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Abstract <p>Brittle creep is a time-dependent process in which brittle rocks undergo inelastic deformation under constant applied stress through micro-crack nucleation, interaction, and coalescence. As these micro-cracks accumulate, they reach a critical density and arrangement, referred to as the microstructural critical level of damage, which leads to strain rate acceleration. While macroscopic proxies (e.g., axial, lateral, and volumetric strain) often characterize this critical state, they fail to capture small-scale (i.e., millimeter and smaller) fracture processes and damage connectivity. This study employed percolation theory to quantify the critical damage level at the onset of accelerating creep by assessing crack connectivity, a key factor in brittle rock failure. Unconfined brittle creep experiments synchronized with two-dimensional digital image correlation (2D-DIC) monitoring were conducted on prismatic Stanstead granite specimens under varying stress levels. 2D-DIC data were used to track small-scale damage and evaluate connectivity within the percolation framework. Results show that the derived metrics for the microstructural critical level of damage were consistent and independent of applied stress and time to failure. Moreover, while critical crack density correlated with macroscopic creep behavior, only the largest connected crack cluster directly governed the transition to accelerating creep and ultimate specimen instability. For rocks exhibiting moderate to high strength variability, it is recommended that the specimen-specific crack damage (CD) stress threshold better accounts for this variation than the UCS; accordingly, we recommend using the constant creep driving stress normalized by CD as a primary creep loading indicator, offering a consistent metric for strain rate and time to failure.</p> Highlights <p><UnorderedList Mark="Bullet"> <ItemContent> <p>Small-scale damage evaluation using a strain-based method during brittle creep</p> </ItemContent> <ItemContent> <p>Application of percolation theory to track damage connectivity during creep experiments</p> </ItemContent> <ItemContent> <p>Quantifying the microstructural critical level of damage at the transition to accelerating creep</p> </ItemContent> </UnorderedList></p>

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Critical State of Damage at the Onset of Acceleration Creep in Stanstead Granite Evaluated Using 2D-DIC and Percolation Theory Approach

  • 期刊论文

  • 发表日期：

    2025年11月18日

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  • Mehrdad Imani,
  • Ahmadreza Hedayat,
  • Gabriel Walton

摘要

Abstract

Brittle creep is a time-dependent process in which brittle rocks undergo inelastic deformation under constant applied stress through micro-crack nucleation, interaction, and coalescence. As these micro-cracks accumulate, they reach a critical density and arrangement, referred to as the microstructural critical level of damage, which leads to strain rate acceleration. While macroscopic proxies (e.g., axial, lateral, and volumetric strain) often characterize this critical state, they fail to capture small-scale (i.e., millimeter and smaller) fracture processes and damage connectivity. This study employed percolation theory to quantify the critical damage level at the onset of accelerating creep by assessing crack connectivity, a key factor in brittle rock failure. Unconfined brittle creep experiments synchronized with two-dimensional digital image correlation (2D-DIC) monitoring were conducted on prismatic Stanstead granite specimens under varying stress levels. 2D-DIC data were used to track small-scale damage and evaluate connectivity within the percolation framework. Results show that the derived metrics for the microstructural critical level of damage were consistent and independent of applied stress and time to failure. Moreover, while critical crack density correlated with macroscopic creep behavior, only the largest connected crack cluster directly governed the transition to accelerating creep and ultimate specimen instability. For rocks exhibiting moderate to high strength variability, it is recommended that the specimen-specific crack damage (CD) stress threshold better accounts for this variation than the UCS; accordingly, we recommend using the constant creep driving stress normalized by CD as a primary creep loading indicator, offering a consistent metric for strain rate and time to failure.

Highlights

Small-scale damage evaluation using a strain-based method during brittle creep

Application of percolation theory to track damage connectivity during creep experiments

Quantifying the microstructural critical level of damage at the transition to accelerating creep