喷丸三维残余应力场的有限元模拟

运用大型有限元计算软件ABAQUS建立了模拟喷丸残余应力场的三维有限元模型,预测了在相同喷丸强度下玻璃丸和钢丸两种类型弹丸喷射所产生的残余应力场。模拟过程中,分析了线性减缩积分单元的沙漏参数、材料的应变硬化率、喷丸覆盖率以及初始残余拉应力等因素对304不锈钢靶材残余应力分布的影响。从计算结果可以看出,钢丸喷丸产生的残余压应力层较深,但在高覆盖率时,玻璃喷丸产生的残余压应力的平均值比钢丸喷丸处理后产生的大。在有初始残余拉应力(250 Mpa)存在的情况下,两种类型的喷丸处理均能使304不锈钢靶材表面形成残余压应力层,这说明喷丸工艺可以提高奥氏体不锈钢焊接构件的抗应力腐蚀开裂能力。本研究成果为进一步探讨喷丸强化不锈钢焊接头抗应力腐蚀性能的机理奠定了基础。     

A numerically low-cost and high-accuracy periodic FE modeling of shot-peened 34CrNiMo6 and experimental validation

This paper proposed a numerically low-cost 3D FE modeling method for multi-shot shot peening. The low computation cost and high prediction accuracy of shot peening are realized at the same time by the incorporation of random multi-shot with defined spacing between the adjacent simultaneously impinging shots, periodicity, and coverage rate of 100%. With this modeling method, one-step and dual-step multi-shot peening of 34CrNiMo6 steel target is modeled and the produced residual stress is predicted. In order to make the predicted residual stress depth profile more comparable with the measured one by XRD method, the redistribution of residual stress due to the layer removal by electrochemical polishing is simulated using Model Change technique. And the comparison between the prediction and experiment indicates that this improved 3D periodic FE modeling of multi-shot impingement provides very accurate simulation models for one-step and dual-step shot peening. It can substitute for the costly and time-consuming optimization experiments of the shot peening process, especially the multi-step shot peening process. Finally, the evolution of residual stress depth profile in dual-step shot peening process is investigated by using the simulation model and a variation of residual stress towards a more uniform distribution on the finished surface taking place in the second step is discovered by RMS analysis.     

Kinematic modeling and deformation mechanics in shot peening of functional ceramics

The applications of functional ceramics are significantly limited by the brittleness and low reliability. Recent studies have shown that compressive residual stress can be created in ceramics by shot peening, which improves the contact strength and fatigue of ceramic components. However, the formation mechanism of residuals stress in shot peening is yet to understand. In this study, a pressure-dependent plasticity model has been incorporated into a finite element simulation model of shot peening to understand the process mechanism underpinning the residual stress formation. Since shot velocity is the key process parameter to dominate the impact energy which determines the deformation state of the peened surface and the resultant residual stress, a new kinematic model of shots has also been developed by incorporating air drag and travel distance inside and outside the peening nozzle. The results have shown that the shot velocity model can be used to predict shot velocity. The experiment-based model may help understand the process mechanism underpinning the residual stress formation.     

Numerical simulation of Almen strip response due to random impacts with strain-rate effects

Almen intensity is used in the shot peening industry as a standard measure of the residual stress during shot peening and it is employed to ensure the quality of the peening of identical parts. However, relating the intensity to the residual stresses in the strip needs to be established with confidence by realistic simulations. An improved FEM-based approach that simulates the actual process of Almen strip peening is presented in this paper. This approach has some unique features such as employing randomly located shots impacting on a slice of Almen strip and the inclusion of strain-rate dependent target material properties and the lateral deflection of the strip for improved accuracy. The intensity, the corresponding residual stresses and roughness match well with available experimental results. Further, it is shown in this study that the Almen intensity can be correlated well with the residual compressive stresses of the target material using a parameter that depends on the relative dynamic yield strength of the target material.     

