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。     

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...     

AZ31B镁合金激光喷丸强化后疲劳裂纹扩展的数值模拟研究

激光喷丸(LSP)是一种先进的材料表面强化工艺,能有效提高零件的机械性能及其使角寿命.建立了以有限元软件ABAQUS和MSC.Fatigue为平台,面向抗疲劳制造的激光喷丸工艺有限元分析模型.结果表日月激光喷丸可以有效抑制疲劳裂纹扩展,延长疲劳寿命,喷丸次数的增加在一定程度上增大残余应力及疲劳寿命.残余应力抑制疲劳裂纹扩展的原因归结为最终断裂尺寸的增大以及裂纹扩展速度的减小.研究结果为LSP抗疲劳效果的预测提供了有效的方法,对于优化工艺参数,减少试验次数,降低成本具有指导意义.     

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.     

激光冲击强化对TC17表面硬度的影响

TC17钛合金叶片耐磨性较差,在航空发动机恶劣的使用环境下受到冲刷磨损的作用易引发疲劳断裂。研究利用激光冲击强化技术对TC17钛合金进行表面强化,结果表明:激光冲击强化能够显著提高TC17材料硬度,提升材料抗冲刷磨损性能。从不同冲击参数强化后硬度测试结果得出,功率密度4GW/cm2、冲击三次为TC17钛合金最佳的激光冲击强化工艺参数,其硬度提高幅度达到10%以上,并且影响深度超过1mm。激光冲击强化过程中引入的表层晶粒纳米级细化及次表层高密度位错是材料硬度提高的主要原因。     

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.     

The effects of laser peening and shot peening on fretting fatigue in Ti-6Al-4V coupons

This paper describes testing of Ti-6Al-4V coupons in fretting fatigue and compares the effects of mechanical surface treatments on performance. Fretting fatigue tests were performed using a proving ring for fretting load, bridge-type fretting pads, and applied tension-tension cyclic fatigue stress. As-machined (AM), shot peened (SP), and laser peened (LP) coupons were evaluated, and data generated to compare residual stress, surface condition, lifetime, and fractographic detail encountered for each. Near-surface residual stress in SP and LP coupons was similar. The layer of compressive residual stress was far deeper in LP coupons than in SP coupons and, consequently, subsurface tensile residual stress was significantly greater in LP coupons than in SP coupons. SP coupons exhibited a rough surface and had the greatest volume of fretting-induced wear. LP coupons exhibited a wavy surface and had a small volume of wear localized at wave peaks. SP coupons had the greatest fretting fatigue lifetime, with significant improvement over AM coupons. Lifetimes of LP coupons were similar to those for SP coupons at high fatigue stress, but fell between AM and SP coupons at lower fatigue stress. Fractographic evaluation showed that fractures of AM samples were preceded by initiation of fretting-induced cracks, transition of a lead fretting crack to mode-I fatigue crack growth, and crack growth to failure. SP and LP samples exhibited behavior similar to AM samples at high fatigue stress, but in coupons tested at low stress the lead crack initiated subsurface, near the measured depth of maximum tensile residual stress, despite the presence of fretting-induced cracks. The level of fatigue stress above which lead cracks were initiated by fretting was higher for LP than for SP, and was predicted with good accuracy using an analysis based on linear elastic fracture mechanics, the fatigue crack growth threshold stress intensity factor range, and superposition of measured residual stress and applied fatigue stress.     

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.     

基于CATIA与MATLAB开发激光喷丸强化轨迹的方法研究

激光喷丸轨迹路径是喷丸强化工艺的重要环节,首先基于CATIA二次开发,进行激光喷丸强化工艺轨迹规划平台的开发,将喷丸区域CAD几何特征提取与喷丸轨迹规划、生成、渲染及输出功能集成到一体化的人机交互界面,并探究了不同激光光斑形状、表面曲率及喷丸搭接率情况下喷丸轨迹数据点的生成及输出.同时利用MATLAB软件编写喷丸轨迹运...     

