The Effect of Pressure Induced Hoop Stress on Bi-Axially Loaded through Wall Cracked Cylindrical Structures – A Strain Based Method

2011 ◽  
Vol 110-116 ◽  
pp. 1525-1530
Author(s):  
M.V.N. Sivakumar ◽  
B. N. Rao ◽  
S. R. Satishkumar
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Hoop Stress ◽  
Pipeline Steel ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ductile Tearing ◽  
Effect Of Pressure ◽  
Bending Load ◽  
Axially Loaded

This paper presents a simplified strain-based fracture mechanics approach to study the effect of pressure induced hoop stress on bi-axially loaded through walled cracked (TWC) pipes subjected to an external bending load in combination with internal pressure. Elastic-plastic finite element analyses are conducted to establish the relation between global strain and Crack tip opening displacement (CTOD). In the finite element model X65 pipeline steel is considered using power-law idealization of stress-strain, and the inelastic deformations, including ductile tearing effects, are accounted for by use of the Gurson–Tvergaard–Needleman model. Several parameters are taken into account, such as crack length, internal pressure and material hardening. Strain based crack driving force equation is used and maximum load criterion is adopted to determine the critical strain from ductile tearing in the cracked pipeline. The results suggest that presence of pressure-induced hoop stresses increases the fracture response in high-hardening materials and their effects are significant due to large plastic-zone size.

Study of Constraint Issues in Elasto-Plastic Fracture Analysis Using Experimental and Finite Element Simulation

2017 ◽  
Author(s):  
Md Ibrahim Kittur ◽  
Krishnaraja G. Kodancha ◽  
C. R. Rajashekar
Keyword(s):  
Finite Element ◽  
Mild Steel ◽  
Compact Tension ◽  
Specimen Thickness ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
3D Fea ◽  
The Comparative Study ◽  
Crack Tip Opening

In this investigation, the variation of J-integral considering Compact Tension (CT) specimen geometry varying a/W and σ using 2D and 3D elasto-plastic Finite Element (FE) analysis have been studied. Further, the investigation has been done to examine the relationship between the J and δ for varied a/W and σ. The plane stress and plane strain elasto-plastic FE analyses have been conducted on the CT specimen with a/W = 0.45–0.65 to extract the J and Crack-tip Opening Displacement (CTOD) values for mild steel. The comparative study of the variation of dn with a/W of mild steel with earlier results of IF steel is carried out. The study clearly infers the effect of yield stress on the variation of the magnitude of dn with reference to a/W ratio. The present analysis infers that while converting the magnitude of the CTOD to J one needs to carefully evaluate the value of dn depending on the material rather than considering it to be unity. Further, the study was extended to experimental and 3D FEA wherein J-integral and CTOD were estimated using the CT specimen. Experimental results reveal that the crack length, the specimen thickness, and the loading configuration have an effect on the fracture toughness measurements. The error analysis between the results obtained by 3D FEA and experimentation were conducted and found to be within limits.

Strain-Based Failure Criteria for Sharp Part-Wall Defects in Pipelines

1998 ◽  
Author(s):  
Aaron S. Dinovitzer ◽  
Brian A. Graville ◽  
Alan G. Glover
Keyword(s):  
Finite Element ◽  
Failure Criterion ◽  
Local Strain ◽  
Failure Criteria ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Acceptance Criterion ◽  
Linear Finite Element ◽  
Non Linear

Failure criteria in current engineering critical assessment procedures for defects in pipelines and welds are stress-based. For example, failure is presumed to occur when the net section average stress reaches some arbitrary flow stress. These approaches are unrealistic for defects of limited length where loading of the net section (ligament) is essentially strain controlled. In order to improve upon this, the authors developed a strain-based failure criterion for part wall pipe defects in terms of the maximum ligament plastic extension. While this criterion[l] provided a basis for assessing the criticality of blunt defects, with respect to plastic collapse, it did not address sharp or planar defects which promote fracture. As a defect becomes sharper, failure is determined more by local strain at the defect tip which is typically characterized by the crack tip opening displacement (CTOD). This paper describes the development of a sharp/planar defect strain-based failure criterion which relates the maximum ligament extension to the critical CTOD of the material. Two and three dimensional non-linear finite element analyses are used to determine local root extensions of circumferential defects which can be related to the loading, defect and pipe dimensions. The root extensions are calibrated to standard CTOD measurements through non-linear finite element analysis. The failure criterion development process considers various defect lengths, material work hardening rates and material models. The failure criterion is compared with analytical and experimental data to demonstrate its predictive capability. The end result of this work is the development of an alternative acceptance criterion for sharp weld defects permitting more effective repair decisions to be made based on a more uniform level of reliability.

