SDC99钢淬火过程中应力和组织演变的有限元模拟

为了研究钢铁材料在淬火过程中内部组织和应力的变化,以自主研发的SDC99钢为研究对象,考虑相变潜热的影响,采用有限元方法对偏心圆环的淬火过程进行模拟仿真,并对淬火过程中模型的温度场、应力场和组织场的变化进行分析和研究.结果表明:经实验测定淬火过程中温度场及残余应力的分布与模拟结果吻合较好,偏心圆环上最大残余应力出现在45°及315°位置;模型硬度的分布与其马氏体含量分布趋势一致,模拟的硬度值略小于实测值.     

Effect of post-quench delay on stress relieving by cold compression for the aluminium alloy 7050

The objective of this investigation was to determine the influence of post-quench delays on residual stresses in the heat treatable aluminium alloy 7050, when stress relieved by cold compression. Immersion quenching after solution heat treatment introduces high magnitude residual stresses. These residual stresses can be relieved by the controlled application of post-quench plastic deformation. The effect of a delay between quenching and the application of cold compression has been investigated. During this delay, the aluminium alloy undergoes natural aging, which changes the workhardening behaviour of the alloy during subsequent cold compression. Neutron and X-ray diffraction were used to characterise the residual stresses. It was found that reducing the post-quench delay resulted in lower magnitude residual stresses after cold compression.     

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Abstract

The effect of stress on transformation is studied through a series of dilation experiments. The results obtained are used to modify models of transformation kinetics, transformation plasticity, and elastoplastic constitutive relations so as to predict residual stresses after quenching. Results of the simulation show that the modified models are fit to predict residual stresses after quenching, which agree well with experimental results if both transformation plasticity and stress induced transformation are taken into account.     

Prediction of residual stresses in thermally sprayed steel coatings considering the phase transformation effect

The present study is aimed to propose an elastoplastic bilayer model for prediction of residual stresses in thermally sprayed coatings, in which the effect caused by martensite phase transformation for steel coating materials was taken into account. Closed-form solutions of the curvature and stresses within the substrate and coating are obtained for the plastically deformed structures. Applications of the model for prediction of the twin-wire electric arc sprayed high carbon steel coatings were investigated subsequently. In the application case that a thin coating layer deposited with varying temperatures, the martensite phase transformation has a significant effect on the residual stress, e.g. a lower deposition temperature leads to more amount of martensite transformation and then to a lower level of final stress. The model was also used to predict the stress distribution of high carbon steel coating after quenching heat treatment, and the calculation results were compared with the X-ray residual stress measurements. It is found that the residual stresses on the coating surface obtained from the analytical model are closed to that obtained from the experiments.     

Residual stresses at the surface of automotive suspension springs

This study concentrates on the origins of unfavourable stresses at the surface of silicon-manganese automotive suspension springs. The residual stresses have been investigated at the various stages of the spring manufacturing--quenching, tempering and shot peening. Residual stresses from quenching depend in a complex fashion on the microstructural state of the surface and on the variation of the thermal gradient into the quenched spring wire. Contrary to expectations, oil-quenching of decarburised spring wire results in tensile residual stresses at the surface, while water quenching results in compressive residual stresses. The residual stresses do not disappear after tempering. Moreover the shot peening after quenching and tempering, if not conducted properly, may result in small compressive or even tensile residual stresses at the surface, which severely diminishes the fatigue resistance of the suspension springs.     

模具对复合材料构件固化变形的影响分析

通过光纤光栅的方法实验研究了在热压罐成型工艺过程中, 复合材料构件由金属固化模具与复合材料构件热不匹配导致的沿厚度方向和面内的固化残余应力发展, 得到了固化后残余应力沿构件厚度方向和面内的分布情况, 并分析了该残余应力分布的产生机制以及对构件固化后变形的影响。结果表明: 复合材料与模具之间的热不匹配导致的固化残余应变沿构件厚度方向呈梯度分布, 靠近模具端大于远离模具端, 并且该应变会引起构件固化后的翘曲变形, 变形以沿纤维方向为主。     

7075铝合金循环载荷下残余应力松弛的实验研究

采用淬火和喷砂2种强化工艺引入残余应力,分析循环应力作用下7075铝合金应力松弛现象。基于应力松弛机理讨论了2种不同强化工艺下残余应力松弛规律的异同。结果表明,加载应力状态与大小、残余应力的初始分布和冷作硬化是影响残余应力松弛的主要因素。     

Some comments on residual stresses induced during quenching

The quenching process is known, to induce large residual stresses. These stresses cause difficulty in maintaining close tolerances on the components during manufacture. In the present investigation a simple technique has been developed to measure the residual stresses caused due to quenching of plain carbon steel. The results indicate that largo magnitudes of compressive residual stresses are induced beneath the surface due to the quenching process.     

