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ABSTRACT: With a brief review of Poisson's ratio of materials, a correction is made to the formula of Poisson's ratio of rocks in triaxial experiments suggested by the national standard. A specimen from the tight sand reservoir in an oilfield is subjected to triaxial compression, and then methods suggested by the ISRM, the national standard and the conventional method are used respectively to determine Poisson's ratio. The differences among these methods are carefully identified. In the light of the elasto-plastic constitutive equation for rocks, a method based on the critical point of plastic volumetric strain is proposed. This method with physical meaning and practical applicability suggests that Poisson's ratio should be determined when the plastic internal variable equals to zero. Finally an example is presented to illustrate the process of such a method and different Poisson's ratio values acquired by different methods are compared to demonstrate the applicability of this method. 1 INTRODUCTION The term Poisson's ratio was named after the French scientist Poisson who theoretically deduced that the ratio of lateral compressional strain to axial tensional strain of an isotropic elastic bar subjected to axial tension was a constant and equaled to l/4in 1829 (Poisson 1829). Some researchers discussed the range of Poisson's ratio and their physical meaning of their lower and upper bound (Love 1927, Qian 1956, Xia 1984). Lakes firstly reported a novel foam structure, which exhibits a negative Poisson's ratio (Lakes 1987). Since then, some more researchers began to pay attentions to the material with negative Poisson's ratio (Kou 1992, Hao 1992, Wang et al. 1996, Tu &Yang 2008). Huang proposed that the method to measure Poisson's ratio of rock formation under in-situ geostress and he found Poisson's ratio increased with the increasing confining pressure (Huang & Zhuang 1985). You explained the mechanical meaning of Poisson's ratio and invented a method to measure Poisson's ratio by decreasing the confining pressure after triaxial compression tests (You & Hua 1997). Liu studied the anisotropy of Poisson's ratio of rock specimen under different temperatures and confining stress (Liu et al. 2001, 2002). Shan introduced some methods to measure Poisson's ratio which developed recently in the research of the behaviors of elasticity. He also analyzed and compared the limits and conditions of various methods (Shan et al. 2006). Wang studied the variation of Poisson's ratio of rock specimen under uniaxial compression after the peak (Wang 2006). In a review, Gercek (2007) examined the values and applications of Poisson's ratio in rock mechanics. Yu analyzed the relationship of Poisson's ratio under compression and Poisson's ratio under tension (Yu et al. 2008). Yu discovered that the anisotropy of Poisson's ratio increased with the increasing depth of formation (Yu & Tian 2013).
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.34)
- North America > United States > Texas > Fort Worth Basin > Barnett Shale Formation (0.99)
- Europe > United Kingdom > England > London Basin (0.91)
Dynamic behavior of NPR bolt and its application to rock burst control
He, M. C. (China University of Mining and Technology, Beijing) | Li, C. (China University of Mining and Technology, Beijing) | Gong, W. L. (China University of Mining and Technology, Beijing) | Liu, D. Q. (China University of Mining and Technology, Beijing)
ABSTRACT: This paper presents an innovative bolt which has the Negative Poisson's Ratio effect (NPR bolt). The NPR bolt can absorb energy and sustain high constant resistance and large deformation. The working principle of this new type of bolt is introduced and a series of dynamic laboratory tests have been conducted to verify its large deformation resistance and high dynamic bearing capacity. The results of the dynamic tests show that the NPR bolt can withstand repeated impact, and maintain the stability of the constant value under impact load. Finally, the NPR bolt is applied for rock burst control. 1 INTRODUCTION Bolt/Cable-supporting technology is one of effective quasi-supporting means in tunnel, which can reinforce the surrounding rock structure effectively, strengthen the roadway structural strength and improve the stability of surrounding rock significantly, and has gradually become the main measure for tunnel support all over the world (Corbett 1996). As an effective quasi-supporting way in tunnel, bolt-supporting technology, which will change the structure and strength of the surrounding rock, can significantly improve the stability of the rock mass surrounding a tunnel. In addition, with the characteristics of low cost, fast installation, low labour intensity, more utilization of tunnel section, better and safer working conditions, bolt-supporting technology will gradually become a major support way for tunnel support worldwide. It has also represented the main direction of tunnel support technology (Jiang et al. 2014). Because of the superiority of bolting technology, it has more than 50 years development history since the first use in ore, coal system in China in the 1950s. This advanced supporting technology has been widely used in mining, construction, hydropower and other engineering fields, which has become the main supporting method on geotechnical engineering.
