Study Of Effects On Rolling Bearing’s Fatigue Life Considering Load Fluctuation

Rolling bearings often work under the condition of high-frequency pulsating loadin the fields of aviation, aerospace and country defense. As a result, fatigue damageaccumulation will happen between the friction pairs. Fatigue failure will occur whenthe value of damage accumulation comes to a certain extent. The failure modes ofrolling bearings are quite complicated. The existing life calculation model gets thefatigue life through the equivalent treatment of variable load. However, the effect ofload fluctuation is not considered by this method. This paper modified the traditionallife prediction model by combining a new fatigue damage accumulation model andstudied the effects of different factors on bearings’ fatigue life.First, this paper calculated the mechanical properties of rolling bearings under3kinds of pulsating load (sine wave load, square wave load and sawtooth wave load).The conclusion was that contact load, contact angle, contact stress minimum oilthickness will change as the pulsating load periodically. The expressions of contactload and contact angle could be used for the calculation of the fatigue life in themodified life model;Then the modified life model of rolling bearings under pulsating load wasderived by inducing a fatigue damage accumulation model considering loadfluctuation effect and material’s fatigue limit stress. The effects of load type, meanload, load amplitude, load frequency and rolling speed was analyzed under themodified life model and equivalent load method by calculation program writtenthrough Matlab. The result showed that the modified life model took the effect of loadsequence into consideration and it could reflect the effects of all the5factors onrolling bearings’ fatigue life;Finally, high-frequency dynamic fatigue test rig and the status monitoring systemwere set up. The bearing’s rolling condition could be observed during the test. Fatiguetest of deep-groove ball bearing6205was designed and finished by the test rig. Asfatigue failure happened on the bearing, the monitoring index changed obviouslyincluding the rising of frequency offset and bearing’s temperature, the dropping ofdynamic current and the instability of pulsating load. Meanwhile, this paper hasanalyzed the microcosmic surface topography of contact pairs through SEM. Themicrophotograph indicated there was initial fatigue spalling on material’s surfacewhich proved that the test rig can bring out fatigue tests for rolling bearings.