Structural Integrity Assessment of Defected Gas Pipelines Using a Simplified Ductile Damage Model

2021 ◽  
Author(s):  
Ik-Joong Kim ◽  
Cheol-Man Kim ◽  
Jong-Hyun Baek ◽  
Young-Pyo Kim ◽  
Youngseog Lee ◽  
...  
Keyword(s):  
Void Growth ◽  
Structural Integrity ◽  
Fracture Strain ◽  
Damage Model ◽  
Damage Index ◽  
Stress Triaxiality ◽  
Tensile Tests ◽  
Image Correlation ◽  
Integrity Assessment ◽  
Failure Simulation

Abstract The finite element method using the damage model has been increasingly used to predict the failure of various structures. Thus, various damage models were presented, and recently, a phenomenological model called the local fracture strain model was presented, making it easy and accurate to predict the damage of the structure. This model has the advantage of defining fracture strain as a function of stress triaxiality with only a few notched tensile tests but has a limitation because it does not consider the damage evolution because of the void growth. This study presents an enhanced damage model that improves the accuracy of the failure simulation of defected structures by adding a parameter that considers stiffness degradation according to void growth to the damage model based on the fracture strain. Therefore, loading-unloading tests were conducted and the damage index of fracture was identified using a three-dimensional digital image correlation system. The failure simulation results using the proposed damage model were compared with experimental, such as notched tensile, SENT, and full-scale burst tests.

The Precise Determination of the Johnson–Cook Material and Damage Model Parameters and Mechanical Properties of an Aluminum 7068-T651 Alloy

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
B. Bal ◽  
K. K. Karaveli ◽  
B. Cetin ◽  
B. Gumus
Keyword(s):  
Mechanical Properties ◽  
Strain Rate ◽  
Physical Simulation ◽  
Damage Model ◽  
Rolling Direction ◽  
Stress Triaxiality ◽  
Material Model ◽  
Tensile Tests ◽  
Model Parameters ◽  
Element Analysis

Al 7068-T651 alloy is one of the recently developed materials used mostly in the defense industry due to its high strength, toughness, and low weight compared to steels. The aim of this study is to identify the Johnson–Cook (J–C) material model parameters, the accurate Johnson–Cook (J–C) damage parameters, D1, D2, and D3 of the Al 7068-T651 alloy for finite element analysis-based simulation techniques, together with other damage parameters, D4 and D5. In order to determine D1, D2, and D3, tensile tests were conducted on notched and smooth specimens at medium strain rate, 100 s−1, and tests were repeated seven times to ensure the consistency of the results both in the rolling direction and perpendicular to the rolling direction. To determine D4 and D5 further, tensile tests were conducted on specimens at high strain rate (102 s−1) and temperature (300 °C) by means of the Gleeble thermal–mechanical physical simulation system. The final areas of fractured specimens were calculated through optical microscopy. The effects of stress triaxiality factor, rolling direction, strain rate, and temperature on the mechanical properties of the Al 7068-T651 alloy were also investigated. Damage parameters were calculated via the Levenberg–Marquardt optimization method. From all the aforementioned experimental work, J–C material model parameters were determined. In this article, J–C damage model constants, based on maximum and minimum equivalent strain values, were also reported which can be utilized for the simulation of different applications.

scholarly journals ADI 1050-6 Mechanical Behavior at Different Strain Rates and Temperatures

2018 ◽  
Vol 925 ◽  
pp. 196-202 ◽  
Author(s):  
Andrew Ruggiero ◽  
Gianluca Iannitti ◽  
Stefano Masaggia ◽  
Federico Vettore
Keyword(s):  
Strain Rate ◽  
Damage Mechanics ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Continuum Damage Mechanics ◽  
Tensile Tests ◽  
Yield Function ◽  
Strain Rates ◽  
The Continuum

An experimental characterization of the austempered ductile iron ISO 17804/JS/1050-6/S was performed carrying out tensile tests under different strain rates, temperatures and stress triaxiality levels. Then, composing a yield function surface, a hardening relation, and a damage criterion, a constitutive model was developed to describe the salient features of the observed macroscopic response. In particular, the Mohr-Coulomb yield function was selected to account for the pressure effect observed on the yield surface. A new hardening relation was proposed in order to account for both strain rate and temperature effects. The Bonora’s damage model, developed in the framework of the continuum damage mechanics, was adopted to capture the failure condition under different stress triaxiality levels. The damage model was appropriately modified to account for the effect of strain rate and temperature on the failure strain.

