Three-Dimensional Thermo-Elastic-Plastic Finite Element Method Modeling for Predicting Weld-Induced Residual Stresses and Distortions in Steel Stiffened-Plate Structures

The objective of the present paper is to develop nonlinear finite element method models for predicting the weld-induced initial deflection and residual stress of plating in steel stiffened-plate structures. For this purpose, three-dimensional thermo-elastic-plastic finite element method computations are performed with varying plate thickness and weld bead length (leg length) in welded plate panels, the latter being associated with weld heat input. The finite element models are verified by a comparison with experimental database which was obtained by the authors in separate studies with full scale measurements. It is concluded that the nonlinear finite element method models developed in the present paper are very accurate in terms of predicting the weld-induced initial imperfections of steel stiffened plate structures. Details of the numerical computations together with test database are documented.

Finite element analysis on temperature field and residual stress of welding assembly for I-beam and end-plate

Based on full scale model of 1-beam and end-plate welding assembly with medium plate, welding temperature field and residual stress were simulated, infrared thermometers were employed to measure the real-time temperature Jbr verification purposes. Results show that the measured thermal cycle curves match well with the simulation result. Simulation results of welding residual stress indicate that the values of longitudinal and transverse stress on the upper surface of the plate are higher than the normal stress; higher tensile stresses exist at the end of the web weld toes and in the central area of the flange weld toes. The dangerous zones are located at the central areas of weld toes of the flange welds and near weld toes of the web welds.

3D Finite Element Numerical Simulation of Residual Stresses on Electron Beam Welded BT20 Plates

A three-dimensional finite-element model (FEM) used for calculating electron beam (EB) welding temperature and stresses fields of thin plates of BT20 titanium has been developed in which the nonlinear thermophysical and thermo-mechanical properties of the material has been considered. The welding temperature field, the distributions of residual stresses in as-welded (AW) and electron beam local post-weld heat treatment (EBLPWHT) conditions have been successfully simulated. The results show that: (1) In the weld center, the maximum magnitude of residual tensile stresses of BT20 thin plates of Ti alloy is equal to 60%- 70% of its yield strength σs. (2) The residual tensile stresses in weld center can be even decreased after EBLPWHT and the longitudinal tensile stresses are decreased about 50% compared to joints in AW conditions. (3) The numerical calculating results of residual stresses by using FEM are basically in agreement with the experimental results. Combined with numerical calculating results, the effects of electron beam welding and EBLPWHT on the distribution of welding residual stresses in thin plates of BT20 have been analyzed in detail.

STRESS FIELD ANALYSIS OF EXTRA-HEIGHT FORGING DIE USING FINITE ELEMENT METHOD

ＴｈｅｅｘｔｒａｈｅｉｇｈｔｆｏｒｇｉｎｇｄｉｅｉｎＳｏｕｔｈｅｗｅｓｔＡｌｕｍｉｎｉｕｍＦａｂｒｉｃａｔｉｏｎＰｌａｎｔｉｓａｓｐｅｃｉａｌｄｉｅｆｏｒｍａｋｉｎｇａｒｍａｍｅｎｔａｎｄｓｐｅｃｉａｌｃｉｖｉｌｐｒｏｄｕｃｔｓｉｎＣｈｉｎａ．Ａ...

Three-dimensional finite element analysis of process-induced residual stress in resin transfer molding process

A three-dimensional finite element analysis of process-induced residual stress in resin transfer molding (RTM) process is presented. The finite element method (FEM) was employed to solve the coupled equations involved in the transient heat transfer and the cure kinetics of the resin, and the distributions of internal temperature and cure degree of the composite at any instant time were obtained. The self-consistent field micro-mechanics model was used to predict the cure-dependent mechanical properties of the composites. Thermal expansion and cure shrinkage were included in the analysis. The thermo-elastic mechanical governing equations were solved using the incremental stress-strain relationship based FEM and the residual stress development was predicted. The present results were validated by the comparisons with the pertinent literature. The numerical example of a half cylinder was presented. The results show that it is necessary to carry out the three-dimensional analysis due to the complex distributions of temperatures, cure degrees and process-induced stress for thick parts, which can be predicted at any point within composite structures in the present analysis.

