Application of Stress-Modified Fracture Strain Model to Full-Scale Pipes With a Circumferential Crack in the Center of Welds

2016 ◽  
Author(s):  
Ho-Wan Ryu ◽  
Hune-Tae Kim ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim
Keyword(s):  
Finite Element ◽  
Numerical Method ◽  
Fracture Strain ◽  
Damage Model ◽  
Full Scale ◽  
Piping System ◽  
Damage Analysis ◽  
Integrity Assessment ◽  
Material Discontinuities ◽  
Strain Model

A lot of welded joints are required to connect the junctions of components in the complex piping system. The structural integrity assessment on welded pipes is especially important, because the weldments are susceptible to material discontinuities, flaws and residual stresses. Finite element (FE) damage analysis can be useful and effective method for an accurate assessment on extensive structures. For the case of welded joint, the numerical method is necessarily required to assess complex features because of material discontinuities and flaws. This study provides a simple numerical method to simulate ductile tearing in welded full-scale pipes. Stress-modified fracture strain model is applied to finite element analysis with a stress reduction technique. An element-size-dependent critical damage model is also implemented in the full-scale pipe simulations. From the results of simulation, deformation response and characteristic loads are compared with experimentally measured values to verify the application of damage model on weld material. As a result, the predictions of finite element damage analysis are in good agreement with experiments.

Ductile Fracture Simulation of CRIEPI STPT 410 Pipe With Circumferential Crack

2014 ◽  
Author(s):  
Hyun-Suk Nam ◽  
Young-Ryun Oh ◽  
Jae-Jun Han ◽  
Chang-Young Oh ◽  
Yun-Jae Kim ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Crack Growth ◽  
Fracture Strain ◽  
Damage Model ◽  
Full Scale ◽  
Ductile Crack ◽  
Size Dependent ◽  
Element Size ◽  
Ductile Crack Growth ◽  
Strain Model

This paper provides simulation of ductile crack growth in full-scale cracked pipe tests using an element-size dependent damage model. This method is based on the stress-modified fracture strain damage model. The stress-modified fracture strain model is determined to be incremental damage in terms of stress triaxiality and fracture strain for dimple fracture from tensile test result with FE analyses technique. To validate the proposed method, this research analyses STPT 410 cracked pipes test at 300°C taken from CRIEPI (Central Research Institute of Electric Power Industry). In order to calibrate the stress-modified fractures strain model, tensile tests and fracture toughness tests were compared with simulated results using element-size dependent damage model. Tensile specimen and fracture toughness specimen were extracted from STPT 410 steel pipe. The calibrated damage model predicts ductile crack growth in 5 type circumferential cracked pipes bending test. And these results were compared with the experimental results. The results show that the proposed method can simulate ductile crack growth in full-scale cracked pipe tests.

Applicability of Net-Section Collapse Load Approach to Multiple-Cracked Pipe Assessment: Numerical Study

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Myeong-Woo Lee ◽  
So-Dam Lee ◽  
Yun-Jae Kim
Keyword(s):  
Finite Element ◽  
Test Data ◽  
Parametric Study ◽  
Fracture Strain ◽  
Numerical Study ◽  
Damage Analysis ◽  
Collapse Load ◽  
Fracture Test ◽  
Strain Model

In this paper, applicability of net-section collapse load approach to circumferential multiple-cracked pipe assessment is investigated using finite element (FE) damage analysis. The FE damage analysis based on the stress-modified fracture strain model is validated against limited fracture test data of two circumferential surface-cracked pipes. Then, the systematic parametric study is performed using the FE damage analysis for symmetrical and asymmetrical surface-cracked pipes. It is found that predictions using the net-section collapse load approach tend to be more accurate with increasing the distance between two symmetrical cracks. For asymmetrical cracks, it is found that the deeper crack plays a more important role and that the existing net-section collapse load expression can be potentially nonconservative. Idealization to symmetrical cracks based on the deeper crack is proposed.

scholarly journals A progressive damage model of textile composites on meso-scale using finite element method: static damage analysis

2013 ◽  
Vol 48 (25) ◽  
pp. 3091-3109 ◽  
Author(s):  
Jian Xu ◽  
Stepan Vladimirovitch Lomov ◽  
Ignaas Verpoest ◽  
Subbareddy Daggumati ◽  
Wim Van Paepegem ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Damage Model ◽  
Textile Composites ◽  
Progressive Damage ◽  
Damage Analysis ◽  
Progressive Damage Model ◽  
Meso Scale ◽  
Element Method

Numerical Study on Longitudinal Distance Effect on Failure Stress of Non-Aligned Twin Cracked Pipe

