LY2铝合金激光冲击处理实验研究

分析激光冲击处理技术及相对于传统强化方式的优点,针对LY2航空铝合金材料,设计进行试件激光冲击处理实验,通过对激光冲击处理前后材料性能的测试,分析激光冲击处理对LY2铝合金材料疲劳寿命、强度性能的影响.     

奥氏体不锈钢1Cr18Ni9Ti激光冲击强化研究

对奥氏体不锈钢１Ｃｒ１８Ｎｉ９Ｔｉ进行激光冲击强化,观察了激光冲击强化层显微组织与结构的变化并测定了激光冲击强化层内的显微硬度和残余应力。结果表明：１Ｃｒ１８Ｎｉ９Ｔｉ激光冲击强化层中有高密度的位错和大量的孪晶,显微硬度显著提高并产生较高的残余压应力,１Ｃｒ１８Ｎｉ９Ｔｉ激光冲击强化区还发生了形变诱发马氏体相变。     

激光冲击提高航空铝合金疲劳寿命的研究

分析了激光冲击改善航空铝合金疲劳性能的机理；讨论了涂层及约束层的重要作用。对２０２４和７４７５铝合金进行了优化激光冲击试验。结果表明：提高了这些铝合金的疲劳寿命，获得了均匀稳定的位错显微组织和表面残余压应力。     

激光冲击强化7075铝合金熔焊接头的疲劳性能

激光冲击强化（LSP）技术具有残余压应力场深、冷作硬化程度低和强化区域可控等优点,在焊接结构表面改性方面应用前景广阔。对2 mm厚度的7075-T6铝合金激光-电弧复合焊接接头实施了激光冲击强化处理,对比分析了强化前后接头的硬度、残余应力、疲劳寿命以及疲劳裂纹形核机制。结果表明,焊缝中心的最高硬度由强化前的152 HV提高到强化后的175 HV,有效强化层深度约为100 μm;经激光冲击强化后,焊缝区呈现残余压缩应力,最大残余压应力为-200 MPa;9组焊接接头试样的平均疲劳寿命为675 937周,约为强化前疲劳寿命（262 297周）的2.6倍;疲劳裂纹萌生位置从具有高度应力集中的表面缺陷转移至强化层以下的亚表面,进而有效地提高了疲劳裂纹的形核寿命。     

喷丸对激光辅助成形铝合金样件拉-拉疲劳性能的影响

为了研究激光辅助成形样件的疲劳性能及喷丸处理的作用规律,以2024铝合金板材为对象,对原始、激光辅助成形以及激光辅助成形后再喷丸等样件的微观组织、显微硬度、残余应力和拉-拉疲劳性能进行了对比分析研究.结果表明:激光辅助成形后,样件的组织和微结构未发现明显变化,但其硬度和残余拉应力水平有所下降;喷丸处理的激光辅助成形样件...     

激光冲击对TC11钛合金组织和力学性能的影响

对TC11钛合金进行激光冲击强化处理,通过透射电子显微镜观察不同参数下TC11钛合金的微观组织变化,用显微硬度计和X射线应力测试仪分别测试材料表层硬度和残余应力,并通过TC11钛合金标准疲劳试片高周振动疲劳试验验证激光冲击对其疲劳性能的影响.试验结果表明:激光冲击波作用后表面组织结构发生明显变化,当冲击次数增加,先后出现了高密度位错、位错胞和纳米级晶粒等微观组织特征.冲击10次后,表面残余应力最高达到-632.5MPa,相应的塑性变形层深度达到1500μm左右;同时表面硬度在冲击1次即可提高19%,硬度影响深度为700μm,随着次数增加而提高,但幅度不大.经3次冲击处理的TC11钛合金标准疲劳试片的疲劳极限由原始483MPa提高到593MPa.      

激光冲击中应力状态和显微组织变化对金属疲劳性能影响

从应力状态与显微组织的变化两个方面分析了激光冲击强化改善金属疲劳性能的机理.首先研究了残余应力的作用,认为激光冲击强化产生的残余压应力降低了零部件承受的平均应力水平.然后利用位错理论分析了金属经激光冲击强化引起的显微组织变化,认为激光冲击强化在材料表层产生了大量位错、晶界以及亚晶界等缺陷,这些缺陷阻碍了位错的移动,使金属得到强化.     

激光喷丸对7075铝合金搅拌摩擦焊接头的影响

以7075铝合金试样的搅拌摩擦焊接头为对象,利用激光喷丸和常规喷丸工艺对其进行后续处理,通过试验对比分析了激光喷丸工艺对表面粗糙度、显微硬度、接头残余应力、裂纹扩展、疲劳寿命的影响。结果表明,经激光喷丸处理的搅拌摩擦焊接头的表面粗糙度远小于常规喷丸处理的接头表面,而对接头显微硬度的影响差异不大。激光喷丸可改变接头的残余应力分布,是增强搅拌摩擦焊接头抗疲劳性的有效方法,对其他焊接接头及构件的激光喷丸处理具有一定的参考价值。     

小功率激光器激光冲击强化铝合金的研究

通过小功率脉冲激光冲击强化ＬＹ１２ＣＺ铝合金的试验研究，发现材料的疲劳寿命和显微硬度有显著提高。通过断口扫描（ＳＣＡＮ）、透射电镜（ＴＥＭ）及金相分析对试样经激光冲击后的显微组织变化及强化机理进行了分析。     

钢制叶片激光冲击强化与渗铝的组合应用

采用扫描电子显微镜(SEM),X射线衍射(XRD)等手段研究了激光冲击强化(LSP)对钢制叶片渗铝层的影响,结果表明渗铝后进行激光冲击强化会对渗铝层造成破环,而在渗铝之前进行激光冲击强化则能提高渗层质量.从残余应力和显微组织变化两方面分析了渗铝高温作用对不锈钢材料激光冲击强化效果的影响,激光冲击强化产生的残余压应力在510℃渗铝温度环境下保温150min仍有-295MPa稳定存在,晶粒细化组织也没有明显长大,激光冲击不锈钢材料的残余应力和微观组织具有良好的热稳定性.振动疲劳对比试验结果验证了“LSP+渗铝”组合工艺对不锈钢材料的强化效果,在660MPa应力水平下,采用该组合工艺试片的疲劳寿命为3.98×106,为原渗铝试片疲劳寿命的14倍左右.      