Genetic algorithm-finite element method inversion of the factors determining the recent tectonic stress field of part of East Asia area

Genetic algorithm finite element method (GA FEM) is applied to the study of tectonic stress field of part of East Asia area. From the observed stress distribution, 2 D elastic plane stress inversion is made to deduce the boundary forces and investigate controlling factors. It is suggested that the continent continent collision is the dominant factor controlling the Chinese tectonic stress field. The ocean continent convergence along the subduction zone is an important factor. There exists tensile boundary force along the marginal sea.

Finite element analysis of welding residual stress of aero engine blisk by controlling heat input

In order to improve aero engine performance, it is necessary to reduce the welding residual stress of aero engine blisk. In this paper, finite element method was employed to simulate electron beam welding process of blisk, in accordance with the deducing formula（ p = kh ） , the heat input is changed with the weld depth to control welding residual stress of blisk. The calculation results show that welding residual stress of blisk can be controlled effectively by reducing the heat input on the conditions of meeting the demand of weld penetration and guaranteeing the welding quality, a new theoretical method and some numerical data are provided for controlling welding residual stress of blisk.

Finite Element Simulation of Residual Stress Determination Based on Spherical Indentation Accumulation Morphology

The introduction of residual stress during the processing of materials has an important impact on the properties of the materials, so it is important to accurately measure the residual stress of the material. This paper established a finite element model of spherical indentation under the action of non-equivalent biaxial residual stress. Then we extracted the full-field accumulation state near the indentation under different stress states from the simulation results and summarized the pile height distribution near the indentation under different stress states. From the simulation, we found that the maximum pile-up height near the indentation point presented a regular trend.

Finite element analysis on stresses field of normalized layer thickness within ceramic coating on aluminized steel

Multilayer ceramic coatings were fabricated on steel substrate using a combined technique of hot dipping aluminum(HDA) and plasma electrolytic oxidation(PEO). A triangle of normalized layer thickness was created for describing thickness ratios of HDA/PEO coatings. Then, the effect of thickness ratio on stresses field of HDA/PEO coatings subjected to uniform normal contact load was investigated by finite element method. Results show that the surface tensile stress is mainly affected by the thickness ratio of Al layer when the total thickness of coating is unchanged. With the increase of Al layer thickness, the surface tensile stress rises quickly. When Al2O3 layer thickness increases, surface tensile stress is diminished. Meanwhile, the maximum shear stress moves rapidly towards internal part of HDA/PEO coatings. Shear stress at the Al2O3 /Al interface is minimal when Al2O3 layer and Al layer have the same thickness.

Finite Element Analysis on Plane Stress Crack Growth in a Power-Law Hardening Material

Aim To determine numerically the field characteristics in the vied at the tip of a place crack growing steadily in a power-law hardening material. Meteods. Methods on the Euler mode and small-scale yield assumption, the numerical results were given by nonlinear finite element analysis. Results The numerical results of the shape of the active plastic sone, the angular distribution of stresseses and Clack tip opening displacement (CTOD) in the vicinity at the hp of the steadily groWing CraCk are determined. Conclusion The comparison between the numerical results given by the present wort and those given by analytic asymptotic analysis shows that the present work reached a very high accuracy.

Residual stress with asymmetric spray quenching for thick aluminum alloy plates

Solution and quenching heat treatments are generally carried out in a roller hearth furnace for large-scale thick aluminum alloy plates.However,the asymmetric or uneven spray water flow rate is inevitable under industrial production conditions,which leads to an asymmetric residual stress distribution.The spray quenching treatment was conducted on self-designed spray equipment,and the residual stress along the thickness direction was measured by a layer removal method based on deflections.Under the asymmetric spray quenching condition,the subsurface stress of the high-flow rate surface was lower than that of the low-flow rate surface,and the difference between the two subsurface stresses increased with the increase in the difference in water flow rates.The subsurface stress underneath the surface with a water flow rate of 0.60 m^(3)/h was 15.38 MPa less than that of 0.15 m^(3)/h.The simulated residual stress by finite element(FE)method of the high heat transfer coefficient(HTC)surface was less than that of the low HTC surface,which is consistent with the experimental results.The FE model can be used to analyze the strain and stress evolution and predict the quenched stress magnitude and distribution.