A strain-based approach to study interaction between non-coplanar through-thickness edge notches

2018 ◽  
Vol 53 (8) ◽  
pp. 687-698 ◽  
Author(s):  
Kaveh Samadian ◽  
Stijn Hertelé ◽  
Wim De Waele
Keyword(s):  
Brittle Fracture ◽  
Failure Modes ◽  
Structural Integrity ◽  
Equivalent Strain ◽  
Image Correlation ◽  
Combination Rules ◽  
Full Field ◽  
Integrity Assessment ◽  
Double Edge ◽  
Fundamental Insight

Structural integrity assessment procedures to assess the effect of interaction between multiple adjacent flaws normally consist of two stages. First, alignment rules categorize non-coplanar flaws as aligned or non-aligned. Second, combination rules classify aligned flaws as interacting or non-interacting. Although these criteria are applied to different failure modes like brittle fracture, elastic–plastic fracture and plastic collapse, most of them were developed based on linear elastic fracture mechanics for the sake of simplicity. However, there are very limited references available for the technical background of these criteria. This lack of justifying backgrounds becomes more critical when applying these procedures to any other failure modes other than brittle fracture. This article studies the interaction between non-coplanar edge notches in scenarios of large deformation. Hereto, strain patterns are studied through full-field deformation measurements utilizing both experimental and numerical tools. Digital image correlation is used to measure strain during experiments and to verify the finite element analyses. The results show that in addition to the crack driving force, which represents a local response of notches, the global strain distribution within the specimen in terms of strain patterns can be used to probe the interaction between non-coplanar flaws. The authors suggest a novel criterion based on the trajectory of maximum equivalent strain to distinguish between aligned and non-aligned flaws. This study is based on double-edge notched tension specimens and gives a fundamental insight into flaw interaction in failure modes other than brittle fracture.

Void Growth and Coalescence in Porous Plastic Solids With Sigmoidal Hardening

2019 ◽  
Vol 86 (9) ◽  
Author(s):  
Padmeya P. Indurkar ◽  
Shailendra P. Joshi
Keyword(s):  
Void Growth ◽  
Damage Model ◽  
Stress Triaxiality ◽  
Unit Cell ◽  
Porous Solid ◽  
Effective Response ◽  
Porosity Evolution ◽  
Aspect Ratios ◽  
Spherical Voids ◽  
Void Growth And Coalescence

Abstract This paper presents an analysis of void growth and coalescence in isotropic, elastoplastic materials exhibiting sigmoidal hardening using unit cell calculations and micromechanics-based damage modeling. Axisymmetric finite element unit cell calculations are carried out under tensile loading with constant nominal stress triaxiality conditions. These calculations reveal the characteristic role of material hardening in the evolution of the effective response of the porous solid. The local heterogeneous flow hardening around the void plays an important role, which manifests in the stress–strain response, porosity evolution, void aspect ratio evolution, and the coalescence characteristics that are qualitatively different from those of a conventional power-law hardening porous solid. A homogenization-based damage model based on the micromechanics of void growth and coalescence is presented with two simple, heuristic modifications that account for this effect. The model is calibrated to a small number of unit cell results with initially spherical voids, and its efficacy is demonstrated for a range of porosity fractions, hardening characteristics, and void aspect ratios.

OS0410 Evaluation of Stress Triaxiality and Fracture Strain of Automotive Steel Sheet Using Digital Image Correlation

2016 ◽  
Vol 2016.22 (0) ◽  
pp. _OS0410-1_-_OS0410-2_
Author(s):  
Daichi KANAZAWA ◽  
Satoru YONEYAMA ◽  
Kuniharu USHIJIMA ◽  
Junya NAITO ◽  
Shota CHINZEI
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Steel Sheet ◽  
Fracture Strain ◽  
Stress Triaxiality ◽  
Image Correlation ◽  
Automotive Steel

scholarly journals Influence of Strain and Stress Triaxiality on the Fracture Behavior of GB 35CrMo Steel during Hot Tensile Testing

2018 ◽  
Vol 2018 ◽  
pp. 1-11 ◽  
Author(s):  
Zheng Li ◽  
Yajun Zhou ◽  
Sanxing Wang
Keyword(s):  
High Temperature ◽  
Tensile Testing ◽  
Crack Formation ◽  
Fracture Strain ◽  
Stress Triaxiality ◽  
Fracture Morphology ◽  
Tensile Tests ◽  
35Crmo Steel ◽  
Size Growth ◽  
High Temperature Tensile

To better understand cavitation nucleation and crack initiation in 35CrMo steel during high-temperature tensile processing and the effect of stress triaxiality on its fracture behaviors, uniaxial and notch high-temperature tensile tests were performed. The microstructure, fracture morphology, fracture strain, and stress triaxiality of the tested 35CrMo steel were then characterized and discussed. The results showed that crack formation in 35CrMo steel included stages of nucleation, growth, and microcavity aggregation. Scanning electron microscopy and energy-dispersive X-ray spectroscopy demonstrated that crack formation was closely related to the presence of steel inclusions. High-temperature tensile testing of samples with different notch radii showed that the fracture strain of 35CrMo steel was decreased with increasing stress triaxiality, that is, increased stress levels corresponded to decreased material plasticity. In addition, the recrystallization degree was decreased with increased stress triaxiality, and the grain size growth was slowed. The failure of 35CrMo steel occurred via ductile fracture, and low stress triaxiality, and high temperature conditions induced large and deep dimples on the fracture surface.

