A Model to Predict the Effect of Pre-Strain on the Fracture Toughness of Line Pipe Steel

2002 ◽  
Author(s):  
Andrew Cosham ◽  
Naoto Hagiwara ◽  
Naoki Fukuda ◽  
Tomoki Masuda
Keyword(s):  
Fracture Toughness ◽  
Plastic Deformation ◽  
Theoretical Model ◽  
Plastic Strain ◽  
Ductile Fracture ◽  
Experimental Studies ◽  
Uniaxial Tensile ◽  
Stress Strain ◽  
Line Pipe ◽  
Strained Material

New and existing pipelines can be subjected to high plastic strains. Denting a pipeline causes permanent plastic deformation. Onshore pipelines subject to subsidence, frost heave or earthquake loading can experience significant plastic strain during service. Offshore pipelines that are reeled prior to laying, or are laid in deep water, or are operating at high temperatures and high pressures, can experience significant plastic strain both prior to, and during, service. Experimental studies have indicated that pre-strain (permanent plastic deformation) has a detrimental effect on the fracture toughness of steel; it reduces the resistance to crack initiation, reduces the resistance to crack growth, and increases the transition temperature. Consequently, there is a need for a thorough understanding of the effect of pre-strain on the fracture toughness of line pipe. Accordingly, a theoretical model for predicting the effect of tensile pre-strain on the ductile fracture toughness has been developed using the local approach. The effect of pre-strain is expressed in terms of an equation for the ratio of the fracture toughness of the pre-strained material to that of the virgin (not pre-strained) material. The model indicates that the effect of tensile pre-strain on the material’s fracture toughness can be characterised in terms of the effect of pre-strain on the stress-strain characteristics of the material, the critical fracture strain for a stress state corresponding to that during pre-strain, and several parameters that relate to the conditions for ductile fracture (or cleavage fracture). The implications of the model are that it may be possible to estimate the reduction in toughness caused by pre-strain simply from a full stress-strain curve of the virgin material. The model has been validated against the results of crack tip opening displacement (CTOD) tests conducted by Tokyo Gas on two line pipe steels subject to uniaxial tensile pre-strain. It is shown that the predictions and trends of the theoretical model are in broad agreement with the test results.

A Model of Pre-Strain Effects on Fracture Toughness

2001 ◽  
Vol 123 (4) ◽  
pp. 182-190 ◽  
Author(s):  
Andrew Cosham
Keyword(s):  
Fracture Toughness ◽  
Stress State ◽  
Ductile Fracture ◽  
Cleavage Fracture ◽  
Critical Strain ◽  
Experimental Studies ◽  
Local Approach ◽  
Stress Strain ◽  
Critical Fracture ◽  
Strained Material

A simple theoretical model for predicting the effect of tensile pre-strain on fracture toughness has been developed using the local approach. The HRR singularity is assumed to describe the stress-strain field around the crack tip. A stress-modified critical strain-controlled model is assumed to describe ductile fracture (and a critical stress-controlled model for cleavage fracture). The Rice and Tracey void growth model is used to characterize the variation of the critical strain with the stress state. The model further assumes that the fracture process does not change with increasing pre-strain. The effect of pre-strain is expressed in terms of an equation for the ratio of the fracture toughness of the pre-strained material to that of the virgin material. The model indicates that the effect of tensile pre-strain on fracture resistance can be characterized in terms of the effect of pre-strain on the stress-strain characteristics of the material, the critical fracture strain for a stress state corresponding to that during pre-strain, and several parameters that relate to the conditions for ductile fracture (or cleavage fracture). Previous experimental studies of the effect of pre-strain on toughness are summarized and compared with the predictions of the model.

About Relation Between Irradiation Hardening of Ferritic Steels and Ductile Fracture Toughness Decrease

2009 ◽  
Author(s):  
Jiri Novak
Keyword(s):  
Fracture Toughness ◽  
Temperature Dependence ◽  
Ductile Fracture ◽  
Stress Level ◽  
Deformation Theory ◽  
Strain Curve ◽  
Stress Strain Curve ◽  
Stress Strain ◽  
Irradiation Hardening ◽  
Ductile Fracture Toughness

