喷丸工艺对17CrNi2Mo钢喷丸层残余应力分布及残余奥氏体含量的影响

采用不同的喷丸工艺对渗碳淬火17CrNi2Mo钢进行表面强化处理,研究了喷丸工艺对喷丸层残余应力分布及残余奥氏体含量的影响。结果表明:喷丸能在17CrNi2Mo钢表层产生残余压应力,且残余压应力随层深增加而先增加后减小;增大喷丸强度,喷丸层的表面残余压应力、最大残余压应力及其影响层深均增大;增加喷丸次数可增大表面残余压应力和最大残余压应力;喷丸能降低喷丸层的残余奥氏体含量,喷丸强度或喷丸次数越大,残余奥氏体含量越低;残余奥氏体含量随层深增大而增加。     

水射流喷丸强化残余应力场的有限元模拟

针对水射流的高湍动特性与受喷靶体材料复杂的弹塑性形变行为,提供一种水射流喷丸强化残余应力场的有限元分析方法.基于准静态压力分布和非线性轴对称面分布载荷,采用多线性各向同性强化的Mises率不相关弹塑性模型,应用Prandtl-Reuss塑性增量理论及增量初应力法,利用线性斜坡载荷加载制度,运用ANSYS有限元软件模拟不同压力作用下水射流喷丸在2A11铝合金材料表层产生的残余应力场,获得残余应力场的分布规律及残余应力沿层深和径向的变化规律,指出残余应力沿层深分为残余压应力区和残余拉应力区,沿径向分为第Ⅰ残余压应力区、残余拉应力区和第Ⅱ残余压应力区,得到表面残余压应力、表层最大残余压应力、残余压应力层深度随着喷丸压力的增加而增大.为验证有限元模拟的正确性,对喷丸表面残余压应力进行试验验证,结果表明,有限元法计算的表面残余压应力值与试验数据近似吻合.     

喷丸工艺参数对H13钢表面质量的影响

为了研究喷丸工艺参数对H13钢表面质量的影响,对H13钢喷丸处理前后的表面粗糙度、表层硬度、表层残余应力及截面显微组织进行了试验检测分析。结果表明:H13钢表面粗糙度随喷丸压力增大而增大;从45°到90°时,粗糙度随着喷丸角度的增大而增大。随着喷丸压力和角度的增大,H13钢的表面硬度增大,且形成300μm左右的硬化层;当喷丸压力从0.2MPa升到0.55MPa,表面硬度则从54.5HRC提高到60HRC。喷丸后表面形成残余压应力,且与喷丸角度呈现单调递增的关系。残余应力深度随着喷丸压力的增大而增大,并在喷丸压力为0.5MPa时趋于稳定。喷丸压力为0.55MPa时残余压应力层深为480μm;喷丸角度从45°到90°,残余压应力层深从350μm增加到470μm。     

不同强度喷丸处理后铝锂合金表面的残余应力

在不同喷丸强度下对铝锂合金进行了表面喷丸处理,采用X射线衍射法和盲孔法分析了其表面及近表层的残余应力。结果表明:采用不同喷丸强度处理后试样表面90°方向(平行喷嘴移动方向)的残余压应力高于0°方向(垂直喷嘴移动方向)的,90°方向的衍射峰积分宽度大于0°方向的,说明喷丸强化后试样在90°方向产生了更大的微应变;试样近表层残余压应力随层深的增加先增大后减小,最终趋于0;较高强度喷丸处理后试样表面和距表面0.15mm内的残余压应力小于较低喷丸强度处理的,而最大残余压应力、最大残余压应力深度以及残余压应力场深度均大于较低强度喷丸处理后的。     

基于ANSYS/LS-DYNA的受控喷丸工艺过程仿真

将喷丸过程简化为丸粒撞击工件的模型,丸粒看作刚性体,运用ANSYS/LS-DYNA软件进行了数值模拟,分析了覆盖率对残余压应力分布的影响,得出在不完整喷丸覆盖率下工件表面会产生残余拉应力.在单个丸粒模型中,将丸粒的材料改为塑性硬化材料,分析丸粒的速度对残余压应力分布的影响,得出丸粒的材料参数一定时,存在最优喷丸速度,丸速过高会导致丸粒的变形能增加,而使工件表层的最大压应力值和应力层深度下降.     

