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.     

钛合金激光冲击强化层的残余应力及显微组织

对TC6钛合金进行了激光冲击强化(LSP),对强化层的残余应力分布进行了测试,应用透射电子显微镜对强化层的显微组织进行了观察。结果表明:TC6钛合金LSP的最佳功率密度为4GW.cm-2,LSP能在材料表层产生高的残余压应力场,表面残余压应力可达530.4 MPa;LSP可在钛合金表层产生高密度位错和纳米晶,纳米晶尺寸在10～100nm。     

Study on effect of time parameters of laser shock peening on residual stresses using FE simulation

Laser shock peening (LSP) is the newest and most innovative surface treatment technique. LSP residual stress distribution is affected by many parameters. Of them, the parameters are main factors that determine the convergence of finite element analysis (FEA) and characteristic of pressure pulse of laser system. The parameters, related to the convergence of FE simulation, are stability limit time for the stable convergence of results, and solution time for dynamic analysis. The other parameters, related to characteristics of pressure pulse of laser system, are pressure pulse duration time and laser pulse interval time for multiple LSP. In the present work, we have conducted to confirm the influence of time parameters of LSP system on residual stress results using FEA, and we have also predicted optimized range of time parameters.     

Effects of simulation parameters on residual stresses for laser shock peening finite element analysis

By using finite element analysis, we proposed an applicable finite element method of laser shock peening (LSP) and discussed various parameters, such as solution time, stability limit, dynamic yield stress, peak pressure, pressure pulse duration, laser spot size, and multiple LSP. The effects of parameters related to the finite element simulation of the LSP process on the residual stresses of 35CD4 30HRC steel alloy are discussed. Parametric sensitivity analyses were performed to establish the optimum processing variables of the LSP process. In addition, we evaluated the effects of initial residual stress, such as welding-induced residual stress field.     

Finite Element Modeling of the Technology of Multiple Laser Shock Processing of Materials Using the Eigenstrain Method

The laser shock processing (LSP) of material is an efficient modern technology of processing of metal materials, during which significant compressive residual stresses contributing to an increase in their strength and tribological and operational characteristics are generated in the subsurface area. The finite element modeling of the technology of multiple laser shock processing is carried out using the eigenstrain method. The level of the compressive residual stresses arising under LSP is determined. It is shown that the residual stresses on the surface of the VT-6 alloy grow from 510 to 830MPa with an increase in the number of pulses from 1 to 4, and the depth of the zone of the compressive residual stresses increases respectively from 1.26 mm after the first pulse to 1.60 mm after the fourth pulse.     

喷丸与激光喷丸强化高强度钢对比试验

为了考察和对比喷丸(SP)和激光喷丸(LSP)2种表面强化技术对金属零件的强化效果,以30CrMnSiNi2A钢为试样,进行喷丸和激光喷丸强化处理试验。试验结果显示,2种强化试样的残余压应力和硬度都有较大的提高。分别测定了喷丸强化和激光喷丸强化试样在同一应力水平下的疲劳寿命,并运用扫描电镜分析了两者的疲劳断口。试验结果表明,激光喷丸强化试样中值疲劳寿命是喷丸强化试样的1.11~2.75倍,激光喷丸强化比喷丸强化在提高金属零件表面性能方面的效果更佳。     

Wear and friction of 6061-T6 aluminum alloy treated by laser shock processing

Laser shock processing (LSP) is becoming an important surface treatment to induce a compressive residual stress field, which improves fatigue and fracture properties of components. In this work, we examine the effect of laser shock processing on the wear and friction behavior of 6061-T6 aluminum alloy. Wear rate and friction coefficient evolution are investigated for different process parameters of LSP. Roll-on-flat tribometer is used with different loading conditions. Hardness and residual stresses are assessed as well. It is observed that wear rate decreases as pulse density increases; this is explained in light of residual stress distribution.     

航空铝合金激光激波强化工艺

用激光激波强化工艺对LY2航空铝合金进行了表面强化试验研究,测试了强化前后材料的性能.结果表明:经激光激波强化后材料表面残余压应力提高了约100 MPa,强化深度达1.5mm,是普通喷丸强化的2～5倍.     

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...     

激光冲击强化对TC4钛合金单面修饰激光焊接接头疲劳性能的影响

对TC4钛合金单面修饰激光焊接接头进行激光冲击强化,对比强化前后焊接接头的疲劳寿命,在光学显微镜和扫描电镜下观察断口疲劳断裂特征,并从焊接接头的显微硬度、微观组织、残余应力分布等方面综合分析激光冲击强化对TC4钛合金单面修饰激光焊接接头的强化机理。试验结果表明：未强化和强化试样均在焊缝咬边处萌生疲劳裂纹,强化试样疲劳寿命是未强化试样疲劳寿命的3.77~9.15倍,强化试样焊缝咬边处马氏体细化,显微硬度提高,焊缝表面呈残余压应力分布,焊缝咬边处残余压应力达-564.37±9.85MPa。晶粒细化和高幅值残余压应力综合作用下抑制了焊缝咬边处疲劳裂纹的萌生,且增大了裂纹扩展阻力,从而提高了焊接接头疲劳性能。     

激光冲击强化与喷丸提高不锈钢疲劳性能对比研究

对不锈钢材料1Cr11Ni2W2MoV进行了激光冲击强化和喷丸强化后表面粗糙度和残余应力测试分析,与喷丸相比,激光冲击强化对试件表面形貌和表面粗糙度的影响更小,产生的残余压应力更大。对光滑试件和2种强化后试件的振动疲劳对比试验表明,激光冲击强化能显著提高不锈钢材料振动疲劳寿命,是喷丸的2倍以上。     

