3D numerical study on microwave induced stresses in inhomogeneous hard rocks

Toifl, Michael; Meisels, R.; Hartlieb, Philipp; Kuchar, F.; Antretter, Thomas

doi:10.1016/j.mineng.2016.01.001

Cited by 80 publications

(23 citation statements)

References 33 publications

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“…The presented results show that a range of larger cracks can also be introduced in some distance to the irradiation spot. Presumably this is due to stresses originating in the centre which are not just associated to different microwave absorption properties but also to physical phase changes like elongation of minerals under temperature load [6,18].…”

Section: Discussionmentioning

confidence: 99%

“…Consequently, an inhomogeneous thermal field on the grain level is expected. Recently, several numerical studies of rocks with heterogeneous microstructures showed that the resulting stresses around the phase boundaries of strongabsorbing particles are high enough to initiate cracks which can propagate further into the material [2][3][4][5][6][7][8]. It was already demonstrated that these thermally induced cracks may lead to a significant reduction in resistance during size reduction in comminution processes [9].…”

Section: Introductionmentioning

confidence: 99%

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Experimental Study on Microwave Assisted Hard Rock Cutting of Granite

Hartlieb

Grafe

2017

Berg Huettenmaenn Monatsh

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This paper describes the influence of high-power microwave irradiation on the forces needed to cut granite with a conical pick. Granite samples have been irradiated with 24 kW at 2450 MHz with an open ended waveguide. The effect of microwave treatment was assessed by linear cutting tests with a conical pick.Microwave irradiation lead to an extensive network of cracks. The linear cutting tests provide a comparison of treated and non-treated parts and show that peak as well as average forces needed for cutting this very hard and abrasive material are reduced significantly. The average cutting force is reduced from 7.06 to 6.39 kN, equalling 10 %, from the untreated to the irradiated part, respectively. Keywords

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Study on Microwave Assisted Hard Rock Cutting of Granite

Hartlieb

Grafe

2017

Berg Huettenmaenn Monatsh

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“…As shown in the literature, cracks will mainly develop along grain boundaries (Toifl et al 2016) and, depending on the applied microwave power and frequency, a certain orientation along the surface might be achieved (Hartlieb and Grafe 2017). Also, the crack opening cannot be influenced.…”

Section: Microwave Crackingmentioning

confidence: 99%

Theoretical Investigations on the Influence of Artificially Altered Rock Mass Properties on Mechanical Excavation

Hartlieb

Bock

2017

Rock Mech Rock Eng

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guaranteeing the access to mineral deposits and for extracting the valuable minerals from these deposits. Mechanical excavation tools like full-face tunnel boring machines and roadheaders use either discs or conical picks for applying the required forces into the rock mass. The efficiency of the processes is mainly governed by the mechanical properties of the rock type, especially strength and abrasivity. Roadheaders are limited by a uniaxial compressive strength of 150 MPa, TBMs by roughly 300 MPa. In particular, the development of underground mines furthermore requires a high flexibility of the used equipment which is mainly characterised by the turning radius of the machine. The rather simple relationship is the harder the rock, the bigger the machine, the lower the flexibility.In order to improve the performance of their machines, most machine manufacturers on the market have introduced new machine concepts recently. Many of which change the cutting principle and apply the so-called undercutting technology (e.g. Aker Wirth "Mobile Tunnel Miner", Atlas Copco "Mobile Miner", Joy Mining "Oscillating Disc Cutter", Caterpillar "Rock Straight system" and Sandvik "MX650" (Sifferlinger et al. 2017)).In addition to changing the machine concept, the goal of extended research activities all over the world during the last decade is focussed on overcoming the highlighted restrictions. The major focus is set on artificially altering the rock mass properties in order to ease the machines' life by reducing the UCS and rock mass rating. This can be done by introducing cracks and/or slots in the rock mass which help the subsequent cutting process with a conical tool. The technologies under consideration are high-power lasers Parker et al. 2003;Graves and Bailo 2005), microwaves (Toifl et al. 2017; Hartlieb and Grafe 2017), high-pressure water jets (Ciccu and Grosso 2010;Miller 2016) and activated tools (Keller and DrebenstedtAbstract This study presents a theoretical analysis of the influence of the rock mass rating on the cutting performance of roadheaders. Existing performance prediction models are assessed for their suitability for forecasting the influence of pre-damaging the rock mass with alternative methods like lasers or microwaves, prior to the mechanical excavation process. Finally, the RMCR model was chosen because it is the only reported model incorporating a range of rock mass properties into its calculations. The results show that even very tough rocks could be mechanically excavated if the occurrence, orientation and condition of joints are favourable for the cutting process. The calculated improvements in the cutting rate (m 3 /h) are up to 350% for the most favourable cases. In case of microwave irradiation of hard rocks with an UCS of 200 MPa, a reasonable improvement in the performance by 120% can be achieved with as little as an extra 0.7 kWh/m 3 (= 1% more energy) compared to cutting only.

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“…In the mining numerical simulation, it was found out that the highest temperatures and temperature gradients appeared in the absorbing grains enriched area, as thermal expansion induced stress exceeds the strength of the material, cracks initiate in the mineral grain boundaries [11][12][13]. Meanwhile, the anisotropy of the rock affects the distribution of temperature and stress in the ores [14][15][16]. For the hard rocks' breakage, the reaction of different kinds of rocks under microwave irradiation has been studied.…”

Section: Introductionmentioning

confidence: 99%

The thermal damaging process of diorite under microwave irradiation

Yuan

Zeng

et al. 2018

Frattura Ed Integrità Strutturale

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Laboratory tests have been conducted to investigate the effects of thermal damage on diorite under microwave irradiation. The sample rocks were heated to high temperature range of 300 to 800 ℃ in a single-mode microwave furnace. The experimental results show that the rocks started to crack at 500 ℃ and completely disintegrated at 700 ℃. The intensities of quartz diffraction peaks were almost unchanged while the diffraction peak intensity of hornblende gradually decreased with temperature increasing. In addition, the chlorite diffraction peak disappeared at 500 ℃. The compressive strength of the sample decreased to 40% at 600 ℃ and it approached zero at 700 ℃. In this paper, the possible reasons for the thermal effects on the fracture of diorite were discussed, which can be related to water evaporation,

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3D numerical study on microwave induced stresses in inhomogeneous hard rocks

Cited by 80 publications

References 33 publications

Experimental Study on Microwave Assisted Hard Rock Cutting of Granite

Experimental Study on Microwave Assisted Hard Rock Cutting of Granite

Theoretical Investigations on the Influence of Artificially Altered Rock Mass Properties on Mechanical Excavation

The thermal damaging process of diorite under microwave irradiation

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