Simplified FEA Models in the Analysis of the Redistribution of Beneficial Compressive Stresses in Welds During Cyclic Loading

2018 ◽  
Author(s):  
B. L. Josefson ◽  
J. Alm ◽  
J. M. J. McDill
Keyword(s):  
Cyclic Loading ◽  
Residual Stresses ◽  
Compressive Stress ◽  
Welding Process ◽  
Plastic Behavior ◽  
Element Analysis ◽  
Compressive Stresses ◽  
Static Contact ◽  
Weld Toe ◽  
Compressive Residual Stresses

The fatigue life of welded joints can be improved by modifying the weld toe geometry or by inducing beneficial compressive residual stresses in the weld. However, in the second case, the induced compressive residual stresses may relax when the welded joint is subjected to cyclic loading containing high tensile or compressive stress peaks. The stability of induced compressive stresses is investigated for a longitudinal gusset made of a S355 steel. Two methods are considered; either carrying out a high frequency mechanical impact (HFMI) treatment after welding or alternatively using low transformation temperature (LTT) electrodes during welding. The specimen is then subjected to a cyclic loading case with one cycle with a tensile peak (with magnitude reaching the local yield stress level) followed by cycles with constant amplitude. A sequential finite element analysis (FEA) is performed thereby preserving the history of the elasto-plastic behavior. Both the welding process and the HFMI treatment are simulated using simplified approaches, i.e., the welding process is simulated by applying a simplified thermal cycle while the HFMI treatment is simulated by a quasi-static contact analysis. It is shown that using the simplified approaches to modelling both the welding process and HFMI treatment gives results that correlate qualitatively well with the experimental and FEA data available in the literature. Thus, for comparison purposes, simplified models may be sufficient. Both the use of the HFMI treatment and LTT electrodes give approximately the same compressive stress at the weld toe but the extent of the compressive stress zone is deeper for HFMI case. During cyclic loading it is shown that the beneficial effect of both methods will be substantially reduced if the test specimen is subjected to unexpected peak loads. For the chosen load sequence, with the same maximum local stress at the weld toe, the differences in stress curves of the HFMI-treated specimen and that with LTT electrodes remain. While the LTT electrode gives the lowest (compressive) stress right at the well toe, it is shown that the overall effect of the HFMI treatment is more beneficial.

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.

scholarly journals Thermal Effects on Surface and Subsurface Modifications in Laser-Combined Deep Rolling

2021 ◽  
Vol 5 (2) ◽  
pp. 55
Author(s):  
Robert Zmich ◽  
Daniel Meyer
Keyword(s):  
Surface Layer ◽  
Residual Stresses ◽  
Thermal Loads ◽  
Deep Rolling ◽  
Mechanical Loads ◽  
Thermomechanical Process ◽  
Compressive Stresses ◽  
New Process ◽  
Negative Effect ◽  
Compressive Residual Stresses

Knowledge of the relationships between thermomechanical process loads and the resulting modifications in the surface layer enables targeted adjustments of the required surface integrity independent of the manufacturing process. In various processes with thermomechanical impact, thermal and mechanical loads act simultaneously and affect each other. Thus, the effects on the modifications are interdependent. To gain a better understanding of the interactions of the two loads, it is necessary to vary thermal and mechanical loads independently. A new process of laser-combined deep rolling can fulfil exactly this requirement. The presented findings demonstrate that thermal loads can support the generation of residual compressive stresses to a certain extent. If the thermal loads are increased further, this has a negative effect on the surface layer and the residual stresses are shifted in the direction of tension. The results show the optimum range of thermal loads to further increase the compressive residual stresses in the surface layer and allow to gain a better understanding of the interactions between thermal and mechanical loads.

scholarly journals Validation of Welding Simulations Using Thermal Strains Measured with DIC

2011 ◽  
Vol 70 ◽  
pp. 129-134 ◽  
Author(s):  
Maarten De Strycker ◽  
Pascal Lava ◽  
Wim Van Paepegem ◽  
Luc Schueremans ◽  
Dimitri Debruyne
Keyword(s):  
Residual Stresses ◽  
Cross Section ◽  
Circular Cross Section ◽  
Welding Process ◽  
Weld Bead ◽  
Image Correlation ◽  
Steel Tubes ◽  
Element Analysis ◽  
Strain Evolution ◽  
The Cross

