Fatigue Behavior of Line Pipes Subjected to Severe Mechanical Damage

1999 ◽  
Vol 121 (4) ◽  
pp. 369-374 ◽  
Author(s):  
N. Hagiwara ◽  
N. Oguchi
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Hoop Stress ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Mechanical Damage ◽  
Ductile Crack ◽  
Ductile Crack Growth ◽  
Power Law Equation ◽  
Dent Depth

Fatigue behavior of electrically resistance welded (ERW) line pipes with a gouge in a dent was experimentally investigated. After denting and machining a gouge, fluctuating internal pressure was applied to line pipes. The fatigue behavior differed above and below the threshold Q(Qth), as a function of defect size and fracture toughness. When Q < Qth, ductile crack growth was observed with a consequent decrease in fatigue life. On the contrary, fatigue crack growth was observed when Q ≧ Qth. Fatigue life was predictable with an experimentally based power law equation incorporating dent depth, gouge depth, and hoop stress amplitude when Q ≧ Qth.

Fatigue Behavior of Line Pipes Subjected to Severe Mechanical Damage

1998 ◽  
Author(s):  
Naoto Hagiwara ◽  
Noritake Oguchi
Keyword(s):  
Hoop Stress ◽  
Stress Amplitude ◽  
Fatigue Behavior ◽  
Mechanical Damage ◽  
Fatigue Tests ◽  
Pressure Loading ◽  
Ductile Crack Growth ◽  
Stress Fluctuation ◽  
Power Law Equation ◽  
Dent Depth

Fatigue tests were carried out on ERW line pipes 200 mm and 300 mm in diameter with a severe gouge in dent type defect. Hoop stress fluctuation between 15% and 30% of the yield stress of the pipe materials was applied by cyclic internal pressure loading. By the parameter Q, a function of defect size and fracture toughness, fatigue behavior could have been well explained. Fatigue behavior differed above and below the threshold Q (Qth. When Q<Qth, crack propagation was initially associated with ductile crack growth, and therefore, fatigue life, Nf, decreased to less than 1000 cycles. On the contrary, Nf was larger than 1000 cycles when Q≧Qth. Nf was predictable with a power law equation incorporating dent depth, gouge depth, and stress amplitude when Q≧Qth. A gouge in a dent with Q<Qth, requires immediate repair or replacement.

Assessment of Ductile Crack Growth Based on a Local Approach

2006 ◽  
Author(s):  
Tae-Rin Lee ◽  
Yoon-Suk Chang ◽  
Jae-Boong Choi ◽  
Young-Jin Kim
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Stress Triaxiality ◽  
Mechanical Damage ◽  
Ductile Crack ◽  
Local Approach ◽  
Crack Growth Behaviour ◽  
Damage Models ◽  
Ductile Crack Growth ◽  
Comparison Results

The influence of stress triaxiality was a matter of concern on ductile fracture to explain geometry dependent fracture resistance characteristics of specimens and real structures during past two decades. Regarding the issue, recently, interests for local approach and micro-mechanical damage models are increased again in accordance with progress of computational environments. In this paper, the applicability of a local approach is investigated through a series of finite element (FE) analyses incorporating both a modified GTN model and a Rousselier model as well as fracture toughness tests. The ductile crack growth behaviour of SA515 Gr.60 carbon steel is assessed to guarantee transferability of fracture resistance curve from typical specimens with different in-plane and out-of-plane sizes. The material parameters are determined by calibration of test results and corresponding numerical analyses results, and used to simulate the fracture behaviour of CT specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. Finally, the Rousselier model is applied to estimate J-R curves of circumferential through-wall cracked pipe. The comparison results showed that the two damage models can be used as promising solutions for ductile crack growth simulation.

Assessment of Geometry Independent Fracture Resistance Characteristics Based on Local Approach

2005 ◽  
Vol 297-300 ◽  
pp. 2403-2409 ◽  
Author(s):  
Yoon Suk Chang ◽  
T.R. Lee ◽  
Jae Boong Choi ◽  
Young Jin Kim
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Mechanical Damage ◽  
Material Behavior ◽  
Ductile Crack ◽  
Local Approach ◽  
Ductile Crack Growth ◽  
Comparison Results

The influences of stress triaxiality on ductile fracture have been emphasized to explain the geometry independent fracture resistance characteristics of specimens and structures during past two decades. For the estimation of this material behavior, two-parameter global approach and local approach can be used as case by case manner. Recently, the interests for the local approach and micro-mechanical damage model are increased again due to progress of computational environments. In this paper, the applicability of the local approach has been assessed through a series of finite element analyses incorporating both modified GTN model and Rousselier model. The ductile crack growth behaviors are examined to guarantee the transferability on different sizes and geometries of C(T) specimens and SE(T) specimens. The material fitting constants are determined from calibration of tensile tests and numerical analyses results, and used to simulate the fracture behaviors of typical specimens. Then, a comparison is drawn between the numerically estimated crack resistance curves and experimentally determined ones. The comparison results show a good agreement and the two damage models are regarded as promising solutions for ductile crack growth simulation.