- Geology > Geological Subdiscipline > Geomechanics (0.91)
- Geology > Rock Type > Sedimentary Rock > Organic-Rich Rock > Coal (0.49)
- Materials > Metals & Mining (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- North America > Canada > Nova Scotia > Sydney Field (0.99)
- Europe > United Kingdom > England > London Basin (0.91)
Research on Mechanical Behaviour of Unit Cells of Strengthened Re-Entrant Honeycomb for Anti-Collision Ship Side Structures
Yu, Rong (Wuxi Institute of Technology, Wuxi) | Yu, Shengjie (China Ship Scientific Research Centre, Wuxi) | Zeng, Yang (School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan / Hubei Key Laboratory of Naval Architecture and Ocean Engineering Hydrodynamics) | Liu, Jingxi (School of Naval Architecture and Ocean Engineering, Huazhong University of Science and Technology, Wuhan / Hubei Key Laboratory of Naval Architecture and Ocean Engineering Hydrodynamics)
ABSTRACT Mechanical behavior of strengthened re-entrant hexagonal unit cells for anti-collision ship side structures under quasi-static planar compression was conducted by experimental test and FEA in the present research. Four types of re-entrant unit cells which are strengthened by narrow rib, curved ribs, rhombic ribs and polyurethane foam were presented. FE analyses were carried out to simulate the quasi-static compressive tests, satisfactory agreements were achieved between the FEA and experimental deformed shapes and load–displacements. Test and FE results show that the foam filled unit cell has a significant advantage in specific energy absorption capability. The present investigations provide useful insight into the strengthened re-entrant hexagonal unit cell, the foam filled honeycomb lead to excellent load carrying capability and energy absorption capability as expected, and would be used in the development of novel light weight energy absorbing honeycomb structure for ship side anti-collision. INTRODUCTION Negative Poisson's ratio structures undergo a transverse contraction when subjected to longitudinal compression, or undergo a lateral expansion under longitudinal stretching. The word "auxetic" was coined firstly to describe the microporous polyethylene foam with negative Poisson's ratio (Yunan, P, 2012). The so-called auxetic materials/structures with negative Poisson's ratio have been discovered and attracted attentions in the past few decades. Negative Poisson's ratio has in fact been found in a wide variety of natural materials including zeolite ( Grima, JN, 2000 ) cubic elemental metal (Ray, H, 1998), and even biological materials such as cow teat skin (Caroline, L, 1991) and human tendon (Ruben, G, 2015). Meanwhile, artificial auxetic materials and structures with negative Poisson's ratio have been discovered and attracted attentions. Systematic research on artificial auxetic structure firstly started in 1985 by Almgren (1985). A re-entrant structural topology was established theoretically by ideal structure of rods, hinges, and springs. Since then, a plenty of auxetic topologies with negative Poisson's ratio have elaborated: re-entrant topology (Lakes, R 1987), double array topology (Ma, L, 2018), chiral topology (Jiang, YY, 2017), rotating unit topology ( Grima, JN, 2000 ), random voronoi topology (Gao, RC, 2019), and hybrid topology ( Zhou, L, 2018 ).