喷丸工艺对18Cr2Ni4WA钢残余应力影响的有限元模拟

采用ANSYS/LS-DYNA有限元软件模拟了在不同弹丸速度和半径下喷丸强化后18Cr2Ni4WA钢的表层残余应力分布,并进行了试验验证。结果表明:18Cr2Ni4WA钢表层中最大残余压应力随着弹丸速度或弹丸半径的增加均先增大后减小,当弹丸速度为120m·s-1、弹丸半径为0.6mm时喷丸强化效果较佳;喷丸后钢表层残余应力分布的模拟结果和试验结果相吻合,证明了模型的准确性。     

裂纹柔度法测喷丸残余应力的研究

本文利用裂纹柔度法检测喷丸45钢板的残余应力大小及分布,并将其检测结果与X射线法测得的结果进行比较。试验发现,二者具有相近的分布趋势,硬化层深分别为900μm和820μm,最大残余压应力分别在近表层300μm处约471.4MPa和在近表层120μm处约446.4MPa,即裂纹柔度法可用于喷丸板类构件内部残余应力的测定,且结果准确可靠。     

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。     

喷丸齿轮残余应力数值分析与仿真

对比齿轮表层经喷丸处理和未喷丸处理效果,运用X射线应力测定仪进行齿轮表面残余应力测试实验,分析喷丸强化与齿轮表面残余应力之间的关系;基于有限元方法开展齿轮喷丸残余应力场数值模拟分析与仿真,建立基础撞击简化模型,分析揭示喷丸强化处理后齿面表层应力分布规律;讨论弹丸速度和直径大小对表面残余压应力变化的影响,相关结论对于工程实践具有一定的指导意义和参考价值。     

前混合水射流多弹丸喷丸模型及残余应力场的数值模拟

针对前混合水射流的液固湍动特性与喷丸过程多重非线性耦合作用行为,提供一种射流喷丸强化残余应力场的有限元分析法。采用液固两相流动理论与计算流体动力学方法分析喷嘴内流特性,建立射流多弹丸喷丸模型;基于弹丸速度冲击载荷加载制度,利用多线性各向同性强化弹塑性模型,应用动态接触对称罚函数法,运用ABAQUS软件模拟不同弹丸数量作用下射流喷丸在45钢材料表层产生的残余应力场,获得残余应力场的分布规律及残余应力沿深度的变化规律;得出射流喷嘴内流呈均质流流型,不同弹丸数量射流喷丸在材料表层产生的径向残余应力沿深度的变化规律相同,但在材料表面产生的径向残余压应力值受喷丸模型影响较大,对弹丸分三层排列、相邻弹丸之间径向和周向中心距离均为弹丸半径的多弹丸喷丸模型,数值模拟获得的表面径向残余压应力值与射流喷丸试验数据基本吻合。     

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.     

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.     

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.     

铝合金超声波喷丸成形制件表面完整性研究

采用试验方法对AA2024-T351进行数控超声波喷丸成形,研究了超声波喷丸成形制件的显微硬度、残余应力场、表面形貌、表面粗糙度及半高宽等随超声波喷丸过程参数变化的规律,定性地探讨了AA2024-T351超声波喷丸后表面完整性的改善状况。结果表明:超声波喷丸后,制件的显微硬度得到了明显提高（最大增幅为20%）,同时在材料表面产生了一定厚度的硬化层（深度约为300μm）;制件内部引入数值较高、分布呈现梯度形式的残余压应力场,残余压应力场的临界深度在500~650μm之间,在距表面200μm处产生了最大残余压应力;制件表面形成一道道犁沟,表面喷丸区域的粗糙度Ra有一定程度的增大;制件表面层的半高宽值变大,深度在125μm左右,半高宽的增大表明材料冷作硬化程度加大、晶体内部位错密度有一定程度的增大。显微硬度的提高、残余压应力场的引入及表面层组织的细化有助于喷丸成形制件疲劳寿命、抗磨损和抗腐蚀性能的提高。     

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.     

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。     

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。     

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.     

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。     

Experimental study on grinding-induced residual stress in C-250 maraging steel

Residual stress plays a significant role in the performance of a part, while the residual stress in the ground maraging steel, which is often used in the manufacture of precision parts, is rarely mentioned. In order to understand the variations of residual stress in ground maraging steel and provide insight into the controlled-stress grinding process of the steel, the surface and subsurface residual stress distributions in ground C-250 maraging steel (3J33) were studied. The results show that the mechanical effects dominate the thermal effects in the dry grinding process, indicated by only compressive residual stress generated in the ground workpiece. Furthermore, more insights into the residual stress distribution were provided by proposing four residual stress distribution parameters including surface residual stress, peak compressive residual stress, the depth of peak compressive residual stress, and residual stress penetration depth. The variations of these parameters were comprehensively studied. Results show that the surface residual stress and peak compressive residual stress depend greatly on the grinding speed and higher grinding speed generates larger compressive residual stress, while the depth of peak compressive residual stress varies slightly with the grinding parameters. The residual stress penetration depth increases with the increase of the grinding speed and grinding depth, and decreases with the increase of the workpiece speed. The results in this study can be used to assist in controlled-stress grinding applications for high performance critical parts of maraging steel.