Method for Measuring Residual Stresses Induced by Boring in Internal Surface of Tube and Its Validation with XRD Method

Residual stresses can have a strong effect on the usability of machined parts,and the X-ray diffraction(XRD)measuring equipment,which is commonly used to measure residual stresses,is very expensive.This paper presents a method of measuring the residual stresses induced by boring in the internal surface of a tube with much cheaper equipment.The method,called the strain-based method is mainly based on the strains measured on the external surface of the tube.It is proposed on the basis of the very long tube assumption.The finite element method(FEM)analysis is thus used to validate the length of the tube.Guided by the FEM results,an appropriate length of the tube is chosen,and the residual stresses are obtained from both the strain-based method and the XRD method.Stress profiles obtained from both two methods are compared.The comparison result indicates that the profiles of the two methods agree well with each other.Therefore,it can be concluded that the accuracy of the strain-based method is high enough,and it can be applied to residual stress measurement in practice.

Finite Element Numerical Simulation and PIV Measurement of Flow Field inside Metering-in Spool Valve

The finite element method （FEM） and particle image velocimetry （PIV） technique are utilized to get the flow field along the inlet passage, the chamber, the metering port and the outlet passage of spool valve at three different valve openings. For FEM numerical simulation, the stream function ψ-vorticity ω forms of continuity and Navier-Stokes equations are employed and FEM is applied to discrete the equations. Homemade simulation codes are executed to compute the values of stream function and vorticity at each node in the flow domain, then according to the correlation between stream function and velocity components, the velocity vectors of the whole field are calculated. For PIV experiment, pulse Nd： YAG laser is exploited to generate laser beam, cylindrical and spherical lenses are combined each other to produce 1.0 mm thickness laser sheet to illuminate the object plane, Polystyrene spherical particle with diameter of 30-50 μm is seeded in the fluid as a tracing particles, Kodak ES 1.0 CCD camera is employed to capture the images of interested, the images are processed with fast Fourier transform （FFT） cross-correlation algorithm and the processing results is displayed. Both results of numerical simulation and PIV experimental show that there are three main areas in the spool valve where vortex is formed. Numerical results also indicate that the valve opening have some effects on the flow structure of the valve. The investigation is helpful for qualitatively analyzing the energy loss, noise generating, steady state flow forces and even designing the geometry structure and flow passage.

FEM SIMULATION OF RESIDUAL STRESSES INDUCED BY LASER SHOCK WITH OVERLAPPING LASER SPOTS

The finite element method is presented to attain the numerical simulation of the residual stresses field in the material treated by laser shock processing. The distribution of residual stresses generated by a single laser shock with square and round laser spot is predicted and validated by experimental results. With the Finite Element Method （FEM） model, effects of different overlapping rates and impact sequences on the distribution of residual stresses are simulated. The results indicate that： （1） Overlapping laser shock can increase the compressive residual stresses. However, it is not effective on the growth of plastically affected depth; （2） Overlapping rate should be optimized and selected carefully for the large area treatment. Appropriate overlapping rate is beneficial to obtain a homogeneous residual stress field; （3） The impact sequence has a great effect on the residual stress field. It can greatly attenuate the phenomenon of the “residual stress hole” to obtain a homogeneous residual stress field.

Evolution of residual stress field in 6N01 aluminum alloy friction stir welding joint

Based on the characteristics of friction stir welding( FSW) and Coulomb friction work theory,the residual stresses field of FSW joints of 6 N01 aluminum alloy( T5),which was used in high speed train,were calculated by using the ANSYS finite element software. During the FEM calculation,the dual heat source models namely the body heat source and surface heat source were used to explore the evolution law of the welding process to the residual stress field. The method of ultrasonic residual stress detecting was used to investigate the residual stresses field of the 6 N01 aluminum alloy FSW joints. The results show that the steady-state temperature of 6 N01 aluminum alloy during FSW is about 550 ℃,and the temperature mutates at the beginning and at end of welding. The longitudinal residual stress σ_x is the main stress,which fluctuates in the range of-25 to 242 MPa. Moreover,the stress in the range of shaft shoulder is tensile stress that the maximum tensile stress is 242 MPa,and the stress in the outside of shaft shoulder is compressive stress that the maximum compressive stress is 25 MPa. The distribution of the tensile stress in the welding nugget zone( WNZ) is obviously bimodal,and the residual stress on the advancing side is higher than that on the retreating side. With the increasing of the welding speed,the maximum temperature decreased and the maximum residual stress decreased when the pin-wheel speed kept constant. With the increasing of the pin-wheel speed,the maximum temperature of the joint increased and the maximum residual stress increased when the welding speed was constant. The experimental results were in good agreement with the finite element results.

