26th International Association for Management of Technology Conference - IAMOT 2017

Due to the current demand to reduce the power consumption particularly in the transportation sector intensive research is carried out to reach resource efficiency. To fulfill future trends in resource efficiency machine elements offer possibilities to enhance the surface andpart properties and to reduce the components weight and costs. By applying residual stresses to bearing surfaces it could be proven, that the bearing fatigue life can be increased by a factor of 2.5. For this purpose manufacturing processes have to be adopted. With an enhanced surface the machine dimension can be reduced to fulfill the required function. In a next step hybrid machine elements with tailored material properties are designed and manufactured. Concerning this, a shaft with an integrated raceway made out of a higher strength material then the shaft itself was developed. The raceway of the shaft acts as the inner ring of a bearing. This complex machine element combines various requirements in one part like resistance against elongation, stiffness and a surface under cyclic rolling contact fatigue. For the hybrid shaft the raceway should resist the rolling contact fatigue and mechanical wear, while the main material for the shaft consists of a more lightweight and cheaper material. In order to manufacture said shaft, intensive research on the whole product engineering process is done. Simulations were performed proving the reliability of the concept. Doing so, the resulting stress field from the superimposition of load stresses and residual stresses is computed based on the model of Ioannides, Bergling and Gabelli [1]. The approach consists of a FE model of a bearing inner ring that has been developed in order to calculate the three dimensional stress state. As input variables the Hertzian pressure as external load and residual stress depth profiles, which are defined as initial stresses in the model, are used. The maximum of the applied Hertzian pressure is *pmax*=2500 MPa. A result of the numerical calculation is the orthogonal shear stress beneath the surface. The size and location of the maximum is required for the fatigue life model of Ioannides, Bergling and Gabelli. It is based on the model of Lundberg and Palmgren [2] and is expanded with a stress fatigue limit. A proper fatigue stress criterion has to be used, which in this case is the criterion of Dang-Van [3]. This includes the maximum orthogonal shear stress and the local hydrostatic pressure *phyd*, corrected for residual and hoop stress. The hydrostatic pressure can also be calculated with the FE model. The concept was evaluated with bearings manufactured by various machining processes to achieve subsurface residual stresses. A significant increase in bearing fatigue life could be proven. Current work is done to evaluate hybrid machine elements. Doing so a test rig was set up and tests on first tailored formed machine elements were ¬¬conducted. These first results and the feasibility of the concept are presented. With the presented findings machine elements with tailored properties can be designed whereby resources can be saved due to components lower weight and costs. [1] Ioannides, E., Bergling, G., Gabelli, A., “An analytical formulation for the life of rolling bearings”, Acta Polytechnica Scandinavica, Mechanical engineering series No. 137, 1999 [2] Lundberg, G. ; Palmgren, A.: “Dynamic Capacity of Rolling Bearings“, Acta polytechnica. Mechanical engineering series, Generalstabens Litografiska Anstalts Förl., 1947 [3] Dang Van K.: “Sur la resistance la fatigue des metaux”, Sci Tech Armement 1973:47