Analysis of Fretting Fatigue of Cavitation Shotless Peened Ti–6Al–4V

Fretting fatigue behavior of cavitation shotless peened titanium alloy, Ti–6Al–4V coupons was investigated using finite element method and a critical plane-based multi-axial fatigue parameter. Cavitation shotless peening (CSP)-induced compressive residual stress, which was larger at the contact surface than its counterpart from the shot peening (SP). However, compressive residual stress decreased more sharply with distance from the contact surface in CSP than in SP. Analysis using a critical plane-based multi-axial fatigue parameter demonstrated that the crack initiation would occur inside the cavitation shotless peened specimen which matched with the experimental observations. On the other hand, crack initiation would occur on the contact surface in the shot peened specimen which again was in agreement with experiments. The analysis also showed that the crack propagation part of the total fretting fatigue life was longer in the shot peened specimen than in the cavitation shotless peened specimen while the crack initiation part was almost equal from both peening methods. Therefore, CSP could not improve the fretting fatigue life/strength as much as the SP did but it improved relative to the un-peened specimen.     

GH742合金激光冲击强化后的表面残余应力

采用X射线衍射法对GH742合金激光冲击强化后的表面残余应力进行了测试,采用云纹干涉结合盲孔法对残余应力随深度的分布进行了测试。结果表明:GH742合金经激光单点冲击后,表面残余压应力最高可达1 180MPa,且残余压应力层深度达到1.2mm;50%光斑搭接率强化后的表面残余压应力约为1 100MPa。     

Shot peening simulation based on SPH method

Shot peening is a complex surface-treating process which is usually employed to improve the fatigue strength of metallic part or members. In dealing with shot peening simulation, existing literatures apply finite element method (FEM) to establish only a single shot or several shots models, thus the effect of a mass of shots impacting repeatedly and the interaction among adjacent shots are ignored. To overcome these defects of FEM models, smoothed particle hydrodynamics (SPH) coupled FEM modeling is presented, in which the shots are modeled by SPH particles and the target material is modeled by finite elements. Contact algorithm is used to simulate the interaction between shots and target. Utilizing this model, material model for shots is established, the relationships between compressive residual stress and peening frequencies, coverage, and velocities are analyzed. Steady compressive residual stress can be gotten by multiple peening; higher coverage can improve the compressive residual stress; faster velocities can induce greater and deeper maximum residual stress in target subsurface. The simulation results agree well with the existing experimental data. The study will not only provide a new powerful tool for the simulation of shot peening process, but also be benefit to optimize the operating parameters.     

Optimization of peened-surface laser shock conditions by method of finite element and technique of design of experiments

This paper presents a numerical simulation of the laser shock peening (LSP) process using the finite element method. The majority of controlling parameters of the LSP process have been taken into account. The LSP loading has been characterized by the use of a repetitive time Gaussian increment pressure applied uniformly at a circular impacted zone. The utilized model of the treated material behaviour law is the Johnson-Cook’s visco-elastic-plastic coupled with damage. The proposed model leads to determine the LSP surface modifications: (i) the in-depth residual stresses, (ii) the induced plastic strains and (iii) the superficial damage. These modifications can be significantly induced in few cases, particularly when the operating conditions are not well optimized. An application is carried out on the laser peened titanium aero-engine super alloy Ti-6Al-4V. A satisfactory correlation between the computed and experimental results is observed. Also, it is noted that the computed superficial damage values increase with the growth of the maximal peak pressure of the laser spot, which are physically consistent. Otherwise, in order to optimize the laser peening operating conditions, a design of experiments is established. It allows having surface-response relationships between the operating parameters and the three announced induced effects.     

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。     

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。     

IMPROVING FATIGUE STRENGTH OF METALS USING ABRASIVE WATERJET PEENING

Abrasive waterjet (AWJ) peening has been proposed as a viable method of surface treatment for metal orthopedic devices. In this study the influence of AWJ peening on the compressive residual stress, surface texture and fatigue strength of a stainless steel (AISI 304) and titanium (Ti6Al4V) alloy were studied. A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the primary parameters contributing to the surface texture and magnitude of surface residual stress. The influence of AWJ peening on the fatigue strength of the metals was evaluated under fully reversed cyclic loading. It was found that AWJ peening results in compressive residual stress and is primarily influenced by the abrasive size and treatment pressure. The residual stress of the AISI 304 ranged from 165 to over 460 MPa. Using the optimum treatment parameters for maximizing the residual stress, the endurance strength of Ti6Al4V was increased by 25% to 845 MPa. According to results of this study AWJ peening is a viable method of surface treatment for applications that require an increase in surface roughness and maintenance or increase in fatigue strength, qualities that most often are not available from a single process.     

IMPROVING FATIGUE STRENGTH OF METALS USING ABRASIVE WATERJET PEENING

Abrasive waterjet (AWJ) peening has been proposed as a viable method of surface treatment for metal orthopedic devices. In this study the influence of AWJ peening on the compressive residual stress, surface texture and fatigue strength of a stainless steel (AISI 304) and titanium (Ti6Al4V) alloy were studied. A design of experiments (DOE) and an analysis of variance (ANOVA) were used to identify the primary parameters contributing to the surface texture and magnitude of surface residual stress. The influence of AWJ peening on the fatigue strength of the metals was evaluated under fully reversed cyclic loading. It was found that AWJ peening results in compressive residual stress and is primarily influenced by the abrasive size and treatment pressure. The residual stress of the AISI 304 ranged from 165 to over 460 MPa. Using the optimum treatment parameters for maximizing the residual stress, the endurance strength of Ti6Al4V was increased by 25% to 845 MPa. According to results of this study AWJ peening is a viable method of surface treatment for applications that require an increase in surface roughness and maintenance or increase in fatigue strength, qualities that most often are not available from a single process.     

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.