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.     

Effect of input variability on the quality of laser shock processing

Laser shock processing (LSP) involves high-energy laser radiation combined with suitable overlays to generate high-pressure pulses on the surface of the metal. The stress wave generated due to high pressure pulses propagates into the material causing the surface layer to yield and plastically deform, and thereby, develop a significant residual compressive stress in the surface region of the substrate material. The developed compressive stress field is beneficial to improve surface properties such as fatigue, wear, and corrosion. To improve the understanding of the shock hardening process, investigation into the physical processes involved is necessary. In the first part of this paper, the temporal variation in the pressure intensity and spot size is calculated by using a two-dimensional recoil pressure prediction model. Using an explicit non-linear FEA code, ANSYS LS-DYNA, the deformation behavior and residual stresses in the substrate material are predicted. In the second part, a probabilistic approach to the modeling and analysis of LSP is presented in this paper. Various factors that affect the probabilistic performance of the LSP are grouped into categories and a select number of factors known to be significant, for which the variability could be assessed, are modeled as random variables (such as recoil pressure, laser beam spot size, substrate material properties and others). The potential of the probabilistic approach in predicting the structural integrity of the laser-shocked components is addressed.     

Two-sided laser shock processing

The principles of two-sided laser shock processing (LSP) are considered. The differences between two-sided and one-sided laser shock processing are noted. For the example of a thin VT-6 titanium-alloy plate, finite-element modeling is used to investigate the residual stress field when using two-sided LSP. The distribution of surface microhardness is analyzed.     

激光冲击强化对LZ50车轴钢疲劳性能影响试验研究

为了研究激光冲击强化对LZ50车轴钢疲劳性能的影响,对LZ50车轴钢车轴试样进行激光冲击强化处理并在JD-1轮轨模拟试验机上进行了旋转弯曲疲劳试验。结果显示：采用不同参数激光冲击强化处理的2个试样,硬度分别增大18%和27%;对LZ50车轴钢试样的过盈配合面进行激光冲击处理后产生了塑性变形层,形成了较高的残余压应力;试验后试样过盈配合表面两侧区域都可见明显的环形损伤带,出现了以剥落和犁沟为特征的磨损形貌,损伤机制为磨粒磨损、氧化磨损和剥层。激光冲击前后试样断口形貌特征相似,疲劳源呈多源性;在裂纹扩展区域段观察到大量的准解理小面,属于脆性穿晶断裂;瞬断区内出现大量韧窝和二次裂纹。激光冲击强化处理显著提高了车轴钢的疲劳寿命,不同激光冲击强化参数处理的2个车轴试样疲劳寿命比未处理试样疲劳寿命分别提高31%和21%。     

激光冲击处理对曲轴磨损性能的影响

利用激光冲击波对曲轴球墨铸铁进行表面强化处理,利用摩擦磨损试验机研究激光冲击处理球墨铸铁QT700的磨损性能,利用金相显微镜分析激光冲击处理后其表面微结构,同时采用XRD分析激光冲击处理后球墨铸铁表面马氏体与残余奥氏体的含量。结果表明,激光冲击处理后球墨铸铁具有理想的表面形貌和较高的表面硬度,其抗磨性能大幅度提高,有利于提高其疲劳寿命。     

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.     

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。     

Effects on mechanical properties in electron beam welding of TC4 alloy by laser shock processing

The surface of TC4 titanium alloy welding line by electron beam welding (EBW) was processed by high power Q-switched and repetition-rate Nd: glass laser. Effects of laser power and spot diameter on residual stress and microhardness of the TC4 alloy welding line by laser shock processing (LSP) have been analyzed. Results show that residual stresses almost do not change as laser power is 45.9 J, spot diameter is ϕ9 mm; While laser power is 45.9 J, spot diameter less than ϕ3 mm, the distribution of residual stress in welding line occurs obvious variation, which residual stress increase obviously with spot diameter decrease. When power density is bigger than 1.8 × 10¹⁰ W/cm², residual stresses of electron beam welding line occur change by LSP, which improve obviously residual stress distribution; while laser power is bigger than 1.2 × 10¹⁰ W/cm², the surface micro-hardness of electron beam welding line occurs change by LSP, which improve obviously micro-hardness distribution. Mechanical properties of TC4 titanium alloy welding line will be improved by LSP, which provides experimental foundation for further controlling the distributions of residual stress and micro-hardness during laser shock processing. __________ Translated from Journal of Jiangsu University (Natural Science), 2006, 27(3): 207–210 [译自: 江苏大学学报 (自然科学版)]     

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。     

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.     

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.

     

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.     

