Abstract
Based on the review of a wide range of literature, this paper finds that: (1) the average specific surface energy of various single crystals is only 0.8 J/m2. (2) The average specific fracture energy of the rocks with a pre-crack under static cleavage tests is 4.6 J/m2. (3) The average specific fracture energy of the rocks with a pre-cut notch but with no pre-crack under static tensile fracture (mode I) tests is 4.6 J/m2. (4) The average specific fracture energies of regular rock specimens with neither pre-made crack nor pre-cut notch are 26.6, 13.9 and 25.7 J/m2 under uniaxial compression, tension and shear tests, respectively. (5) The average specific fracture energy of irregular single quartz particles under uniaxial compression is 13.8 J/m2. (6) The average specific fracture energy of particle beds under drop weight tests is 74.0 J/m2. (7) The average specific fracture energy of multi-particles in milling tests is 72.5 J/m2. (8) The average specific energy of rocks in percussive drilling is 399 J/m3, that in full-scale cutting is 131 J/m3, and that in rotary drilling is 157 J/m3. (9) The average energy efficiency of milling is only 1.10%. (10) The accurate measurements of specific fracture energy in blasting are too few to draw reliable conclusions. In the last part of the paper, the effects of inter-granular displacement, loading rate, confining pressure, surface area measurement, premade crack, attrition and thermal energy on the specific fracture energy of rock are discussed.
Highlights
Rock fracture occurs in various engineering operations such as rock drilling, cutting, boring, crushing, grinding and blasting, and it requires energy
The specific fracture energy is estimated by wf = w0f ∕11 ; w∗f is the specific fracture energy measured at small magnitude by Friedman et al (1972) NB notched beam; the numbers in the brackets are the quantity of rock speciemns
Compression tests with regular cylindrical basalt specimens by Lindholm et al (1974) indicated that the energy input required to fracture basalt in compression increased with decreasing temperature and increasing strain rate, and the energy to fracture the rock largely increased with increasing confining pressure
Summary
Rock fracture occurs in various engineering operations such as rock drilling, cutting, boring, crushing, grinding and blasting, and it requires energy. The energy efficiency is about 10% in percussive rock drilling (Carrol 1985), 3–5% in rock crushing (Prasher 1987), 1% in ball and rod milling (or grinding) (Chi et al 1996; Alvarado et al 1998; Fuerstenau and Abouzeid 2002), and about 6% in rock blasting (Ouchterlony et al 2003; Sanchidrián et al 2007). These low energy efficiencies result in a huge amount of energy wastage and make mining operations much worse than other industrial sectors in terms of energy utilization. In the last part of the paper the factors influencing the specific fracture energy of rock are discussed
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