铝合金弹性预应力超声喷丸成形试验

超声喷丸作为一种新型的板料成形技术,具有易操作,能耗少及优良成形性能等优点,广泛应用于板料成形中。但自由状态下,超声喷丸成形也易发生球面变形,因而提出了弹性预应力超声喷丸成形方法,以2024-T351铝合金壁板为研究对象,分析预弯力矩大小、成形轨迹和壁板厚度对成形曲率半径及成形性能的影响。试验中通过控制壁板展向的弯曲曲率来实现弹性预弯。结果表明:预应力超声喷丸能够大幅度减小壁板展向的成形曲率半径,同时增大弦向成形曲率半径,且随着预弯曲率半径的减小,这种减小和增大的效应随之逐渐增大。此外,与自由状态相比,预应力超声喷丸能够产生幅度和深度更大的残余压应力场,且表面粗糙度并未随着预弯曲率的增大而增加。分析认为,弹性预应力超声波喷丸能够进一步提高受喷材料的成形曲率并在一定程度上减小球面变形趋势,对大变形大厚度的单曲率零件成形具有重要的意义。     

Effect of prestressed ultrasonic peen forming parameters on bending curvature and spherical deformation of plate

The elastic prestressed ultrasonic peen forming (UPF) was adopted in order to solve problems of insufficient bending deformation and large spherical deformation of plate during free UPF. The theoretical analysis of prestressed UPF and the influence of elastic prebending moment on deformation were analyzed. Spherical deformation coefficient was defined to quantificationally describe the spherical deformation. Experiments were conducted to compare the differences between free UPF and prestressed UPF processes and the effects of processing parameters on bending curvature and spherical deformation coefficient were studied. The results show that peening trajectory in chordwise direction is beneficial to enlarging spanwise bending deformation and decreasing spherical deformation coefficient. Large prebending curvature is helpful to increase spanwise bending deformation and decrease chordwise deformation, thereby obviously decreasing spherical deformation coefficient. Large spanwise deformation can be obtained under large firing pin velocity, small plate thickness and small offset distance. Large firing pin velocity plays a positive role in decreasing spherical deformation, while plate thickness and offset distance have little effect on it. Above all, prebending curvature and peening trajectory are the most important factors during prestressed UPF process. This study provides guidance for parameters optimization of prestressed UPF for wing plate with large thickness.     

An analytical approach to relate shot peening parameters to Almen intensity

Shot peening is widely used in the automotive and aerospace industries to improve the fatigue strength of metal components by introducing near-surface plastic strains and compressive residual stresses. This mechanical treatment is primarily controlled by monitoring Almen (peening) intensity, which corresponds to the arc height at saturation of standardized test strips exposed to the shot stream. However, the same Almen intensity may be obtained by using small shots impacting the surface at high velocity or by using large shots impacting the surface at low velocity. This paper describes a model for predicting Almen intensity based on an analytical model for shot peening residual stresses. Theoretical results for different sets of peening parameters were consistent with published experimental results and revealed that although different combinations of shot peening parameters can produce the same Almen intensity, each combination resulted in a different through thickness residual stress distribution.     

316L不锈钢的低能量激光冲击强化工艺

以316L不锈钢作为模型材料,系统研究了低能量高重频激光冲击强化工艺。建立了激光光斑覆盖率概念,对于直径d为0.4~0.8 mm 间的光斑,其饱和覆盖率在6~7之间。在此饱和覆盖率条件下,机械手移动速率v与光斑直径d的匹配关系为v=70d。最大残余压应力随着光斑直径的减小而增大,当光斑直径d为0.4 mm时获得最大残余压应力为662 MPa,残余压应力影响层深度为565 μm。激光冲击强化区域表面粗糙度未明显增加,但与未冲击区域存在一定高度台阶。在1.59 GW/cm²激光功率密度下,该台阶高度为23 μm。     

喷丸数值模拟中一种高效方法

目的 从减小分析步时间的角度出发,调整弹丸随机分布间距,研究提高模拟计算效率的方法。方法 以SAE1070弹簧钢为研究对象,在S230弹丸速度为40 m/s条件下,分析弹丸间垂直间距、水平间距和弹丸冲击方式对模拟结果的影响。结果 在不考虑弹丸间相互作用的前提下,有限元模拟中弹丸间可存在重叠,只要弹丸垂直间距大于0.07 mm,水平间距大于0.4 mm,弹丸随机生成模拟得到的诱导应力分布、塑性应变分布、粗糙度的结果在小偏差范围内收敛,与弹丸间无重叠的模拟结果相近。在满足弹丸间距阈值的前提下,采用同时冲击和顺序冲击方式得到的诱导应力分布在压应力部分区域存在一定偏差,但应力分布曲线整体较为接近,同时冲击的计算时间缩短了约90%。在此基础上,确定合适的弹丸分布,在不同弹丸直径、速度下进行阿尔门试片喷丸模拟,通过对比阿尔门强度值论证了模拟方法的有效性。结论 这种按层分布同时冲击,并在满足间距阈值的前提下尽可能减小间距的弹丸设置方法,保证了模拟精度,提高了计算效率,为数值模拟的应用提供了优化计算成本的新思路。     