基于CATIA与MATLAB开发激光喷丸强化轨迹的方法研究

激光喷丸轨迹路径是喷丸强化工艺的重要环节,文中首先基于CATIA二次开发,进行激光喷丸强化工艺轨迹规划平台的开发,将喷丸区域CAD几何特征提取与喷丸轨迹规划、生成、渲染及输出功能集成到一体化的人机交互界面,并探究了不同激光光斑形状、表面曲率及喷丸搭接率情况下喷丸轨迹数据点的生成及输出。同时利用MATLAB软件编写喷丸轨迹运动模拟仿真界面,分析模拟轨迹结果的可靠性。结果表明:借助CATIA二次开发及MATLAB编程,实现轨迹平台用于激光喷丸轨迹生成及结果输出的基本功能,并能对喷丸工艺轨迹可视化模拟分析,为后续激光喷丸工艺的数值模拟及试验工作提供一定支持。     

Effect of high power diode laser surface melting on wear resistance of magnesium alloys

In the present work, an attempt has been made to improve the surface hardness and wear properties of magnesium alloys AZ31 and AZ61 through solid solution hardening and refinement of microstructures using a 1.5 kW high power diode laser (HPDL) as a heat generating source. One millimetre thick uniform overlapping melt tracks were produced on Mg alloy samples. Laser-melted samples were subjected to a two-body abrasive wear test using a modified pin-on-disc set up. The hardness and wear resistance of laser-melted samples were found far better than the as-received Mg alloy substrates. Scanning electron microscopy was used to examine microstructure of the laser-melted layers and the worn surface morphology. Fine microstructures were observed with an average grain size of less than 5 μm.     

Experimental study on a noncontact method using laser displacement sensors to measure vibration stress in piping systems

This study presents a noncontact measurement method of vibration induced stress (vibration stress) using multiple laser displacement sensors and clarifies its applicability to piping vibration. In the beam structures such as piping, the stress due to bending deformation can be caused by vibration. In the presented method, the vibration displacement in the beam structures induced by the bending deformation is measured at three different locations using laser displacement sensors in a noncontact manner and the vibration stress is estimated by a simple calculation based on the beam theory. First, an applicability validation of the presented method was done by a vibration test using a cantilevered beam plate. This validation was done by comparing measurements by the presented method and the conventional method using strain gauges. Next, an experimental validation was conducted by the vibration test using a pipe specimen, and the applicability to the piping vibration was confirmed.     

Inheritance and the residual stress in the surface layer of machine parts

A method is proposed for calculating the residual stress in the surface layer of ground corrosion-resistant steel parts.     

Design of a laser welded thin metal tube structure incorporating welding distortion and residual stress

The welding process, incorporating rapid heating and cooling, generates distortion and residual stress in the welded structures. In the design of a high quality welded structures, the weld distortion and residual stress have to be considered in advance. Especially, for the thin metal welded structures, the thermal distortion and residual stress have a severe effect on the structure’s precision, fatigue strength, buckling strength and so on. This study aims to analyze the design candidates of a laser welded thin metal tube structure in the view point of welding distortion and residual stress. Three design candidates were fabricated, and then the distortion was measured. And the residual stress distributions were calculated by using a commercial FEM package. The analysis results show that the distortion and residual stress were affected according to the position of weld line and the design of structure. By using the analyses the best one among the three design candidates was selected finally.     

Effect of curvature radius on the residual stress of thin-walled parts in laser direct forming

The International Journal of Advanced Manufacturing Technology - In laser direct forming, part geometry especially the curvature radius has a significant effect on the residual stress of the...     