硬质合金刀具高能离子源增强多弧镀AlCrTiSiN梯度涂层制备及性能研究

采用离子源增强的多弧离子镀新技术,在硬质合金刀具表面制备了不同含Si层梯度结构的AlCrTiSiN梯度涂层,并对涂层组织结构、残余应力、结合强度、摩擦磨损以及铣削和钻削加工灰铸铁性能进行了详细的研究。结果表明：不同含Si层梯度结构的AlCrTiSiN涂层主要由固溶的(Al,Cr) N、(Al,Ti) N相和非晶态Si₃N₄相组成。其中,含Si层梯度变化最缓和的G3(Gradient 3)涂层具有较高的结合强度,较低的残余压应力、摩擦因数和磨损率。铣削和钻削试验显示,涂层刀具的切削磨损机理主要表现为磨粒磨损和粘着磨损。G3涂层降低了磨粒磨损,其刀具的铣削和钻削寿命均最高,这主要得益于其含Si层的梯度设计、适当的压应力(-3.8 GPa)以及良好的膜基结合强度。研究结果表明,通过对含Si层进行梯度设计可显著提高涂层刀具的切削性能。     

低摩擦速度下CT80油管摩擦磨损性能

研究采油过程中CT80油管与电缆在0.01～0.13 m/s速度下对摩时的摩擦磨损行为及其对油管剩余强度的影响。采用扫描电子显微镜及金相显微镜对油管组织、磨损表面及截面特征进行表征。结果表明:CT80油管的磨损量、壁厚减薄量与摩擦因数随摩擦速度增加先增大,速度达到0.07 m/s后趋于平稳;磨损率随着摩擦速度增加先增大后降低,最大磨损率对应的摩擦速度为0.07 m/s;采油过程中磨粒磨损与腐蚀磨损共同作用于油管,随着摩擦速度升高磨粒磨损造成的损失降低,腐蚀磨损造成的损失升高;随着摩擦速度增加油管的剩余抗挤毁强度以及剩余抗内压强度先降低后趋于平稳。     

陶瓷磨削残余应力对表面性能的影响

陶瓷零件的磨削表面必然要附加一层残余压应力 ,其对零件的使用性能影响较大。本文主要针对陶瓷材料磨削表面残余应力对疲劳磨损和表面硬度的影响进行实验研究。试验结果表明 :与金属材料相比 ,Zr O2 陶瓷材料的磨削残余应力对零件的摩擦磨损性能的影响要小得多。磨削、研磨及加热三个试件组的磨损量随摩擦时间呈现一定的变化规律。残余拉应力在一定程度上加速陶瓷零件的磨损 ,残余压应力可适当减缓陶瓷零件的磨损 ,其数值变化对零件性能的影响很小。随着残余压应力值的增加 ,表面硬度值也在逐渐增加 ,当残余压应力增加到一定值后表面硬度值开始下降。     

多层涂层的摩擦学研究进展

多层涂层与单一涂层相比具有优异的力学性能：低的内应力、高附着力、适当的硬度刚度比、低的摩擦及磨损。简要综述了多层涂层在摩擦学领域内新的研究进展，概括了目前多层涂层的制备方法及结构设计，并对今后的发展趋势作了探讨。     

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。     

制动条件下石墨对铜基摩擦材料瞬时摩擦性能的影响

为研究石墨对铜基摩擦材料瞬时摩擦性能的影响,采用粉末冶金技术制备铜-SiO2和铜-石墨-SiO2烧结材料,通过干摩擦惯性试验,在始末速度不同的制动区间,测试材料的瞬时摩擦因数、瞬时磨损率,并观察摩擦表面形貌的变化。结果表明:在高速度制动区间,石墨的存在使得铜基摩擦材料摩擦因数的稳定性明显提高,磨损率降低,原因在于铜-石墨-SiO2材料剥落石墨颗粒的分隔和保护作用,减弱冲击波动,从而提高瞬时摩擦因数稳定性并降低磨损;但较低制动速度时,石墨的存在反而提高了磨损率,原因在于摩擦层对颗粒的包裹度和基体强度降低。     

MoS2/C复合涂层在不同对磨副下的冲击磨损行为研究

在基于动能控制的冲击磨损设备上,以球-平面接触的方式,探究304不锈钢基体和MoS_2/C复合涂层在不同对磨副冲击下的磨损行为,并分析摩擦界面响应及磨损机制。结果表明:随着冲击副材料的弹性模量增加,冲击接触峰值力以及能量吸收率逐渐上升,对应的磨损量及磨损率也随之提高;MoS_2/C复合涂层的接触应力、能量吸收率以及磨损均要低于304不锈钢基体;涂层的冲击磨损形式主要为材料的剥落与磨屑堆积,磨损机制为塑性变形以及摩擦氧化。     

Influence of Thermal Fatigue on the Wear Behavior of Brake Discs Sliding against Organic and Semimetallic Friction Materials

ABSTRACT

In this article, brake discs are exposed to high thermal stress, causing thermal fatigue damage. The aim of this work is to study the evolution of the wear behavior of brake disc materials, such as cast iron, chromium steel, and metal matrix composites, under the influence of thermal fatigue. The brake disc specimens are heated and then cooled rapidly. Then, wear tests are carried out using a pin-on-disc-type tribometer. Organic and semimetallic friction materials are used for all wear tests. The results show that thermal fatigue affects the structure of the contact surfaces of all of the disc specimens by increasing their roughness. Furthermore, the wear rate of the friction materials increased, except a reduction of the wear rate is noted for the semimetallic friction material rubbing against cast iron. Moreover, thermal fatigue has no significant influence on the coefficient of friction. The worn surface of the metal matrix composite sliding against semimetallic friction material is characterized by abrasive and adhesive wear mechanisms.