2024铝合金超声冲击成形数值分析研究

发布时间：2018-06-17 04:15

本文选题：有限元模拟 + 非均匀残余应力分布　；参考：《天津大学》2015年博士论文

【摘要】：超声冲击成形是一种新的适用于小曲率板件成形的无模冷加工成形方法。应用该方法进行材料成形,可以在成形构件表面产生残余压应力层,提高其机械性能。超声冲击成形方法适用于大尺寸薄板成形,在加工制造领域,特别是航天航空制造领域拥有广阔的应用前景。本文开展2024铝合金试件自由和预应力超声冲击成形过程数值分析研究,对于弄清超声冲击成形机理、促进该方法的应用具有重要的理论意义和实际应用价值。根据超声冲击成形的物理过程,提出了分阶段建立超声冲击成形子模型的方法,建立了三阶段自由超声冲击成形数值分析模型(超声冲击子模型、数据扩展子模型和试件成形子模型)和四阶段预应力超声冲击成形数学模型(预应力施加子模型、超声冲击子模型、数据扩展子模型和试件成形子模型),对各受控参数下的窄板和方板试件超声冲击成形过程进行了数值分析。在超声冲击子模型中,分析了自由状态下冲击过程中能量的转换、应力波及等效塑性应变传递等规律,探讨了冲击速度、冲击针质量及形状、冲击枪运行速度和偏移距离等受控参数对残余应力的分布规律。指出试件内部的残余应力分布是非均匀的,试件表层的平均残余压应力在冲击枪偏移方向上的值大于在冲击枪运行方向上的值,且冲击速度和冲击枪偏移距离对残余应力的影响较大。应用数据扩展模型,将超声冲击子模型获得的应力应变数据进行扩展,并导入到试件成形子模型中进行数值分析,获得自由超声冲击下单曲率窄板试件变形和双曲率方板试件变形,并分析各受控参数对试件成形量的影响规律,指出残余应力分布与试件变形量之间的关系。通过对比窄板和方板试件的变形量,探讨试件表层残余压应力对试件成形的促进作用和试件内部残余拉应力与试件刚度变化对试件成形的抑制作用,分析其在不同受控参数下的影响程度。应用预应力超声冲击成形模型进行数值分析,探索了不同预应力状态对试件成形的影响规律,指出试件的预弯方向的变形随着预弯半径的降低逐渐增加,与预弯相垂直方向的变形逐渐降低;通过对比窄板和方板试件的预应力超声冲击成形,明确了残余应力分布和试件刚度变化在成形过程中的作用,指出试件刚度变化对成形的影响较大。提出了复杂轨迹的超声冲击成形数值分析方法,进行了“回”字形冲击轨迹成形的数值模拟研究,证明了该方法能对较规则的超声冲击轨迹成形进行数值模拟与成形预测。应用该方法获得的模拟试验结果表明,采用间隔区域冲击的预应力冲击轨迹可以获得单曲率柱面成形;采用圆形自由超声冲击轨迹可以获得双曲率球面成形。
[Abstract]:Ultrasonic impact forming is a new cold forming method without die for small curvature sheet forming. With this method, the residual compressive stress layer can be produced on the surface of the formed member, and its mechanical properties can be improved. Ultrasonic impact forming method is suitable for large scale sheet forming, and has a wide application prospect in the field of machining and manufacturing, especially in the field of aerospace manufacturing. In this paper, the numerical analysis of the free and prestressed ultrasonic impact forming process of 2024 aluminum alloy specimen is carried out, which has important theoretical significance and practical application value for clarifying the ultrasonic impact forming mechanism and promoting the application of this method. According to the physical process of ultrasonic impact forming, the method of establishing sub-model of ultrasonic impact forming in stages is put forward, and the numerical analysis model of three-stage free ultrasonic impact forming (ultrasonic percussive model) is established. Data extension sub-model and specimen forming sub-model, and four-stage pre-stressed ultrasonic impact forming mathematical model (prestressing force applied sub-model, ultrasonic impact sub-model), The ultrasonic impact forming process of narrow plate and square plate specimens under various controlled parameters was numerically analyzed by using the data extender model and the specimen forming sub-model. In the ultrasonic percussive model, the laws of energy conversion, stress and equivalent plastic strain transfer in the free state are analyzed, and the impact velocity, the quality and shape of the impact needle are discussed. Distribution of residual stress by controlled parameters such as velocity and offset distance of impact gun. It is pointed out that the distribution of residual stress inside the specimen is non-uniform, and the average residual compressive stress in the surface layer of the specimen is larger in the direction of deviation of the impact gun than in the direction of movement of the impact gun. The impact velocity and the offset distance of the impact gun have great influence on the residual stress. Using the data expansion model, the stress and strain data obtained from the ultrasonic percussive submodel are extended and introduced into the specimen forming sub-model for numerical analysis. The deformation of single curved narrow plate specimen and double curvature square plate specimen under free ultrasonic impact is obtained. The effect of controlled parameters on specimen forming quantity is analyzed and the relationship between residual stress distribution and specimen deformation is pointed out. By comparing the deformation of narrow plate and square plate, the paper discusses the promoting effect of the surface residual compressive stress on the forming of the specimen and the restraining effect of the residual tensile stress inside the specimen and the change of the stiffness of the specimen on the forming of the specimen. The degree of its influence under different controlled parameters is analyzed. By using the pre-stress ultrasonic impact forming model, the influence of different prestressing states on the specimen forming is studied. It is pointed out that the deformation of the pre-bending direction of the specimen increases with the decrease of the pre-bending radius. The vertical deformation decreases gradually with the prebending phase, and the effect of residual stress distribution and specimen stiffness change in the forming process is clarified by comparing the prestressed ultrasonic impact forming of narrow plate and square plate specimen. It is pointed out that the stiffness change of the specimen has a great influence on the forming. In this paper, a numerical analysis method of ultrasonic impact trajectory with complex trajectory is proposed, and the numerical simulation of "return" shaped impact trajectory forming is carried out. It is proved that this method can be used to simulate and predict the formation of regular ultrasonic impact trajectory forming. The simulation results obtained by this method show that the single curvature rate cylindrical forming can be obtained by using the prestress impact trajectory in the spacer zone and the double curvature spherical forming can be obtained by using the circular free ultrasonic impact trajectory.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TG663

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