The Experimental And Theoretical Investigation N Fracture Of Rock-Type Materials Under Compressive Loading

The experimental investigation and theoretical analysis are made in this thesis for the cracking properties of rock-type materials under compressive loading . Some important laws are recognized , and the relative criteria and models are presented .The rectangle gypsum specimen with a oblique crack is used in the experimental study , on which the uniaxial compressive loading or the biaxial one is exerted . the cracking location , the cracking angle , the critical loading , the concentration of compressive stress , the region of tension stress , cracking model , and the condition of II model cracking are studies , which provide the first hand datum for us to understand the compressive cracking of rock in detail . To obtained the condition of biaxial compressive loading , we design a transverse loading device with the hydromatic servo . Combining it with electron universal testing machine , the expected state is gotten . the stress change near by the tip of a crack is kept watch on in whole course by the strain testing points which are arranged on a large scale combining with the dynamical strain testing device with multichannel , in which the ratio of lateral compressive loading and axial one is increased in equimultiple . In order to reflect the change law in the process of the compressive cracking in detail , and look for the turn point from I model cracking to II model cracking , the compressed crack is designed as a flat ellipsis with various ratio of the short axial and long one , and laid in equi-interval from 0?to 90?Based on the experimental results and statistical analysis of the datum , and using the mechanical model and the method of complex function , the micromechanism of some important phenomena are studied . the focal points are the stress characteristics at the beginning of cracking, the compressive stress intensity factor , its change regularity and its effect on cracking , the geometrical range and confined condition of Griffith's cracking (cracking at the tip of crack ) , the frictional property on crack surface and the closing process of crack, and their effects on the stress intensity factor , the micro-mechanism and macro-condition of I model cracking ( tensile cracking) and II model cracking ( shear cracking).Based on the basis of mechanism analysis for the compressive cracking of rock , some viewpoints of traditional fracture mechanics are revised , a new fracture criterion in which the discernment of cracking model is preconditioned is presented , which can predict not only cracking dominated by tensile stress , but also cracking dominated by shear stress in the compressive cracking of rock . So , the content of traditional fracture mechanics is extended . The calculating results based on the criterion given in this paper are in good consistent with the experimental ones , which testify the correctness and reliability of our theory .In order to simulate and predict the extensional path of compressive cracking of rock in a clear , simple and effective style , a analogy method , that is stream function method , is presented , which is based on the correspondence principle between elastic solid and viscous liquid . It is proved that streamlines of liquid are equal to traces of principal stress of solid . Using the superimposition principle , the extensional path of the uniaxial compressive or the biaxial compressive cracking of rock can be simulated and predicted , and its correctness is testified by the experimental results .Main outcomes in this paper are following :1 . The cracking location is not always at the tip of crack for a open crack under the compressive loading , which is related to the oblique angle and the dulled degree of crack , and the loading pattern . But the cracking is always in I model for a open crack . It is recognized that only in the limited condition , the cracking location is at the tip of crack for a open crack .2 . There are two critical angles in the compressive cracking of rock . In the low critical angle , the minimal loading is needed for th...