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《Journal of Zhejiang University(Engineering Science)》 2007-11
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Frequency sweep method for crankshafts' fatigue crack growth rate measurement

ZHOU Xun,YU Xiao-li(College of Mechanical and Energy Engineering,Zhejiang University,Hangzhou 310027,China)  
Normal methods for fatigue crack size measurement are limited to simply samples and not applicable to components with complex structure and/or with crack in special position,such as crankshafts.A novel frequency sweep method was presented to realize dynamic measurement of crack size.According to the regularity that the resonance frequency will drop as the crankshaft's crack growth, the method dynamically tracks the crack size's growth rate on a resonant fatigue test rig by scanning the spectra of the resonant system.After the crankshaft was broken,the crack shape and size were measured according to the fracture morphology.Finite element modal analysis of the resonant system was conducted to accurately calculate the crack size at various test-cycle time point.As an associated result,the dynamic measurement curve of crack's size,i.e.a-N curve,was given.Seven point incremental polynomial method was applied to fitting the a-N curve,and the crack growth rate at each cycle,i.e.the da/dN-N curve,was obtained.Then the stress intensity factor of the crankshafts' crack was calculated by using finite element analysis(FEA) with 15-node quarter singular element applied.The stress intensity factors at every crack size and each cycle of the crankshaft's crack were derived.Finally a case was illustrated and the fatigue crack growth rate curve was plotted.
【CateGory Index】: TG115
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