Application of Ductile Cracking Criterion to the Assessment of Girth Weld Integrity for High Strength Linepipe

2005 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
Satoshi Igi ◽  
Teruki Sadasue
Keyword(s):  
Crack Initiation ◽  
Plastic Strain ◽  
Large Deformation ◽  
Material Properties ◽  
Equivalent Plastic Strain ◽  
High Strength ◽  
Small Scale ◽  
Pipeline System ◽  
Ductile Crack ◽  
Notch Tip

Fracture behavior of high strength linepipes with weld defects is of great interest for the integrity of pipeline system. Especially, in the seismic or permafrost area, where large ground displacement can be expected, linepipe materials need to have sufficient resistance against brittle and ductile fracture under large deformation. Wide plate tensile test with surface flaw in the girth weld metal of X100 linepipe demonstrated that tensile limit is dominated by ductile crack initiation and its propagation. Conditions for ductile crack initiation for the base materials and girth weld joints of Grade X80 and X100 linepipes were investigated in this study. It was shown that ductile cracking occurs in the notch tip region of the wide plate specimen when notch tip equivalent plastic strain reaches the same critical value as determined by the small-scale tests. Therefore, “the equivalent plastic strain” in the critical regions can be used as a transferable parameter to predict ductile crack initiation behavior. Assessment methodology for tensile limit of high strength linepipe girth weld with respect to preventing ductile cracking was proposed. The effect of strength matching of girth weld and base metal Y/T ratio on limit remote strain as well as allowable defect size was investigated analytically. Increasing strength matching and lowering Y/T ratio of base material can lead to higher limit strain to ductile cracking of girth weld. These effects of material properties were validated by weld wide plate tensile tests. Therefore, careful selection of material properties should be important to improve resistance against ductile cracking of linepipe girth welds under large deformation field.

Application of Damage Mechanics Modeling to Strain Based Design With Respect to Ductile Crack Initiation

2010 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Hitoshi Sueyoshi ◽  
Satoshi Igi
Keyword(s):  
Crack Initiation ◽  
Plastic Strain ◽  
Critical Condition ◽  
Equivalent Plastic Strain ◽  
Material Behavior ◽  
Specimen Geometry ◽  
Small Scale ◽  
Ductile Crack ◽  
Material Parameters ◽  
Linepipe Steels

Limit state condition in the tensile failure for the strain based-design (SBD) currently considering is the point of maximum load which is evaluated by curved wide plate (CWP) testing or full scale pipe tensile testing. Maximum loading point is understood as the onset of instability of the structure. However, the material behavior controlling structural instability is not well understood since it includes many aspects of material response such as local strain concentration, ductile crack initiation and stable crack growth. In order to clearly specify the material property suitable for SBD, it is important to understand the fundamental behavior of the linepipe steels that leads to ductile crack initiation and following ductile tearing. In this paper, critical condition for ductile crack initiation was investigated by both small scale and large scale testing, notched round bar and wide plate testing, by using X80 and X100 linepipe steels and welds. Two different analytical procedures, equivalent plastic strain criterion and damage mechanical analysis, were applied to evaluate the local material conditions for ductile crack initiation. As was already verified by many other researches, the critical equivalent plastic strain can be used as the local criterion for ductile crack initiation which is not affected by specimen geometry. However, equivalent plastic strain is still macroscopic parameter that is not reflected by microscopic feature of the steel. Therefore, the Gurson-Tvergaard damage mechanical model was applied to further understand microscopic material behavior to ductile crack initiation. Material parameters for G-T model were carefully evaluated depending on the microscopic characteristics of each steel. By selecting appropriate material parameters, the critical condition for ductile crack initiation was estimated by the critical void volume fraction, which is independent of specimen geometry. Effect of microstructural characteristics on crack initiation was also investigated in this study.

