Papers

@article{li_effects_2026,

title = {Effects of Confining Pressure on Mode I Fracture Toughness Considering Jacketed and Unjacketed Conditions},

author = {Yan Li and Miguel Herbón-Penabad and Andrea Muñoz-Ibáñez and Leandro R. Alejano and José Alvarellos-Iglesias and Jacobo Canal-Vila and José María Segura-Serra and Jordi Delgado-Martín},

url = {https://doi.org/10.1007/s00603-025-04878-x},

doi = {10.1007/s00603-025-04878-x},

issn = {1434-453X},

year  = {2026},

date = {2026-01-01},

urldate = {2026-01-01},

journal = {Rock Mechanics and Rock Engineering},

volume = {59},

number = {1},

pages = {1393–1403},

abstract = {Accurate assessment of mode I fracture toughness (KIc) in rocks under in-situ stress conditions is critical for analyzing various geomechancial problems in underground rock engineering. Typically, KIc is determined through unconfined tests. Under confining pressure, researchers often refer to the apparent mode I fracture toughness (KIc*), where specimens are typically jacketed to isolate from confining fluids. Although rocks are porous media that naturally contain fluids, relatively few studies have investigated the toughness behavior of unjacketed specimens under confining pressure, a scenario prone to rock-fluid interactions. In this study, we measured the KIc and KIc* of pseudo-compact tension (pCT) specimens of granite, limestone, sandstone, and polymethyl-methacrylate (PMMA) under two conditions: covered with a waterproofing rubber (jacketed) or directly exposed to the confining fluid (unjacketed). PMMA served as an impermeable reference material. Tests were conducted at room temperature and confining pressures ranging from 0.1 to 25 MPa. Results show that KIc* is material-dependent for both jacketed and unjacketed specimens. Jacketed specimens generally exhibit significantly higher KIc* values compared to unjacketed ones. However, KIc* values obtained from unjacketed specimens better reflect the actual stress state and fracture behavior under in-situ conditions, as both the mechanical and hydraulic properties of the rock interact concurrently during the development of the fracture process zone. These findings emphasize the importance of selecting appropriate testing conditions for accurately assessing fracture toughness in rocks, which has implications for the evaluation of stability, fracturing and fluid flow in rocks in underground environments.},

keywords = {Confining fluid, Confining pressure, Mode I fracture toughness, Pseudo-compact tension (pCT) test, Underground in-situ environment},

pubstate = {published},

tppubtype = {article}

}

@article{li_experimental_2026,

title = {Experimental assessment of mode I fracture toughness and fracture energy in four rock types using the textitpCT testing method with two notch radii},

author = {Yan Li and Miguel Herbón-Penabad and Jorge Castro and Marina Miranda and Tonglu Li and Jordi Delgado-Martín},

url = {https://www.sciencedirect.com/science/article/pii/S1365160925003296},

doi = {10.1016/j.ijrmms.2025.106352},

issn = {1365-1609},

year  = {2026},

date = {2026-01-01},

urldate = {2026-01-01},

journal = {International Journal of Rock Mechanics and Mining Sciences},

volume = {197},

pages = {106352},

abstract = {Understanding mode I fracture behavior in rocks is essential for handling geomechanical problems, including tunneling, mining, and hydraulic fracturing. This study investigates the mode I fracture toughness (KIC) and specific fracture energy (Gc and Gf) in one sandstone, one limestone and two marble lithologies using the pseudo-compact tension (pCT) test. To assess the influence of the notch radius, specimens were prepared with two notch radii: 0.15 mm (thin) and 0.5 mm (thick). The key novelty lies in comparing notch radius effects across multiple lithologies while explicitly accounting for heterogeneity via ultrasonic wave velocities and micro X-ray fluorescence elemental mapping. Results show that, for the limestone and the marbles, the thick notch yields higher values of KIC, Gc, Gf. In contrast, the sandstone shows the opposite trend, with higher values for thin-notch specimens. This behavior is likely attributed to its high porosity, where stress concentration around pores can generates secondary crack tips near the blunt notch tip, that reduce the fracture toughness and energy dissipation. Across all rocks, Gf > Gc, indicating substantial dissipation by microcracking and grain-boundary processes beyond pure surface-energy creation. In addition, a thinner notch improves repeatability and reduces data dispersion, thereby mitigating heterogeneity effects on measured parameters. These findings provide practical guidance on selection of notch radius and highlight the importance of multiscale heterogeneity characterization for advancing rock mechanics research and refining fracture testing methods, thereby improving accuracy and reducing variability.},

keywords = {Mode I fracture toughness, Notch radius, Pseudo-compact tension (CT) test, Rock heterogeneity, Specific fracture energy},

pubstate = {published},

tppubtype = {article}

}

@article{li_simple_2024,

title = {A simple pseudo-Compact tension (textitpCT) test apparatus to determine the mode I fracture toughness},

author = {Yan Li and Miguel Herbón-Penabad and Andrea Muñoz-Ibáñez and Tonglu Li and Jordi Delgado-Martín},

url = {https://www.sciencedirect.com/science/article/pii/S0263224124012272},

doi = {10.1016/j.measurement.2024.115342},

issn = {0263-2241},

year  = {2024},

date = {2024-10-01},

urldate = {2026-04-21},

journal = {Measurement},

volume = {238},

pages = {115342},

abstract = {We introduce a simplified pseudo-compact tension (pCT) test apparatus, specifically designed to accurately determine the mode I fracture toughness (KIC) under direct tension conditions for rocks and other geomaterials. The device is compatible with conventional multipurpose loading frames typically available in many geomechanics laboratories. The mechanical behavior of the designed apparatus and the accuracy of the KIC determinations have been assessed through a 3D finite element model elaborated with ABAQUS and experimentally validated using aluminum and polymethyl methacrylate (PMMA) specimens under digital image correlation (DIC) examination technique. Results confirm the good performance of the new pCT apparatus, since it provides sufficient stiffness while yielding KIC values consistent with the reference pCT apparatus. Both devices measured an average KIC value of 1.80MPa m1/2 for PMMA specimens. This new device provides a cost-effective entry to the versatile pCT fracture toughness testing methodology, ensuring accurate and reproducible test results.},

keywords = {Digital image correlation (DIC), Mode I fracture toughness, Notch length, Pseudo-compact tension (CT) test, Stress intensity factor},

pubstate = {published},

tppubtype = {article}

}