Document Type: Original Research Paper

Authors

School of Mining Engineering, College of Engineering, University of Tehran, Tehran, Iran

10.22044/jme.2020.9818.1903

Abstract

The dynamic fracture characteristics of rock specimens play an important role in analyzing the fracture issues such as blasting, hydraulic fracturing, and design of supports. Several experimental methods have been developed for determining the dynamic fracture properties of the rock samples. However, many used setups have been manufactured for metal specimens, and are not suitable and efficient for rocks. In this work, a new technique is developed to measure the dynamic fracture toughness of rock samples and fracture energy by modifying the drop weight test machine. The idea of wave transmission bar from the Hopkinson pressure bar test is applied to drop weight test. The intact samples of limestone are tested using the modified machine, and the results obtained are analyzed. The results indicate that the dynamic fracture toughness and dynamic fracture energy have a direct linear relationship with the loading rate. The dynamic fracture toughness and dynamic fracture energy of limestone core specimens under the loading rates of 0.12-0.56kN/µS are measured between 9.6-18.51MPa√m and 1249.73-4646.08J/m2, respectively. In order to verify the experimental results, a series of numerical simulation are conducted in the ABAQUS software. Comparison of the results show a good agreement where the difference between the numerical and experimental outputs is less than 4%. It can be concluded that the new technique on modifying the drop weight test can be applicable for measurement of the dynamic behavior of rock samples. However, more tests on different rock types are recommended for confirmation of the application of the developed technique for a wider range of rocks.

Keywords

[1]. Khandouzi, G.H., Mollashahi, M. and Moosakhani, M. (2019). Numerical simulation of crack propagation behavior of a semi-cylindrical specimen under dynamic loading. Frattura ed Integrità Strutturale. 50:29-37; DOI: 10.3221/IGF-ESIS.50.04.

[2]. Saghafi, H.A., Ayatollahi, M.R. and Sistani, M. (2010). A modified MTS criterion (MMTS) for mixed mode fracture toughness assessment of brittle materials. Material science and engineering: A. 527:5624-30.

[3]. Chen, C.S. Pan, E. and Amadei, B. (1998). Fracture mechanics analysis of cracked discs of anisotropic rock using the boundary element method. International journal of rock mechanics & mining sciences. 35:195-218.

[4]. Khandouzi, G.H., Mirmohhamadlou, A. and Memarian, H. (2014). Dynamic fracture behavior of cubic and core specimen under impact load. Rock engineering and rock mechanic. 149-54. DOI: 10.1201/b16955-22.

[5]. Franklin, J.A. and Atkinson, B.K. (1988). Suggested methods for determining the fracture toughness of rock. Int J Rock Mech Min Sci goe-mechanics Abstract. 25 (2):71–96.

[6]. Fowell, R.J., Xu, C. and Chen, J.F. (1995). Suggested method for determining mode-I fracture toughness using cracked chevron-notched Brazilian disc (CCNBD) specimens. Int J Rock Mech Min Sci goe-mechanics Abstract. 32 (1):57–64.

[7]. Chunan. T. and Xiaohe, X. (1990). A new method for measuring dynamic fracture toughness of rock, engineering fracture mechanics. International journal of fracture Mechanics. Vol. 35, NO. 4/S, pp. 783-791.

[8]. Wang, Q.Z., Feng, F., Ni, M. and Gou, X.P. (2011). Measurement of mode I and mode II rock dynamic fracture toughness with cracked straight through flattened Brazilian disc impacted by split Hopkinson pressure bar. Engineering Fracture Mechanics. 78:2455–69.

[9]. Wang. Q.Z., Zhang, S. and Xie, H.P. (2009). Rock Dynamic Fracture Toughness Tested with Holed-cracked Flattened Brazilian Discs. Proceedings of the International Congress and Exposition, Orlando, Florida USA. 50:877-85.

