多次激光冲击导致的Ti17合金层裂

为研究激光冲击Ti17合金中厚样品的层裂特性和层裂阈值,对样品(厚5 mm)表面进行单点连续1~8次激光冲击,激光工艺参数为:频率1 Hz,脉宽15 ns,激光能量30 J,方形光斑4 mm×4 mm。采用白光干涉仪、超声波无损检测技术和扫描电镜,分析和检测中厚样品冲击区域的表面形貌、内部损伤以及层裂形貌。实验结果表明,连续从4次到5次激光冲击中厚样品的表面凹坑深度增加值最大为64.5%。连续5次激光冲击为中厚样品层裂阈值,层裂面积随冲击次数增加而增加。连续5~8次激光冲击中厚样品层裂厚度的实验值为280~310μm。层裂机理为韧性微孔洞的形核、增长和汇合,形成晶界失效和晶内失效。研究结果可为激光冲击强化整体叶盘改性提供工艺参考。

激光冲击强化Al7050–T7451合金紧固孔的残余应力研究

为研究不同激光冲击强化轨迹对Al7050–T7451合金紧固孔残余应力的影响,改善紧固件疲劳寿命,采用ABAQUS有限元模型和生死单元技术,对Al7050–T7451合金紧固孔开展先强化后开孔和先开孔后强化的残余应力数值模拟试验研究。研究结果表明,4个十字交叉光斑激光冲击强化Al7050–T7451合金表面S;残余压应力数值模拟结果接近试验测试值,先强化后开孔数值模拟结果与试验测试值接近,验证模型正确性。与先开孔后强化相比,先强化后开孔Al7050–T7451合金紧固孔的表面S;残余压应力值更大。与2个横向光斑相比,2个纵向光斑激光冲击强化紧固孔的表面S;残余压应力值更大。与2个光斑相比,4个十字交叉光斑激光冲击强化紧固孔的表面S;残余压应力值更大。研究结果为改善激光冲击强化紧固孔疲劳寿命奠定基础。

激光冲击强化叶片的防层裂研究

为了避免激光冲击强化叶片边缘产生层裂,提高叶片强化效果,在叶片背面采用吸波层技术进行激光冲击强化,研究无吸波层、铝箔吸波层、铝箔和水帘吸波层三种情况下的叶片背面形貌。结果表明:无吸波层的叶片背面产生了层裂现象,铝箔吸波层的叶片背面铝箔有凸起现象,铝箔和水帘吸波层的叶片背面铝箔无凸起现象。因此,吸波层对激光冲击强化叶片的效果具有重要影响。

激光冲击2050铝锂合金残余应力及疲劳性能研究

激光冲击强化是一种先进的材料表面抗疲劳制造技术,本文采用正交试验方法研究了激光冲击2050铝锂合金表面残余应力分布规律,获得了优化的激光冲击参数,并在此参数下验证了疲劳寿命增益。研究结果表明:激光冲击强化诱导的残余应力与试样的几何特性相关性较强,而激光冲击参数本身搭接率对残余应力的影响大于激光能量、大于冲击次数,最佳工艺参数为激光功率密度5.30 GW·cm^(-2)、搭接率50%、2次冲击。采用此参数冲击后260 MPa和200 MPa应力水平下疲劳寿命分别提高了22%和63%。

激光冲击强化TC17叶片前缘模拟件的抗FOD性能

为研究激光冲击强化(LSP)叶片前缘抗外物损伤(FOD)性能,设计截面尺寸近似叶片前缘的缺口模拟件。采用YAG激光器(30 J和15 ns)和方形光斑(4 mm×4 mm)对TC17模拟件的缺口尖端进行双面LSP。采用X射线衍射仪、透射电镜、高频疲劳试验机和扫描电镜分别对LSP前后的残余应力、微观组织、疲劳性能和疲劳断口进行测试分析。结果表明,与未强化缺口模拟件相比,LSP-TC17合金的表面残余压应力最大值为-403MPa。LSP-TC17合金表面形成高密度位错、孪晶和纳米晶。LSP-TC17缺口模拟件的疲劳强度提高55.6%。TC17缺口模拟件的疲劳强化机理为高幅残余压应力和表面纳米晶。研究结果为LSP-FOD叶片奠定理论基础并提供工艺参考。

A micro-scale strain rosette for residual stress measurement by SEM Moiré method

In this paper,a new method combining focused ion beam(FIB)and scanning electron microscope(SEM)Moirétechnique for the measurement of residual stress at micro scale is proposed.The FIB is employed to introduce stress relief like the macro ring-core method and fabricate gratings with a frequency of 5000 lines/mm on the measured area of the sample surface.Three groups of gratings in different radial directions are manufactured in order to form a micro-scale strain rosette.After milling ring-core by FIB,the deformation incurred by relief of the stress will be recorded with the strain rosette.The displacement/strain field can be measured using SEM scanning Moiréwith random phase-shifting algorithm.In this study,the Nickel alloy GH4169 sample(which was processed by laser shock peening)is selected as a study object to determine its residual stress.The results showed that the components of the in-plane principal stresses were-359 MPa and-207 MPa,respectively,which show good agreement with the results obtained from the available literature.

