Key Takeaways & Executive Findings
- •• A novel micro-tensile testing method enables reliable real-time high-temperature tensile strength measurements on granite, validated by a power-law size effect model with errors below 6%. • Granite tensile strength exhibits non-monotonic temperature dependence: it increases up to 300 °C, then decreases with sharp drops at 400–500 °C and 600–700 °C. • Thermal damage in granite under high temperatures is driven by mineral dehydration, phase transformations, and differential thermal expansion. • The proposed approach addresses the challenge of limited standard sample availability for deep hot dry rock mechanical testing.
Abstract
The tensile strength of rocks under real-time high-temperatures is essential for enhanced geothermal system development. However, the complex occurrence and deep burial of hot dry rocks limit the quantity and quality of standard samples for mechanical testing. This paper compared the tensile strengths obtained from Brazilian splitting tests on standard samples (with a diameter of 50 mm and a thickness of 25 mm) and micro-tensile samples (with a diameter of 50 mm and a thickness of 25 mm) of two types of granites. A power-law size effect model was established between the two sets of data, validating the reliability of the testing method. Then, miniature Brazilian splitting under real-time high-temperature, combined with X-ray diffraction (XRD) revealed temperature-dependent strength variations and microstructural damage mechanisms. The results show that: (1) The comparison error between the tensile strength obtained by the fitting model and that of the measured standard samples was less than 6%. (2) In real-time high-temperature conditions, tensile strength of granite exhibited non-monotonic behavior, increasing below 300 °C before decreasing, with sharp declines at 400–500 °C and 600–700 °C. (3) Thermal damage stems from the differences in the high-temperature behavior of minerals, including dehydration, phase transformation, and differential expansion.
1. Introduction
Hot dry rock (HDR) is a type of high-temperature rock mass primarily made up of granite that has minimal permeability and porosity. Since HDR resources are great examples of abundant, clean, low-carbon, and environmentally friendly power, encouraging their effective development has gained a lot of attention from researchers [1,2]. At present, the enhanced geothermal system (EGS) is commonly employed to enhance the efficiency of HDR geothermal energy extraction [3]. This system primarily employs hydraulic fracturing technology to create an interconnected fracture network within the geothermal reservoir, enabling heat exchange between the fluid and the high-temperature rock mass, thereby facilitating the extraction of thermal energy [4].
However, the mechanical characteristics of the rock mass will alter greatly from those at room temperature during the extraction process due to continuous high temperature and stress [5], thereby affecting the fracturing effect in geothermal reservoirs [6]. To effectively exploit HDR resources and ensure the long-term durability of engineering structures, it is essential to gain a comprehensive understanding of the mechanical behavior and damage formation mechanisms of deep granite under real-time high-temperature conditions.
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LI Xianzhong, TIAN Yinnan, LI Zhenhua, HENG Shuai, ZHANG Xiaodong, LIU Bing (2025). A new technical approach for real-time tensile strength testing of high-temperature granite based on micro-tensile testing technology. SinoTechIntel Verified Research. https://doi.org/10.1016/j.ijmst.2025.07.003
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Frequently Asked Questions
What is the main contribution of this paper?
The paper introduces a new micro-tensile testing approach for measuring the real-time high-temperature tensile strength of granite, validated by a power-law size effect model, and reveals the temperature-dependent strength variations and microstructural damage mechanisms.
How does granite tensile strength change with temperature?
Granite tensile strength increases up to 300 °C, then decreases with sharp declines at 400–500 °C and 600–700 °C, showing non-monotonic behavior.
What causes thermal damage in granite?
Thermal damage is caused by differences in high-temperature behavior of minerals, including dehydration, phase transformation, and differential expansion.
Why is micro-tensile testing important for hot dry rock research?
It allows reliable tensile strength measurements on small samples, overcoming the limitations of standard sample availability for deep hot dry rock, and is validated by comparison with standard samples.
What is the size effect model used in this study?
A power-law size effect model was established between tensile strengths from standard and micro-tensile samples, with comparison errors less than 6%, validating the reliability of the micro-testing method.
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