激光冲击强化铝合金小孔构件的疲劳寿命研究

研究了激光冲击强化对7050-T7451铝合金小孔件疲劳寿命和断口形貌的影响。采用ABAQUS对峰值压力2.7GPa下小孔构件孔壁与表面上的应力分布进行了研究,并基于仿真结果对试样进行激光冲击强化试验和疲劳拉伸试验。结果显示,激光双面冲击强化在板料两侧形成一定深度的残余压应力影响层,而在中心形成一定范围的残余拉应力层,这也是导致疲劳源由孔角向孔壁中心转移的主要原因;在应力水平165.8MPa、195.0MPa和275.4MPa下,试样的疲劳寿命分别平均可增大451%、216%、116%;经激光冲击强化后,试样的疲劳源位置由孔角转移至孔壁内部,且疲劳裂纹扩展区面积明显增大。研究表明,激光冲击强化能明显改善铝合金小孔构件的疲劳性能,但强化效果随外加载荷的增加逐渐减小。     

激光冲击强化对钛合金高温微动疲劳寿命的影响

为了解高温工作环境下激光冲击强化工艺(LSP)对钛合金材料微动疲劳寿命的影响,开展了强化前后TC11钛合金在室温、300°C和500°C下的微动疲劳试验并测试了试验件表层的残余应力及硬度。结果表明:随着温度的升高,激光冲击强化对TC11钛合金微动疲劳寿命的提高倍数逐渐减小。在轴向载荷为400MPa,法向载荷为65.5MPa时,经激光冲击强化后TC11钛合金试验件在室温、300°C和500°C下的微动疲劳寿命分别为强化前的5.5倍、3.5倍和1.7倍;强化后试验件表层的残余应力会在高温下发生松弛,且松弛程度会随温度的升高而增大,这是激光冲击强化效果随温度升高而逐渐弱化的主要原因。     

Laser Shock Peening of Aluminum Alloy 7050 for Fatigue Life Improvement

The effects of laser shock peening (LSP) on improving fatigue life of aluminum alloy 7050 are investigated.Surface hardness is increased corresponding to a high dislocation density induced by LSP.The X-ray diffraction stress measurement shows that LSP results in prominent increase of surface compressive stress,quasi-symmetrically distributed in the laser peened region.The fatigue life of the alloy 7050 in rivet fastener hole structure is notably improved owing to LSP.The sequence of LSP and fastener hole preparation also influence the fatigue cycle life of the alloy.     

Residual Strength of Stiffened LY12CZ Aluminum Alloy Panels with Widespread Fatigue Damage

Experimental and analytical investigations on the residual strength of the stiffened LY12CZ aluminum alloy panels with widespread fatigue damage （WFD） are conducted. Nine stiffened LY12CZ aluminum alloy panels with three different types of damage are tested for residual strength. Each specimen is pre-cracked at rivet holes by saw cuts and subjected to a monotonically increasing tensile load until failure is occurred and the failure load is recorded. The stress intensity factors at the tips of the lead crack and the adjacent WFD cracks of the stiffened aluminum alloy panels are calculated by compounding approach and finite element method （FEM） respectively. The residual strength of the stiffened panels with WFD is evaluated by the engineering method with plastic zone linkup criterion and the FEM with apparent fracture toughness criterion respectively. The predicted residual strength agrees well with the experiment results. It indicates that in engineering practice these methods can be used for residual strength evaluation with the acceptable accuracy. It can be seen from this research that WFD can significantly reduce the residual strength and the critical crack length of the stiffened panels with WFD. The effect of WFD crack length on residual strength is also studied.     

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.     

TC4钛合金激光冲击强化数值模拟

采用连续显式动态冲击策略对航空用TC4钛合金进行激光冲击强化数值模拟研究.根据冲击波能量变化曲线确定单次冲击求解时间为3000ns,并分析了应力波传播过程.在此基础上开展多点冲击模拟,分析了功率密度、冲击次数和光斑搭接率对残余应力、应变场的影响.得出增加功率密度对增大表面残余压应力的效果更好;增加冲击次数对增大残余压应...     

激光冲击残余应力场的有限元分析

建立模拟激光冲击残余应力场的非线性弹塑性有限元模型,预测AISI 304奥氏体不锈钢厚、薄靶材经激光冲击后表面以及内部的残余应力场分布.模拟过程中,考虑材料高应变率(106s-1)下的力学性能和激光诱导冲击波的精确加载,分析激光功率密度、激光光斑尺寸、激光脉宽、激光冲击次数、激光单面与双面冲击等激光冲击参数以及初始残余应力等因素对不锈钢靶材残余应力分布的影响.数值模拟结果与X射线衍射法测量值吻合较好.在有初始残余拉应力(250MPa)存在的情况下,激光冲击仍能使304奥氏体不锈钢靶材形成残余压应力层,说明激光冲击工艺可提高奥氏体不锈钢焊接构件的抗应力腐蚀开裂能力.