scholarly journals Elastoplastic Fracture Analysis of the P91 Steel Welded Joint under Repair Welding Thermal Shock Based on XFEM

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1285 ◽  
Author(s):  
Kai Yang ◽  
Yingjie Zhang ◽  
Jianping Zhao
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Thermal Shock ◽  
Power Plants ◽  
Welded Joint ◽  
Welding Process ◽  
Simulation Method ◽  
Fracture Analysis ◽  
P91 Steel ◽  
Repair Welding

P91 steel is a typical steel used in the manufacture of boilers in ultra-supercritical power plants and heat exchangers in nuclear power plants. For the long-term serviced P91 steel pressurized structures, the main failure mode is the welded joint failure, especially the heat affected zone (HAZ) failure. Repair welding technique is an effective method for repairing such local defects. However, the thermal shock composed of high temperature and thermal stress in the repair welding process will pose a critical loading condition for the existing defects near the heat source which cannot be detected by conventional means. So, the evaluation of structural integrity for the welded joint in the thermal-mechanical coupling field is necessary. In this work, the crack propagation law in the HAZ for the P91 steel welded joint was investigated under repair welding thermal loads. The weld repair model of the P91 steel welded joint was established by ABAQUS. The transient temperature field and stress field in repair welding process were calculated by relevant user subroutines and sequential coupling simulation method. The residual stress was determined by the impact indentation strain method to verify the feasibility of the finite element (FE) model and simulation method. In order to obtain the crack propagation path, the elastoplastic fracture analysis of the welded joint with initial crack was performed based on the extended finite element method (XFEM). The influence of different welding linear energy on the crack propagation was analyzed. The results show that the cracks in the HAZ propagate perpendicular to the surface and tend to deflect to the welding seam under repair welding thermal loads. The crack propagation occurs in the early stage of cooling. Higher welding linear energy leads to larger HAZ and higher overall temperature. With the increase of welding linear energy, the length and critical distance of the crack propagation increase. Therefore, low welding linear energy can effectively inhibit the crack propagation in the HAZ. The above calculation and analysis provide a reference for the thermal shock damage analysis of repair welding process, which is of great significance to improving the safety and reliability of weld repaired components.

Dynamic Crack Propagation and Arrest in PWR Pressure Vessel Steel: Interpretation of Experiment With the X-FEM Method

2007 ◽  
Author(s):  
B. Prabel ◽  
S. Marie ◽  
A. Combescure
Keyword(s):  
Finite Element ◽  
Crack Propagation ◽  
Strain Rate ◽  
Thermal Shock ◽  
Crack Growth ◽  
Split Hopkinson Pressure Bar ◽  
Dynamic Crack Propagation ◽  
Dynamic Crack ◽  
Pressure Vessel Steel ◽  
Vessel Steel

In the frame of analysis of the pressure thermal shock in a PWR RVP and the associated R&D activities, some developments are performed at CEA on the dynamic brittle propagation and crack arrest. This paper presents a PhD work on the modeling of the dynamic brittle crack growth. For the analyses, an important experimental work is performed on different geometries using a French RPV ferritic steel: Compact Tension specimens with different thickness, isothermal rings under compression with different positions of the initial defect to study a mixed mode configuration, and a ring submitted to thermal shock. The first part of this paper details the test conditions and main results. To propose an accurate interpretation of the crack growth, a viscous-elastic-plastic dynamic model is used. The strain rate influence is taken into account based on Cowper-Symond’s law (characterization was made from Split Hopkinson Pressure Bar tests). To model the crack propagation in the Finite Element calculation, eXtended Finite Element Method (X-FEM) is used. The implementation of these specific elements in the CEA F.E. software CAST3M is described in the second part of this paper. This numerical technique avoids re-meshing, because the crack progress is directly incorporated in the degrees of freedom of the elements crossed by the crack. The last part of this paper compares the F.E. predictions to the experimental measurements using different criteria. In particular, we focused on a RKR (Ritchie-Knott-Rice) like criterion using a critical principal stress in the front of the crack tip during the dynamic crack extension. Critical stress is found to depend on crack speed, or equivalently on strain rate. Good results are reported concerning predictive simulations.

Influence of Cooling Time t8/5 on Impact Toughness of P460NL1 Steel Welded Joints

2020 ◽  
Vol 1157 ◽  
pp. 154-160
Author(s):  
Simon A. Sedmak ◽  
Mihajlo Aranđelović ◽  
Radomir Jovicic ◽  
Dorin Radu ◽  
Ivica Čamagić
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Impact Energy ◽  
Welded Joint ◽  
Welding Process ◽  
Impact Testing ◽  
Cooling Time ◽  
Initiation And Propagation ◽  
Higher Temperature ◽  
Total Impact

The results of impact testing of welded joint specimens taken from a welded plate made of P460NL1 steel are presented in this paper, and analysed with regards to the cooling time t8/5, that was previously calculated. The aim was to determine how the cooling times that were measured, some of which were below the minimum required values, affected the toughness, in terms of total impact energy and its components, crack initiation and crack propagation energy. In addition, this analysis included the effects of temperatures measured at the opposite ends of the plate during the welding process, since this had also affected the cooling times for each welding pass. After observing the differences in total, crack initiation and propagation energy between the tested specimens taken from different parts of the welded plate, it was determined that the specimens from the part where the higher temperatures were measured had shown better, more uniform results, whereas the average total impact energy for specimens from both groups were very similar. It was also noticed that the ratio of crack propagation to crack initiation was more favourable (greater) in the case of specimens from the second group (with higher temperature), as the values of crack initiation energy decreased slightly and the crack propagation energy increased.