超高应变率激光冲击不同厚度Al7050合金的层裂研究（英文）

分析不同工艺参数(工艺1和工艺2)激光冲击不同厚度Al7050合金的层裂特性,研究Al7050合金的层裂机理和层裂阈值。采用光子多普勒测速(PDV)系统和扫描电镜(SEM),分析工艺1激光冲击0.33 mm厚Al7050合金的自由面质点速度和自由面层裂断口形貌。采用超声波无损检测、光学显微镜(OM)和扫描电镜(SEM),分析工艺2激光冲击5mm厚Al7050合金的层裂大小、层裂厚度和层裂断口形貌。研究结果表明,基于PDV测试数据,获得激光冲击0.33 mm厚Al7050合金的层裂强度和激光冲击应变率。0.33mm厚Al7050合金的自由面断口形貌被详细分析。随着连续激光冲击次数增加,5mm厚Al7050合金的层裂尺寸增加,层裂厚度范围为343μm到364μm。层裂机理为微空洞的韧性断裂和直裂纹的脆性断裂的混合断裂。单点连续5次激光冲击为5 mm厚Al7050合金的层裂阈值。与基体材料相比,单点连续5次激光冲击5mm厚Al7050合金的表层显微硬度提高,而自由面附近的显微硬度降低。研究结果不仅为激光冲击强化铝合金的层裂行为研究提供重要见解,而且为激光冲击强化工业应用避免层裂提供基础研究。

连续激光冲击强化7050铝合金中厚板的过喷效应

基于连续激光冲击强化7050铝合金中厚板的表面完整性和内部层裂,提出了一种激光冲击强化的过喷效应。7050铝合金中厚板尺寸为50 mm×50 mm×5 mm(长×宽×高)。激光工艺参数为激光能量30 J,光斑尺寸4 mm×4 mm,脉宽15 ns和单点连续多次激光冲击(LSP-1~LSP-8)。表面形貌,表面残余应力,深度方向显微硬度和截面微观组织分别用超景深三维形貌仪,X射线衍射仪,显微硬度仪和金相显微镜测试分析。研究结果表明:单点连续5次激光冲击诱导7050铝合金中厚板表面微凹坑凸起高度为197.8μm和山脊高度为130.8μm。从单点连续4次激光冲击到单点连续5次激光冲击,试样表面残余应力由压应力转换为拉应力。单点连续5次激光冲击后,试样背层产生了低显微硬度的加工软化现象。单点连续5次激光冲击为7050铝合金中厚板的层裂阈值。研究结果有益于激光冲击强化工业应用中避免层裂和改善强化效果。

Investigation of Surface Integrity on TC17 Titanium Alloy Treated by Square-spot Laser Shock Peening

Laser shock peening（LSP） is an innovative surface treatment method,which has been shown to greatly improve the fatigue life of many metallic components.This work investigates surface integrity of TC17 titanium alloy treated by LSP with innovative square laser spot.Nd：glass laser with duration of 30 ns and spot size of 4 mm×4 mm is applied.The surface morphology and surface residual stress of the TC17 titanium alloy,treated with varying peening parameters such as laser power density and overlapping ratio,have been studied in detail.The results show that laser pulse energy greatly influences surface morphology and surface residual stress around single-spot treated areas,and compressive residual stresses are saturated as laser pulse energy is over 55 J.There are significantly different surface morphologies and residual stress distributions at the overlapped areas with different overlapping ratios.A relative smooth surface is produced with uniform compressive residual stress distribution at an overlapping ratio of 8 %.The experiment of residual stress relaxation is implemented by measuring residual stress at the center of four overlapped spots and by four point bending fatigue test at the frequency of 105 Hz.The compressive residual stresses induced by LSP are found to relax quite slowly under cyclic fatigue loading.

Study of the location of testing area in residual stress measurement by Moiré interferometry combined with hole-drilling method

This paper investigates the effect of the location of testing area in residual stress measurement by Moiréinterferometry combined with hole-drilling method.The selection of the location of the testing area is analyzed from theory and experiment.In the theoretical study,the factors which affect the surface released radial strainεr were analyzed on the basis of the formulae of the hole-drilling method,and the relations between those factors andεr were established.By combining Moiréinterferometry with the hole-drilling method,the residual stress of interference-fit specimen was measured to verify the theoretical analysis.According to the analysis results,the testing area for minimizing the error of strain measurement is determined.Moreover,if the orientation of the maximum principal stress is known,the value of strain will be measured with higher precision by the Moiréinterferometry method.