Two-Parameter Criteria for Ductile Crack Initiation and Propagation in High-Grade Line Pipes

2007 ◽  
Vol 348-349 ◽  
pp. 493-496
Author(s):  
Yoichi Kayamori ◽  
P.S.J. Crofton ◽  
Roderick A. Smith
Keyword(s):  
Crack Initiation ◽  
Plastic Strain ◽  
Driving Force ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
High Grade ◽  
Ductile Crack ◽  
Force Curve ◽  
Crack Driving Force ◽  
The Relationship

Full-scale burst test data of high-grade line pipes for high-pressure gas pipelines were referred to, and 3-D elastic-plastic finite element analysis was carried out using the test data for the calculation of fracture parameters. Ductile crack initiation was evaluated by the intersection of a toughness locus and a crack driving force curve, where the toughness locus was indicated by the relationship between the critical equivalent plastic strain and the stress triaxiality, and the crack driving force curve was shown by a history of the equivalent plastic strain and the stress triaxiality at characteristic distance. In addition, ductile crack rapid propagation was assessed by the relationship between the critical CTOA and the global constraint factor, where the critical CTOA remained almost constant because of high constraint.

Ductile Cracking Evaluation of X80/X100 High Strength Linepipes

2004 ◽  
Author(s):  
Teruki Sadasue ◽  
Satoshi Igi ◽  
Takahiro Kubo ◽  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
...  
Keyword(s):  
Plastic Strain ◽  
Equivalent Plastic Strain ◽  
Base Material ◽  
Prediction Method ◽  
High Strength ◽  
Critical Conditions ◽  
Opening Displacement ◽  
Cracking Behavior ◽  
Surface Flaws ◽  
Notch Tip

The ductile cracking behavior of girth weld joints, in X80 and X100 grade linepipe, was investigated using single edge notched (SENT) specimens, notched round bar (NRB) specimens and wide plate (WP) specimens. FE analyses were carried out to evaluate critical conditions for ductile cracking at the notch tip. The effect of Y/T ratio of base material on ductile cracking for welded joints was also studied. Ductile cracking from the notch tip in WP specimens can be estimated by using the critical equivalent plastic strain, which can be obtained from SENT or NRB specimens. In addition, a simplified prediction method for ductile cracking by using effective opening displacement was proposed and its validity demonstrated by comparison to the equivalent plastic strain at the notch tip. With respect to the influence of material properties on ductile cracking behavior, deformability of joint to ductile cracking was enhanced by reduction of Y/T ratio of base material. Based on the experimental results and FE analyses, pipe design to prevent ductile cracking from surface flaws under large deformation was discussed.

Ductile Crack Extension Analysis for X80 Bending Deformation Using Damage-Based Model

2014 ◽  
Author(s):  
Satoshi Igi ◽  
Mitsuru Ohata ◽  
Takahiro Sakimoto ◽  
Kenji Oi ◽  
Joe Kondo
Keyword(s):  
Plastic Strain ◽  
Simulation Model ◽  
Crack Growth ◽  
Crack Extension ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Notch Tip

This paper presents experimental and analytical results focusing on the strain limit of X80 linepipe. Ductile crack growth behavior from a girth weld notch is simulated by FE analysis based on a proposed damage model and is compared with the experimental results. The simulation model for ductile crack growth accompanied by penetration through the wall thickness consists of two criteria. One is a criterion for ductile crack initiation from the notch-tip, which is described by the plastic strain at the notch tip, because the onset of ductile cracking can be expressed by constant plastic strain independent of the shape and size of the components and the loading mode. The other is a damage-based criterion for simulating ductile crack extension associated with damage evolution influenced by plastic strain in accordance with the stress triaxiality ahead of the extending crack tip. The proposed simulation model is applicable to prediction of ductile crack growth behaviors from a circumferentially-notched girth welded pipe with high internal pressure, which is subjected to tensile loading or bending (post-buckling) deformation.

scholarly journals Investigation of Notch-Induced Precise Splitting of Different Bar Materials under High-Speed Load

