Cerchar abrasivity test – laboratory testing and numerical simulation To the Faculty of Geosciences, Geoengineering and Mining of the Technischen Universität Bergakademie Freiberg approved THESIS to attain the academic degree of Doctor of Engineering Dr.-Ing. submitted by Dipl.-Ing. Guangzhe Zhang born on the June 28, 1982 in Shenyang, PR China Reviews: Prof. Dr.-Ing. habil. Heinz Konietzky, TU Bergakademie Freiberg, Germany Prof. Dr. Michael Alber, Ruhr-Universität Bochum, Germany Date of the award: 17.06.2020 Declaration I, Guangzhe Zhang, declare that the Ph.D. thesis entitled “Cerchar abrasivity test – laboratory testing and numerical simulation” contains no material that has been submitted previously, in whole or in part, for the award of any other academic degree or diploma. Except where otherwise indicated, this thesis is my own work. __________________ Place, Date, Signature I II Acknowledgements Having struggled and been perseverant. The long and laborious journey would not be finished without the help of a number of people. I would like to express my sincere gratitude to Prof. Heinz Konietzky, my supervisor, for his invaluable guidance, helpful advice, patience and continuous support through my doctoral study at the Chair for Rock Mechanics, Geotechnical Institute, Technical University Bergakademie Freiberg. I would like to thank Prof. Shouding Li at the Institute of Geology and Geophysics at the Chinese Academy of Sciences, Dr. Reinhard Kleeberg at the Institute for Mineralogy, Dr. Klinger Mathias at the Institute for Energy Process Engineering and Chemical Engineering, Dr. Patrick Gehre at the Institute for Ceramic, Glass and Construction Materials for their technical support. Acknowledge is extended to the colleagues and friends at the Geotechnical Institute for the encouragement and support during my stay here. I specially mention Prof. Wengang Dang, Dr. Thomas Frühwirt, Dr. Martin Herbst, Dr. Zhengyang Song, Dr. Fei Wang, Mr. Gerd Münzberger, Mrs. Beatrice Tauch, Mr. Yufeng Zhao, Mr. Vishal Vilas Yadav and Mr. Jian Zhao. I would like to express appreciation to the China Scholarship Council (CSC) for the financial support of my study. Deepest gratitude is expressed to my family, my father Xuechao Zhang, my mother Xin Guan and my wife Dr. Jin Zhao for their selfless love, understanding and support. My sweet heart daughter Shuyu Zhang, I love you. III IV Abstract Abrasivity is a characteristic property of rocks. Rock abrasivity has influence on tool wear, energy consumption and construction time and is therefore an important parameter in rock engineering. Over the years, a number of testing methods have been developed to define and quantify the abrasive potential of rocks. Due to simple design and convenient handling, Cerchar abrasivity test and its index, Cerchar abrasivity index, are most commonly used to assess the rock abrasivity. Besides the abrasivity index, various parameters can be derived from the Cerchar test thanks to the development of a special designed testing device. Diverse parameters like scratching force, applied work and specific energy can be used to estimate the cutting efficiency. Moreover, a new composite parameter named Cerchar abrasion ratio is proposed, which considers both, the wear on the stylus tip and the material removal on the rock surface and can be regarded as an indicator to evaluate the cutting effectivity. Since the development of Cerchar abrasivity test, major attentions are focused on the abrasion of the stylus, but minor attentions are paid to investigate the mechanical behavior of rocks against the action of the stylus during the scratching process. The scratch groove produced on the rock surface is observed under a scanning electron microscope. The Cerchar wear mechanism can be explained as follows: mineral grains are detached from damaged surface by fracturing after plastic deformation on stressed surface. Transition from plastic deformation-induced to cracking-induced wear are related to the rock microstructure. For the Cerchar test, various factors affecting the Cerchar abrasivity index have been studied, which can be divided into testing condition-based and geotechnical-based factors. The influence of some dominant testing condition-based factors including surface condition, testing distance and velocity on the test result is investigated by using the new designed testing device, in which the sliding distance and scratching velocity can be exactly controlled during the test. Results show that the surface condition can affect the result of Cerchar index, especially for hard and inhomogeneous rocks, while the testing distance and velocity have no obvious influence on the Cerchar index. V As far as it is known, in rock mechanics, anisotropic features of rocks can affect the experimental results significantly. In the original Cerchar specification, testing procedure for stratified or foliated rocks is not specially discussed. Due to this, the influence of rock anisotropy on the Cerchar abrasivity index is investigated based on two intact metamorphic rocks of slate and gneiss. However, no significant dependency is found. Cerchar scratch test is simulated based on a quasi-homogeneous model made of sandstone with respect to its mineralogical-mechanical properties. The numerical simulation is conducted by using the discrete element method-based particle flow code of PFC3D. As a result, the simulated scratching force shows a good agreement with the experimental result. A gap between numerical and experimental studies can be attributed to the testing condition-based factors, such as rock mineralogy and microstructure, scratching velocity and depth of scratch, tool abrasion and temperature. Based on the calibrated sandstone model, numerical simulations of rock cutting are conducted under different testing conditions. The influence of tool geometry like tip shape, tip angle and tip wear, and cutting parameters including cutting velocity, depth of cut and rake angle on the cutting force and crack pattern is studied. VI Table of contents Declaration ....................................................................................................................................... I Acknowledgements ....................................................................................................................... III Abstract .......................................................................................................................................... V Table of contents .......................................................................................................................... VII List of figures ............................................................................................................................. XIII List of tables ............................................................................................................................... XIX Nomenclature ............................................................................................................................. XXI 1. Background and introduction .................................................................................................. 1 1.1 Definition and determination of rock hardness ......................................................................... 1 1.2 Definition and determination of rock abrasivity ....................................................................... 1 1.2.1 Silica content .................................................................................................................. 2 1.2.2 Quartz content ................................................................................................................. 2 1.2.3 Abrasive mineral content ................................................................................................ 3 1.2.4 Equivalent quartz content ............................................................................................... 3 1.2.5 Vickers hardness number of rock ................................................................................... 4 1.2.6 LCPC abrasivity coefficient ........................................................................................... 5 1.2.7 Abrasion value ................................................................................................................ 6 1.2.8 Schimazek wear index .................................................................................................... 7 1.2.9 Rock abrasivity index ..................................................................................................... 8 2. State of the art .......................................................................................................................... 9 2.1 Cerchar abrasivity test............................................................................................................... 9 2.2 Influence of various factors on Cerchar abrasivity index ....................................................... 11 2.2.1 Testing apparatus .......................................................................................................... 11 2.2.2 Applied load ................................................................................................................. 12 VII 2.2.3 Stylus metallurgy and hardness .................................................................................... 12 2.2.4 Surface condition .........................................................................................................