to consult look-up tables, which require the calculation of the Weibull stress parameter. This paper details findings from an investigation into a method to determine the parameters defining failure loci for steels. The work involves the use of finite element analysis and two damage models which consider void growth in ductile materials. The first model is the Rice and Tracey model, which determines void growth based on stress triaxiality and plastic strain, and the second is the GTN local approach, which considers void initiation, growth and coalescence to define a yield surface for the material. The yield surface is governed by numerous parameters which enable the definition of the void volume fraction of the material at the various stages preceding fracture. Previous work has demonstrated independence of the parameters used to define the toughness loci to the critical void size when defined using the Rice and Tracey approach. The work presented in this paper demonstrates similar behaviour using the GTN model, with independence of the constraint benefit to the governing parameters. The toughness determined using the GTN approach is calculated from J-R type curves obtained by simulating crack growth in idealised constraint scenarios: specifically applying a T-Stress to boundary layer models, where a boundary layer model is an idealised high constraint scenario. It is shown in this paper that, whilst independence is demonstrated to the GTN parameters, there are discrepancies between the toughness loci derived using the GTN model and those using the Rice and Tracey approach. The reasons for this are discussed and are predicted to be due to load order effects, in that constraint reduces through loading, which may not be captured accurately using the boundary layer model. An introduction to the next phase of work, which does accurately include these effects, is also provided.

Atomistic investigation of the T-stress effect on fracture toughness of copper and aluminum single crystals

2018 ◽  
Vol 32 (8) ◽  
pp. 3765-3774 ◽  
Author(s):  
Gi Hun Lee ◽  
Young Jin Chung ◽  
Sang Min Na ◽  
Hyeon Gyu Beom
Keyword(s):  
Fracture Toughness ◽  
Single Crystals ◽  
Stress Effect ◽  
T Stress

scholarly journals Analysis of Mixed-Mode I/II/III Fracture Toughness Based on a Three-Point Bending Sandstone Specimen with an Inclined Crack

2021 ◽  
Vol 11 (4) ◽  
pp. 1652
Author(s):  
Xin Pan ◽  
Jiuzhou Huang ◽  
Zhiqiang Gan ◽  
Shiming Dong ◽  
Wen Hua
Keyword(s):  
Fracture Toughness ◽  
Mixed Mode ◽  
Mode I ◽  
Mixed Mode Fracture ◽  
Pure Mode ◽  
Inclined Crack ◽  
Tangential Strain ◽  
Mode Fracture ◽  
Fracture Parameters ◽  
T Stress

The crack-propagation form may appear as an arbitrary mixed-mode fracture in an engineering structure due to an irregular internal crack. It is of great significance to research the mixed-mode fracture of materials with cracks. The coupling effect of multiple variables (crack height ratio, horizontal deflection angle and vertical deflection angle) on fracture parameters such as the stress intensity factors and the T-stress are the key points in this paper. A three-point bending specimen with an inclined crack was proposed and used to conduct mixed-mode fracture research. The fracture parameters were obtained by finite element analysis, and the computed results showed that the pure mode I fracture and mixed-mode fractures (mode I/II, mode I/III and mode I/II/III) can be realized by changing the deflection angles of the crack. The pure mode I and the mixed-mode fracture toughness of sandstone were obtained by a series of mixed-mode fracture experiments. The experimental results were analyzed with the generalized maximum tangential strain energy density factor criterion considering T-stress. The results showed that the non-singular term T-stress in the fracture parameters cannot be ignored in any mixed-mode fracture research, and the generalized maximum tangential strain energy density factor criterion considering T-stress can better predict the mixed-mode fracture toughness than other criteria.

Effects of T-Stress on Fracture Behavior of Central-Cracked Stiffened Plate

2019 ◽  
Vol 795 ◽  
pp. 389-394
Author(s):  
Xing Ling Huang ◽  
Ying Hua Liu
Keyword(s):  
Fracture Toughness ◽  
Fracture Behavior ◽  
Three Dimensional ◽  
Crack Arrest ◽  
Assessment Procedure ◽  
Stiffened Plate ◽  
T Stress ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Two Parameter

Traditionally, the stress intensity factor (SIF) is solely focused on in the fracture analyses of stiffened plate, while the T-stress is usually ignored. However, the fracture toughness is influenced by T-stress and the effects need to be studied. By means of three-dimensional finite element method, the characteristics of mode I SIF and in-plane T-stress are investigated in the double symmetrical central stiffened plate (DSC-SP). Then the fracture toughness is corrected with in-plane T-stress based on the two-parameter model in the R6 assessment procedure. Lastly, the curves of corrected fracture toughness and crack arrest effect are obtained in the stiffened plate. The results show that the T-stress is dependent on the size and integrity of the stiffener, and has significant effects on the fracture toughness of stiffened plate. Compared with the traditional estimation of the crack arrest effect of the stiffener, the evaluation is more reasonable when the influences of in-plane T-stress are taken into account.

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