Correlation regimes in fluctuations of fatigue crack growth

TL;DR

This study explores how fatigue crack growth fluctuations in polycrystalline materials exhibit distinct correlation regimes, revealing micro-structural influences on crack dynamics through statistical and physical modeling.

Contribution

It introduces a model capturing short-term correlations and long-term independence in fatigue crack growth, linking micro-structure to crack dynamics using fracture mechanics and data decomposition.

Findings

Identifies two correlation regimes in fatigue crack growth fluctuations.

Links micro-structure to intermittent correlated crack dynamics.

Validates damage measure using Karhunen-Loève decomposition.

Abstract

This paper investigates correlation properties of fluctuations in fatigue crack growth of polycrystalline materials, such as ductile alloys, that are commonly encountered in structures and machinery components of complex electromechanical systems. The model of crack damage measure indicates that the fluctuations of fatigue crack growth are characterized by strong correlation patterns within short time scales and are uncorrelated for larger time scales. The two correlation regimes suggest that the 7075-T6 aluminum alloy, analyzed in this paper, is characterized by a micro-structure which is responsible for an intermittent correlated dynamics of fatigue crack growth within a certain scale. The constitutive equations of the damage measure are built upon the physics of fracture mechanics and are substantiated by Karhunen-Lo\`{e}ve decomposition of fatigue test data. Statistical orthogonality of the estimated damage measure and the resulting estimation error is demonstrated in a Hilbert space setting.