Finite Element Modeling of Ductile Tearing of Pipeline-Steel in Cracked Plates

2004 ◽  
Author(s):  
Yu Chen ◽  
Steve Lambert
Keyword(s):  
Finite Element ◽  
Void Nucleation ◽  
Pipeline Steel ◽  
Damage Model ◽  
Tensile Load ◽  
Maximum Load ◽  
Void Coalescence ◽  
Ductile Tearing ◽  
Numerical Predictions ◽  
Measured Load

The purpose of this work was to develop a three-dimensional finite element model to simulate ductile tearing in pipeline-steels. The measured load versus displacement histories for single edge notch tension (SENT) and surfaced-cracked wide plate specimens, both made of X-70 pipeline-steel plates and subject to tensile load, were numerically predicted using the proposed damage model. In the numerical model, progressive damage was restricted to a predetermined ductile tearing zone. The material damage behaviour in this tearing zone was described in terms of a Gurson-Tvergaard (G-T) isotropic constitutive model, which accounts for micro-void nucleation and growth. The criterion for the onset of void coalescence was determined via the Thomason criterion. Experimentally measured load-displacement histories for all specimens were accurately reproduced by the proposed model, irrespective of different plate width, thickness and crack configurations. The numerical predictions were in good agreement with experimental test data in terms of both the maximum load and the corresponding displacement at maximum load. The proposed damage model was also used to numerically estimate the effect of crack growth on maximum load for these cracked specimens. The results in this paper demonstrate the potential of the proposed damage model as an engineering tool for analyzing ductile tearing in application to defect assessment of surface cracked pipes.

Finite Element Modelling of Static and Fatigue Failure of Composite Repair System in Offshore Pipe Risers

2014 ◽  
Vol 875-877 ◽  
pp. 1063-1068 ◽  
Author(s):  
Park Hinn Chan ◽  
Kim Yeow Tshai ◽  
Michael Johnson ◽  
Hui Leng Choo
Keyword(s):  
Finite Element ◽  
Internal Pressure ◽  
Low Cycle Fatigue ◽  
Failure Mechanisms ◽  
Repair System ◽  
Fe Model ◽  
Composite Surface ◽  
Composite Repair ◽  
Bending Load ◽  
Static Conditions

The static and cyclic failure mechanisms of offshore pipe riser repaired with a designated laminate orientation of carbon/epoxy (C/E) system were studied. The finite element (FE) model takes into account failure mechanisms of the composite sleeve inter-layer delamination, debonding at the steel riser-composite surface interface, and the maximum permissible strain of the repaired riser. Design conditions of the combined static loads (coupled internal pressure, longitudinal tensile and transverse bending) were determined through a limit state analysis [1,2]. The limiting static bending load that causes catastrophic failure under a coupled internal pressure and tensile loadings was determined through Virtual Crack Closure Technique (VCCT). The effects of cyclic bending, mimicking the typical scenarios experienced in pipe riser exposed to dynamic subsea environment, were evaluated and compared against the static conditions. The low cycle fatigue of the composite repair system (CRS) is simulated using a direct cyclic analysis within a general purpose FE program, where the onset and fatigue delamination/disbonding growth are characterized through the Paris Law.

The Prediction of Fatigue Crack Opening Behavior Using Cyclic Crack Tip Opening Displacement by Finite Element Analysis

2006 ◽  
Vol 324-325 ◽  
pp. 295-298 ◽  
Author(s):  
Hyeon Chang Choi
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Fatigue Crack ◽  
Crack Opening ◽  
Crack Tip ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Element Size ◽  
Crack Tip Opening

An elastic-plastic finite element analysis (FEA) is performed to examine the opening behavior of fatigue crack, where the contact elements are used in the mesh of the crack tip area. The relationship between fatigue crack opening behavior and cyclic crack tip opening displacement was studied in the previous study. In this paper, we investigate the effect of the element size when predict fatigue crack opening behavior using the cyclic crack tip opening displacement obtained from FEA. The cyclic crack tip opening displacement is well related to fatigue crack opening behavior.

Elastic-Plastic Finite Element Analysis of the Effect of the Compressive Loading on Fatigue Crack Tip Parameters

2008 ◽  
Vol 392-394 ◽  
pp. 980-984 ◽  
Author(s):  
Y. Sha ◽  
Hui Tang ◽  
Jia Zhen Zhang
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Compressive Stress ◽  
Kinematic Hardening ◽  
Compressive Loading ◽  
Crack Tip ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Element Analysis ◽  
Elastic Plastic

In this paper, a detailed elastic-plastic finite element analysis of the effect of the compressive loading on crack tip plasticity is studied based on the material’s kinematic hardening model. Five centre-cracked panel specimens with different crack lengths are analyzed. The analysis shows that in a tension-compression loading the maximum spread of the crack tip reverse plastic zone increases with the increase of the compressive stress and the near crack tip opening displacement decreases with the increase of the compressive stress at the same nominal stress intensity factor. The applied compressive stress is the main factor controlling the near crack tip parameters.