We showed recently that temperature dependence of the ductile fracture toughness can be predicted on the base of two assumptions: 1) assumption of constant characteristic length, 2) assumption of proportionality between J-R curve slope and deformation work in unit volume, evaluated from zero to critical strain for initiation of deformation bands determined in plane strain geometry for material modeled by deformation theory of plasticity. Temperature dependence of ductile fracture toughness results simply from temperature dependence of the stress-strain curve. Irradiation hardening changes stress-strain behavior in a qualitatively different way: It is observed that irradiation hardening to certain yield stress level changes the stress-strain curve of the material in the same way as prestraining of the unirradiated material to the same flow stress level does. Equivalence of irradiation and prestraining concerns all key properties of deformation theory; namely the secant modulus should be taken from the stress-strain curve of unirradiated material. With exception of this specific feature, the task of finding relative fracture toughness decrease by irradiation is the same as prediction of relative decrease of fracture toughness by temperature change. In the frame of the corresponding theory, relative decrease of ductile fracture toughness expressed by J-R curve slope can be obtained from the stress-strain curve of unirradiated material and irradiation hardening level. Quantitative results are presented for the weld metals 72W and 73W, studied in the Fifth Irradiation Series in the Heavy-Section Steel Irradiation Program, and compared with experimental data.

scholarly journals Investigation on the ductile fracture of a high-strength dual-phase steel with anisotropic damage mechanics model

2021 ◽  
Author(s):  
Zinan Li ◽  
Wenqi Liu ◽  
Fuhui Shen ◽  
Sebastian Münstermann ◽  
Junhe Lian
Keyword(s):  
Plastic Deformation ◽  
Ductile Fracture ◽  
Fracture Behavior ◽  
Dual Phase Steel ◽  
High Strength ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Dual Phase ◽  
Plasticity Model ◽  
Anisotropic Plastic

In this study, a hybrid experimental and numerical investigation is implemented to characterize the plasticity and ductile fracture behavior of a high-strength dual-phase steel. Uniaxial tensile tests are conducted along the three typical directions of rolled sheet metals for the anisotropic plastic behavior, while the hydraulic bulge test is applied for the flow behavior under equiaxial biaxial tension. Further tensile tests are conducted on various featured dog-bone specimens to study the fracture behavior of the material from the uniaxial to plane-strain tension. On the numerical side, the evolving non-associated Hill48 (enHill48) plasticity model considering anisotropic hardening and plastic strain ratio evolution is employed to describe the anisotropic plastic deformation. The extended enHill48 model with damage and fracture formulation is further calibrated and validated in the study to describe the ductile fracture behavior of the steel under various stress states. Through a comparison of the results based on the evolving anisotropic model with the isotropic Mises model, it is concluded that even for materials that show only minor initial plastic anisotropy, it could develop a non-negligible influence on the large plastic deformation and the prediction of both deformation and fracture shows profound improvement with the evolving anisotropic plasticity model.

Experimental Evaluation of the Size Effect on the Ductile and Brittle Fracture Toughness of a Steel Pressure Vessel

2009 ◽  
Vol 614 ◽  
pp. 41-46
Author(s):  
Zhao Xi Wang ◽  
Hui Ji Shi ◽  
Jian Lu
Keyword(s):  
Fracture Toughness ◽  
Plastic Deformation ◽  
Brittle Fracture ◽  
Size Effect ◽  
Ductile Fracture ◽  
Deformation Zone ◽  
High Stress ◽  
Small Scale ◽  
Plastic Deformation Zone ◽  
Zone Size

Experiments of fracture toughness with non-standard SENB specimens of five different thicknesses were performed to investigate the size effect on the ductile and brittle fracture for different temperatures. From the experimental results it is found that size effects both brittle and ductile fracture with the same trend but for different mechanical reasons. The ductile fracture toughness increases firstly with increased plastic deformation zone size and plastic fracture strain under general yielding conditions, and then drops down due to the plastic deformation zone size not changing much which is less than the residual ligament width and the increase of the proportion of the high stress triaxiality zone to the whole specimen. The fracture toughness of the lower shelf increases with increasing thickness of the plastic deformation zone size under small scale yielding conditions, and then drops down due to the increase of the high out-of-plane constraint.