NUMERICAL SIMULATION OF CONTROLLING IN TITANIUM ALLOY SHEETS WELDING RESIDUAL STRESS BY TRAILING PEENING

It is a promising and new technology to apply welding with trailing peening to control welding stress and distortion of titanium alloy. Numerical simulation of conventional welding and welding with trailing peening of the titanium alloy sheet is carried out, using nonlinear finite element theory and the engineering analysis software MARC. The result shows that welding with trailing peening technology reduces longitudinal residual stress in welding joint effectively, and it is more effective to reduce residual stress to peen the weld than to peen the weld toe. It is a effective result that other technolooy and method used in welding can never achieved.     

基于ABAQUS的大尺寸弹丸喷丸过程数值模拟

利用ABAQUS软件建立了单弹丸和多弹丸的喷丸有限元模型,研究了大弹丸喷丸2024铝板的动力学过程,分析了弹丸直径和喷丸覆盖率对板材塑性应变和沿弹坑表面及厚度方向残余应力的影响。模拟结果表明,增加弹丸直径可以使板材塑性应变层及残余压应力层深度增大,弹坑尺寸及弹坑"凸边"附近的残余拉应力也随之增大;塑性应变层和压应力层深度随喷丸覆盖率的提高而增大,但覆盖率达到一定程度时增加不再明显。     

A 3D FE model with plastic shot for evaluation of equi-biaxial peening residual stress due to multi-impacts

A 3D multi-impact finite element (FE) model for evaluation of peening residual stress is presented. Combined peening factors by Kim et al. are applied to the 3D symmetry-cell originally contrived by Meguid et al. To describe the feature of multi-impacts, concepts such as FE peening coverage, impact sequence and cycle-repetition are introduced. We successfully extracted the equi-biaxial stress from the simulations of diverse single-cycle and multi-cycle impacts. At four impact locations of FE symmetry-cell, surface and maximum residual stresses converge to equi-biaxial stress, and convergence improves with the number of repetitions of cycle. Impact velocity needed for comparing the FE solution with the XRD result is determined from the Almen arc height and coverage. It is further found that the simulation set with plastic shot produces residual stress consistent with the experimental XRD result.     

喷丸方法对不规则构件表面残余应力分布规律的影响

目的 优化喷丸强化工艺,提升喷丸工艺的强化效果。方法 采用预定义场和基于移动矢量的快速建模方法,实现满足表面全覆盖和不同喷丸方法的有限元模拟。通过对模拟结果中的应力值进行局部坐标转换,分析不同喷丸方法条件下残余应力沿受喷构件表面切线方向的分布规律。结果 在喷射方向固定的喷丸方法中（方法-1）,弹丸撞击角度在不同区域内的变化范围为60°~90°,且随弹丸撞击角度的增加,弹丸撞击时的动能消耗率和应变能转变率分别由71.6%和5.3%提高到89.0%和7.5%,表面覆盖率也随之增加。在喷射角度固定的喷丸方法中（方法-2）,弹丸撞击角度始终为90°,表面覆盖率分布均匀,从而使得在凸圆弧面、斜面和凹圆弧面内采用方法-2获得的表面残余应力比方法-1的大,且两者差值沿+x方向呈现先增加、后保持稳定、再减少的变化规律。结论 与喷射方向固定的喷丸方法相比,采用喷射角度固定的喷丸方法,因弹丸撞击角度大,弹丸撞击动能消耗率及应变能转变率高,且表面全覆盖能得以保证,构件在凸圆弧面、斜面和凹圆弧面内能获得较大的表面残余压应力值。     

On the effect of the orientation of sheet rolling direction in shot peen forming

Peen forming is commonly used in the aerospace industry to shape large and thin panels, such as wing skins. This manufacturing process uses shot peening to introduce unbalanced compressive stresses near the surface of the component. These stresses tend to bend the panel and, when optimized, lead to the desired contour. Sheet materials often exhibit both elastic and plastic anisotropy, which can alter the development of curvatures. Since peen forming relies on compressive stresses to upset equilibrium, resulting curvatures may also be affected by initial stresses in the part. In this work, the influence of the rolling direction orientation with respect to the sample was investigated experimentally and numerically for the first time for aluminium alloy 2024-T3 specimens. Although maximum deflections were only slightly dependent on the rolling direction orientation, it was found that radii of curvature varied by as much as 10% with respect to this parameter. Finite element simulations allowed quantification of the individual effects of non-equibiaxial initial stresses and elastic orthotropy. It was found that these factors can significantly influence curvature development. Comparison of experimental and numerical results suggested that plastic anisotropy should also be taken into account in future studies. The tools developed in this study show promises for the accurate prediction of peen forming process for large scale components.     