Residual stresses arising in materials deformed by bending in surface-active media

The distribution of residual stresses in rectangular beams after loading by clear bending in inactive, surface-plasticizing and surface-hardening media was investigated. It was found that the residual stresses in a more plastic structural component are typically opposite in sign to active load stresses, whereas in a harder component they are coincident with the latter. The influence of residual stresses on the point defect distribution in the samples after deformation is discussed.     

Cold rolling influence on residual stresses evolution in heat-treated AA7xxx T-section panels

This article describes a novel cold working method for relaxing residual stresses in extra-long quenched T-section panels. Distortion led by quench-induced residual stresses in components is usually a great concern for the aviation industry. In this study, the influence of cold rolling on the residual stresses in a scale-down quenched AA7050 T-section specimen is experimentally and numerically investigated. An integrated numerical model was built to predict the quenching and the subsequent cold rolling processes. High levels of compressive stress around the surfaces of quenched T-profile specimens and the tensile surface residual stresses (RS) in the quenched and cold rolled specimens were predicted via numerical analysis, the surface stresses magnitude and distribution have, therefore, been quantified via X-ray diffraction (XRD) technique. The deflection of quenched specimens experienced 1.5% and 3% cold rolling was measured as well. In addition, to examine the cold rolling effect on the mechanical properties of T-profile specimens, hardness tests were carried out on quenched and cold rolled T-section specimens. It concludes that with 1.5% cold rolling the residual stresses in the core part of quenched material can be effectively relieved to an extent of lower than 83 MPa, with limited change for the material properties.     

淬火应力场对铝合金厚板固有频率的影响

建立7075铝合金厚板淬火残余应力场数学模型,理论与实验探讨振动时效中淬火残余应力场对板固有频率的影响。结果表明,板尺寸、密度、均匀性等物理材料特性确定时,其固有频率主要受到残余应力场的分布状态影响,且高阶固有频率受残余应力的影响比低阶固有频率大。淬火残余应力场总是增大板的固有频率,振动时效消减或均匀化残余应力的同时,也将降低各阶次固有频率。     

The effects of forging pressure and temperature field on residual stresses in linear friction welded Ti6Al4V joints

Linear friction welding (LFW), as a solid state joining process, has been developed to manufacture and repair blisks in aeroengines. The residual stresses after welding may greatly influence the performance of the welded components. In this paper, the distribution of residual stresses in Ti6Al4V joints after LFW was investigated with numerical simulations. The effects of applied forging pressure and temperature field at the end of the oscillating stages on the residual stresses within the joints were investigated. The results show that, the residual tensile stresses at the welded interface in the y-direction are the largest, while the largest compressive stresses being present at the flash root in the z-direction. Furthermore, the forging pressure and temperature field at the end of the oscillating stages strongly affect the magnitude of the residual stresses. The larger forging pressure produced lower residual stresses in the weld plane in all three directions (x-, y-, and z-directions). Larger variance, σ, which decides the Gaussian distribution of the temperature field, also yields lower residual stresses. There is good agreement between simulation results and experimental data.     

Analysis of the distribution of thermal residual stresses in bonded composite repair of metallic aircraft structures

In this study, the distribution of the thermal residual stresses due to the adhesive curing in bonded composite repair is analysed using the finite element method. The computation of these stresses comprises all components of the structures: cracked plate, composite patch and adhesive layer. In addition, the influence of these residual stresses on the repair performance is highlighted by analysing their effect on the stress intensity factor at the crack tip. The obtained results show that the normal thermal stresses in the plate and the patch are important and the shear stresses are less significant. The level of the adhesive thermal stresses is relatively high. The presence of the thermal stresses increases the stress intensity factor at the crack tip, what reduce the repair performance.     

Analysis of residual stress and distortion resulting from quenching in large low-alloy steel shafts

Abstract

In order to predict residual stresses and distortion caused by quenching in a large low-alloy steel shaft, a computer program based on the finite element method was developed, and uniaxial restraint testing of the transient strain during cooling was carried out. Using the program, the transient stresses occurring during quenching are calculated by a step-by-step procedure, and the effects of transformational behaviour on residual stresses and distortion discussed. The results show that the transient stresses and the transformation affect each other, and that residual stresses and distortion are strongly related to the transformational behaviour.