2018 ◽  
Author(s):  
Thanh-Long Nguyen ◽  
Myeong-Woo Lee ◽  
Kunio Hasegawa ◽  
Yun-Jae Kim
Keyword(s):  
Fracture Strain ◽  
Numerical Study ◽  
Distance Effect ◽  
Failure Stress ◽  
Axial Distance ◽  
Damage Analysis ◽  
Asme Code ◽  
Bending Stresses ◽  
Strain Model ◽  
Longitudinal Distance

In this study, the effect of longitudinal distance H between non-aligned twin cracks is investigated using finite element damage analysis. The FE damage analysis based on the stress-modified fracture strain model is used to calculate the failure stress of non-aligned twin cracked pipe. Parametric study on the axial distance H between non-aligned twin cracks with various crack depths and lengths were conducted and compared with predictions using the alignment rules and the net-section collapse load approach for single crack provided in ASME Code. It is shown that the trend of the predicted collapse bending stresses for the non-aligned twin cracked pipes using FE damage analysis are different from the ones using the alignment rule.

A finite element ductile failure simulation method using stress-modified fracture strain model

2011 ◽  
Vol 78 (1) ◽  
pp. 124-137 ◽  
Author(s):  
Chang-Sik Oh ◽  
Nak-Hyun Kim ◽  
Yun-Jae Kim ◽  
Jong-Hyun Baek ◽  
Young-Pyo Kim ◽  
...  
Keyword(s):  
Finite Element ◽  
Fracture Strain ◽  
Ductile Failure ◽  
Simulation Method ◽  
Failure Simulation ◽  
Strain Model

Significance of Finite Compliance of a Cracked Piping System on Fracture Integrity Assessment

2005 ◽  
Author(s):  
I. A. Khan ◽  
V. Bhasin ◽  
K. K. Vaze ◽  
A. K. Ghosh ◽  
H. S. Kushwaha
Keyword(s):  
Finite Element ◽  
Driving Force ◽  
Piping System ◽  
Combined Effects ◽  
Finite Element Analyses ◽  
Crack Driving Force ◽  
Integrity Assessment ◽  
Linear Elastic ◽  
The Stability ◽  
Integrity Analysis

One of the thrust areas in the integrity analysis of cracked nuclear piping system is concern with the reduction in moment, at the crack section due to combined effects of local and global residual compliance. However an important consideration in the design of piping system, which is generally not considered, is the re-distribution of load that occurs due to finite compliance of the piping system. The load at the crack section reduces while it increases generally at support/anchor locations, which may be high stressed locations. In case of stiff-piping system this re-distribution of load may be quite significant. Hence for the complete integrity of the piping system these un-cracked locations should also be re-assessed. A generalized procedure is suggested to take care of the reduction in load at the cracked section and corresponding increase in reactions at the support/anchor locations in a 3-D cracked piping system. Thus the stability of cracked section as well as other highly stressed locations can be simultaneously assessed. Here it is assumed that the remaining piping system behaves in a linear elastic manner and the plasticity remains confined to the cracked section only. Detailed finite element analyses are performed on circuitous (3-D) cracked piping system to validate the developed approach. Results presented in this article clearly show that due to reduction in moment the crack driving force, for the same external load, reduces significantly.

Effects of Side Groove on Fracture Toughness

2015 ◽  
Author(s):  
Ho-Wan Ryu ◽  
Hune-Tae Kim ◽  
Jae-Jun Han ◽  
Yun-Jae Kim ◽  
Jong-Sung Kim ◽  
...  
Keyword(s):  
Test Data ◽  
Fracture Strain ◽  
Failure Criteria ◽  
Compact Tension ◽  
Damage Analysis ◽  
Pipe Material ◽  
Ductile Tearing ◽  
Different Shapes ◽  
Strain Model ◽  
Good Agreement

This paper describes ductile tearing simulation for compact tension (C(T)) specimens using FE damage analysis based on the stress-modified fracture strain model. The side groove effect on J-resistance curve was estimated by experimental and analytical ways. In this paper, SA508 Grade 1A low alloy steel pipe material was considered. Tensile and C(T) specimens are simulated to determine the failure criteria with finite element method. Then, different shapes of C(T) specimens are analysed and the results from simulations are compared with test data for verification of proposed method. Overall, the predicted simulation results show good agreement with test data.