42CrMo钢精车加工表面残余应力有限元仿真研究

基于ABAQUS软件建立了42CrMo锻钢活塞外圆精车加工的二维切削仿真模型,采用单因素法研究了切削参数对残余应力的影响规律.结果 表明:42CrMo钢精车加工过程中,热应力引起的残余拉应力起主导作用,已加工表面产生残余拉应力并沿深度方向迅速转变为压应力.残余应力层深度随进给量和背吃刀量的增大而增大,切削速度对残余应力层深度影响不显著.表面残余拉应力随切削速度和进给量的增大而增大,背吃刀量对表面残余应力影响不显著.最大残余拉应力出现在工件已加工表面以下,表面残余应力、最大残余拉应力和最大残余压应力随切削参数的变化趋势与切削温度随切削参数的变化趋势基本一致.     

Tribological analysis of fracture conditions in thin surface coatings by 3D FEM modelling and stress simulations

A tribological analysis of deformations and stresses generated and their influence on crack generation and surface fracture in a coated surface loaded by a sliding sphere in dry conditions is presented. A three-dimensional finite element method (3D FEM) model has been developed for calculating the first principal stress distribution in the scratch tester contact of a diamond spherical tip with 200 μm radius sliding with increasing load on a 2 μm thick titanium nitride coated steel surface. The model is comprehensive in that sense that it considers elastic, plastic and fracture behaviour of the surfaces. The hard coating will be stretched and accumulates high tensile stresses. At the same time, it is carrying part of the load and thus reducing the compressional stresses in the substrate under the sliding tip. The first crack is initiated at the top of the coating from bending and pulling actions and it grows down through the coating. The fracture toughness of the coating is calculated by identifying from a scratch test experiment the location of the first cracks and the crack density and using this as input data.     

Investigation of the coupled distribution of initial and machining-induced residual stress on the surface of thin-walled parts

Residual stress on the machined surface and the subsurface is known to influence the distortion of thin-walled parts. Therefore, it is essential to predict the distribution of surface residual stress accurately. In this paper, the coupled distribution law of initial residual stress and machining-induced residual stress is investigated. Firstly, a model with initial residual stress is established and incorporated into thermal mechanical coupled finite element model of 2-D cutting. Then, a tensile fixture is designed to impose initial stress into a thin-walled part of Al-6061, and cutting experiments are carried out. The residual stress distribution is measured by X-ray diffraction/electropolishing method. The results of experiments and simulation show that in the plastic deformation zone, the initial residual stress has no significant influence on the distribution of the machining-induced residual stress. In the elastic deformation zone, the stress that linear grows along depth from zero to initial residual stress is superimposed on machining-induced residual stress. The mathematical model of stress coupling distribution on the surface of thin-walled parts is established by numerical method. Finally, it is found that the effect of coupled stress distribution on distortion is more significant with the decrease of thickness (from 3 to 0.5 mm) of the thin-walled parts.     

Comprehensive residual stress distributions in a range of plate and pipe components

A comprehensive review of through thickness transverse residual stress distributions in a range of as-welded and mechanically bent components made up of a range of steels has been carried out, and simplified generic transverse residual stress profiles for a plate and pipe components have been proposed. The geometries consisted of welded pipe butt joints, T-plate joints, tubular T-joints, tubular Y-joints and a pipe on plate joints as well as cold bent tubes and pipes. The collected data covered a range of engineering steels including ferritic, austenitic, C-Mn and Cr-Mo steels. Measured residual stress data, normalised with respect to the parent material yield stress, has shown a good linear correlation versus the normalised depth of the region containing the residual stress resulting from the welding or cold-bending process. The proposed simplified generic residual stress profiles based on the mean statistical linear fit of all the data provides a reasonably conservative prediction of the stress intensity factors. Whereas the profiles for the assessment procedures are fixed and case specific, the simple bilinear profiles for the residual stresses obtained by shifting the mean and bending stress from the mean regression line have been proposed and validated.     

复合材料板应力集中数值模拟分析及光弹性实验验证

荷载作用下复合材料构件应力分布状态的分析是工程实践中的一个重要环节。构件中的应力集中现象将使其产生疲劳裂纹,也能使脆性材料制成的零件发生静载断裂。而对应力集中区域的有限元计算分析是一种数值模拟方法,有一定局限性,但其有效性可以通过相应的光弹性实验加以验证。