Experiment And Simulation On Vibration Aided Tensile And Compressive Process Of Aluminum Alloy

Vibration aided plastic forming (VPF) can effectively reduce the forming force and friction between tooling and workpiece, improve the formability of metallic materials and surface finish of workpiece, and thus making the VPF a distinctive and promising technology for materials forming process. Recently, research on theory and technology of VPF became a focus for scholars home and abroad. Research on design of VPF equipment and effect of vibration on the plastic behavior of materials can promote the development of the equipment for VPF and its application in the engineering and is of great theoretical and engineering value.This thesis firstly developed a set of equipment used for vibration aided tensile test and vibration aided compression test, which adopted the method of combining traditional analytic calculation with finite element (FE) optimization. Thereby, a series of vibration aided Al6061tensile tests and vibration aided Al2A12compression tests were carried out, the influence of vibration parameters, loading method and loading time on stress, strain and forming limits of aluminum alloys was researched, and the law of influence was explained referring to the theory of volume effect and surface effect. Based on ABAQUS, finite element analysis (FEA) on vibration aided6061tensile test and vibration aided2A12compression test was conducted.Dimension of key parts of VPF equipment was designed based on theoretical basis of vibration, and static analysis, modal analysis and harmonic response analysis on transducer, amplitude transformer and tooling were conducted using ANASYS Workbench. In designing the transducer, based on result of modal analysis, the size of prestressed bolt and applied preload was optimized with the method of single-factor, and final designing scheme is M20in diameter,125mm in length,40kN in preload. In designing the amplitude transformer, the deviation between actual frequency and designed frequency and deviation between actual nodal plane and designed nodal plane were taken into consideration. The thickness of clamped position and size of connecting hole were used as variables to construct objective function, which was equal to the sum of squared deviation of frequency and nodal plane, and the thickness of clamped position and size of connecting hole were optimized and redesigned. A set of equipment used for VPF was developed. The working frequency is15kHz, and output amplitude is about5μm.A series of vibration aided Al6061tensile tests were carried out and indexes such as softening, early peak, later peak, revert strain range and revert rate were defined according to the changing feature of true stress vs. true strain curves got from tensile tests. With the aid of those indexes, the law of influence of amplitude, applying method on softening and hardening was quantitatively described. Softening and hardening both existed in vibration aided tensile test, where softening reduced stress and hardening decreased the tension limit. Overall, vibration behave as a kind of extrinsic superimposed driving effect in vibration aided tensile test. FE model of vibration aide tensile test was established based on ABAQUS, and the result verified the law of influence of amplitude and frequency on stress and strain in vibration aided tensile test. However, there were some difference between the value obtained from FEA and that from actual tensile test because the order of magnitude of time interval to collect data in actual tensile test was different from the order of magnitude of increment in FE calculation.A series of Al2A12compression test under the condition of static state&dry friction, static state&lubrication, vibration&dry friction, and vibration&lubrication were conducted. The law of influence of friction, aspect ratio of sample and applied time on vibration aided compression test was revealed. In static compression test, with the increase of aspect ratio, the resistance of friction on2A12samples decreased and average stress of dry friction compression test got close to that of lubrication compression. In vibration aided compression test, stress of dry friction vibration aided compression test was larger than that of lubrication vibration aided compression test, but softening of dry friction vibration aided compression test was smaller than that of lubrication aided compression test. Besides, the curve of lubrication vibration aided compression test behaved comparatively more stable, which was with less wave number and small amplitude because the lubrication on the contacting surface worked as a damper, weakening and delaying the surface effect. Based on ABAQUS, the model of compression test under different condition was established and thus a series of FEA on the process was conducted. According to the result of FE simulation, the law of influent of friction, amplitude and loading time on stress and strain of compression test was verified and explored.