不同激光冲击工艺参数对40Cr钢表面应力应变影响的模拟试验研究

发布时间：2018-07-18 08:54

【摘要】：激光冲击强化作为一种前沿的表面处理技术,具备“三高一快”(高压、高能、超快、高应变率)特点,可以广泛应用在金属和零部件的强化上。各国研究人员已经对激光冲击强化技术进行了系统研究,但都是在航空铝合金材料方面,而在航空工业有重要作用的高质量合金钢的科学研究则比较少。40Cr钢在航空工业上常使用在高速和冲击负荷小的工作环境中,而传统的表面强化方法主要存在效率低、温度高、工作环境差等缺点。针对上面提到的问题,本文以40Cr钢为研究对象,采用ABAQUS有限元软件系统研究了不同工艺参数(冲击次数、光斑直径、冲击波加载时间、激光能量和压力幅值上升时间)对激光冲击强化的影响。对不同的搭接率布置方案激光冲击强化进行了分析。研究了正反表面同时冲击和间隔冲击在残余应力和表面变形的差异,并探讨了正反表面间隔冲击两次,三种顺序对残余应力和“残余应力洞”的影响。采用脉冲激光器对40Cr钢方块试样进行激光冲击强化处理并与模拟结果进行对比。分析“残余应力洞”产生原理、以及不同工艺参数对其影响,研究了两种对“残余应力洞”抑制的方法。(1)通过ABAQUS有限元软件构建了三维分析模型,研究了不同工艺参数对冲击强化在残余应力、应变和表面变形等方面的影响规律并分析了对“残余应力洞”问题的影响。对40Cr钢进行了较为系统的激光冲击强化数值模拟研究,分析了不同工艺参数对其强化效果的影响规律。以不同激光冲击强化次数为例,激光冲击次数为1次、2次和3次时,残余压应力最大值分别为468.36 MPa、540.87 MPa和556.31MPa,压应力影响层深度也不断增大。随着冲击强化次数增大在表面变形、等效塑性应变方面也随之增加。分析了不同参数对“残余应力洞”问题的影响,阐明了并不是冲击次数越多、脉冲加载时间越长,能量越大对强化效果就越好。(2)研究了不同光斑搭接率布置方案下的激光冲击强化效果,为后续大面积激光冲击强化奠定了基础。研究了正反表面同时冲击和间隔冲击在残余应力、表面变形和等效塑性应变的差异。研究得出了随光斑搭接率的增大,试样表面变形和残余应力分布变得相对均匀的结论。当光斑搭接率较小和较大时,表面变形数值会比较大。正反表面同时冲击比间隔冲击在正反表面应力分布上有更好的一致性。(3)分析了正反表面间隔冲击两次,三种冲击顺序的优劣。正反表面间隔冲击两次有三种冲击顺序,冲击顺序一:正反正反;冲击顺序二:正正反反;冲击顺序三:正反反正。采用冲击顺序一和冲击顺序二在正面的残余压应力比反面的大,采用冲击顺序三,结果正好相反,冲击顺序二产生的“残余应力洞”现象最小。(4)对40Cr钢进行了不同能量的激光冲击强化处理,通过分析不同能量下激光冲击强化后试样残余应力分布的试验结果与模拟结果的异同,从而验证了数值模拟结果的准确性。研究了抑制“残余应力洞”问题的方法。针对不同能量的激光冲击强化处理,通过X射线应力测试仪对冲击后试样表面和深度方向的残余应力进行了测量并与模拟数值对比。试验获得表面压应力最大值为461 MPa,与模拟得到的压应力最大值447.5 MPa很相近。研究了通过二元光学衍射将圆形光斑改变为方形光斑和使用光斑搭接率进行大面积激光冲击可以有效地抑制“残余应力洞”问题。得出了激光冲击最优搭接率应该在50%~75%之间选择的结论。
[Abstract]:Laser shock strengthening, as a front surface treatment technology, has the characteristics of "three high and one fast" (high pressure, high energy, super fast, high strain rate), which can be widely used in the strengthening of metal and parts. The scientific research of high quality alloy steel which plays an important role in air industry, less.40Cr steel is often used in the working environment of high speed and low impact load in aeronautical industry, and the traditional method of surface hardening mainly has the disadvantages of low efficiency, high temperature and poor working environment. In view of the problems mentioned above, 40Cr steel is the research object in this paper. The influence of different process parameters (impact times, spot diameter, shock wave loading time, laser energy and pressure amplitude rising time) on laser shock intensification is studied by using the ABAQUS finite element software system. The laser impact intensification of different lap rate arrangement is analyzed. The simultaneous impact and interval impact on the positive and negative surfaces are studied. The difference between the residual stress and the surface deformation, and the influence of the positive and negative surface interval impact two times, the effect of the three sequence on the residual stress and the "residual stress hole". The pulse laser is used to strengthen the laser shock treatment of the 40Cr steel block specimen and compare it with the simulation results. The effect of process parameters on two kinds of "residual stress holes" was studied. (1) a three-dimensional analysis model was constructed by ABAQUS finite element software, and the influence of different process parameters on the impact strengthening on residual stress, strain and surface deformation was studied and the effect on the "residual stress hole" was analyzed. 40C A relatively systematic numerical simulation of laser impact strengthening was carried out in R steel, and the influence of different process parameters on its strengthening effect was analyzed. The maximum number of residual stresses was 468.36 MPa, 540.87 MPa and 556.31MPa, and the depth of the stress affected layer, when the number of laser impact strengthening times was 1 times, 2 times and 3 times, respectively. As the number of impact strengthening increases on the surface, the equivalent plastic strain also increases. The influence of different parameters on the "residual stress hole" is analyzed, and it is stated that the more the impact times, the longer the pulse loading time is, the better the energy is, the better the strengthening effect is. (2) research on the overlap ratio of different light spots. The effect of laser shock enhancement under the set scheme is the foundation for the subsequent large area laser shock strengthening. The difference of residual stress, surface deformation and equivalent plastic strain is studied at the simultaneous impact and interval impact on the positive and negative surfaces. The results show that the surface deformation and residual stress distribution of the specimen are relatively uniform with the increase of the overlap rate of the spot. When the lap rate is small and large, the surface deformation value will be larger. The positive and negative surface impact is better consistent with the distribution of the stress distribution on the positive and negative surface. (3) the positive and negative surface interval impact is two times, and the three kinds of impact sequence are good and bad. The positive and negative surface interval impact has three kinds of impact order, the impact is impacted. Sequence one: positive and negative positive and negative; impact sequence two: positive and negative reaction; impact order three: positive and negative inverse. The residual pressure stress in the frontal sequence and impact order two is larger than the reverse side, using the impact order three, the result is the opposite, the "residual stress hole" is the least. (4) different energy is carried out to 40Cr steel. By analyzing the laser shock intensification treatment, the accuracy of the numerical simulation results is verified by analyzing the difference between the experimental results and the simulated results of the residual stress distribution of the specimen after the laser shock intensification under different energy. The method to suppress the "residual stress hole" is studied. The X ray should be used for the laser shock strengthening treatment of different energy. The force tester measured the residual stress in the surface and depth direction of the specimen after impact and compared with the simulated numerical value. The maximum surface pressure stress of the test was 461 MPa, which was similar to the simulated maximum compressive stress of 447.5 MPa. The circular spot was changed to square spot by two element optical diffraction and the use of light spot lap. The problem of "residual stress hole" can be effectively suppressed by large area laser shock. The conclusion that the optimal lap rate of laser shock should be selected between 50%~75% can be obtained.
【学位授予单位】：江苏大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG665

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