The Fatigue Property Research of Steel Q345 Butt Welded Joint

2014 ◽  
Vol 692 ◽  
pp. 424-427
Author(s):  
Wei Ping Ouyang ◽  
Liang Sheng Chen ◽  
Xiu Dong Xu
Keyword(s):  
Finite Element ◽  
Stress Distribution ◽  
Finite Element Modeling ◽  
Significant Influence ◽  
Welded Joints ◽  
Welded Joint ◽  
Fatigue Property ◽  
Fracture Analysis ◽  
Fatigue Tests ◽  
Fatigue Properties

The fatigue property of the butt welded joint has significant influence to hoisting equipment’s design, manufacture and using safety for its extensive application. This paper conducted a study on the fatigue properties of a series of the most commonly used thickness steel Q345 butt welded joints. Through fatigue tests and fracture analysis, the fatigue pattern and fracture law of the joints were revealed. Combining with the finite element modeling, the all field stress distribution situation was obtained. This has profound reference significance to hoisting machinery research.

Benchmark of Finite Elements and Extended-Finite Elements Methods for Stress Intensity Factors and Crack Propagation

2018 ◽  
Author(s):  
Rémi Lacroix ◽  
Axelle Caron ◽  
Sandrine Dischert ◽  
Hubert Deschanels ◽  
Moïse Pignol
Keyword(s):  
Finite Element ◽  
Stress Intensity ◽  
Finite Elements ◽  
Crack Propagation ◽  
Stress Intensity Factors ◽  
Power Plants ◽  
Classical Case ◽  
Finite Elements Method ◽  
Intensity Factors ◽  
Numerical Predictions

Stress intensity factors (SIFs) are a major feature in regulatory analyses of Nuclear Power Plants (NPP) components, as they allow to rule on the acceptability of defects when compared to a critical experimental value (K1c). Simplified and robust evaluations of SIFs have been provided in major regulations standards for cracks having usual geometries and locations in major components. However, their evaluations still require a significant effort in the case of important deviations of the geometry of cracks regarding the usual semi-elliptical shape, or in the case of specific geometries of components, and specific locations of cracks in components. In these cases, time-consuming Finite Element meshes must be constructed, either manually or using semi-automatical tools, to represent the components and its defect(s). This method can become particularly costly, especially in the case of fatigue crack propagation. The eXtended-Finite Elements Method (X-FEM) has been proposed to overcome this issue. The representation of the defect is carried out by the level-set method, and specific enrichment functions are used to represent the solution near the crack surface and the crack front. This paper proposes a benchmark of numerical predictions of stress intensity factors using SYSTUS software [5]. It will be based on: a) Available analytical solutions; b) Classical Finite Element method; c) EXtended-Finite Elements Method. The classical case of a circular and elliptical crack in a semiinfinite body is first presented. Then the case of a circumferential crack in a valve under a thermo-mechanical loading is analyzed. The accuracy of the different methods is then compared and discussed.

Crack Propagation Calculation for Axial Cracks in Hollow Cylinders Subjected to Thermal Shock

2021 ◽  
Author(s):  
Diego F. Mora M. ◽  
Markus Niffenegger
Keyword(s):  
Fracture Toughness ◽  
Finite Element ◽  
Crack Propagation ◽  
Weight Function ◽  
Thermal Shock ◽  
Initial Crack ◽  
Fe Model ◽  
Simple Method ◽  
Hollow Cylinders ◽  
Fracture Arrest

Abstract The core region of the RPV can be considered a hollow circular cylinder disregarding the geometrical details due to nozzles. This contribution investigates the prediction capabilities for crack initiation, crack growth and arrest by means of a rather simple method based on the closed-weight function formula for the stress intensity factor (SIF) for axial cracks in hollow cylinders subjected to thermal shock. The method is explained together with some illustrative examples for real low allow steel used in nuclear applications. In order to obtain the temperature and stress distribution in the cylinder during the thermal shock, a finite element (FE) model is defined to obtain the uncoupled solution of these two fields needed for the closed-weight function. Since the material exhibits a ductile-brittle transition fracture behavior, the temperature-dependent fracture toughness for initiation and for arrest are described using the ASME model. The solution for the SIF is based on linear elastic fracture mechanics (LEFM) and therefore only elastic material is assumed and the crack can propagate in brittle manner. The crack initiates propagation if the SIF value at the crack tip reaches the fracture toughness (for initiation) and propagates unstably in mode I unless the fracture arrest toughness is reached. The quality of the solution is checked by comparing the obtained solution for a “stationary” crack with the calculated extended finite element method (XFEM) solution for the same loading transient. The results show that for some geometries of the cylinder, the crack stops and in some other cases the crack propagates until the cylinder fails. The combined closed-weight function-initiation-growth-arrest (WFF-IGA) algorithm does not require expensive computational resources and gives fast reliable results. The WFF-IGA method provides a powerful and economical way to predict the crack propagation and arrest of the initial crack. This is an advantage when an optimization of the structure is needed.

