Issue 27

G. Kuidong et alii, Frattura ed Integrità Strutturale, 27 (2014) 43-52; DOI: 10.3221/IGF-ESIS.27.06 48 shown in Tab.1. The shape and interrelated geometric parameters are shown in Fig.5. Fig.6 shows the theoretical and experimental vertical fracture angle under different cutting angle, the difference less than 5 percent between them indicates that the established vertical mechanical model of rock fragment is valid. Properties Value Modulus of elasticity E (GPa) 19 Density ρ (kg/m 3 ) 2650 Fracture toughness K I (MPa . m 1/2 ) 1.1 Compression strength σ c (MPa) 103.2 Tensile strength σ t (MPa) 7.1 Table 1 : Mechanical properties of marble. Figure 4 : Laboratory furniture of rock cutting linearly: 1-rock specimen; 2-guideways; 3-clamping device of conical pick; 4-conical pick; 5- advancing hydro-cylinder. Figure 5 : Geometric feature parameters of rock fragment. Figure 6 : Vertical fracture angle of experiments and theoretical model. Verification of peak cutting force The k is a geometric factor of the pick independent of material properties which has been mentioned in front contents. In reference [18], the researchers also took an intensive study and detailed explanation of the k . According to Eq.5, the k can be obtained by experiments. Fig.7 is the variation curve of cutting force in rock cutting process, which corresponds to Fig.5. So, the k can be expressed as: 2 2 2 2 F I I T c max 2 tan 4 tan cos cos ( )d E K d K d k W E P h E P h h         (18)