Residual stresses can affect the performance of steel tubes in many ways and as a result their magnitude and distribution is of particular interest to many applications. Residual stresses in cold-rolled steel tubes mainly originate from the rolling of a flat plate into a circular cross section (involving plastic deformations) and the weld bead that closes the cross section (involving non-uniform heating and cooling). Focus in this contribution is on the longitudinal weld bead that closes the cross section. To reveal the residual stresses in the tubes under consideration, a finite element analysis (FEA) of the welding step in the production process is made. The FEA of the welding process is validated with the temperature evolution of the thermal simulation and the strain evolution for the mechanical part of the analysis. Several methods for measuring the strain evolution are available and in this contribution it is investigated if the Digital Image Correlation (DIC) technique can record the strain evolution during welding. It is shown that the strain evolution obtained with DIC is in agreement with that found by electrical resistance strain gauges. The results of these experimental measuring methods are compared with numerical results from a FEA of the welding process.

Numerical Simulation of Welding Induced Residual Stresses in a Circular Hollow Section T-Joint

2006 ◽  
Author(s):  
Suraj Joshi ◽  
Cumali Semetay ◽  
John W. H. Price ◽  
Herman Nied
Keyword(s):  
Residual Stresses ◽  
Cross Sections ◽  
Mining Industry ◽  
Welding Process ◽  
Civil Structures ◽  
Element Analysis ◽  
Hollow Section ◽  
3 Dimensional ◽  
Circular Hollow Section ◽  
Intense Heat

Heavily welded circular hollow cross sections (CHS) are a common feature in civil structures such as draglines used in the mining industry and other off-shore structures. The sheer mass of the weldment and the application of intense heat generated during the welding process give birth to significant residual stresses in the structure. Often, residual stresses are high enough to act to accelerate factors such as corrosion, crack growth and fatigue. The objective of this research investigation was to predict welding generated residual stresses in a typical CHS T-Joint using Sysweld+, a welding Finite Element Analysis software. The T-joint is the first of the four lacings welded on to the main chord of a BE 1370 mining dragline cluster (designated All) of a type which is often used in the mining industry in Australia. This work examines a massive 3-dimensional geometry, which is on a much larger scale than those examined in existing studies. The paper presents the results of the simulation of residual stresses generated during the welding process in a single weld pass and compares them with the approach used in the commonly used document R6-Revision 4, Assessment of the Integrity of Structures Containing Defects.

Fracture of Ceramics with Near Surface Gradient Residual Stresses

2007 ◽  
Vol 333 ◽  
pp. 97-106
Author(s):  
Marc Anglada
Keyword(s):  
Fracture Toughness ◽  
Residual Stresses ◽  
Graded Materials ◽  
Near Surface ◽  
Apparent Fracture Toughness ◽  
Surface Gradient ◽  
Compressive Stresses ◽  
Small Cracks ◽  
Monolithic Ceramics ◽  
Compressive Residual Stresses

The fracture toughness and strength of ceramics can be improved with respect to monolithic ceramics by developing graded materials as laminates composed of periodic alternating layers of one material separated by layers of a second material. The second layer must contain residual compressive stresses which are induced during densification because of differential thermal contraction of the layers. The overall residual stresses increase the apparent fracture toughness of the laminate. However, most deleterious natural flaws and most of the damage induced in service by the environment, contact loading, wear, etc, are small cracks on the surface of the outer layer, so that the effect of the laminate residual stresses on these cracks should be rationalised to understand their behaviour. This work presents an analysis of the influence of the gradient residual stresses on the behaviour of surface cracks under bending and indentation in materials with outer layers either with tensile or compressive residual stresses.