MST/8     

Multidroplet Impact Model for Prediction of Residual Stresses in Water Jet Peening of Materials

In this article, a multidroplet impact model, proposed for predicting residual stresses induced on materials subjected to water jet peening, is presented. This approach considers the impact pressure distribution due to high-velocity droplets impinging on the material surface instead of stationary pressure distribution for prediction of residual stresses on water jet-peened surfaces. It makes use of Reichardt's theory for predicting the velocity distribution of droplets and liquid impact theory for predicting the impact pressure and duration of impact of high-velocity droplets. For predicting residual stresses on the surface and subsurface of material subjected to water jet peening, finite element modeling approach was adopted by using transient elastoplastic finite element analysis by considering an impingement of a set of droplets in succession to one another over a certain time period after which this pressure is released. The effectiveness of the proposed approach was demonstrated bv comparing the predicted residual stresses with those predicted by using the single set of droplets approach proposed by Rajesh et al. [6]. Finally, the practical relevance of the proposed approach was shown by comparing the predicted results with the experimental results obtained by water peening of 6063-T6 aluminium alloy.     

Determination of the stressed state of main pipelines in the zones of circular welds

By using the numerical-experimental method based on the solution of inverse problems of the theory of shells with residual strains and the experimental data obtained by nondestructive methods, we determine the distribution of residual stresses near a circular weld in the main pipeline. The nonuniformity of the distribution of residual stresses under gauges of the measuring instruments is taken into account. The average characteristics of stresses with regard for the structural changes in the zone of thermal influence are found experimentally (by using measuring instruments). __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 99–104, March–April, 2006.     

Using three-dimensional finite element analysis for simulation of residual stresses in railway wheels

One of the most important issues in railway wheels is residual stresses. It is desirable to produce less residual stresses when possible and to decrease the remaining residual stresses in the wheels. The objective of this paper is to provide an estimation of the residual stresses in the rail wheel caused by the stress field from heat treatment process of a railway wheel. A three-dimensional nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. After forging or casting, railway wheels are heat-treated to induce the desirable circumferential compressive residual stress in the upper rim. Finite element analysis model is presented applying the elastic–plastic finite element analysis for the rail wheel under variable thermal loads. Calculative analysis applying a finite element method (FEM) has been used to predict residual stresses. The quenching and annealing segments of the wheel manufacturing process are simulated using a decoupled heat transfer and stress analysis. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.     

Synchrotron diffraction investigation of the distribution and influence of residual stresses in fatigue

This paper presents some results obtained from synchrotron diffraction investigations into two somewhat related areas of interest to the fatigue community. Firstly, the influence of fatigue cycling on the distribution and magnitude of residual strains and stresses and, secondly, the residual strains and stresses engendered around a growing fatigue crack. Its main premise is that modern tools such as automated synchrotron strain scanning offer the potential for more complete insight into the distribution of residual strains and stresses and their influence on fatigue performance. The first part of the work was accomplished using friction‐stir welded (FSW) and metal‐inert gas (MIG) welded specimens. The particular interest in these specimens was obtaining detailed knowledge regarding as‐welded variation in residual stresses between specimens, the location of peak values relative to local microstructure and stress concentrations, and of their modification during fatigue cycling. Such information may indicate a route forward to the selection of welding process parameters for optimised fatigue performance. The second part of the work considered an established fatigue crack in a compact tension (CT) specimen and examined the ability of synchrotron diffraction to characterize the stresses associated with the plastic enclave around a fatigue crack. This work is of interest in the context of better knowledge of crack‐tip shielding by plasticity‐induced closure and its incorporation into life prediction methodologies.     

Evaluation of residual stresses in PVD-coatings. Part 1. Review

We present a review of the results of investigations on residual stresses in plasma-vacuum coatings obtained by the physical vapor deposition methods. The data on the character of residual stresses and factors influencing their values and distribution are analyzed. The works are considered that investigate the effect of residual stresses on the physico-mechanical characteristics of the substrate–coating system. Recommendations on the further studies of residual stresses in PVD-coatings and the improvement in their level control are presented.     

Numerical and experimental validation of residual stresses of laser‐welded joints and their influence on the fatigue behaviour

In this work laser‐welded tube‐tube specimens made of aluminium alloys AlMg3.5Mn and AlSi1MgMn T6 were experimentally tested under constant and variable amplitude loading, under pure axial and pure torsion loading. In order to evaluate the influence on fatigue behaviour of the residual stresses, because of the welding process, some specimens were subjected to postweld heat treatment and then were tested. The numerical analyses, using finite element (FE), were carried out to obtain a reliable estimation of the residual stress in the specimen. The numerical results were in a good agreement with experimental ones obtained by means of hole‐drilling method. Finally, the residual stress distribution was superimposed to stress distribution because of fatigue loads obtained by FE analyses applying local concept, to calculate the stresses in the crack initiation zone and to understand the different types of failure that occurred in as‐welded and relieved specimens.