喷丸残余应力场有限元模拟研究进展

喷丸强化处理工艺可以显著提高金属材料的抗疲劳和抗应力腐蚀等性能,这与喷丸后在金属表面层形成的残余应力场紧密相关,因此对喷丸残余应力的大小及分布进行预测具有重要意义。对近年国内外喷丸残余应力场的有限元模拟进行评述,总结出6种典型的残余应力分析模型,分别是二维轴对称模型、四对称面模型、三对称面模型、双对称面模型、单对称面模型和无对称边界条件的有限元模型,比较了不同模型的特点及应用现状。介绍了当前几种新的残余应力分析有限元模型:随机三维模型和周期性边界条件模型,根据其原理和特点认为其本质是无对称边界条件模型和对称边界条件有限元模型的延伸。针对空化水喷丸、激光喷丸和超声波喷丸等新工艺,新喷丸过程的数值模拟一般是以机械喷丸工艺的数值模拟方法为基础进行改进,主要采用弹丸撞击法和等效载荷法。对未来喷丸残余应力数值模拟研究进行了展望,认为从组织强化角度深入研究喷丸强化机理、建立更符合实际喷丸工艺的有限元模型、开发新算法以及将有限元法和离散元法进行结合是值得关注的研究方向。     

Residual stress behaviors induced by laser peening along the edge of curved models

Laser peening (LP) induces high-magnitude compressive residual stresses in a small region of a component. The compressive residual stresses cause plastic deformation that is resistant to fatigue fracture. Fatigue cracks are generally nucleated at critical areas, and LP is applied for those regions so as to delay the crack initiation. Many critical regions are located on the edge of the curved portion of structures because of stress concentration effects. Several investigations that are available for straight components may not give meaningful guidelines for peening curved components. Therefore, in this paper, we investigate residual stress behaviors induced by LP along the edge of curved models. Three curved models that have different curvatures are investigated for peening performance. Two types of peening configurations, which are simultaneous corner shot and sequential corner shots, are considered in order to obtain compressive residual stresses along an edge. LP simulations of multiple shots are performed to identify overlapping effects on the edge portion of a curved model. In addition, the uncertainty calculation of residual stress induced by LP considering laser pulse duration is performed.     

Effect of shot peening coverage on fatigue limit in round bar of annealed medium carbon steel

Shot peening is an effective and economical technique for improving the fatigue strength of metallic components by inducing compressive residual stress and hardening the layer near the surface. The effect is generally evaluated by main two parameters: coverage and peening intensity. However, the valuable coverage for improving the fatigue strength depends on the shape of the target material. In this study, the effect of coverage on fatigue limit in round bar of annealed medium carbon steel was experimentally studied. The fatigue limits for shot peened round bar specimens with 140–2300% coverage increased 14–25% by comparing those for non-peened round bar specimens. The valuable range of coverage was 280–60% in the used material and shot peening condition for improving the fatigue limit in short time. The result indicates that the valuable coverage of the round bar material is higher than full coverage to improve the fatigue limit of the material due to the effect of incident angle on round bar, even though the degree depends on the materials and shot peening conditions.     

喷丸强化残余应力对疲劳性能和变形控制影响研究进展

作为机械表面强化技术之一,喷丸强化使工件表层发生形变硬化,引入较高的残余压应力,减少了疲劳应力作用下微裂纹的萌生并抑制其扩展,从而显著提高零件的抗疲劳断裂和抗应力腐蚀开裂的能力。基于喷丸残余应力解析计算模型,从余弦函数模型、接触应力模型和球腔膨胀模型三个方面介绍喷丸强化残余应力的产生,进而对喷丸残余应力的仿真预测及影响规律进行论述。为了提高试件疲劳强度而引入的残余压应力会带来影响形位精度的变形,基于此阐述了喷丸残余应力对疲劳性能的影响及其在疲劳过程中的演化,同时论述了喷丸残余应力变形预测及控制的研究现状,最后对喷丸残余应力未来的研究内容与发展方向进行展望。     

Abrasive waterjet machining simulation by SPH method

Abrasive waterjet machining (AWJM) is a non-conventional process. The mechanism of material removing in AWJM for ductile materials and existing erosion models are reviewed in this paper. To overcome the difficulties of fluid–solid interaction and extra-large deformation problem using finite element method (FEM), the SPH-coupled FEM modeling for abrasive waterjet machining simulation is presented, in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FE. The two parts interact through contact algorithm. The creativity of this model is multi-materials SPH particles, which contain abrasive and water and mix together uniformly. To build the model, a randomized algorithm is proposed. The material model for the abrasive is first presented. Utilizing this model, abrasive waterjet penetrating the target materials with high velocity is simulated and the mechanism of erosion is depicted. The relationship between the depth of penetration and jet parameters, including water pressure and traverse speed, etc., are analyzed based on the simulation. The results agree with the experimental data well. It will be a benefit to understand the abrasive waterjet cutting mechanism and optimize the operating parameters.     

Finite element analysis of shot-peening effect on fretting fatigue parameters

Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters.     