An Experimental and Numerical Study of the Effect of Pre-Strain on the Fracture Toughness of Line Pipe Steel

2004 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins ◽  
Andrew Palmer
Keyword(s):  
Fracture Toughness ◽  
Pipe Steel ◽  
Numerical Study ◽  
Experimental Studies ◽  
Ground Movement ◽  
Tensile Fracture ◽  
Material Damage ◽  
Virgin Material ◽  
Line Pipe ◽  
Line Pipe Steel

Oil and gas pipelines may be subject to high plastic strains, either intentionally as a result of the method of installation, or the requirements of the design and operation, or accidentally (due to mechanical damage), before they enter service (transportation, construction/installation, etc.) and during operation. Pre-strain is introduced by denting, cold bending, land slides, subsidence, frost heave, ice gouging, earthquake induced ground movement, reeling, installation in deep water, and wrinkling or buckling. Material subjected to pre-strain will have different material properties to that of the virgin material. Previous experimental studies have indicated that pre-strain has a detrimental effect on the fracture toughness of steel: it reduces the resistance to crack initiation, reduces the resistance to crack growth, and increases the transition temperature. To investigate the effect of pre-strain on the fracture toughness of line pipe steel a programme of tests and numerical analyses has been undertaken. The results of tensile, notched tensile, fracture toughness (J-integral and CTOD) and Charpy V-notch impact tests of virgin (not pre-strained) material, prestrained material and artificially strain aged material are reported. It is shown that the effect of pre-strain can be simulated numerically using a finite element model incorporating the influence of material damage through a Gurson-Tvergaard constitutive model. The properties of the virgin material that influence the effect of pre-strain on toughness are discussed. The role of material damage (void nucleation and growth, etc.) during the introduction of pre-strain is shown to be less significant than the changes to the tensile properties and ductility caused by pre-strain. The effect of tensile pre-strain on fracture toughness can be characterised in terms of the effect of pre-strain on the stress-strain characteristics of the material, the critical fracture strain, and several parameters that relate to the conditions for ductile fracture (or cleavage fracture). A simple, engineering approximation to the effect of pre-strain on fracture toughness for application to pipeline design and fitness-for-purpose assessment is proposed in terms of the true strain at the tensile strength of the virgin material.

Derivation of Stress, Strain, Temperature, Strain-Rate Relation for Plastic Deformation

1947 ◽  
Vol 14 (3) ◽  
pp. A229-A230
Author(s):  
J. D. Lubahn
Keyword(s):  
Plastic Deformation ◽  
Plastic Strain ◽  
Strain Rate ◽  
Plastic Flow ◽  
Stress Strain ◽  
Rate Relation ◽  
Temperature Strain

Abstract This paper carries out the derivation and correction of an equation previously presented by J. H. Hollomon and the author, relating to stress for plastic flow (σ), plastic strain (ϵ), strain rate (ϵ.), and temperature (T).

The Behaviour of a Nominally Isotropic 0.17 per cent Carbon Cast Steel under Complex Stress Systems at Elevated Temperatures

1949 ◽  
Vol 161 (1) ◽  
pp. 182-186
Author(s):  
A. E. Johnson
Keyword(s):  
Experimental Study ◽  
Plastic Deformation ◽  
Carbon Steel ◽  
Plastic Strain ◽  
Elevated Temperatures ◽  
Cast Steel ◽  
Complex Stress ◽  
Stress Strain ◽  
General Stress ◽  
Short Time

The work described in this paper is part of an approved programme, undertaken to investigate the behaviour of an isotropic 0·17 per cent carbon steel under general stress systems at elevated temperatures. It relates to an experimental study, and analysis of the time independent plastic strain properties in short-time tensile and torsion tests at temperatures between 20 and 550 deg. C. (68 and 1,022 deg. F.). The object of the investigation is to obtain relations between stress, strain, time, and temperature, to afford a basis of design in cases where steels are subjected to plastic deformation under general stress systems at elevated temperatures. Pure tensile and torsion tests have been made at temperatures of 20, 150, 350, 450, and 550 deg. C. (68, 302, 662, 842, and 1,022 deg. F.), and at various rates of stressing. The results of these tests have been analysed, and information derived concerning the nature of the criterion of elastic failure for this material, and the nature of the stress-plastic strain relations after plastic strain has been established. The effect of rate of stressing on these latter relations has been examined.

