Bionic Investigation On Anti-fatigue Capability To Surface Morphology Of Automobile Gears

Gears are the most important components of the automobile transmission system which transfer power and change the speed ratio. The quality of anti-fatigue properties dominates the service life of gear. Because of the characteristics of the gear transmission, gear works under cyclic loading and the continuous working state. Fatigue failure of gears is very universal because of its bad working condition. Maintaining or replacing the failure gear leads to enormous economic loss for the enterprise and society. So prolonging the life-span of gears is the hot issue to be solved for the gear industry, and the main index is to improve the fatigue-resistance of gears.Many researchers have made great efforts in improving the fatigue-resistance of gears and obtained greater progress. Some researches about enhancing fatigue-resistance of gear were focused on the following ways: exploiting some new gear materials, improving the machining precision or some surface modification methods. However, exploiting some new materials will increase more costs. The means of improving the machining precision is restricted by equipment. The hardening layer on the whole gear surface formed through traditional mortification techniques is thinner. So it's necessary to find some new methods to improve the fatigue-resistance of gears and figure out the anti-fatigue mechanisms of gears.Researches about bionics have found that some typical living creatures have evolved their reasonable body surface structures through millions of years. These characters have some typical functions, such as the capability of bearing load, lowering resistance of wearing and good anti-fatigue capability. Based on the theory of bionic modification and mortification, the micro bionic morphology was designed through imitating the simple surface shape of living creature body in this paper. The characters of anti-fatigue of gear were studied through the fatigue tests. Based on the bionics principles, nine kinds of bionic concave modalities with different sizes and distance were designed. Because of the micro geometry size and complex form of the bionic concave units, the traditional machinery methods cannot satisfy the manufacturing requirement, the laser texturing technology was adopted to manufacture the bionic micro-morphology. All samples were processed by the CT—200Ⅱlaser manufacturing machine. The technical parameters of the laser texturing on gear surface were obtained. Laser texturing technique has higher precision, speed and stability. The hardness and metallographic test showed that laser treating could make the partial area of the gear surface totally differ from the matrix material. High hardness layer and metallurgical structure of fine grain were obtained, and this kind of surface had higher anti-wear ability, fatigue intensity and anti-corrosion.The experimental investigations of anti-fatigue intensity for 9 kind of bionic surface micro-morphology gear model samples were completed by CL-100 gear testing machine. Experimental scheme was arranged based on the experimental optimum design theory. The method of film formation was adopted to observe and record the failure damage morphology of gear teeth, and the ratio of the gear teeth pitting area was measured. It was found that the ratio of the gear teeth pitting area of the bionic micro-configuration gear model samples were all smaller than that of the normal gear model sample. The max value is 2.98%, and the min value is 0.43%, which are smaller than the value of ratio of the normal gear tooth pitting area 3.13%. The bionic microcosmic surface micro-morphology with the best anti-fatigue properties was optimized. The diameter of the concave of the optimized bionic surface micro-configuration was 100μm, the radial center distance of the concaves was 450μm, and the axial center distance of the concaves was 850μm.In order to get the information about how the gear teeth pitting formation and growth, the contrast experiments were carried out between the normal gear and bionic anti-fatigue gear. Then the anti-fatigue mechanism of the bionic surface micro-morphology was obtained. The suitable hardened layer distribution of teeth surface was formed by laser texturing. The hardness along hardened layer depth direction evenly distribution and without apparently descending gradient made the life long before pitting corrosion, and the cracks had no choice but to round the unit or change the propagation direction, when they met the higher hardness bionic concave units. There is residual compressive stress zone around the bionic concave unit, which counteracts the tensile stress and delays the crack initiation and propagation. The concave unit can work as oil receiver, which can improve the lubrication condition of gear contact region. Some of the abrasive dusts were collected by the concave unit, and the moving state of the abrasive dust was changed, which can reduce the gear tooth surface abrasion. The surface area of gear teeth was increased because of the existence of the concave unit. And it leads to the increase of heat dissipating rate, so the degradation of lubricant and plastic deformation of gear teeth were avoided. Above all, the bionic surface micro- morphology significantly prolonged the life-span of the gear.The thesis utilized the nonlinear finite element to analyze gear contact of two and three dimensional material surfaces. The 2D model of the gear was created with the help of a auxiliary software—CAXA, and 3D entity model of gear was built based on the parameterized modeling function of CATIA. Then by the excellent data exchange interface between CAD and ANSYS, the model was transferred into ANSYS and the contact stresses were calculated with finite element method. The results of 2D simulation showed that the peaks of equivalent stress and the contact pressure of bionic anti-fatigue were all smaller than that of the normal gear, and the stress distribution on the gear surface was similar. But the value of Von Mises stress in the tooth contact region of the normal gears was bigger than that of bionic anti-fatigue gears. And the distribution of contact pressure of bionic anti-fatigue gears is discontinuous. The three dimensional statics analysis of gears contact was completed. In the process of 3D simulations, the values and the distribution of stress were compared with bionic anti-fatigue gears and normal gears in detail. The thesis got mechanic character of the gear contact by using the software ANSYS, such as equivalent stress and contact pressure, which was very useful to probe the process and the mechanism of gear fatigue failure and life-span forecasting.It is found that the fatigue resistance of gear processed to bionic surface by laser is improved remarkable. This research is significant to improve the life-span of gear. The means of preparing bionic surface materials has many nice characteristics such as easy to operate,lowering cost, better fatigue-resistance and so on. This method extended bionic research to gear contact, and it develops a new technique for improving the fatigue-resistance of gear.