300M钢件表面的喷丸强化

针对300M钢材料研究了4种不同喷丸工艺。分别对喷丸层的残余应力、组织结构、显微硬度及其分布和表面粗糙度进行了测试与分析。结果表明,高硬度陶瓷丸在较低的喷丸强度下可以获得较高的残余压应力,且不会大幅度提高表面粗糙度值;钢丝切丸喷丸后虽然得到比较好的残余应力分布,但伴随的是表面粗糙度值的大幅提高;大粒径高强度钢丝喷丸不会使残余压应力水平得到很好的提高,而是会大幅增加粗糙度值;钢丝切丸+陶瓷丸的复合喷丸强化工艺在粗糙度改变不大的前提下,可以获得较好的强化效果和表层组织结构。     

超声滚压工艺研究

超声滚压工艺是一项复合超声冲击强化和滚压于一体的表面强化工艺,其优点是既能得到足够的压力层深度,又能得到较低的表面粗糙度值。研究了不同加工参数对弧高和表面粗糙度的影响,结果表明:步距、静压力和路径规划对弧高和表面粗糙度有着显著的影响,且发现残余压应力分布对于滚压方向敏感,滚压方向的残余压应力比其垂向的残余压应力小。Inconel 718材料经超声滚压强化后的表面粗糙度值可降低至Ra0.1μm,压力层深度可达0.5 mm,且具有较好的热稳定性。     

基于DEM-FEM的微粒喷丸仿真分析

微粒喷丸作为一种新兴的喷丸工艺,由于工艺试验数据与仿真技术的缺失,其作用机理尚未探明。基于ABAQUS二次开发,采用离散元与有限元（DEM-FEM）相结合的方法,构建考虑初始残余应力与硬化层梯度的随机多弹丸微粒喷丸弹塑性模型,探究微粒喷丸的喷射速度与覆盖率对残余应力分布和表面粗糙度的影响规律。发现随着微粒喷丸喷射速度的增加,靶体表面粗糙度的算术平均偏差Sa线性增加;覆盖率达到100%后,覆盖率大小对Sa与残余压应力分布影响不大;喷射速度对于微粒喷丸的最大残余压应力值影响不大,但对残余应力层的厚度有显著影响。通过DEM-FEM耦合方法对微粒喷丸机理进行探究,为工艺参数的制定提供理论支撑。     

表面强化处理对工业纯钛焊接接头电化学腐蚀性能的影响

为了改善焊接接头的性能,延长其使用寿命,实验采用喷丸强度为0.15A的超声喷丸处理(USSP)方式对工业纯钛TA2焊接接头进行强化。通过OM、SEM、TEM分别对TA2焊接接头各区域组织及腐蚀形貌进行观测,对不同工艺处理试样的残余应力值、表面粗糙度进行了测定,并对超声喷丸后试样表面进行热处理和表面打磨,研究了不同表面残余应力及表面粗糙度对焊接接头焊缝区域在80℃ 的10% HCl溶液中的电化学腐蚀性能。结果表明,USSP强化处理纯钛焊接接头耐腐蚀性能有所提升。经退火处理后,随着退火时间的增加,耐腐蚀性能先增加后降低,退火0.5h时,自然腐蚀电位最高,电流密度最低,耐腐蚀性能最优。经表面打磨处理,腐蚀速率主要由扩散步骤控制,产生浓差极化,随着打磨强化层的增加,扩散速率加快,耐腐蚀性能有提高。打磨至强化层2/5处时,耐腐蚀性能提升明显。     

先进喷丸成形技术及其应用与发展

介绍了包括预应力喷丸成形技术、数字化喷丸成形技术、双面喷丸成形技术、激光喷丸成形技术、超声喷丸成形技术和高压水喷丸成形技术等新型喷丸技术,并对这些喷丸技术的基本原理、研究和应用现状以及发展趋势进行了分析,对我国开展喷丸成形技术的研究和开发具有指导意义。     