Anisotropic Behavior in Plasticity and Ductile Fracture of an Aluminum Alloy

2015 ◽  
Vol 651-653 ◽  
pp. 163-168 ◽  
Author(s):  
Yan Shan Lou ◽  
Jeong Whan Yoon
Keyword(s):  
Plastic Deformation ◽  
Aluminum Alloy ◽  
Ductile Fracture ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Anisotropic Plasticity ◽  
Dog Bone ◽  
Associate Flow Rule ◽  
Anisotropic Plastic

Anisotropic mechanical behavior is investigated for an aluminum alloy of 6K21-IH T4 both in plastic deformation and ductile fracture. Anisotropic plastic deformation is characterized by uniaxial tensile tests of dog-bone specimens, while anisotropy in ductile fracture is illustrated with specimens with a central hole, notched specimens and shear specimens. All these specimens are cut off at every 15º from the rolling direction. The r-values and uniaxial tensile yield stresses are measured from the tensile tests of dog-bone specimens. Then the anisotropic plasticity is modeled by a newly proposed J2-J3 criterion under non-associate flow rule (non-AFR). The testing processes of specimens for ductile fracture analysis are simulated to extract the maximum plastic strain at fracture strokes as well as the evolution of the stress triaxiality and the Lode parameter in different testing directions. The measured fracture behavior is described by a shear-controlled ductile fracture criterion proposed by Lou et al. (2014. Modeling of shear ductile fracture considering a changeable cut-off value for stress triaxiality. Int. J. Plasticity 54, 56-80) for different loading directions. It is demonstrated that the anisotropic plastic deformation is described by the J2-J3 criterion with high accuracy in various loading conditions including shear, uniaxial tension and plane strain tension. Moreover, the anisotropy in ductile fracture is not negligible and cannot be modeled by isotropic ductile fracture criteria. Thus, an anisotropic model must be proposed to accurately illustrate the directionality in ductile fracture.

scholarly journals Visualization of the damage evolution for Ti–3Al–2Mo–2Zr alloy during a uniaxial tensile process using a microvoids proliferation damage model

2021 ◽  
Vol 40 (1) ◽  
pp. 310-324
Author(s):  
Ying Tong ◽  
Jiang Zhao ◽  
Guo-zheng Quan
Keyword(s):  
Plastic Deformation ◽  
Damage Evolution ◽  
Volume Fraction ◽  
Tensile Deformation ◽  
Damage Model ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Strain Rates ◽  
Stress Strain ◽  
Gtn Damage Model

Abstract Understanding the damage evolution of alloys during a plastic deformation process is significant to the structural design of components and accident prevention. In order to visualize the damage evolution in the plastic deformation of Ti–3Al–2Mo–2Zr alloy, a series of uniaxial tensile experiments for this alloy were carried out under the strain rates of 0.1–10 s−1 at room temperature, and the stress–strain curves were achieved. On the other hand, the finite element (FE) models of these uniaxial tensile processes were established. A microvoids proliferation model, Gurson–Tvergaard–Needleman (GTN) damage model, was implanted into the uniaxial tensile models, and the simulated stress–strain curves corresponding to different GTN parameter combinations were obtained. Based on the simulated and experimental stress–strain curves, the GTN parameters of this alloy were solved by response surface methodology (RSM). The solved GTN parameters suggest that higher strain rate can enhance the proliferation and coalescence of microvoids. Furthermore, the uniaxial tensile tests over different strain rates were simulated using the solved GTN parameters. Then, the damage processes were visualized and evaluated. The result shows that the degradation speed of this alloy is slow at the initial stage of the tensile deformation and then accelerates once the voids volume fraction reaches a critical value.

Model for the variation of the residual stress state during plastic deformation under uniaxial tension

1998 ◽  
Vol 33 (5) ◽  
pp. 367-372 ◽  
Author(s):  
T Gurova ◽  
J R Teodósio ◽  
J M A Rebello ◽  
V Monin
Keyword(s):  
Residual Stress ◽  
Plastic Deformation ◽  
Surface Layer ◽  
Theoretical Model ◽  
Bulk Material ◽  
Uniaxial Tensile ◽  
Uniaxial Tensile Test ◽  
Surface Residual Stress ◽  
Residual Stress State ◽  
The Difference

A theoretical model has been developed to explain the variation of surface residual stress introduced by shot-peening with external plastic deformation, during a uniaxial tensile test. The model is based on the difference of yield stress values of the shot-peened surface layer and the remaining bulk material. It has been shown that the model fits well with experimental results obtained for the base metal and heat-affected zone of a 5.0Cr-0.5Mo steel.

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