Statistical evaluation of the service life of a complex shaped, large-scale part

Abstract

1. A method is proposed for calculating the service life of actual parts according to the parameter of failure probability with the use of fatigue resistance characteristics of large-scale models, which is suitable for calculations concerning parts of arbitrary complex shape given representative statistical data about loading. The method is recommended for engineering calculations of service life according to fatigue strength criteria on a probability basis for different unique complex shaped parts for which direct fatigue tests are impossible. 2. The basic stages of the calculation are: statistical evaluation of loading on the part; fatigue tests on large-scale models of the actual part, making possible integral consideration of the effect of stress state on fatigue resistance of the complex shaped gauge section; determination of the fatigue limit distribution function for the actual part; calculation of the service life distribution function of the actual part. 3. Experimental verification was obtained for the high reliability of calculated stress state parameters in complex-shaped parts under torsion by the proposed method based on fatigue test results for large-scale specimens. Application to the wobbler spindle of the Pilger mill at the 220 plant in the CTRW gave a service life distribution function L with a median value L=1.8 years of rolling mill operating time, agreeing with data from VNIImetmash on the service life of this spindle. 4. Numerical evaluation of fatigue failure probability for critical large-scale, complex-shaped parts, carried out by this method in the working design stage, is necessary to provide the specific γ-percent service life of the machine as a whole.