Characterization of Thermal Effect on the Rock Dynamic Fracture Using High-Speed Three-Dimensional Digital Image Correlation (3D-DIC)
Xing, Haozhe (Monash University / Commonwealth Scientific and Industrial Research Organisation) | Wu, Gonglinan (Monash University / Commonwealth Scientific and Industrial Research Organisation) | Zhang, Qianbing (Monash University) | Dehkhoda, Sevda (Commonwealth Scientific and Industrial Research Organisation) | Zhao, Jian (Monash University)
Abstract Dynamic compression and Brazilian Disc (BD) tests were performed on heated sandstone with split Hopkinson pressure bar (SHPB) at different strain rates. The sandstones were treated under the temperatures of 20 °C, 200 °C, 400 °C, 800 °C and 1200 °C. The full-field and real-time fracturing processes were captured by the high-speed 3D-DIC technique with resolution of 256 × 256 pixels and 200,000 frames per second (fps). The effect of heat on crack initiation stress thresholds, and the stability of crack development were investigated together with the dynamic Poisson's ratio and elastic modulus. The density and wave velocity were found to decrease with temperature increase of the heat treatment. The results also showed that strain rate effect still exists in the high temperature treated sandstones; however, within a critical range (temperatures between 400 °C and 800 °C), the reduction in compressive and tensile strength is followed by a rise. The thermal effect on the distribution and evolution of the strain localization under compressive loading were discussed. 1. Introduction With an increasing demand in resource and space, the utilization of underground spaces, where high temperature may occur, is more and more important. The thermal effect on the rock mechanics will influence the efficiency of the rock excavation and the safety of the rock engineering. The underground spaces, also, experience dynamic loadings from various sources such as impact, explosion and earthquake. However, temperature and strain rate have opposite effects on the stress and strain. Increasing the strain rate or decreasing the temperature will lead to higher stress levels, but lower values of strain (Zhang and Zhao, 2014). Therefore, the understanding of the coupled effect of high temperature and strain rate on the dynamic behaviour of rocks is essential. The thermal effect on rock dynamics has attracted extensive attentions from researchers. The dynamic fracture toughness of Fangshan gabbro and Fangshan marble subjected to high temperature was measured by (Zhang et al., 2001) with the short rod (SR) method on SHPB. It was found that temperature variation affects the dynamic fracture toughness of the two rocks to a limited extent within the tested temperature ranges. This result was different from the results obtained under the static loading condition. Yin et.al. investigated effect of thermal treatment on the dynamic fracture toughness of Laurentian granite (LG) conducted based on notched semi-circular bend (NSCB) test (Yin et al., 2012). The thermally induced micro-cracks within the rock samples were then examined by scanning electron microscope (SEM). They found that at temperatures below 250 °C, the thermal expansion of grains led to an increase in the toughness of the rock. At treatment temperatures above 450 °C, the sources of weaknesses such as grain boundaries and phase transition of silicon were depleted resulting in decrease of fracture toughness. Similar pattern was also found in tensile strength in Brazilian disc tests done by (Yin et al., 2015) on Laurentian granite after being treated with high temperature. These results showed that dynamic tensile strength first increases and then decreases with a linear increase of loading rate. Liu and Xu employed the SHPB method to conduct uniaxial compression and split tensile tests on Qinling biotite/granite samples, which were treated under high temperatures and then cooled naturally to room temperature (Liu and Xu, 2014). These researchers also concluded the effect of high temperature on the dynamic tensile and compressive strength. Huang and Xia used computed tomography (CT) to quantify the damage induced by the heat-treatment and correlated it with the dynamic compressive strength of Longyou sandstone which was obtained by SHPB (Huang and Xia, 2015). Further investigations by (Liu and Xu, 2015) were carried out on the influences of coupled temperature/strain rate effect on dynamic compressive mechanical behaviours of sandstone. No obvious strain rate effect was observed in tests conducted under high temperature compared to ones at room temperature when ratios of dynamic compressive strength, peak strain, and energy absorption ratio of rock were studied. Similar research was implemented on granite by (Fan et al., 2017), and results showed that the dynamic energy absorption capacity increases below 400 °C but then decreases as the temperature increases to 800 °C. The effect of thermal treatment on energy absorption capacity was more obvious under a smaller impact pressure in granite samples. The dynamic mechanical behaviours of coal samples exposed to elevated temperatures were also examined with SHPB unit (Yu et al., 2017). In this study, the anthracite specimens were preheated up to 500°C in an oxygen-free environment. The results showed that coal gradually loses its dynamic bearing and anti-deformation capacities with increase in temperature, especially after 300°C.
