小孔构件激光冲击与芯棒挤压复合强化方法及疲劳特性研究

发布时间：2018-04-08 07:22

本文选题：复合强化　切入点：结构孔　出处：《江苏大学》2017年硕士论文

【摘要】：孔是结构件上易产生疲劳断裂的地方之一,飞机上存在着相当数量的孔构件,为提高其疲劳寿命,激光冲击强化技术及冷挤压强化技术都是较为高效的强化方法,本文尝试将这两者结合起来,实现全新的复合强化。本文通过理论分析、数值计算方法,研究了复合与非复合强化方式对孔结构件应力分布及疲劳寿命的影响,探索了超声振动辅助传统芯棒挤压强化过程的力学特性,并进行了复合挤压强化相关试验。本文的主要研究工作及成果如下:(1)从理论上分析了激光冲击强化、冷挤压强化机理及其影响因素,分析了强化处理后的残余应力的分布,及其对疲劳寿命的影响,提出采用复合强化实现激光冲击与芯棒挤压强化的互补,分析了复合强化对疲劳裂纹的抑制作用。(2)基于ABAQUS软件进行复合与非复合强化数值模拟,分析了不同工艺参数对其残余应力分布的影响规律。结果显示,激光冲击强化时峰值压力高、作用时间长,其强化效果好;冷挤压强化时挤入端与挤出端的应力分布不一致,3%~4%左右的挤压量较为合理;复合强化时,先激光冲击强化后芯棒挤压强化产生了激光冲击作用完全被芯棒挤压强化所覆盖,但其强化效果稍优于单芯棒挤压强化;先冷挤压后激光冲击强化工艺顺序,可以有效改善冷挤压引起的挤入端与挤出端的差异,同时有效解决激光冲击强化造成孔壁中部残余拉应力问题,实现了激光冲击强化与芯棒挤压强化的相互补充。试验结果表明,7050-T7451试样经过复合强化后,其疲劳寿命有很大的提高。(3)芯棒挤压强化采用超声振动辅助芯棒挤压强化,降低了拉拔力,有效防止芯棒的断裂;超声挤压强化的呼吸振动和纵向振动模态比较研究,结果认为采用呼吸式超声振动挤压形式,其效果更好,在工程实际中可优先采用呼吸式超声振动;不同挤压量下,随着超声频率的增加拉拔力降低幅度明显;芯棒挤压强化后激光冲击复合强化过程中,加入防变形芯棒能够有效降低孔角的变形情况的发生。
[Abstract]:The hole is one of the places where fatigue fracture is easy to occur on the structural parts. In order to improve the fatigue life of the aircraft, the laser shock strengthening technology and the cold extrusion strengthening technology are more efficient strengthening methods.This paper attempts to combine the two to achieve a new compound strengthening.Through theoretical analysis and numerical calculation, the effects of composite and non-composite strengthening modes on stress distribution and fatigue life of pore structure are studied, and the mechanical properties of ultrasonic vibration assisted traditional mandrel extrusion strengthening process are explored.The related experiments of composite extrusion strengthening were also carried out.The main research work and results of this paper are as follows: (1) the mechanism of laser shock strengthening, cold extrusion strengthening and its influencing factors are theoretically analyzed, and the distribution of residual stress after strengthening treatment and its influence on fatigue life are analyzed.The complementary effect of laser shock and mandrel extrusion strengthening is proposed by using composite strengthening. The restraining effect of composite strengthening on fatigue crack is analyzed. The numerical simulation of composite and non-composite strengthening is carried out based on ABAQUS software.The influence of different process parameters on residual stress distribution was analyzed.The results show that the peak pressure is high and the action time is long, and the strengthening effect is good, the stress distribution of the extrusion end and extrusion end is not consistent with the extrusion end during cold extrusion strengthening, the extrusion quantity of about 4% is reasonable, and when the laser is strengthened,The laser impact effect was completely covered by the extrusion strengthening of the mandrel rod, but the strengthening effect was slightly better than that of the single mandrel extruding strengthening.It can effectively improve the difference between the extrusion end and the extrusion end caused by cold extrusion, at the same time, it can effectively solve the problem of residual tensile stress in the middle of the hole wall caused by laser impact strengthening, and realize the mutual supplement between laser impact strengthening and mandrel extrusion strengthening.The test results show that the fatigue life of the specimen 7050-T7451 has been greatly improved after the composite strengthening. The extrusion strengthening of the mandrel adopts ultrasonic vibration assisted extrusion strengthening, which reduces the drawing force and effectively prevents the fracture of the mandrel.The comparative study on the modes of respiratory vibration and longitudinal vibration strengthened by ultrasonic extrusion is made. The results show that it is better to adopt the mode of ultrasonic vibration of breathing type, which can be preferred in engineering practice.With the increase of ultrasonic frequency, the pull-out force decreases obviously, and the deformation of hole angle can be effectively reduced by adding anti-deformation mandrel in the process of laser impact composite strengthening after extruding and strengthening of mandrel.
【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;TG379

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