Issue 27

G. Kuidong et alii, Frattura ed Integrità Strutturale, 27 (2014) 43-52; DOI: 10.3221/IGF-ESIS.27.06 44 established based on elastic fracture mechanics theory; finally, the reliability and accuracy of PCF model is verified with experimental date. T HEORETICAL MODEL he problem of the indentation of the plane surface of elastic solid with a rigid body was first considered by Boussinesq [10], then Sneddon [11] adopted hankel transforms and elementary solution to solve the Boussinesq problem, and the total penetration depth and force of the rigid body were presented. Therefore, the applied force of conical pick on rock could be approximately expressed as:   2 2 2 tan 1 Eh P v     (1) where: P is the penetration force of conical pick; E is elastic modulus of rock;  is semi-angel of conical pick;  is poisson ratio of rock; h is the penetration depth of conical pick. Integrating Eq.1 with respect to the penetration depth, the work W E can be obtained and it is expressed as:     2 3 2 2 0 0 tan tan 1 3 1 h h E E E W P dh h dh h v v            (2) Therefore, when the main rock fragment formed, the total work W T can be expressed as:   max 3 2 2 tan 3 1 T E W h v     (3) where h max is the maximum penetration depth at the time of main rock fragment formed. The fracture surface of main rock fragment is simplified without influence of PCF prediction, and it is shown in Fig.1. As Fig.1 shown, the new fracture surface area A of main rock fragment can be expressed as: 2 2 tan tan tan sin sin cos d d ef A          (4) where: e and f are the geometry shape parameters of main rock fragment; d is cutting depth of conical pick; θ is horizontal fracture angles; ψ is vertical fracture angle. Figure 1 : Schematic diagram of fracture surface of rock fragment. T