Estimation of Residual Stresses in Steel Welded Joints Using Three Dimensional Finite Element Analysis

2018 ◽  
Author(s):  
Shivdayal Patel ◽  
B. P. Patel ◽  
Suhail Ahmad
Keyword(s):  
Residual Stress ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Residual Stresses ◽  
Boundary Conditions ◽  
Welding Speed ◽  
Welded Joints ◽  
Plate Thickness ◽  
Welding Process ◽  
Element Analysis

Welding is one of the most used joining methods in the ship industry. However, residual stresses are induced in the welded joints due to the rapid heating and cooling leading to inhomogenously distributed dimensional changes and non-uniform plastic and thermal strains. A number of factors, such as welding speed, boundary conditions, weld geometry, weld thickness, welding current/voltage, number of weld passes, pre-/post-heating etc, influence the residual stress distribution. The main aim of this work is to estimate the residual stresses in welded joints through finite element analysis and to investigate the effects of boundary conditions, welding speed and plate thickness on through the thickness/surface distributions of residual stresses. The welding process is simulated using 3D Finite element model in ABAQUS FE software in two steps: 1. Transient thermal analysis and 2. Quasi-static thermo-elasto-plastic analysis. The normal residual stresses along and across the weld in the weld tow region are found to be significant with nonlinear distribution. The residual stresses increase with the increase in the thickness of the plates being welded. The nature of the normal residual stress along the weld is found to be tensile-compressive-tensile and the nature of normal residual stress across the weld is found to be tensile along the thickness direction.

Engineering Critical Assessment of Post Weld Heat Treatment for Full-Encirclement Tees Greater Than 1.25 Inches

2019 ◽  
Author(s):  
Kolton Landreth ◽  
Qi Li ◽  
Raghav Marwaha
Keyword(s):  
Heat Treatment ◽  
Residual Stresses ◽  
Welding Process ◽  
Post Weld Heat Treatment ◽  
Critical Assessment ◽  
Material Strength ◽  
Mechanical Reinforcement ◽  
Element Analysis ◽  
Pipeline Design ◽  
Weld Heat

Abstract Full-encirclement split tee fittings for hot tapping and plugging (HT&P) wrap completely around the pipeline and are welded in place. The welded joint provides mechanical reinforcement of the pipe and branch. When full-encirclement hot tap tees are welded to pipelines 24 inches in diameter or larger, the header must often be at least 1.25 inches thick to pass the required calculations for reinforcement. This means the joint will require post weld heat treatment (PWHT) according to ASME B31.8 and CSA Z662. However, PWHT can be extremely dangerous and impractical, potentially elevating temperature to the point where material strength of the pressurized pipeline is compromised. An engineering critical assessment per ASME FFS-1/API 579 indicated PWHT may not be required for a full-encirclement hot tap tee over 1.25 inches thick. Specifically, research showed that the residual stresses developed during the welding process may not limit the design of a full-encirclement tee or lead to shorter pipeline design life. This paper illustrates how a “more rigorous analysis” per paragraph 802.2.2[b] of ASME B31.8 and paragraph 4.3.12.2 of CSA Z662 may help operators avoid the PWHT requirement. It discusses the finite element analysis (FEA) simulations researchers used to induce residual stresses in a carbon steel fitting. The residual stresses induced in the fitting were used as initial condition for plastic collapse and fatigue evaluations.

A Computational Model of Backlay Welding for Controlling Residual Stresses in Welded Pipes

1981 ◽  
Vol 103 (3) ◽  
pp. 226-232 ◽  
Author(s):  
F. W. Brust ◽  
E. F. Rybicki
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Computational Model ◽  
Welding Process ◽  
Computational Results ◽  
Intergranular Stress Corrosion ◽  
Inner Surface ◽  
Piping Systems ◽  
Intergranular Stress Corrosion Cracking ◽  
Compressive Residual Stresses

Intergranular Stress Corrosion Cracking (IGSCC) has been a problem in Boiling Water Reactor (BWR) piping systems. One method for retarding IGSCC is to eliminate tensile residual stresses at the pipe inner surface in the heat affected zone produced by the welding process. A method called backlay welding can be effective in producing compressive residual stresses at the pipe inner surface. This paper describes a computational model and its use in examining the effectiveness of the backlay welding process. The model has demonstrated an ability to predict weld-induced residual stresses for a variety of pipe sizes and welding conditions. Computational results for backlay welding are in agreement with residual stress data. The mechanisms causing residual stresses and the effect of the number of backlay weld layers on residual stresses are discussed.