[10]. Nikita, F. Morozov., Yuri, V. petrov., Vladimir, I. Smirnov. (2009). Dynamic Fracture of Rocks. 7th EUROMECH Solid Mechanics Conference. Lisbon, Portugal. September 7th-11th.

[11]. Chen, R. Xia, K., Dai, F., Lu, F. and Luo, S.N. (2009). Determination of dynamic fracture parameters using a semi-circular bend technique in split Hopkinson pressure bar testing. Engineering Fracture Mechanics. 76:1268–76.

[12]. Dai. F., Chen, R., Iqbal, M.J. and Xia, K. (2010). Dynamic cracked chevron notched Brazilian disc method for measuring rock fracture parameters. International Journal of Rock Mechanics & Mining Sciences. 47: 606–13.

[13]. Yao. W. and Xia, K. (2019). Dynamic notched semi-circle bend (NSCB) method for measuring fracture properties of rocks: Fundamentals and applications. Journal of rock mechanics and geotechnical engineering. 11: 1066-1093.

[14]. Shi. X., Yao. W., Liu. D., Xia. K., Tang. T. and Shi. Y. (2019). Experimental study of the dynamic fracture toughness of anisotropic black shale using notched semi-circular bend specimens. Engineering fracture mechanics. 205: 136-151.

[15]. Liu. X.R., Yang. S.Q., Huang. Y.H. and Chen. J.L. (2019). Experimental study on the strength and fracture mechanism of sandstone containing elliptical holes and fissures under uniaxial compression. Engineering fracture mechanics. 205: 205-217.

[16]. Omer, Y.B., ozkan, o. and Atban, R.A. (2017). The effect of nanosilica on charpy impact behavior of glass/epoxy fibr rienfoced composite laminate. Periodical of engineering and natural science, 5: 322-327.

[17]. Abrate, S. (2011). Impact engineering of composite structures. Springer Wien New York, Printed in Italy. ISBN 978-3-7091-0522-1.

[18]. Lorriot, T., Martin, E., Quenisset, J.M. and Rebiere, J.P. (1998). Dynamic analysis of instrumented CHARPY impact tests using specimen deflection measurement and mass-spring models. International Journal of Fracture. (91):299-309.

[19]. Jiang, F. and Vecchio, K.S. (2009). Hopkinson Bar Loaded Fracture Experimental Technique: A Critical Review of Dynamic Fracture Toughness Tests. Applied Mechanics. DOI: 10.1115/1.3124647.

[20]. Chunhuan, G., Fengchun, J., Ruitang, L. and Yang Y. (2011). Size effect on the contact state between fracture specimen and supports in Hopkinson bar loaded fracture test. Int JFract.169:77–84.

[21]. Sheikh, A. K., Arif, A.F.M. and Qamar. S.Z. (2002). Determination of fracture toughness of tool steels. The 6th Saudi Engineering Conference, KFUPM, Dhahran. 5:169.

[22]. Zhang, B.Q. and Zhao, J. (2014). A review of dynamic experimental techniques and mechanical behavior of rock materials. Rock mechanic and rock engineering. (47):1411-78.

[23]. Manhan, M.P. and Stonesifer, R.B. (2007). Studied toward optimum instrumented striker designs. European structure integrity society. (30):221-8.

[24]. Knapp, J., Altmann, E., Niemann, J. and Warner, K.D. (1998). Measurement of shock events by means of strain gauges and accelerometers. Measurement Elsevier. (24):87-96.

[25]. Lou, J., Ying, K., He, P. and Bai, J. (2005). Properties of Savitzky–Golay digital differentiators. Digital Signal Processing. (18):122-36.

[26]. Ouchterlony, F. (1981). Extension of compliance and stress intensity formulas for the single edge cracked round bar in bending. ASTM STP 678. 166-182.

[27]. Saouma, V.E. (2000). Lecture Notes in fracture mechanics. CVEN.6831, University of Colorado, Boulder. CO:80309-0428, 2000.