scholarly journals Failure Prediction for the Tearing of a Pin-Loaded Dual Phase Steel (DP980) Adjusting Guide

2019 ◽  
Vol 9 (24) ◽  
pp. 5460 ◽  
Author(s):  
Seokmoo Hong ◽  
Jinkyoo Kim ◽  
Taehwan Jun
Keyword(s):  
Large Strain ◽  
Damage Model ◽  
Failure Prediction ◽  
Strain Range ◽  
Complex Loading ◽  
Tensile Tests ◽  
Material Behavior ◽  
Image Correlation ◽  
Failure Behavior ◽  
Loading Mode

Owing to their outstanding strength, in recent years, there has been an increased use of advanced high-strength steel (AHSS) sheets in the automotive sector. Their low formability, however, poses a challenge to forming, and failure prediction requires accurate knowledge of its material behavior over a large strain range up to ultimate failure, in order to exploit their full capacity in forming, but also in crash events. For predicting the fracture of an adjusting guide loaded by a pin, first, the force–displacement data are extracted from tensile tests using DP980 specimens of diverse shapes, all of which represent a certain loading mode. Using digital image correlation (DIC), we determine the stress triaxialities corresponding to the diverse loading conditions and establish the triaxiality failure diagram (TFD), which serves as the basis for the generalized incremental stress state-dependent damage model (GISSMO). Then, the damage parameters (necking and failure strains) are determined for each loading mode by reverse engineering-based optimization. Finally, these damage parameters are applied to the adjusting guide, and the numerical results are compared with the experimental data. Comparisons of the external load–displacement curves and the local equivalent strain distributions show that using the damage model with the material parameters obtained in here allows for the accurate prediction of the guide’s failure behavior, and the applicability of GISSMO to complex loading cases.

Buckling Assessment of Carbon Steel Pressure Vessels During PWHT

2018 ◽  
Author(s):  
Shunji Kataoka
Keyword(s):  
Elevated Temperature ◽  
Carbon Steel ◽  
Structural Integrity ◽  
Strain Curve ◽  
Tensile Tests ◽  
Pressure Vessels ◽  
Vertical Position ◽  
Strength Criteria ◽  
Integrity Assessment ◽  
Steel Material

Post weld heat treatment (PWHT) is often applied to welded pressure vessels and piping to increase the mechanical and metallurgical properties. During the PWHT, a pressure component made of a carbon steel to which PWHT is applied, is heated up to the temperature around 620 deg.C with +/− 25 deg.C tolerances and that elevated temperature is kept for 1 to 2 hours. The local PWHT of the vertical pressure vessel is sometimes planned at a construction site with vertical position, because of some restrictions relating to construction, such as limited access route to the vessel location, and limited space large capacity cranes. In the situation, it is important to assure the structural stability during PWHT. Except wind loads, it is considered that the stress applied in the shell during PWHT is usually not significant, however there have been no published strength criteria corresponds to the PWHT conditions. In this paper, the new elevated temperature tensile tests and constant stress creep strain tests of A516-Gr.70, a typical carbon steel material for pressure vessels, are conducted. Several examples of the numerical analysis using isochronous stress strain curve considering creep effect are presented. From the test result, the importance of the consideration of the creep deformation on the structural integrity assessment of PWHT operation is clarified.

Size Effects on Fracture in Uncontained Plasticity Conditions in 304(L) Stainless Steel

2011 ◽  
Author(s):  
Andrew P. Wasylyk ◽  
Andrew H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Plastic Zone ◽  
Crack Growth ◽  
Structural Integrity ◽  
Plastic Zone Size ◽  
Compact Tension ◽  
Specimen Size ◽  
Image Correlation ◽  
Local Approach ◽  
Integrity Assessment

In the structural integrity assessment of structures containing defects, ductile tearing and plastic collapse are treated as competing failure mechanisms. The validity of fracture toughness measurements in test specimens is limited by the development of plasticity ahead of the crack tip. Compact Tension (CT) specimens are commonly used to characterise the ductile fracture toughness. Three sizes of CT specimens (thickness 25, 15 and 10mm) were tested using the unloading compliance technique and the J-Resistance curve characterised. Concurrently, the development of the plastic zone was monitored on the surface of specimens using digital image correlation. This enabled the plastic zone size to be correlated with the evolution of crack growth. It was found that in all specimens no crack growth occurred prior to plastic yielding of the un-cracked ligament on the specimen surface. Furthermore, a reduction in initiation and tearing toughness was observed with reduction in specimen size. The Rice and Tracey local approach was developed to predict the specimen size effect.

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