Fatigue life assessment for large components based on rainflow counted local strains using the damage domain

• A method for the fatigue assessment of large components is presented.
• The method uses rainflow counted local strains measured under industrial conditions.
• The calculation model was calibrated and validated via variable amplitude tests.
• Using a constant damage sum results in a satisfactory accuracy of the assessment.
• The accuracy can be improved by considering the damage potential of the load spectra.

The present paper deals with the fatigue life assessment of the large components which are common in heavy plant engineering. A calculation model was developed to estimate the degree of utilisation of structural components based on rainflow counted local strains measured on machines during industrial use. A local approach was followed, but not in the classical cycle by cycle definition, since this information is generally not available from the measurements. For calculation, the rainflow data is transformed element-wise into the damage domain using the damage parameter as defined by Bergmann. The calculation model was calibrated for the ductile iron EN-GJS-400-15U by strain controlled constant and variable amplitude fatigue tests with lives that extended into the high cycle domain. Furthermore, the calculation model was validated by a strain controlled variable amplitude control test. The variable amplitude tests are based on measured rainflow data. For preparation, a method of omitting load cycles from the primary data that had a negligible damage contribution prior to load sequence reconstruction was developed. The sensitivity of the material to mean stress was considered in the process by utilising the damage domain.The comparison of calculated results using the calibrated calculation model with experimental results from the control test shows a satisfactory match when using a constant characteristic damage sum as a failure criterion. The accuracy of the computation can be increased by considering the damage potential of the load spectra.