scholarly journals Material Assessment of Canadian SAW Line-Pipes

1998 ◽  
Author(s):  
D. K. Mak ◽  
W. R. Tyson
Keyword(s):  
Fracture Toughness ◽  
Grain Size ◽  
Yield Strength ◽  
Notch Toughness ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Ductile Tearing ◽  
Average Grain Size ◽  
Grade One

Eight pipes, manufactured between 1952 and 1981, have been collected from various Canadian pipeline companies and tested. They include six pipes from the field made in the 1950’s and 1960’s of X52 grade, one experimental pipe manufactured in the early 1970’s of X65 grade, and a modern clean steel of X70 grade manufactured in 1981. The steels have been characterized by chemical composition, grain size, yield and tensile strengths, notch toughness (Charpy V-notch absorbed energy), and fracture toughness (J-integral and crack-tip opening displacement). The modern steel has much lower carbon content and much smaller grain size compared to the pipes manufactured in the 1950’s and 1960’s. The former is a fully-killed controlled-rolled steel while the latter are semi-killed ferrite-pearlite steels. All eight pipes have ferrite-pearlite microstructures, with the average grain size ranging from 4 to 14 μm. The transverse yield strength was found to be significantly higher (by about 20%) than the longitudinal yield strength. Notch toughness and fracture toughness were similar for pipes manufactured in the 1950’s and 1960’s. In comparison, the modern steel has much higher toughness and higher strength. J-integral and CTOD δ were found to be related by J = m σyδ with m = 1.8 and σy the transverse yield strength. The J-integral at 0.2 mm crack growth was consistent with a linear correlation with the upper-shelf Charpy energy. All the steels in this study fractured by ductile tearing in slow loading in spite of the low toughness of the older steels. It is suggested that, in the absence of Charpy upper shelf data, a reasonable representative toughness for resistance to axial surface flaws propagating by ductile tearing is J = 120±15 kJ/m2.

Strain-Based CTOD and J-Integral Estimations for Pipelines With a Surface Crack Under Large Plastic Strain and Internal Pressure

2020 ◽  
Vol 142 (5) ◽  
Author(s):  
Youn-Young Jang ◽  
Ju-Yeon Kang ◽  
Nam-Su Huh ◽  
Ik-Joong Kim ◽  
Young-Pyo Kim
Keyword(s):  
Internal Pressure ◽  
Surface Crack ◽  
Material Properties ◽  
J Integral ◽  
Crack Tip Opening Displacement ◽  
Large Plastic Strain ◽  
Opening Displacement ◽  
Definition Of ◽  
Crack Tip Opening ◽  
Tensile Strain Capacity

Abstract Engineering solutions for crack-tip opening displacement (CTOD) and J-integral estimations for pipelines with a surface crack are proposed based on parametric finite element (FE) analyses for various geometries, material properties, and internal pressure conditions. Two kinds of CTOD definitions are considered in relation to strain-based estimation solutions for dealing with confusion regarding the definition of CTOD and to extend the applicability of tensile strain capacity (TSC) assessment. Moreover, influence functions of internal pressure are also suggested to take account of the effect of internal pressure on TSC. Using the proposed solutions, TSCs for cracked X65 and X70 pipes were assessed based on initiation and ductile instability. Curved wide plate tests were performed to obtain experimental TSCs, which were compared with those from the proposed solutions. Moreover, TSCs from the proposed solutions were also compared with those from other TSC-predicted models in order to assess their validity.

Numerical Analysis of High Pressure Cold Bend Pipe to Investigate the Behaviour of Tension Side Fracture

2012 ◽  
Author(s):  
Celal Cakiroglu ◽  
Amin Komeili ◽  
Samer Adeeb ◽  
J. J. Roger Cheng ◽  
Millan Sen
Keyword(s):  
Finite Element ◽  
High Pressure ◽  
Internal Pressure ◽  
Experimental Studies ◽  
Element Model ◽  
Combined Loading ◽  
Element Analysis ◽  
Bend Pipe ◽  
Bending Load ◽  
Bending Loads

The cold bend pipelines may be affected by the geotechnical movements due to unstable slopes, soil type and seismic activities. An extensive experimental study was conducted by Sen et al. in 2006 to understand the buckling behaviour of cold bend pipes. In their experiments, it was noted that one high pressure X65 pipe specimen failed under axial and bending loads due to pipe body tensile side fracture which occurred after the development of a wrinkle. The behaviour of this cold bend pipe specimen under bending load has been investigated numerically to understand the conditions leading to pipe body tension side fracture following the compression side buckling. Bending load has been applied on a finite element model of the cold bend by increasing the curvature of it according to the experimental studies conducted by Sen [1]. The bending loads have been applied on the model with and without internal pressure. The distribution of the plastic strains and von Mises stresses as well as the load–displacement response of the pipe have been compared for both load cases. In this way the experimental results obtained by Sen [1] have been verified. The visualization of the finite element analysis results showed that pipe body failure at the tension side of the cold bend takes place under equal bending loads only in case of combined loading with internal pressure.

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