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (1.00)
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
Effect of Cyclic Thermal Shock on Mechanical Properties and Brittleness of Granite
Li, N. (Sinopec Petroleum Exploration and Production Research Institute) | Wang, H. B. (Sinopec Petroleum Exploration and Production Research Institute) | Zhang, S. C. (China University of Petroleum (Beijing)) | Zou, Y. S. (China University of Petroleum (Beijing)) | Zhang, Z. P. (China University of Petroleum (Beijing)) | Zhou, T. (Sinopec Petroleum Exploration and Production Research Institute)
ABSTRACT: This paper aims to investigate the effect of cyclic thermal shock on mechanical properties and brittleness of granite. Uniaxial compression tests and brittleness evaluation was performed on granite samples after cyclic heating and water-cooling treatment. Further, characteristics of microscopic thermal cracking was investigated by SEM observation to reveal the temperature-dependent response of macro mechanical properties. Experimental results show that uniaxial compression strength, Young's modulus, and brittleness index slightly decreased with the increasing of number of cycles when the thermal treatment temperature was 300 °C. As the thermal treatment temperature increased to 400 °C, obvious thermal cracking was induced and network of cracks with apparent aperture was created. Consequently, significant degradation in uniaxial compression strength and Young's modulus occurred and the plasticity was enhanced due to the thermal damage. Additionally, the degradation in mechanical strengths and brittleness tends to be mainly induced in the early cycles of thermal treatments. Experimental results may be beneficial for understanding the exploitation process of hot dry rock geothermal energy. 1. Introduction During the stimulation and the heat extraction processes in hot dry rock geothermal formations, temperature field variation caused due to the cold-water injection commonly occurs (Ghassemi, 2012; Olasolo et al., 2016; Jin et al. 2019). According to the study of Jansen et al. (1993), the difference in thermal expansion coefficients between adjacent crystalline grains and the temperature gradient can induced thermal stress. When the thermal tensile strength exceeds the cohesion strength of adjacent grains or the strength of grain, inter- or intragranular cracks tend to be created, which further influence the mechanical properties of the rock (Liu et al. 2010; Heap et al. 2017). A large number of researches have been carried out to investigate the influence of temperature on mechanical properties of granite (Xu et al. 2010; Brotóns et al. 2013; Kong et al. 2016; Yin et al. 2016; Yang et al. 2017; Kumari et al. 2018; Wu et al. 2019). Generally, laboratory experiments were performed on sample under heating condition or after heating and cooling treatment. Zuo et al. (2011) studied the thermal cracking characteristics of Beishan granite by SEM, and characterized the thermal cracking behavior using fractal analysis model. It was indicated that with the increasing of temperature, the thermal cracking behavior was dominated by from intergranular cracks to intra-granular or mixed cracks. However, the temperature-dependent response of mechanical properties may be different among various types of granite. This can be accounted for by the fact that the thermal cracking characteristics of rock are related to not only the thermal treatment temperature but also the heating or cooling rate, mineral composition, and microstructure of rocks, etc. (Finnie et al. 1979; Kumari et al. 2017). Wang et al. (2013) compared the mechanical properties of preheated granite after air-cooling and rapid water-cooling treatments. Experimental results show that the mechanical properties of granite samples after rapid water-cooling treatment degraded more severely than that after air-cooling treatment. Shao et al. (2015), Zhang et al. (2017), and Kumari et al. (2017), also investigated the thermal shock effect on mechanical properties of granite after heating and water-cooling treatments. In summary, tensile strength, uniaxial compression strength, Young's modulus, and fracture toughness tend to be reduced with the increasing of thermal treatment temperature. However, these experiments performed after single-cycle thermal treatment. To date, investigation into the cyclic thermal shock effect on mechanical properties and brittleness of granite are still scarce.
- Asia > China (0.71)
- North America > United States > Texas (0.28)
- Research Report > New Finding (0.88)
- Research Report > Experimental Study (0.69)
- Geology > Rock Type > Igneous Rock > Granite (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Materials (1.00)
- Energy > Oil & Gas > Upstream (1.00)
- Energy > Renewable > Geothermal > Geothermal Resource > Hot Dry Rock (0.45)