预弯工艺参数对UOE焊管O成形的影响

采用有限元分析方法研究了焊管UOE成形技术预弯工艺参数——预弯弧度和预弯半径对O成形的影响。研究发现,预弯工艺可以改善板料O成形后的曲率分布,在预弯弧度大于25°时,O成形后管坯的边缘直边现象得到明显改善。随预弯弧度的增加,O成形后的管坯曲率逐渐趋于均一,但是成形载荷随预弯弧度的增加而增加。预弯半径为焊管名义半径的1.0～1.3倍时,可以获得较好的形状,过大或过小都会使O成形后管坯的曲率沿弧长方向急剧变化。在相同压缩率的情况下,在上述合理的预弯半径范围内所需成形载荷较大,但是在相同变形载荷下,采用上述预弯半径仍然可以优先获得较好的形状。     

激光冲击强化技术在核电领域的研究进展

激光冲击强化技术属于改善金属性能的重要表面形变强化技术,因其独特的技术优势在航天及船舶领域获得广泛应用。 随着科技的发展研发出多种激光冲击强化技术,并逐渐开始在核电装备领域获得应用,然而针对该技术在核电领域的研究进展缺乏系统的综述。先通过介绍不同表面形变强化技术,叙述激光冲击强化技术的发展,阐述激光冲击强化机制,最后综述激光冲击强化技术在核电领域的应用研究进展。总结发现,激光冲击强化技术可有效改善核电领域材料力学、摩擦磨损及腐蚀性能,但传统和添加辅助手段激光冲击强化技术受约束层和吸收层影响较大,无涂激光冲击强化技术对金属易产生热效应, 飞秒激光冲击强化影响层浅且强化效果差,不同工艺技术在核电领域提升摩擦磨损性能研究较少。对不同工艺激光冲击强化机理及在核电领域材料不同性能的提升进行深入研究,为进一步提升激光冲击强化技术在核电领域材料的应用提供理论基础,可为核电领域关键装备进行强化、提升核电装备运行寿命提供参考。     

冲击波动态传播特性对激光喷丸残余应力场的影响

以TC4钛合金为研究对象,基于Johnson-Cook本构模型,分析了高应变率效应对激光喷丸过程中塑性波波速的影响。通过三维有限元方法模拟了不同作用参数激光喷丸诱导冲击波的传播过程,探讨了多次激光喷丸作用后残余压应力饱和现象的产生机理及利用该效应获得均匀表面残余压应力的方法。结果表明:高应变率效应对激光喷丸作用过程中塑性波速度有显著影响,塑性波的速度与所产生的塑性应变呈反比关系。功率密度越大,初始产生的塑性应变越大,塑性波速度越小,冲击波能量衰减越快,冲击波压力幅值降低越快;相同激光喷丸功率密度,随着作用次数的增加,产生的塑性应变逐渐减小,塑性波速度增大,冲击波压力衰减变缓,使激光喷丸诱导的残余压应力逐渐增大;作用次数达到3~4次时,衰减过程基本相似,诱导的残余压应力增幅不大,作用效果基本达到饱和。利用多次激光喷丸作用产生的饱和效应,当激光光斑搭接率超过50%时,即可使搭接区域作用次数达到3次及以上,使激光喷丸作用效果达到饱和,可获得均匀的表面残余压应力。     

钛合金薄壁叶片喷丸变形的研究

目的 研究喷丸工艺对钛合金薄壁叶片变形的影响,找到解决喷丸变形的方法 .方法 对钛合金薄壁叶片进行喷丸强化,采用三坐标测定喷丸前后叶片的尺寸变化情况.结果 在喷丸强度和覆盖率一致的前提下,采用不同的路径对叶片进行喷丸后,叶片的变形趋势和变形量没有很大差异.叶片进行喷丸后,采用相同的喷丸强度对叶片进行二次喷丸,叶片几乎不发生变形,需要采用更高的喷丸强度进行二次喷丸才可以使叶片发生变形.在喷丸之前对叶片进行真空去应力,虽然叶片表面的残余应力有相应减少,但与不进行真空去应力的叶片相比,喷丸变形情况没有发生太大的改变.结论 可采用喷丸前预变形和喷丸校正的方法 解决喷丸变形的问题,使得叶片喷丸后的尺寸达到图纸的要求.     

超窄间隙焊剂带约束电弧电压及电流波形特征

为认清焊剂带约束电弧在超窄间隙中的作用,在放置焊剂带的I形坡口中进行熔化极电弧焊接试验.试验发现,坡口侧壁根部焊剂带裸露高度,控制着坡口侧壁的熔化高度;当裸露高度很小时,电弧的作用范围主要集中在坡口的底部,短路结束燃弧开始时弧长较长,在电压波形上表现为初始燃弧电压高,随后快速降低;电流波形反映出较高的短路电流峰值.结果表明,随裸露高度的增加,电弧作用范围从坡口底部向侧壁扩张,电弧长度缩短,瞬时燃弧电压降低,燃弧后电压下降速度变慢,甚至不再下降;同时反映出短路频率提高,短路电流峰值减小,瞬时短路出现几率增加.