FEM of residual stress and surface displacement of a single shot in high repetition laser shock peening on biodegradable magnesium implant

Laser shock peening (LSP) is one of the prominent surface processing techniques to improve the mechanical characteristics by inducing compressive residual stress on the specimen surface. Generally, LSP is performed using high energy, low repetition pulsed laser. Recently, High repetition laser shock peening (HRLSP) on biodegradable magnesium alloys has been reported. Increased speed and reduced operating costs are the key highlights of HRLSP. This work is aimed towards understanding of the residual stress profile beneath the specimen surface, where a Finite element method (FEM) has been proposed to show the ability of a tightly focussed nanosecond laser pulse for peening magnesium. The depth of maximum compressive residual stress of 48 MPa at 28 mm beneath surface was the result of the simulation. Also the Von Misses stress was analytically found to be 31.5 MPa, which is similar to the value from FEM at 30 MPa. Furthermore, the plastic displacement of FEM at 4.02 µm compares reasonably well with the experimental result at 3.698 µm, thereby validating the Finite element model. If increase in CRS can be created by single shot of laser pulse, it can be concluded that the same can be done beneath the entire magnesium surface using appropriate scanning protocols.

     

TiB_2/Al复合材料喷丸后微区残余应力的有限元模拟

采用ANSYS/LS-DYNA有限元分析软件建立了颗粒增强TiB2/Al复合材料的喷丸模型,并对喷丸后残余应力分布进行了预测;然后对复合材料进行了喷丸试验,对残余应力进行了检测;将试验结果与模拟结果进行了对比。结果表明:该复合材料喷丸后残余应力分布的试验结果与模拟结果基本相符;喷丸后最表层部分增强体呈拉应力状态,在材料残余压应力场内,由于增强体和基体材料力学性能的差异,增强体的残余应力值普遍大于基体中的。     

Abrasive Waterjet Machining Simulation by Coupling Smoothed Particle Hydrodynamics / Finite Element Method

In dealing with abrasive waterjet machining(AWJM) simulation,most literatures apply finite element method(FEM) to build pure waterjet models or single abrasive particle erosion models.To overcome the mesh distortion caused by large deformation using FEM and to consider the effects of both water and abrasive,the smoothed particle hydrodynamics(SPH) coupled FEM modeling for AWJM simulation is presented,in which the abrasive waterjet is modeled by SPH particles and the target material is modeled by FEM.The two parts interact through contact algorithm.Utilizing this model,abrasive waterjet with high velocity penetrating the target materials is simulated and the mechanism of erosion is depicted.The relationships between the depth of penetration and jet parameters,including water pressure and traverse speed,etc,are analyzed based on the simulation.The simulation results agree well with the existed experimental data.The mixing multi-materials SPH particles,which contain abrasive and water,are adopted by means of the randomized algorithm and material model for the abrasive is presented.The study will not only provide a new powerful tool for the simulation of abrasive waterjet machining,but also be beneficial to understand its cutting mechanism and optimize the operating parameters.     

Simulation on Residual Stress of Shot Peening Based on a Symmetrical Cell Model

The symmetrical cell model is widely used to study the residual stress induced by shot peening. However, the correlation between the predicted residual stresses and the shot peening coverage, which is a big challenge for the researchers of the symmetrical cell model, is still not established. Based on the dynamic stresses and the residual stresses outputted from the symmetrical cell model, the residual stresses corresponding to full coverage are evaluated by normal distribution analysis. The predicted nodal dynamic stresses with respect to four corner points indicate that the equi-biaxial stress state exists only for the first shot impact. Along with the increase of shot number, the interactions of multiple shot impacts make the fluctuation of the nodal dynamic stresses about an almost identical value more and more obvious. The mean values and standard deviations of the residual stresses gradually tend to be stable with the increase of the number of shot peening series. The mean values at each corner point are almost the same after the third peening series, which means that an equi-biaxial stress state corresponding to the full coverage of shot peening is achieved. Therefore, the mean values of the nodal residual stresses with respect to a specific transverse cross-section below the peened surface can be used to correlate the measured data by X-ray. The predicted residual stress profile agrees with the experimental results very well under 200% peening coverage. An effective correlation method is proposed for the nodal residual stresses predicted by the symmetrical cell model and the shot peening coverage.     

