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<p>This study investigates the influence of wet–dry cycling and temperature loading on the microcracking behavior and fracture process zone (FPZ) evolution of sandstone and limestone under Mode I loading, using notched semi-circular bending tests in combination with acoustic emission (AE), digital image correlation (DIC), and thin-section microscopy. Through frequency-domain analysis of AE data, four distinct stages in the development of the FPZ were identified: micro-crack formation, crack nucleation, macro-crack initiation, and propagation. The results show that within the low-temperature range (25–100&#xa0;°C), the fracture toughness of the rocks increases with temperature; however, in the high-temperature range (300–500&#xa0;°C), the fracture toughness significantly decreases, with a marked acceleration in the reduction after reaching the critical temperature. High-temperature treatments also led to a significant increase in AE activity and energy release, particularly at 300&#xa0;°C and 500&#xa0;°C, where the frequency of microcracks and energy release were notably higher. Microscopic analysis revealed a transition in fracture mode from tensile to shear failure, with a significant reduction in FPZ length as the temperature increased. The shortening of FPZ was more pronounced in limestone than in sandstone. At 500&#xa0;°C, the FPZ lengths in sandstone and limestone were reduced by 39.26% and 49.2%, respectively. Furthermore, AE proved superior to DIC in capturing the geometric changes of the FPZ, particularly during the micro-crack formation stage. This study provides valuable experimental data and theoretical insights for rock mechanics and underground engineering, especially in the context of high-temperature environments combined with wet–dry cycling effects.</p><p><b>Highlights</b><UnorderedList Mark="Bullet"> <ItemContent> <p>Effects of wet–dry cycling and temperature (25–500&#xa0;°C) on FPZ evolution in sandstone and limestone.</p> </ItemContent> <ItemContent> <p>Frequency-domain analysis of acoustic emission identifies four FPZ development stages.</p> </ItemContent> <ItemContent> <p>Elevated temperatures enhance acoustic emission activity and energy release.</p> </ItemContent> </UnorderedList></p>

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Mechanism of Fracture Process Zone Development in Sandstone and Limestone Under Mode I Loading Wet–Dry Cycles and Temperature

  • 期刊论文

  • 发表日期：

    2025年4月2日

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  • Chao Wang,
  • Quan Zhang,
  • Manchao He,
  • Shan Guo,
  • Yonggang Jia

摘要

This study investigates the influence of wet–dry cycling and temperature loading on the microcracking behavior and fracture process zone (FPZ) evolution of sandstone and limestone under Mode I loading, using notched semi-circular bending tests in combination with acoustic emission (AE), digital image correlation (DIC), and thin-section microscopy. Through frequency-domain analysis of AE data, four distinct stages in the development of the FPZ were identified: micro-crack formation, crack nucleation, macro-crack initiation, and propagation. The results show that within the low-temperature range (25–100 °C), the fracture toughness of the rocks increases with temperature; however, in the high-temperature range (300–500 °C), the fracture toughness significantly decreases, with a marked acceleration in the reduction after reaching the critical temperature. High-temperature treatments also led to a significant increase in AE activity and energy release, particularly at 300 °C and 500 °C, where the frequency of microcracks and energy release were notably higher. Microscopic analysis revealed a transition in fracture mode from tensile to shear failure, with a significant reduction in FPZ length as the temperature increased. The shortening of FPZ was more pronounced in limestone than in sandstone. At 500 °C, the FPZ lengths in sandstone and limestone were reduced by 39.26% and 49.2%, respectively. Furthermore, AE proved superior to DIC in capturing the geometric changes of the FPZ, particularly during the micro-crack formation stage. This study provides valuable experimental data and theoretical insights for rock mechanics and underground engineering, especially in the context of high-temperature environments combined with wet–dry cycling effects.

Highlights

Effects of wet–dry cycling and temperature (25–500 °C) on FPZ evolution in sandstone and limestone.

Frequency-domain analysis of acoustic emission identifies four FPZ development stages.

Elevated temperatures enhance acoustic emission activity and energy release.