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2461 ◽  
Author(s):  
Yuanzhe Dong ◽  
Yujian Ren ◽  
Shuqin Fan ◽  
Yongfei Wang ◽  
Shengdun Zhao
Keyword(s):  
Crack Initiation ◽  
High Speed ◽  
Splitting Method ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Initiation Zone ◽  
New Type ◽  
Notch Tip ◽  
Maximum Impact Force ◽  
1045 Steel

A notch-induced high-speed splitting method was developed for high-quality cropping of metal bars using a new type of electric-pneumatic counter hammer. Theoretical equations and FE models were established to reveal the crack initiation and fracture mode. Comparative tests were conducted for notched and unnotched bars of four types of steels, i.e., AISI 1020, 1045, 52100, and 304, and the section quality and microfracture mechanism were further investigated. The results show that damage initiates at the bilateral notch tips with peak equivalent plastic strain, and propagates through the plane induced by the notch tip; the stress triaxiality varies as a quasi-sine curve, revealing that the material is subjected to pure shearing at the notch tip, and under compression at the adjacent region. High precision chamfered billets were obtained with roundness errors of 1.1–2.8%, bending deflections of 0.5–1.5mm, and angles of inclination of 0.7°–3.4°. Additionally, the notch effectively reduced the maximum impact force by 21.6–23.9%, splitting displacement by 7.6–18.6%, and impact energy by 27.8–39.1%. The crack initiation zone displayed quasi-parabolic shallow dimples due to shear stress, and the pinning effect was larger in AISI 52100 and 1045 steel; the final rupture zone was characterized by less elongated and quasi-equiaxial deeper dimples due to the combination of shear and normal stress.

Ductile Crack Initiation Behavior of Prestrained Steels

2011 ◽  
Author(s):  
Takehisa Yamada ◽  
Yoichi Yamashita
Keyword(s):  
Crack Initiation ◽  
Void Nucleation ◽  
Equivalent Plastic Strain ◽  
Stress Triaxiality ◽  
Ductile Crack ◽  
Round Bar ◽  
Point Bend ◽  
Materials Used ◽  
Cracked Specimens ◽  
Triaxiality Factor

Ductile crack initiation behaviors were experimentally and analytically investigated using compressively prestrained notched round bar specimen (lower stress triaxiality condition) and four point bend specimen (higher stress triaxiality condition). The materials used were SM400B and HT780. It was observed that ductile crack initiation of notched round bar specimen occurred at the center of specimen and was caused by coalescence of micro voids. Ductile limit curves, which are the relationships between equivalent plastic strain and stress triaxiality factor at ductile crack initiation, were obtained using FE-analyses and experimental results. Ductile crack initiation of four point bend specimens as cracked specimens could be evaluated using ductile crack initiation limit curves obtained from notched round bar specimens if the positions of void nucleation at crack tip are properly considered. It has been found that ductile crack initiation limits can be evaluated using ductile limit curves under both low and high constraint conditions (stress triaxiality conditions.

Study on overlapping of two sequential scans in laser forming

2007 ◽  
Vol 221 (9) ◽  
pp. 993-997 ◽  
Author(s):  
H Shen ◽  
J Zhou ◽  
Z Q Yao
Keyword(s):  
Plastic Strain ◽  
Material Properties ◽  
Structural Model ◽  
Three Dimensional ◽  
High Strength ◽  
Laser Beams ◽  
Laser Forming ◽  
Numerical Investigations ◽  
Localized Heating ◽  
The Difference

Laser forming can utilize localized heating for the forming of high strength alloys and use combinations of straightandcurved lines to produce three-dimensional formedcomponents, which are of significant value to industries of aerospace, shipbuilding, and microelectronics. A three-dimensional non-linear, indirectly coupled thermal—structural model for the overlapping ratio of two sequential laser beams scanning is established, accounting for temperature dependency of material properties. Numerical results are verified by experimental data. Numerical investigations are carried out to examine the difference in plastic strain distributions under different overlapping ratios. The results show that the bending angle is larger when the size of plastic zone on the top surface is wider, although the plastic strain is smaller.

