The special clamp for fatigue of shaft under bending, torsion, and bending-torsion that used on the fatigue machine is designed and manufactured. The low-cycle fatigue experiments of shaft with annular notch under cantilever bending have been made. Through experiments and analysis, the effects of tip radius, depth and open angle of notch on low cycle fatigue life of shaft with annular notch under cantilever bending are obtained. The method and results will play an important role on the fatigue life prediction and anti-fatigue design.
A series multi-axial tension and torsion low cycle fatigue life experiments of Ti-6Al-4V alloy were conducted on the MTS tension and torsion joint testing machine, in which the torsional strain control and non proportional cyclic loading method under the loading paths of circular, rectangular, square, oval and diamond were successively used. The experimental results are compared and analyzed with the results that calculated by the equivalent strain model, the energy method model and the critical plane method model. The results show that the critical plane method is the accurate prediction model to predict the multi-axial low cycle fatigue life of Ti-6Al-4V alloy.
The characteristics of serrated chips were analyzed using the theory of shear-slipping deformation at high speed cutting, with geometric and mathematic models of the chip built. Deformation of continuous chip for scissile metal materials can be analyzed and controlled by analogous methods that are employed at normal cutting speed. Geometrical model about serrated chip for difficult-to-cut material under orthogonal cutting condition is offered by proper simplifying. The nonlinear equations of indices related to some factors for measuring deformation degree of chip have been ascertained. Based on the condition fo forces equilibrium with respect to single serrated chip at the moment when it is to be in shear instability, forces equilibrium equations are obtained, with shear force and shear velocity as well as friction force and flowing velocity for a chip segment found. Finally, energy equations of cutting are acquired from deformation energy and friction work consumed in the course of chip formation, which can be offered to the further study of mechanism of high speed machining and the design of high speed machine tool.
The low cycle fatigue behaviors of TI-6AL-4V alloy controlled by strain were investigated by experiment. The fatigue tests were performed at room temperature, and cyclic strain and stress ratio are 0.1 with triangle load wave. The results show that TI-6AL-4V alloy is soften rapidly under the cyclic tensile stresses and it is harden rapidly under the cyclic compressive stresses during the initial-stage of strain controlled fatigue, and the rates of cyclic soften and cyclic harden are decreased with the fatigue progress. The soften rate is related to the cyclic strain but little to the cyclic stress during the overall fatigue progress. The change of cyclic stress is related to the macro friction stresses. The results of experiment show that obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.
The geometrical model for serrated chip was set up by studying the characteristic of typical chip during high speed machining. According to the adiabatic shear theory under the condition of high speed machining, friction force and flow velocity on back surface of chip as well as shear force and shear velocity on sliding plane were obtained by establishing mechanics and kinetic models via analyzing equilibrium forces exerted on the saw-tooth chip at the moment when the catastrophic thermoplastic instability occurred on slippage plane, then energy equation for cutting was offered. With strain, strain ratio, cutting temperature and deformation hardening considered, deformation equation was found using the principle of minimum energy. Finally, deformation equation and factors that affect deformation during high speed cutting were ascertained by combining analysis of deformation curve with cutting theory.
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