Study On Microstructure Characteristic Test Of Rough Surface Contact Dynamic Characteristics

The mechanical system is made up of mechanical parts according to certain assembly technical requirements. The contact surface of the components is called mechanical joints. The surface of the parts is uneven and composited with many asperities which is different in shape, height and distribution from the microcosmic viewpoint. The complex dynamic characteristics of both stiffness and damping are exhibited under the dynamic load. The dynamic accuracy and performance of the mechanical system is directly affected by the dynamic characteristics of the mechanical joints. It is of great significance to grasp the dynamic characteristics of the mechanical joints to analyze and optimize the dynamic characteristics of the whole machine. However, due to the contact problem of the mechanical surfaces is a complex cross scale geometric physics problem, the formation mechanism of the dynamic characteristics of the mechanical joints has not yet mastered. Therefore, the dynamic characteristic parameters can not be solved analytically. The microscopic structure feature of the contact dynamic characteristics of rough surface is studied in this paper, and the main work is as follows:(1) Based on the classical Hertz contact theory, the contact process of random rough surface is studied. The relationship between the contact load and the relative contact distance and the influence of the roughness and the contact load on the real contact area and the contact stress is analyzed.(2) Based on Fresnel diffraction integral theory, the principle of the recording and reconstruction process of digital holography is analyzed. A digital holographic measurement system is built to measure micro topography and the roughness of rough surface. The measurement and evaluation method of rough surface roughness is studied. And the system is used to measure the surface roughness of the specimen of ASW velocity test and the dynamic characteristic test of the mechanical joints.(3) The mechanism of laser ultrasonic excitation is discussed. The experimental system for measuring the velocity of laser ultrasonic ASW is built by combining the theory of laser ultrasonic transmission and solid sound effect. It is concluded that the contact stress of the mechanical joints increases with the increase of the load and the relationship is nonlinear. Under the same conditions, the larger the surface roughness, the larger the contact stress.(4) A sensor is designed to test the dynamic characteristics of the rough surface contact. The dynamic stiffness and damping of the mechanical joints can be measured in different contact states. The calculating models of normal stiffness and damping which employ the surface area, pressure and roughness as variables are founded. It is concluded the normal dynamic stiffness of unit area method is positively correlated with the surface pressure, which is negatively correlated with the area and roughness. The normal dynamic damping of unit area method is positively correlated with the surface pressure and the area, which is negatively correlated with the roughness.(5) Applying the model, the finite element model of the structure of machine tool bed and column of KVCN1050N is constructed. The finite element analysis and modal test results show that the maximum error is 12.45%, the minimum error is -3.92%, the average error is not more than 7.4%.