Strengthening of wide-flange columns under load

1990 ◽  
Vol 17 (5) ◽  
pp. 835-843 ◽  
Author(s):  
H. Marzouk ◽  
S. Mohan
Keyword(s):  
Finite Element ◽  
Residual Stresses ◽  
Critical Load ◽  
Closed Form Solution ◽  
Welding Process ◽  
Form Solution ◽  
Element Analysis ◽  
Welding Stress ◽  
Existing Structures ◽  
Welding Sequence

The present work deals with formulation of theoretical and analytical methods leading to the development of column strength curves. The formulations were developed for both elastic and inelastic behaviour. Two types of reinforcement have been developed for strengthening the W-shape columns under load. Since the column strength curves are based in part on the magnitude and distribution of residual stresses, it is extremely important to consider the new pattern of residual stresses due to welding process. Also, the welding sequence will affect the magnitude and distribution of residual stresses. Theoretical formulations leading to a closed-form solution for the prediction of critical load were developed for two types of strengthening using the superposition of original residual, new welding, and initial loading stresses. A nonlinear finite element analysis based on the large deformation theory of stability was used to predict the strengthened column critical load. It takes into consideration the effect of cooling residual stresses and new welding residual stresses. The formulations were incorporated with gradual penetration of yielding, the spreading of inelastic zones along the member length, the presence of residual stresses, and strain hardening of the material. Experiments were carried out to determine the actual capacity of strengthened columns. Seven specimens were tested using two and four strengthening plates. The welding stresses were measured through a series of experiments, and it was found that the parabolic distribution is a very close approximation to the actual new welding stress distribution. Key words: reinforcement of steel columns, welding stresses, welding sequence, strengthening of existing structures, buckling, steel plating, finite element.

scholarly journals Long-Term Stability of Residual Stress Improvement by Water Jet Peening Considering Working Processes

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Tadafumi Hashimoto ◽  
Yusuke Osawa ◽  
Shinsuke Itoh ◽  
Masahito Mochizuki ◽  
Kazutoshi Nishimoto
Keyword(s):  
Stress Relaxation ◽  
Residual Stresses ◽  
Microstructure Evolution ◽  
Elevated Temperatures ◽  
Water Jet ◽  
Term Stability ◽  
Long Term Stability ◽  
Compressive Stresses ◽  
Compressive Residual Stresses

To prevent primary water stress corrosion cracking (PWSCC), water jet peening (WJP) has been used on the welds of Ni-based alloys in pressurized water reactors (PWRs). Before WJP, the welds are machined and buffed in order to conduct a penetrant test (PT) to verify the weld qualities to access, and microstructure evolution takes place in the target area due to the severe plastic deformation. The compressive residual stresses induced by WJP might be unstable under elevated temperatures because of the high dislocation density in the compressive stress layer. Therefore, the stability of the compressive residual stresses caused by WJP was investigated during long-term operation by considering the microstructure evolution due to the working processes. The following conclusions were made: The compressive residual stresses were slightly relaxed in the surface layers of the thermally aged specimens. There were no differences in the magnitude of the relaxation based on temperature or time. The compressive residual stresses induced by WJP were confirmed to remain stable under elevated temperatures. The stress relaxation at the surface followed the Johnson–Mehl equation, which states that stress relaxation can occur due to the recovery of severe plastic strain, since the estimated activation energy agrees very well with the self-diffusion energy for Ni. By utilizing the additivity rule, it was indicated that stress relaxation due to recovery is completed during the startup process. It was proposed that the long-term stability of WJP under elevated temperatures must be assessed based on compressive stresses with respect to the yield stress. Thermal elastic–plastic creep analysis was performed to predict the effect of creep strain. After 100 yr of simulated continuous operation at 80% capacity, there was little change in the WJP compressive stresses under an actual operating temperature of 623 K. Therefore, the long-term stability of WJP during actual operation was analytically predicted.

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