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

The shifting of the gears of automotive gearbox is very often. The alternate contact stresses of rolling and sliding are beared by the gears chronically. The fatigue crack and fatigue fracture of the gears is generated very easily. Sometimes the wear abrasion between the gear tooth surfaces are caused by the hard particles in the lubricant. The hard particles even can aggravate the generation and the extension of the fatigue cracks of the gears. The decreasing of the vehicle performance, the replacement of parts, the frequent maintenance and the increasing of the fuel consumption are all caused by the the fatigue failure mostly. The economic loss caused by the fatigue failure is very huge. So it is significant to know how to improve the fatigue strength of the gears for the prolongation of the service life of the gears. Based on the related theories of bionic engineering, it is successful to improve the fatigue strength of the gears through the laser processing of grid surface morphology on the gear tooth surfaces where the fatigue failure are easily generated. It is finally proved that the anti-fatigue performance of the gears with the grid surface morphology is generally better than that of the ordinary gears.Based on the related theories of the bionic engineering, nine kinds of grid surface morpholory had been designed. With the appropriate pulsed laser parameters, the gear tooth surface had been processed by the CT-200 II numerical controled laser engraving machine. The hardness measurement showed that the hardened layer with relatively high hardness had been created at the machining region of the gears.According to the theories of the experimental optimum design, the experimental scheme of orthogonal experimental design had been determined, and the anti-fatigue optimization experiment was carried out within the nine kinds of grid surface morphology. Through the method of direct microscopic obervation, the situation of the fatigue failure of the gears had been observed and analyzed, and the pitting ratio of the nine kinds of grid surface morphology had been obtained. The results showed that the anti-fatigue performance of the majority of experimental points are all better than that of the ordinary gears. The fatigue ratio of the NO.8 exprimental point is the lowest of all. Its fatigue ratio is 2.02%. The fatigue ratio of the NO.1 experimental point is the highest of all. Its fatigue ratio is 4.68%. The fatigue ratio is basically lower than that of the ordinary gears whose fatigue ratio is 4.61%. Finally the best grid surface morphology is that the stripe width is 150μm, the grid lateral and longitudinal distance are respectively 150μ, 300μm.Through the comparison experiment between the gear with the best grid surface morphology and the ordinary gear, the further research was carried out to investigate the law of the anti-fatigue mechanism of the grid surface morphology of the gear. The anti-fatigue machanism is that the hardened layer that was processed by the laser improved the hardness of the gear tooth surface and the anti-fatigue performance of the gear. The releasing of the residual compressive stress that was congregated during the procedure of the laser processing offsetted the part of tension stress of the gear tooth surface in the operation of the gears and prolonged the service life of the gears. The pile-nail effect that is caused by the grid unit body can baffle the generation and extension of the fatigue cracks. The grid surface morphology can help to store the iron cut of the wearing and avoid the grain-abrasion. The grid surface morphology can help to ameliorate the condition of lubrication of the gears. The exitence of the grid surface morphology can enlarge the contact surfaces between the gears and can increase the heat dissipating rate, so the probobality of the thermo-plastic deformation of the gears is much lower than usual.The 2D and 3D numerical simulation was carried out for the contact problems of the gears by applying the ANSYS finite element software. The results showed that the contact pressure of the gear with the grid surface morphology is lower than that of the ordinary gears. When the gear tooth surface beared the alternating load, then the probability of the fatigue crack and the fatigue fracture is much lower than the usual. So the grid surface morphology can improve the anti-fatigue performance of gears and prolong the service life of the gears.The numerical simulation was carried out for the structure fatigue problems of the gears by applying the ANSYS finite element software. The results showed that the Y-Component of displacement, the Displacement vector sum and the von Mises stress of the gear with the grid surface morphology and the ordinary gear had no obvious differences. When the gears beared the same strength of tension /compression stress, then the supporting reverse force of the gear with the grid surface morphology and the ordinary gear were the same. When the gear beared the same strength of the alternating load, the cycle range of the fatigue stress value of the gear with the grid surface morphology is much less than that of the ordinary gear. So the grid surface morphology can improve the anti-fatigue performance of gears and prolong the service life of the gears.