Issue 53

Y.D. Shou et alii, Frattura ed Integrità Strutturale, 53 (2020) 434-445; DOI: 10.3221/IGF-ESIS.53.34 438 Figure 6: The deviatoric stress 1 3   − versus axial strain 1  and transverse strain 3  under the confining pressure of 15 MPa. E LASTOPLASTIC DAMAGE COUPLED MODEL OF COAL - ROCK ontinuum damage mechanics is investigated based on macro phenomenological theory, which deals with dissipative systems. In the dissipative systems, the whole damage process is irreversible and always accompanied by internal energy dissipation. In the study of irreversible processes, some basic principles (such as conservation of mass, conservation of momentum moment, conservation of momentum, etc.) must be satisfied. For irreversible processes, there is always energy dissipation within the system. The irreversible phenomenon of energy dissipation within the system is related to internal state variables. The basic state variables can be taken as thermodynamic temperature and strain. In continuum damage mechanics, the internal state variables involve the elastic strain tensor e  , the plastic strain tensor p  , the cumulative inverse strain p  and the damage variable d and so on. Mechanical characteristics of coal-rock Firstly, elastic modulus, Poisson's ratio, tensile strength, internal cohesion and internal friction angle of coal-rock are the basic mechanical properties of coal. According to the experimental results above, the mechanical properties of coal-rock are low modulus of elasticity, low strength and high Poisson's ratio. Moreover, it is easy to produce plastic deformation. The axial failure stress and modulus of coal-rock are related to confining stress closely. Secondly, many micro-cracks, micro-pores and weak structural planes exist in coal-rock, as shown in Fig. 7. The existence of these micro-cracks determines the internal structure of coal-rock, which lead to the heterogeneity and anisotropy of coal- rock. Therefore, coal-rock is a typical geotechnical material with internal defects. Because the stress concentration at the cracks or the micro-pores will occur in the process of loading, the coal-rock will be destroyed. Figure 7: The micro-pores and micro-cracks in coal-rock [25]. The elastoplastic coupled damage model of coal-rock In this paper, an elastoplastic coupling model is proposed to describe the mechanical properties of coal and rock. Under the isothermal conditions, the state variables are composed of the elastic strain tensor e  , the plastic strain tensor p  , the C