Integrity Assessment of API 5L X65 and X70 Pipelines With Mechanical Damages

2012 ◽  
Author(s):  
Kyu Jung Yeom ◽  
Yong Kwang Lee ◽  
Kyu Hwan Oh ◽  
Cheol Man Kim ◽  
Woo Sik Kim
Keyword(s):  
Finite Element ◽  
Structural Integrity ◽  
Mechanical Damage ◽  
Local Stress ◽  
Assessment Method ◽  
Full Scale ◽  
Burst Pressure ◽  
Element Analysis ◽  
Integrity Assessment ◽  
Failure Pressure

Gas pipelines with mechanical damages could affect the structural integrity and causes local stress and strain concentration. Failures in gas pipeline as leakages that could affect the supply of gas, loss of production, and environmental pollution. It is important to determine if pipelines are fitness-for-service. ASME B31G code is still widely used criterion although the assessment method is the conservative method. Further examinations are needed on the effects of material grade and pipeline shape on the burst pressure of damaged pipelines. The goal of this paper is to predict the failure pressure of mechanical damaged made of API X65 and X70 pipelines, by conducting full scale burst tests and finite element analysis (FEA). Different pipeline grades, effects of gouges, and dent depths were considered for an integrity assessment. The full scale burst tests were performed for pipelines with artificial mechanical damage. The gouge defect was made in a V-notch shape and the dented pipeline was generated using a ball shaped indenter that was pressed into the pipe. A three dimensional FEA was performed to obtain the burst pressure of a pipe with gouge and dent defects as a function of defect depth and length. A FEA was used to simulate the and externally damaged pipes under internal pressure. Failure pressure was predicted with stress based and strain based assessments by the finite element method (FEM).

Full Scale Cyclic Fatigue Testing of Dented Pipelines and Development of a Validated Dented Pipe Finite Element Model

2012 ◽  
Author(s):  
Sanjay Tiku ◽  
Vlado Semiga ◽  
Aaron Dinovitzer ◽  
Geoff Vignal
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Fatigue Testing ◽  
Complex Function ◽  
Element Model ◽  
Full Scale ◽  
Assessment Model ◽  
Integrity Assessment ◽  
Operational Life ◽  
Integrity Management

Dents in buried pipelines can occur due to a number of potential causes; the pipe resting on rock, third party machinery strike, rock strikes during backfilling, amongst others. The long-term integrity of a dented pipeline segment is a complex function of a variety of parameters, including pipe geometry, indenter shape, dent depth, indenter support, pressure history at and following indentation. In order to estimate the safe remaining operational life of a dented pipeline, all of these factors must be accounted for in the analysis. The paper discusses the full-scale dent testing being completed to support the development of pipeline integrity management criteria and is a continuation of the work discussed in previous IPC papers [1,2]. The material and structural response of the pipe test segments during dent formation and pressure loading has been recorded to support numerical model development. The full scale experimental testing is being completed for pipe test specimens in the unrestrained and restrained condition using different indentation depths and indenter sizes. The dents are pressure cycled until fatigue failure in the dent. This paper presents typical data recorded during trial including indentation load/displacement curves, applied pressures, strain gauges along the axial and circumferential centerlines, as well as dent profiles. The use of the full-scale mechanical damage test data described in this paper in calibrating and validating a finite element model based integrity assessment model is outlined. The details of the integrity assessment model are described along with the level of agreement of the finite element model with the full scale trial results. Current and future applications of the integrity assessment model are described along with recommendations for further development and testing to support pipeline integrity management.

Behavior of polyethylene under different triaxial stress states: An experimental and numerical study

2020 ◽  
pp. 146442072097058
Author(s):  
Limei Han ◽  
Yi Zhang ◽  
Shifeng Xue ◽  
Bo Zhou ◽  
Cuiwei Liu
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Damage Evolution ◽  
Fracture Strain ◽  
Damage Model ◽  
Stress Triaxiality ◽  
True Stress ◽  
Triaxial Stress ◽  
Element Simulation ◽  
Stress States

The behavior of a semi-crystalline polymer under different triaxial stress states is studied through the combination of experimental testing and finite element simulation. Polyethylene round bar specimens with four different notch radii were stretched at crosshead speed of 1 mm/min until fracture. The continuum damage mechanics damage model and Gurson–Tvergaard–Needleman damage model were proposed and applied to the finite element simulation. The results of engineering stress–displacement curves determined from finite element simulation match experimental results. Finite element simulation without considering damage and with the consideration of damage was conducted to determine the damaged and undamaged true stress–strain relationship of polyethylene materials, respectively. Damage evolution model was established based on the degradation of true stress. The finite element model was further applied to study the distribution of stress triaxiality for specimens with different notch radii and the effect of stress triaxiality on damage evolution, critical damage parameters, and fracture strain. The results show that the distribution of the stress triaxiality on the cross section of the specimen is not uniform, and as the stress triaxiality increases, the position where the maximum stress triaxiality occurs moves from the center point to two-third the radius from the center. Furthermore, the damaged true stress and the undamaged true stress increases with the decrease of the stress triaxiality when the strain is below 0.3, but decreases with the increase of stress triaxiality when the strain is larger than 0.3. In addition, it was found that the greater the stress triaxiality, the earlier the onset of damage and the faster the evolution, but the smaller the fracture strain.

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