Numerical investigation of surface topography and residual stress after abrasive water jet sequential peening (AWJSP)

Abstract

This article reveals the formation mechanism of surface topography and the formation and coupling mechanism of residual stress field (RSF) after abrasive water jet sequential peening (AWJSP) that can sequential peening on the material surface at a certain distance interval, and proposes a mathematical model of surface dimple characteristic verified by simulation results. In addition, the influences of shot velocity v₀, shot radius R and the distance between the center of adjacent shots D_C on surface topography and RSF were also investigated. Results show the surface dimple forms resulting from the material plastic strain, and the residual stress (RS) is mainly induced by the unrecovered elastic strain resulting from the hindering of plastic strain. Decreasing v₀, R or D_C can decrease the surface roughness R_t, while increasing v₀ and R is beneficial to induce a large and deep compressive RS layer. D_C influences the whole distribution of compressive RS layer directly.     

Compressive Residual Stress into Titanium Alloy Using Cavitation Shotless Peening Method

Cavitation shotless peening (CSP) method, where impacts are generated by a submerged cavitating jet (without shots), was used to introduce compressive residual stress in titanium alloy, Ti-6Al-4V for the purpose of enhancing the conventional fatigue and fretting fatigue life and strength. This method provided higher compressive stress at surface as well as up to a depth of 40 m from the surface than that with the shot peening method. Further, the surface treated by CSP was considerably less rough compared to that by the shot peening method, which is a highly desirable feature to improve the fretting fatigue performance.     

喷丸强化与应力因素对2E12铝合金晶间腐蚀行为的影响

为有效控制2E12铝合金的晶间腐蚀失效行为,采用浸泡腐蚀试验、金相分析技术、扫描电镜分析技术和X射线衍射分析技术等研究了喷丸强化和应力因素对2E12-T3铝合金晶间腐蚀行为的影响规律,并探讨了作用机理。研究结果表明:2E12-T3铝合金具有很高的晶间腐蚀敏感性,拉应力会明显增强其敏感程度,而压应力则会降低其敏感性。采用合理的喷丸强化处理(喷丸强度取0.15 mmN,覆盖率取100%)能够明显降低2E12-T3铝合金的晶间腐蚀敏感性,因为喷丸在铝合金表面引入合理分布的残余压应力,同时使表层晶粒细化,铝合金的电化学活性降低,晶间的选择性腐蚀得到有效控制。然而,喷丸强度过高或喷丸覆盖率过大时,铝合金表面会存在较严重的脱层等损伤性破坏,反而会使2E12-T3铝合金的晶间腐蚀敏感程度提高。     

DD3镍基单晶高温合金喷丸强化后残余应力的有限元模拟

利用有限元分析软件ANSYS/LS-DYNA,通过设立局部坐标系和运用三参数Barlat模型建立了DD3镍基单晶高温合金的喷丸强化有限元模型,并对喷丸后的残余应力进行了有限元模拟和实际测试。结果表明:由于镍基单晶高温合金的各向异性,在不同取向上呈现不同的残余应力状态,且同一晶面不同取向的最小残余压应力出现在组成滑移系的晶向上;模拟结果与试验结果吻合较好。     

Surface durability of powder-forged roller treated by shot peening

To investigate the influence of shot peening on the surface durability of powder-forged rollers, the case-hardened powder-forged rollers with a forging density of 7.5 g/cm³ treated by the single shot peening and the double shot peening were fatigue-tested under a sliding-rolling contact condition. The surface roughness, the surface hardness and the surface compressive residual stress of the rollers were increased by the shot peening. In addition, the pores near the roller surface were deformed by the shot peening. The failure mode of all the test rollers was spalling due to subsurface cracking. The fatigue lives of all the test rollers were improved by the shot peening, and that of the test roller S08, which was shot-peened with the hardest steel shots in this experimental range, was especially improved. The surface durability of the test roller S08 was also most improved by the shot peening. Cracks became difficult to occur and propagate under the roller surface since the pores near the roller surface were deformed by the stronger shot peening. In this study, double shot peening, which generally restrains the increase in surface roughness, was not particularly effective for the improvement in the surface durability of the powder-forged rollers, because the influence of tangential force on fatigue was not always great in a case of subsurface cracking.     

激光冲击钛合金板料的有限元模拟

激光冲击强化技术（LSP）是一种新型的表面处理技术,它利用激光冲击波作用靶材表面而产生残余压应力场.通过有限元软件模拟（FEM）可以分析激光冲击强化处理后靶材的残余压应力场分布,分析材料表面和深度方向的残余应力场的分布情况.先分析了材料的本构模型、激光冲击波的峰值压力的计算、有限元单元类型的选取、边界条件的处理等条件;再通过有限元软件ABAQUS对激光冲击TC4钛合金板料进行了数值模拟,分析了残余应力场的分布特点.