On the Effect of Grain Size on Rock Behavior under Cyclic Loading by Distinct Element Method

نوع مقاله: مقاله پژوهشی

نویسندگان

دانشکده مکانیک سنگ، دانشگاه تربیت مدرس تهران

10.29252/anm.2019.1630

چکیده

It is well-known that the mechanical behavior of rocks under cyclic loading is much different from static loading conditions. In most constructions, the load applied to structures is within dynamic ranges. That’s why a great deal of attention has been paid to this field to identify the dynamic behavior of rocks in more detail. Nevertheless, the nature of dynamic failure in rocks has not yet been identified, particularly when it comes to cyclic loading The purpose of this study was to investigate the influence of grain size on the mechanical behavior of rocks under cyclic loading using numerical modeling by UDEC. A total of three grain-categories with a diameter of 1, 2, and 4 mm were modeled in the software. All models were of Brazilian type with 54 mm diameter. Behavioral parameters required for modeling were determined through laboratory studies and the software was adjusted accordingly. The stresses applied to the samples were in two forms of quasi-static and cyclic loading. The result of static loading is that the smaller the grain size, the model will have a higher elastic modulus. In other words, the elastic modulus of the grain size is inversely related to the grain dimensions. Analysis of data obtained from cyclic loading showed that the amount of strain in samples with smaller grain sizes was lower than the corresponding strain in samples with larger grain sizes during the same loading periods. In other words, the resistance of samples with smaller grain sizes to deformation under cyclic load was higher compared to those with larger grain sizes. Comparison of the stress vectors for these samples showed that with a decrease in grain size, stress distribution in the sample became more uniform and inclusive, and the stress concentration declined. Another important result was that the smaller the grain size, the more the axial stress applied to the sample inclined towards one. This indicated that with a decrease in grain dimensions, the sample behavior approached a plastic behavior.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

On the Effect of Grain Size on Rock Behavior under Cyclic Loading by Distinct Element Method

نویسندگان [English]

  • Abolfazl Dalirnasab
  • kamran goshtasbi
  • hamidreza nejati
Dept. of Rock Mechanics, Tarbiat Modares University, Tehran, Iran
چکیده [English]

It is well-known that the mechanical behavior of rocks under cyclic loading is much different from static loading conditions. In most constructions, the load applied to structures is within dynamic ranges. That’s why a great deal of attention has been paid to this field to identify the dynamic behavior of rocks in more detail. Nevertheless, the nature of dynamic failure in rocks has not yet been identified, particularly when it comes to cyclic loading The purpose of this study was to investigate the influence of grain size on the mechanical behavior of rocks under cyclic loading using numerical modeling by UDEC. A total of three grain-categories with a diameter of 1, 2, and 4 mm were modeled in the software. All models were of Brazilian type with 54 mm diameter. Behavioral parameters required for modeling were determined through laboratory studies and the software was adjusted accordingly. The stresses applied to the samples were in two forms of quasi-static and cyclic loading. The result of static loading is that the smaller the grain size, the model will have a higher elastic modulus. In other words, the elastic modulus of the grain size is inversely related to the grain dimensions. Analysis of data obtained from cyclic loading showed that the amount of strain in samples with smaller grain sizes was lower than the corresponding strain in samples with larger grain sizes during the same loading periods. In other words, the resistance of samples with smaller grain sizes to deformation under cyclic load was higher compared to those with larger grain sizes. Comparison of the stress vectors for these samples showed that with a decrease in grain size, stress distribution in the sample became more uniform and inclusive, and the stress concentration declined. Another important result was that the smaller the grain size, the more the axial stress applied to the sample inclined towards one. This indicated that with a decrease in grain dimensions, the sample behavior approached a plastic behavior.

کلیدواژه‌ها [English]

  • : distinct element method
  • cyclic loading
  • grain size effect on rock behavior
  • rock stiffness
  • distribution of stresses in the rock
  • plastic behavior
[1] J.T. Fredrich, B. Evans, T.F. Wong, Effect of grain size on brittle and semibrittle strength: Implications for micromechanical modelling of failure in compression, Journal of Geophysical Research: Solid Earth, 95 (1990) 10907-10920.
[2] S. Ray, M. Sarkar, T. Singh, Effect of cyclic loading and strain rate on the mechanical behaviour of sandstone, International Journal of Rock Mechanics and Mining Sciences, 36 (1999) 543-549.
[3] J.I. Israelsson, Short descriptions of UDEC and 3DEC, Developments in geotechnical engineering, 79 (1996) 523-528.
[4] M.P. Ahola, A. Thoraval, A.H. Chowdhury, Distinct element models for the coupled THM processes: Theory and implementation, Developments in geotechnical engineering, 79 (1996) 181-211.
[5] A. Shrivastava, K. Rao, Numerical Simulation of Direct Test for Rock, (2010).
[6] Y. Gui, Z. Zhao, J. Kodikara, H.H. Bui, S. Yang, Numerical modelling of laboratory soil desiccation cracking using UDEC with a mix-mode cohesive fracture model, Engineering Geology, 202 (2016) 14-23.
[7] P. Cundall, UDEC 4.0 manual-theory and background, 2004, ITASCA Consulting Group, in, Inc.
[8] Z. Zhang, S. Kou, J. Yu, Y. Yu, L. Jiang, P.-A. Lindqvist, Effects of loading rate on rock fracture, International Journal of Rock Mechanics and Mining Sciences, 36 (1999) 597-611.
[9] R.I. Stephens, A. Fatemi, R.R. Stephens, H.O. Fuchs, Metal fatigue in engineering, John Wiley & Sons, 2000.
[10] M.A. A. Refahi1, E. Poursaeidi3, Developing a Numerical and Analytical Model of Fatigue Crack Growth Rate in Rock, in, Journal of Applied Environmental and Biological Sciences, 2015.
[11] M. Kikuchi, Y. Wada, Y. Shintaku, K. Suga, Y. Li, Fatigue crack growth simulation in heterogeneous material using s-version FEM, International Journal of Fatigue, 58 (2014) 47-55.
[12] E.T. Brown, Rock characterization, testing & monitoring: ISRM suggested methods, (1981).
[13] W.F. Hosford, Mechanical behavior of materials, Cambridge University Press, 2010.
[14] S. Bhat, R. Patibandla, Metal fatigue and basic theoretical models: a review, INTECH Open Access Publisher, 2011.