Shakedown Criterion Employing Actual Residual Stress Field and Its Application in Numerical Shakedown Analysis

Construction of the static admissible residual stress field and searching the optimal field are key tasks in the shakedown analysis methods applying the static theorem. These methods always meet dimension obstacles when dealing with complex problems. In this paper, a novel shakedown criterion is proposed employing actual residual stress field based on the static shakedown theorem. The actual residual stress field used here is produced under a specified load path, which is a sequence of proportional loading and unloading from zero to all the vertices of the given load domain. This ensures that the shakedown behavior in the whole load domain can be determined based on the theorem proposed by K6nig. The shakedown criterion is then implemented in numerical shakedown analysis, The actual residual stress fields are calculated by incremental finite element elastic-plastic analysis technique for finite deformation under the specified load path with different load levels. The shakedown behavior and the shakedown limit load are determined according to the proposed criterion. The validation of the criterion is performed by a benchmark shakedown example, which is a square plate with a central hole under biaxial loading. The results are consistent with existing results in the literatures and are validated by full cyclic elastic-plastic finite element analysis. The numerical shakedown analysis applying the proposed criterion avoids processing dimension obstacles and performing full cyclic elastic-plastic analysis under arbitrary load paths which should be accounted for appearing. The effect of material model and geometric changes on shakedown behavior can he considered conveniently.

Finite element simulation of stress intensity factors in elastic-plastic crack growth

A finite element program developed elastic-plastic crack propagation simulation using Fortran language. At each propagation step, the adaptive mesh is automatically refined based on a posteriori h-type refinement using norm stress error estimator. A rosette of quarter-point elements is then constructed around the crack tip to facilitate the prediction of crack growth based on the maximum normal stress criterion and to calculate stress intensity factors under plane stress and plane strain conditions. Crack was modelled to propagate through the inter-element in the mesh. Some examples are presented to show the results of the implementation.

Modified Layer-Removal Method for Measurement of Residual Stress in Pre-stretched Aluminium Alloy Plate

Residual stress is one of the factors affecting the machining deformation of monolithic structure parts in the aviation industry. Thus, the studies on machining deformation rules induced by residual stresses largely depend on correctly and efficiently measuring the residual stresses of workpieccs. A modified layer-removal method is proposed to measure residual stress by analysing the characteristics of a traditional, layer-removal method. The coefficients of strain release are then deduced according to the simulation results using the finite element method （FEM）. Moreover, the residual stress in a 7075T651 aluminium alloy plate is measured using the proposed method, and the results are then analyzed and compared with the data obtained by the traditional methods. The analysis indicates that the modified layer-removal method is effective and practical for measuring the residual stress distribution in pre-stretched aluminium alloy plates.

Thermo-hydro-mechanical-air coupling finite element method and its application to multi-phase problems

In this paper, a finite element method （FEM）-based multi-phase problem based on a newly proposed thermal elastoplastic constitutive model for saturated/unsaturated geomaterial is discussed. A program of FEM named as SOFT, adopting unified field equations for thermo-hydro-mechanical-air （THMA） behavior of geomaterial and using finite element-finite difference （FE-FD） scheme for so/l-water-air three-phase coupling problem, is used in the numerical simulation. As an application of the newly proposed numerical method, two engineering problems, one for slope failure in unsaturated model ground and another for in situ heating test related to deep geological repository of high-level radioactive waste （HLRW）, are simulated. The model tests on slope failure in unsaturated Shirasu ground, carried out by Kitamura et al. （2007）, is simulated in the framework of soil-water-air three-phase coupling under the condition of constant temperature. While the in situ heating test reported by Munoz （2006） is simulated in the same framework under the conditions of variable temperature hut constant air pressure.

Study on Plasticity Modification for Measuring High Residual Stress by Hole-Drilling Method

Hole-drilling method is a commonly used method for measuring residual stress. The calibration coefficients in ASTM E837-13 a would cause large errors due to the plasticity deformation of materials. In the study, calibration coefficients were modified in the plasticity deformation stage based on the distortion energy theory. The calibration experiment of calibration coefficients was simulated by the finite element model, and the plasticity modification formulas of 7075 aluminum alloy were obtained. From the results of uniaxial tensile loading test, the measuring errors of high residual stress are significantly reduced from-4.071%～53.440% to-5.140% ～ 0.609% after the plasticity modification. This work provides an effective way to expand the application of hole-drilling method.