Review and application of Rainflow residue processing techniques for accurate fatigue damage estimation

Gabriel Marsh,Colin Wignall,Philipp R Thies,Nigel Barltrop,Atilla Incecik,Vengatesan Venugopal,Lars Johanning

doi:10.1016/j.ijfatigue.2015.10.007

Gabriel Marsh, Colin Wignall + Show 5 more

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https://doi.org/10.1016/j.ijfatigue.2015.10.007

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Abstract

Most fatigue loaded structural components are subjected to variable amplitude loads which must be processed into a form that is compatible with design life calculations. Rainflow counting allows individual stress cycles to be identified where they form a closed stress–strain hysteresis loop within a random signal, but inevitably leaves a residue of open data points which must be post-processed. Comparison is made between conventional methods of processing the residue data points, which may be non-conservative, and a more versatile method, presented by Amzallag et al. (1994), which allows transition cycles to be processed accurately.This paper presents an analytical proof of the method presented by Amzallag et al. The impact of residue processing on fatigue calculations is demonstrated through the application and comparison of the different techniques in two case studies using long term, high resolution data sets. The most significance is found when the load process results in a slowly varying mean stress which is not fully accounted for by traditional Rainflow counting methods.

Highlights

Longer term variations in mean stress levels do occur over the 12 h tidal cycle, but are of small amplitude in comparison to the stress response from dynamic wave loading
The concatenation of successive RF residue periods has been shown to enable the same closed hysteresis cycles to be identified as would be produced by RF counting the data as a continuous series
The conventional methods of half-cycle and simple RF counting the residue periods are suitable when the entire stress range seen by a component is contained within the analysed period of data

Summary

Introduction

The calculation of conservative load cycle spectra is a fundamental aspect of fatigue design, requiring an estimate to be made of expected operational loading conditions. Fatigue life can be quantified in terms of time to crack initiation through the concept of linear damage accumulation, or by the application of crack growth models. Both approaches utilise information about the range, mean and number of stress cycles that will occur [1]. Typical methods include level-crossing counting, range-pair counting, reservoir counting, and Rainflow counting. Variations of these algorithms are included in the ASTM cycle counting standard [2]

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