薄壁板预应力超声波喷丸成形实验研究与数值分析

发布时间：2018-11-15 08:32

【摘要】：超声波喷丸成形技术具有设备简单、操作便携、绿色无污染、能耗少、成形后材料综合性能好等诸多优势,在航空航天、国防工业、船舶汽车工业、建筑等众多领域中具有非常广阔的应用前景。但是在自由状态下,超声波喷丸成形也易发生球面变形,而实际需要的零件外形并不总是要求是球面的,一旦发生球面变形,想要消除或改变非常困难,而预应力喷丸成形不仅能够提高零件的成形曲率,还能在一定程度上减小球面变形趋势。本文结合预应力喷丸成形和超声波喷丸成形两种工艺方法,以薄壁板为研究对象,在超声波喷丸成形过程理论分析的基础上,对预应力超声波喷丸成形的成形机理、成形特性以及表面层性能进行了系统的研究,并结合数值分析方法对预应力超声波喷丸的成形过程进行了模拟,主要研究工作如下:(1)理论分析了超声波喷丸的成形过程。以碰撞理论为依据,对超声波喷丸过程中板料的力学状态进行分析,推导出了板料分别发生弹性变形和弹塑性变形时撞针的临界速度,探讨了塑性变形前后凹坑直径、凹坑深度和冲击力的大小以及回弹后残余应力沿深度方向的分布关系,并推导出了预应力状态下残余应力的计算公式,对比分析了自由状态和预应力状态成形曲率半径。(2)对2024-T351铝合金薄壁板进行了预应力超声波喷丸成形试验研究,分析了预弯曲率、成形轨迹、撞针速度、偏置距离以及壁板厚度对壁板成形曲率半径的影响,结果表明了预应力超声波喷丸能够大幅度增大壁板展向(预弯方向)的成形曲率并减小弦向的成形曲率,随着预弯曲率的增加,减小和增大的效应随之逐渐增大,大幅度减小了球面变形趋势。(3)对预应力超声波喷丸后成形件的表面层性能进行了研究,分析了不同工艺参数对试样件的表面形貌、表面粗糙度、显微硬度以及残余应力场的影响,与自由状态相比,预应力状态下成形件的表面粗糙度值略有减小,表面硬度增大,并在材料的表面层产生了更大更深的呈典型的“√”状分布的残余压应力场,表明了预应力超声波喷丸能够获得更好的表面性能。(4)利用ABAQUS软件建立了预应力超声波喷丸成形数值分析模型,分析了不同参数对壁板成形曲率以及残余应力场的影响,并将数值分析结果和试验结果进行比较,二者的数据误差很小,验证了预应力超声波喷丸成形有限元模型的可靠性,为研制开发机翼整体壁板的超声波喷丸成形工艺提供理论及数据参考。
[Abstract]:Ultrasonic shot peening technology has many advantages, such as simple equipment, portable operation, no pollution, less energy consumption, good comprehensive properties of materials after forming, and so on. Architecture and many other fields have a very broad application prospects. But in the free state, the ultrasonic shot peening is also prone to spherical deformation, and the actual part shape is not always required to be spherical, once the spherical deformation occurs, it is very difficult to eliminate or change. Prestressed shot peening can not only improve the forming curvature of parts, but also reduce the deformation trend of spherical surface to a certain extent. In this paper, based on the theoretical analysis of the ultrasonic shot peening process, the forming mechanism of pre-stressed ultrasonic shot peening is analyzed, which is based on the pre-stressed shot peening and ultrasonic shot peening, and the thin-walled plate is taken as the research object. The forming characteristics and surface layer properties are studied systematically, and the pre-stressed ultrasonic shot peening process is simulated with numerical analysis method. The main research work is as follows: (1) the forming process of ultrasonic shot peening is analyzed theoretically. Based on the collision theory, the mechanical state of sheet metal during ultrasonic shot peening is analyzed, and the critical velocity of crashing needle in elastic deformation and elastoplastic deformation of sheet metal is deduced, and the diameter of crater before and after plastic deformation is discussed. The relationship between the depth of the pit and the impact force and the distribution of the residual stress along the depth after springback is derived, and the formula for calculating the residual stress in the state of prestress is derived. The curvature radius of 2024-T351 aluminum alloy thin-walled plate was compared and analyzed. (2) the pre-bending rate, forming track and pin speed of 2024-T351 aluminum alloy thin-walled plate were studied by prestressing ultrasonic shot peening. The results show that prestressed ultrasonic shot peening can greatly increase the forming curvature and decrease the chord curvature of the wall plate, which is influenced by the offset distance and the thickness of the wall plate, and the results show that the ultrasonic shot peening can greatly increase the shape curvature of the plate in the development direction (prebending direction) and decrease the forming curvature in the chord direction. With the increase of prebending ratio, the effect of decreasing and increasing gradually increases, which greatly reduces the tendency of spherical deformation. (3) the surface layer properties of prestressing ultrasonic shot peening are studied. The effects of different process parameters on the surface morphology, surface roughness, microhardness and residual stress field of the specimen are analyzed. Compared with the free state, the surface roughness value of the formed part in the prestressing state is slightly reduced, and the surface hardness increases. A larger and deeper residual compressive stress field is produced in the surface layer of the material with a typical "squared" distribution. The results show that the prestressing ultrasonic shot peening can obtain better surface performance. (4) the numerical analysis model of pre-stressed ultrasonic shot peening is established by using ABAQUS software, and the influence of different parameters on the curvature and residual stress field of slabs is analyzed. The numerical analysis results are compared with the experimental results, and the data error between them is very small, which verifies the reliability of the finite element model of pre-stressed ultrasonic shot peening. It provides theoretical and data reference for the research and development of ultrasonic shot peening process for wing integral panel.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG668

【参考文献】