Modeling of Welding Process and Allied Technologies

2018 ◽  
Vol 769 ◽  
pp. 323-328
Author(s):  
Natalia Astafeva
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Welding Process ◽  
Simulation Method ◽  
The Finite Element Method ◽  
Program Complex ◽  
Weld Joints ◽  
Welding Technology ◽  
Alloy Weld ◽  
Element Method

The paper deals with the simulation technique of Al-Mg-Si alloy weld joints. Complexity of welding is due to the fact that a massive piece is jointed to stamped blanks-package. The main phases of the welding process modeling in a program complex based on the finite element method are considered. The efficiency of use of the computer simulation method for developing the welding technology and determining the method of fixing the parts is shown. Keywords: TIG welding, welding simulations, heat transfer, Sysweld program, the finite element method (FEM).

Finite Element Analysis of Residual Stresses in TT-Welded Joint of a Fixed Jacket Platform

2006 ◽  
Author(s):  
Kh. Rostami ◽  
A. R. M. Gharabaghi ◽  
M. R. Chenaghlou ◽  
A. Arablouei
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Thermal Stresses ◽  
Welded Joint ◽  
Welding Process ◽  
Element Analysis ◽  
Welded Steel ◽  
Buckling Strength ◽  
Structural Distortions ◽  
Weld Toe

Welded steel tubular joints are the kind of connections used extensively in the construction of fixed jacket platforms. The welding process creates considerable tensile residual stresses near the toe of TT-joint due to the rapid cooling and contraction of final welding layers. Welding produces thermal stresses that cause structural distortions, which influence the buckling strength of the structure. In this study thermal elasto-plastic analysis is carried out using ANSYS finite element techniques to evaluate the thermo-mechanical behavior and the residual stresses of the TT-joint. Moreover, the technique of element birth and death is employed to simulate the weld filler variation with time in TT-joint. The results show the considerable tensile residual stress near the weld toe that it may cause crack initiation in this region and threats the fatigue life of joint.

A Review of the Extended Finite Element for Fracture Analysis of Structures

2013 ◽  
Vol 444-445 ◽  
pp. 96-102 ◽  
Author(s):  
Liang Wu ◽  
Li Xing Zhang ◽  
Ya Kun Guo
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Crack Propagation ◽  
Degrees Of Freedom ◽  
Numerical Procedure ◽  
Partition Of Unity ◽  
Fracture Analysis ◽  
Extended Finite Element ◽  
Computational Fracture Mechanics ◽  
Element Method

The extended finite element method (X-FEM) is reviewed and some new developments for fracture analysis of structures is presented. The X-FEM is an extension to the classical finite element method (FEM), using the concepts of partition of unity and meshless approaches. It is specifically designed to improve the performance of the conventional finite element method, while keeping the computational costs at an acceptable level, and avoiding the cumbersome remeshing of FEM in crack propagation problems. The simplicity, flexibility in handling several cracks and crack propagation patterns on a fixed mesh, and the level of accuracy with minimum additional degrees of freedom have transformed X-FEM into the most efficient numerical procedure in the arena of computational fracture mechanics.

Effect of Thermal Input on Finite Element Predictions of Welding Residual Stresses

2011 ◽  
Vol 399-401 ◽  
pp. 1976-1983
Author(s):  
Ai Hui Wu ◽  
Stavros Syngellakis ◽  
B. G. Mellor
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Welded Joint ◽  
Welding Process ◽  
Mechanical Analysis ◽  
Two Dimensional ◽  
Distribution Modelling ◽  
Element Simulation ◽  
Key Factor ◽  
Dimensional Finite Element

A two-dimensional finite element simulation of a welding process is developed for predicting temperature histories and residual stresses in a structural steel butt-welded joint. The purpose of the simulation presented in this paper is the assessment of the effect of uncertainties in thermal material, loading and constraint input on both the thermal and mechanical analysis predictions. The model is validated by comparison with previously welded and tested specimen with published residual stresses measurements. Residual stress results are not sensitive to the thermal analysis input even if the latter has significant influence on temperature distribution. Modelling boundary conditions for both thermal and stress analyses, was identified as a key factor affecting predictions of residual stresses and distortion.

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