Nonlinear Vibratory Stress Relief Method And Application

Vibratory stress relief which has the characteristics of free-pollution, high efficiency, saving time and energy and etc is an effective way to eliminate the residual stress when compared with the natural aging and artificial heat aging. What’s more, it can effectively avoid phenomenons such as oxidation of component, fission caused by uneven heating of components or new stress when cooling during process of thermal aging. But so far its application was limited and there was still great potential which hasn’t been played out yet. One of the important reasons is that the excitation frequency produced by current vibration aging equipment (mostly less than200Hz) is far below than many components’natural frequency and cannot produce the resonance and dynamic stress required by component vibration aging. In addition, some of the components need higher-order vibration mode to eliminate the residual stress, the vibratory aging equipment which produce higher excitation frequency was needed.To solve this problem, according to the principle that output response frequency of nonlinear vibration system can be different from the input excitation frequency, current exciter was used to make effects on the nonlinear vibration system and the nonlinear resonance which is much higher than the original excitation frequency was produced. The nonlinear vibration system uses a close to high inherent frequency’s component’s resonance frequency of the new excitation frequency to act on the component, making it produce the resonance and the corresponding dynamic stress to eliminate the components’residual stress. In this dissertation, steps needed to eliminate residual stress via the nonlinear vibration aging method, the application of nonlinear vibration aging method and the relationship between the nonlinear vibration aging system parameters were studied, and the main research contents include the following parts:(1) Accroding to the principle that "when the superposition of the loading dynamic and residual stress is greater than the material yield strength, reduction of residual stress can be achieved", in order to reduce the workpiece’s residual stress effectively, the distribution of the component’s residual stress was studied and the distribution of dynamic stress’ required, the corresponding component’s vibration mode and amplitude was determined. Based on the combination point of austempering crankshaft in this thesis, and using the thermal elastic plastic finite element method to analyze the distribution law of residual stress when crankshaft go through the austempering process, and then apply the finite deformation theory to analyze the distribution law of residual stress after the cutting process. Thus, we can get the residual stress distribution regularity after the two processes of austempering and cutting by applying stress superposition principle to provide technical basis for the dynamic stress distribution required by component’s vibration aging.(2) To obtain the reduction of vibration dynamic required by the residual stress of austempering crankshaft, the finite element method was applied to establish the dynamic equation of crankshaft to obtain the dynamic characteristics on the condition of external crack drive and self shock inertia force of the crankshaft based on the distrivution law of the residual stress of austempering crankshaft, to analyze the dynamic stress distribution law of austempering crankshaft under different order modal. And to decide the required parameters which meet the needs to eliminate the resonance frequency, vibration mode, the vibrating force and ect required by residual stress.(3) Dynamic characteristics of nonlinear vibration system under the action of traditional vibration exciter were studied. And dynamic analysis model of nonlinear systems was establish and apply the method of multiple scales of nonlinear vibration theory to study the vibration frequency of excitation block and the relationship and law between the exciting force and elastic parameters. Analyze the relationship among the resonance frequency required by the residual stress with higher natural frequency which must be eliminated via solvable condition, vibration mode and exciting force and the quality of nonlinear excitation system and elastic parameters. In order to study the effect that the component has on the dynamic characteristics of nonlinear vibration system, the component is simplified as a elastic element on the nonlinear vibration system. After the excitation system acting on the components, the nonlinear parametric excitation system needs adjustment for the realization of component producing resonance vibration.(4) Taking the austempering crankshaft as an example, a new nonlinear vibration aging device model was designed and developed according to the theoretical research results in this dissertation. Process parameters of support and blessing of austempering crankshaft nonlinear vibration aging device were calculate and selected by using the finite element method. Kinetic model of nonlinear vibration aging system made nonlinear vibration aging and austempering crankshaft was established. Kinetic model was analyzed by the method of multiple scales and the parameters of the structure and nonlinear element required by nonlinear vibration aging equipment was decided.(5) Test platform of austempering crankshaft was established based on the above research. New method of nonlinear vibration aging was verified by analyzing the output and respond of the nonlinear vibration system, and through comparing the experimental results with theoretical analysis.