Behaviour of Brittle Material in Multiple Loading Rates Under Uniaxial Compression

It is of great importance to investigate the effect of loading rate on the behaviour of brittle material such as concrete and rock because engineering structures are subjected to multiple loading conditions. Although material behaviour under single loading mode has been extensively studied, very limited research has been conducted to investigate the performance of brittle materials subjected to varying loading conditions. This paper presents an experimental study of the effects of single and multiple strain rates (ε) on cement mortar samples. The first set of samples was loaded at constant strain rates until failure. For the remaining samples, the first strain rate (0.005 mm/s) was applied to the sample up to a predetermined load, and then the second strain was initiated immediately by using the specially-designed gear system in place in the compression rig. As expected, the increase in strain rate showed an increase in peak strength of the sample with reduced ultimate strain. For multiple strain modes, it was observed that the highest peak strength occurred when the second strain was applied at 50 % of the peak strength of the first strain.     

微量陨石激光熔样稀有气体测定方法

微量陨石激光熔样稀有气体测定方法是一种可以在微米尺度上对几毫克陨石样品进行准确稀有气体同位素分析的方法,克服了传统全岩熔融法在测量时存在样品用量大、前处理过程复杂和样品稀有气体分布不均导致不同组分的宇宙射线暴露历史无法进一步区分等问题。但是由于该方法所用样品体积小和样品用量低,要求实验室具有超低本底的稀有气体提取系统,目前国内在微量陨石稀有气体分析技术方面尚处于起步阶段。本文采用金刚石激光样品窗成功研制了超低本底的气体提取系统,通过系统体积标定和天平称量误差、热本底、干扰元素、质量歧视及质谱灵敏度等参数的校正,在中国科学院地质与地球物理研究所建立了微量陨石激光熔样稀有气体测定方法,并对毫克级微量钙长辉长无球粒陨石Millbillillie粉末标样进行了稀有气体同位素含量和比值测定,计算获得准确一致的宇宙暴露年龄。该方法的建立,将为我国迅速发展的比较行星学和深空探测提供重要技术支撑。     

Experimental Investigation of Drillability Indices of Thermal Granite After Water-Cooling Treatment

Natural Resources Research - Understanding the drillability indices of thermal granite under various water-cooling conditions is of great significance for deep drilling and wellbore stability...     

Major factors influencing proppant behaviour and proppant-associated damage mechanisms during hydraulic fracturing

The ultra-low permeability of shale reservoirs necessitates engineering applications such as hydraulic fracturing to enable the extraction of economically viable amounts of gas. In this process, a high-pressure fluid is injected into the reservoir to create a network of fractures. Proppants are solid, spherical, high-strength particles with size range between 8 and 140 mesh (105 μm–2.38 mm), which are injected into the reservoir simultaneously with fracturing fluid to prompt the opening of the fractures created, and they play a major role in the hydraulic fracturing process. As a result, appropriate management of proppants in shale reservoirs based on precise identification of their behaviour in shale reservoirs is necessary, because unexpected proppant performance or behaviour, commonly known as proppant damage mechanisms, can greatly reduce fracture conductivity. Therefore, it is essential to determine the major factors affecting proppant behaviour in order to maintain constant fracture conductivity. Numerous factors have been found in previous studies, and they can be summarized into three major groups: proppant properties, reservoir properties and hydraulic fracturing production, which affect proppant damage mechanisms. In the present paper, case studies have been provided on the determination of potential factors influencing proppant behaviour, followed by a discussion of their effects on fracture conductivity. The aim of this study is to present current opinions on potential factors influencing proppant behaviour based on a comprehensive literature review.     

Grain-scale analysis of proppant crushing and embedment using calibrated discrete element models

Acta Geotechnica - Proppant crushing and embedment in hydraulically-induced fractures is a major drawback to the recovery of unconventional oil/gas and geothermal energy production. This study...     

Effect of strain rate on strength properties of low-calcium fly-ash-based geopolymer mortar under dry condition

This paper presents the mechanical and elastic properties of inorganic polymer mortar under varying strain rates. The study includes a determination of the compressive strength, modulus of elasticity and Poisson’s ratio at 0.001, 0.005, 0.01 and 0.05 mm/s strain rate. A total of 21 cylindrical specimens having 100 mm length and 50 mm diameter were investigated, and all tests were carried out pursuant to the relevant Australian Standards. Although some variability between the mixes was observed, the results show that, in most cases, the engineering properties of geopolymer mortar compare favourably to those predicted by the relevant Australian Standards for concrete mixtures. It was found that the change in the strain rate causes different behaviour related to the percentage of the ultimate load. The ultimate strength, Young’s modulus and Poisson’s ratio of the geopolymer mortar depend on the strain rate. It was also found that as the strain rate increases, mechanical and elastic properties of geopolymer mortar substantially increase in logarithmic manner.     

3D modeling of stratified and irregularly jointed rock slope and its progressive failure

Little has been published on the three-dimensional (3D) simulation of the progressive failure of rock slopes, possibly because the process of failure involves a complex, nonlinear evolution from initiation, through propagation and crack. In addition, rock is typically anisotropic, which makes it difficult to identify and describe the slope constituents and failure processes accurately. Despite such difficulties, further study of the fracture process is just as important as analyzing stress fields in 3D rock slope failures. In this paper, the 3D realistic failure process analysis code using finite element programming, and an extended version of numerical centrifugal method, is used to simulate slopes failure with different dip angles. The numerical centrifugal analysis results in this paper are found that the critical failure surface develops along the weak structural surface when the slope dip angle β is below 30°; conversely, the failure surface is formed along the toe of circular sliding when β is above 30°. In addition, it is also found that whether or not including the irregularity of joint into modeling to analyze the 3D slope stability problem will lead to a significant difference in factors of safety, it can reach 8.41 % at the same slope angle. Furthermore, the acoustic emission analyzing reveals deformed location characters of rock slope during the failure processes. With such capabilities, the approach contributes significantly to the in-depth study of the mechanisms of rock slope instability process.