Thermal shock effects on the mechanical behavior of granite exposed to dynamic loading
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(2020) 20:66
ORIGINAL ARTICLE
Thermal shock effects on the mechanical behavior of granite exposed to dynamic loading Xiang Li1,2 · Baijin Li2 · Xibing Li2 · Tubing Yin2 · Yan Wang3 · Wengang Dang1 Received: 20 March 2020 / Revised: 24 April 2020 / Accepted: 21 May 2020 © Wroclaw University of Science and Technology 2020
Abstract Under certain extreme conditions in rock engineering works, fast change in temperature in the load-bearing rocks can happen. Known as thermal shock (TS), such process involves rapid temperature rise or drop, which causes fracturing in the rock material and thus can pose as a threat to the stability of the rock structures. To investigate the influence of thermal shock caused by fast cooling on the mechanical property of rock, laboratory tests are performed on heated granite which are cooled with different methods, with the highest cooling rate reaching 167.4 °C/min. The dynamic loading tests are performed on the heated granite specimens utilizing the split Hopkinson pressure bar (SHPB) system. The test results show that the dynamic compressive strength drops with the increase in heating level or cooling rate. This pattern is explained by the nuclear magnetic resonance (NMR) test data that the pores inside the heated granite increase both in size and quantity as heating level or cooling rate rises. Damage patterns of the tested granite specimen fragments are analyzed based on the observation with scanning electron microscope (SEM), and the mechanisms of thermal shock in granite are also discussed. Keywords Thermal shock · Cooling rate · SHPB · Fracture pattern
1 Introduction In rock engineering projects such as deep mining, tunneling and nuclear waste disposal sites, rock structures can be subjected to extreme conditions involving high temperature and rapid temperature change. For example, in a presumable fire accident [1–3], the rock materials can experience sudden temperature rise as fire starts and fast temperature drop in the process of extinguishing the fire with the cooling water. Rapid change in temperature (temperature rise or drop) can cause thermal stress and thus produce fracture in * Yan Wang [email protected] * Wengang Dang [email protected] 1
School of Civil Engineering, Sun Yat-sen University, Zhuhai 519082, China
2
School of Resources and Safety Engineering, Central South University, Changsha 410083, China
3
State Key Laboratory of High Performance Complex Manufacturing, School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China
rocks, which is known as thermal shock (TS) [4–6]. Therefore, although high temperature is widely recognized as a factor affecting the mechanical properties of rocks [7–11], temperature changing rate cannot be overlooked since TS may be induced in the heating or cooling process. It has been proposed that a rate ≥ 2 °C/min seems to be a lower boundary for TS to occur in rocks [4]. However, the fact that the data of temperature changing rate are not available in the thermal treatment
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