K-0805 Development of PFM Code with a Function of Ductile Crack Extension Analysis : Part1: Introduction of Ductile Crack Extension Analysis Function Based on R6 Method

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.

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Stress Intensity Evaluation for Surface Crack with Use of Boundary Element Method and Influence Function Method and the Surface Crack Extension Analysis

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.51-52.69 ◽

1991 ◽

Vol 51-52 ◽

pp. 69-74

Author(s):

R. Yuuki ◽

K. Ejima

Keyword(s):

Stress Intensity ◽

Boundary Element Method ◽

Boundary Element ◽

Surface Crack ◽

Influence Function ◽

Crack Extension ◽

Function Method ◽

Influence Function Method ◽

Extension Analysis ◽

Element Method

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Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds

Volume 3: Design and Analysis ◽

10.1115/pvp2008-61828 ◽

2008 ◽

Author(s):

Mayumi Ochi ◽

Kiminobu Hojo ◽

Itaru Muroya ◽

Kazuo Ogawa

Keyword(s):

Stress Intensity Factor ◽

Stress Intensity ◽

Intensity Factor ◽

Stress Intensity Factors ◽

Crack Extension ◽

Crack Depth ◽

Alloy 600 ◽

Intensity Factors ◽

Axial Crack ◽

Extension Analysis

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.

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The Development of a Surface Crack in a Thick Vessel Under Ductile Tearing

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2009-77374 ◽

2009 ◽

Author(s):

Osama Terfas ◽

Bostjan Bezensek

Keyword(s):

Crack Extension ◽

Driving Forces ◽

Ductile Crack ◽

Ductile Tearing ◽

Surface Flaws ◽

Resistance Curves ◽

The Mean ◽

Surface Breaking Crack ◽

Tearing Resistance ◽

Leak Before Break

The development of the shape and size of a flaw in a pressure vessel is important in fitness-for-service evaluations such as leak-before-break. In this work finite element modelling is used to evaluate the mean stresses and the J-integral around a front of a surface-breaking flaw. These results show non-uniform constraint levels and crack driving forces around the crack front at large deformation levels, which contrast those at low deformation levels. A new procedure is developed to estimate the amount of ductile crack extension around a surface-breaking crack on the basis of ductile tearing resistance curves of deep and shallow cracked fracture mechanics samples. The procedure is applied to surface flaws to simulate ductile crack extension under ductile tearing and show the evolution of the initial flaw shape. Results show that both, initially semi-circular and initially semi-elliptical flaws develop towards the same shape in bending.

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