Evaluation of Ductile Cracking Criterion for Grade X100 Linepipe and Relationship to Large Scale Fracture Behavior

2003 ◽  
Author(s):  
Nobuyuki Ishikawa ◽  
Shigeru Endo ◽  
Alan Glover ◽  
David Horsley ◽  
Masao Toyoda
Keyword(s):  
Plastic Strain ◽  
Ductile Fracture ◽  
Fracture Behavior ◽  
Large Scale ◽  
Notch Root ◽  
Equivalent Plastic Strain ◽  
High Strength ◽  
Fracture Initiation ◽  
Linepipe Steels ◽  
Ductile Fracture Initiation

Recent developments in the manufacturing process of steel plate for high strength linepipe have enabled superior toughness to prevent brittle fracture of the pipe body. Techniques for non-destructive inspection have also improved, and large flaws that could lead to brittle fracture are highly unlikely in recent high strength pipelines. However, large amounts of plastic deformation can be expected in seismic or permafrost regions. Prevention of ductile fracture of the pipe body or weldment therefore becomes a key issue in defining the tensile strain limit. Ductile fracture is considered to occur by growth and coalescence of voids, and is affected by stress triaxiality and plastic straining at the cracked region. Although many studies have been carried out to evaluate ductile cracking criteria, its transferability to large-scale fracture behavior has not been thoroughly investigated. In this study, ductile cracking of high strength linepipe steels, Grade X80 and X100, was investigated. Notched round bar specimens with different notch root radii were tested to determine the precise conditions for initiation of ductile fracture. Stress and strain conditions at the notch regions were evaluated by FE analysis, and the “critical equivalent plastic strain” was defined at conditions corresponding to ductile fracture initiation in the experimental small specimen tests. Ductile crack initiation behavior was also determined for wide plate test specimens by making close observations of the notch root area. 3-D FE analysis of the wide plate tensile test showed that the equivalent plastic strain at the point of ductile fracture initiation was in close agreement with that in the notched round bas specimen. Thus, the “critical equivalent plastic strain,” determined by small notched round bar specimens, can be considered as a transferable criterion to predict large-scale fracture behavior in wide plate tests. Concepts of strain based design in terms of preventing ductile failure from a surface flaw by applying critical strain to cracking were also discussed in this paper. Results were compared to conventional grade linepipe steels and structural steels, showing that recent high strength linepipe steels have higher resistance to ductile cracking than conventional structural steels. In addition, 3-D FE analyses were used in a parametric study to determine the effects of Y/T and uniform strain on the onset of ductile cracking behaviour. The results of these analyses show the relative importance of materials properties on the resistance to ductile cracking.

Biaxial Tensile Test of High Strength Steel Sheet for Large Plastic Strain Range

2012 ◽  
Vol 504-506 ◽  
pp. 59-64 ◽  
Author(s):  
Tomoyuki Hakoyama ◽  
Toshihiko Kuwabara
Keyword(s):  
Plastic Strain ◽  
High Strength Steel ◽  
Deformation Behavior ◽  
Equivalent Plastic Strain ◽  
Strain Range ◽  
High Strength ◽  
Test Material ◽  
Strain Rates ◽  
Stress Space ◽  
Plastic Strain Range

Deformation behavior of high strength steel with a tensile strength of 590 MPa under biaxial tension was investigated for a work equivalent plastic strain range of 0.002 0.16. The test material was bent and laser welded to fabricate a tubular specimen with an inner diameter of 44.6mm and wall thickness of 1.2 mm. Using a servo-controlled tension-internal pressure testing machine, many linear stress paths in the first quadrant of stress space were applied to the tubular specimens. Moreover, biaxial tensile tests using a cruciform specimen were performed to precisely measure the deformation behavior of the test material for a small strain range following initial yielding. True stress-true plastic strain curves, contours of plastic work in stress space and the directions of plastic strain rates were measured and compared with those calculated using selected yield functions. The plastic deformation behavior up to an equivalent plastic strain of 0.16 was successfully measured. The Yld2000-2d yield function most closely predicts the general work contour trends and the directions of plastic strain rates of the test material.

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