Fretting Fatigue Behavior Of UFG-Ti Under High Cycle Load

Fretting fatigue,components are deformed due to specimens subject to external alternating loads or alternating stresses.It exists in mechanical components,aerospace power plants,train wheels and other closely-fitting components,and is known as "industrial cancer".Titanium and titanium alloys are widely used in industry,because of low density,high strength,high temperature resistance,and good corrosion resistance.However,theirs sensitivty to fretting has attracted researchers.This article mainly studies the fretting fatigue behavior of ultrafine-grain pure titanium(UFG-Ti),UFG-Ti is obtained by using industrial pure titanium(TA1)with equal channel angular pressing(ECAP)and rotary swaging(RS).Fretting fatigue experiments are performed on UFG-Ti on an electro-hydraulic servo fatigue tester to obtain fretting fatigue S-N Curves;Observation of fretting fatigue contact wear zone and fracture morphology using SEM and TEM;establishment of cylindrical-plane fretting fatigue model using ABAQUS software;study of axial cyclic stress and friction coefficient on stress and strain distribution of specimen contact area;The SWT critical method uses the improved Coffin-Manson formula to establish a fretting fatigue life prediction model for UFG-Ti.After experiments and analysis,the following conclusions are obtained:Under the verification of Hertz contact theory,stablish a finite element model of a cylindrical pad-plate specimen by ABAQUS,and limit its error to within 5% to ensure the accuracy.It is found that as the cyclic stress increases,the maximum tensile stress in the X direction of the specimen contact surface also increases,and there is a maximum tensile stress at the edge of the contact area,while the compressive stress in the Y direction and the XY direction The change of the shear stress is not large,but the position where the peak appears is shifted.The influence of the friction coefficient on the stress distribution of the contact area is also very limited.As the friction coefficient increases,the width of the contact area is basically unchanged,while the width of the contact closed area increases,and the width of the adhesion area decreases;the maximum tensile stress in the X direction is somewhat Increased,there is a maximum at the edge,the compressive stress in the Y direction does not change significantly,and the maximum shear stress in the XY direction decreases.A model for predicting the fretting fatigue life of UFG-Ti was established by the modified Coffin-Manson equation.The maximum SWT parameter appeared at the edge of the contact surface,which was in agreement with the experimental results.Through comparison,it is found that the error between the fretting fatigue life value predicted by the SWT model and the life value obtained from the experiment remains within 20%.Therefore,the SWT critical method is used to predict the fretting fatigue crack of UFGTi.feasible.The fretting fatigue test of UFG-Ti found that under the same normal load conditions,the cyclic stress increased and the fretting fatigue life decreased.The analysis of the wear zone in the contact area shows that the micro-fine wear mechanism of ultrafine crystal pure titanium is mainly the magic wear and contact fatigue.The crack propagation zone is further divided into a cyclic stress-dominated zone,a normal load-dominated zone,and a combined action zone of cyclic stress and normal load.Observing the transmission structure,it was found that the cyclic stress increased,the original lath structure was broken,the small grains increased,and the dislocation density decreased,thereby reducing the plasticity,reducing the fretting fatigue resistance of ultra-fine crystal pure titanium,and reducing the fretting fatigue life.