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.

Ductile Damage Model Based On Void Growth Analysis for Application to Ductile Crack Growth Simulation

2021 ◽  
Author(s):  
Takehisa Yamada ◽  
Mitsuru Ohata
Keyword(s):  
Crack Growth ◽  
Void Growth ◽  
Damage Evolution ◽  
Damage Model ◽  
Crack Growth Resistance ◽  
Growth Behavior ◽  
Ductile Crack ◽  
Growth Simulation ◽  
Crack Growth Simulation ◽  
Ductile Crack Growth

Abstract The aim of this study is to propose damage model on the basis of the mechanism for ductile fracture related to void growth and to confirm the applicability of the proposed model to ductile crack growth simulation for steel. To figure out void growth behavior, elasto-plastic finite element analyses using unit cell model with an initial void were methodically performed. From the results of those analyses, it was evident that the relationships between normalized void volume fraction and normalized strain by each critical value corresponding to crack initiation were independent of stress-strain relationship of material and stress triaxiality state. Based on this characteristic associated with void growth, damage evolution law was derived. Then, using the damage evolution law, simple and phenomenological ductile damage model reflecting void growth behavior and ductility of material was proposed. To confirm the validation and application of proposed damage model, the damage model was implemented in finite element models and ductile crack growth resistance was simulated for cracked components were performed. Then, the simulated results were compared with experimental ones and it was found that the proposed damage model could accurately predict ductile crack growth resistance and was applicable to ductile crack growth simulation.

Fatigue Behaviour of Dented Pipes Under Internal Pressure: A Numerical-Experimental Approach

2018 ◽  
Author(s):  
Mario A. Polanco-Loria ◽  
Håvar Ilstad
Keyword(s):  
Fatigue Life ◽  
Internal Pressure ◽  
Fatigue Behavior ◽  
Crack Depth ◽  
Fatigue Behaviour ◽  
Experimental Methodology ◽  
Experimental Program ◽  
Metal Loss ◽  
Life Predictions ◽  
Dent Depth

This work presents a numerical-experimental methodology to study the fatigue behavior of dented pipes under internal pressure. A full-scale experimental program on dented pipes containing gouges were achieved. Two types of defects were studied: metal loss (plain dent) and sharp notch. Both defects acting independently reduce the fatigue life performance but their combination is highly detrimental and must be avoided. We did not find a severity threshold (e.g. dent depth or crack depth) where these defects could coexist. In addition, based on numerical analyses we proposed a new expression for stress concentration factor (SCF) in line with transversal indentation. This information was successfully integrated into a simple fatigue model where the fatigue life predictions were practically inside the window of experimental results.

Influence of Weld Residual Stresses on Ductile Crack Behavior in AISI Type 316LN Stainless Steel Weld Joint

2018 ◽  
Author(s):  
Sai Deepak Namburu ◽  
Lakshmana Rao Chebolu ◽  
A. Krishnan Subramanian ◽  
Raghu Prakash ◽  
Sasikala Gomathy
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Crack Growth ◽  
Weld Joint ◽  
Volume Fraction ◽  
Growth Behavior ◽  
Welding Residual Stress ◽  
Crack Growth Behavior ◽  
Ductile Crack ◽  
Ductile Crack Growth

Welding residual stress is one of the main concerns in the process of fabrication and operation because of failures in welded steel joints due to its potential effect on structural integrity. This work focuses on the effect of welding residual stress on the ductile crack growth behavior in AISI 316LN welded CT specimens. Two-dimensional plane strain model has been used to simulate the CT specimen. X-ray diffraction technique is used to obtain residual stress value at the SS 316LN weld joint. The GTN model has been employed to estimate the ductile crack growth behavior in the CT-specimen. Results show that residual stresses influence the ductile crack growth behavior. The effect of residual stress has also been investigated for cases with different initial void volume fraction, crack lengths.

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