An Experimental Study On Processes Of Deformation And Failure For Several Structure Patterns

Continent massifs are divided into blocks of different sizes by different active fault zones. The movement of these blocks controls the earthquake activities in the continent. The time and space distribution of large earthquakes is obviously related to faults on edges of blocks and deformation of blocks. There are several typical patterns of structure at converge of blocks, such as X-shaped, V-shaped, and Y-shaped and so on. The study on these structure types is very significant to seismology. This thesis studies Y-shape and V-shape structure patterns through experimental by the methods of caustics, real time holography and acoustic emission, and furthermore, investigate other three typical faults' influences on the b value of acoustic emission.In the study of real time holography, the interference fringe around the tip of crack is so dense that its order cannot be judged, which is a difficult problem all along. The caustics have used successfully in experimental mechanics. Recently it was introduced to geological experiments. When the caustics technique developed from the study of tensile shear cracks is applied into compressive shear test, its availability should be discussed carefully. This thesis analyzes the feasibility that caustics is applied to measure the stress intensity factor of compressive shear crack. And combining the two methods, a method to judge the fringe order at the crack tip is found. The fringe order at the crack tip N o,J is:where D is the caustic characteristic length, No,J is order of fringe, PJ is a constant, J= I , II, III presents crack mode, and (r, 9 ) is coordination at the crack tip. These equations are also the theoretical relation between caustics and holography. This result is helpful to joint application of the two optical methods.In the test of the Y-shaped structure sample, two types of dense fringes were observed, with the increase of stress. One is the divergent type in which the fringes expand outward from the center. Another is the convergent type in which the fringes contract towards the center. The center of the former is a convex area or a peak, and the center of the latter is a concave area or a valley. The border of these two kinks of areas is called "strain gap", where the sample is not deformed, namely the area without strain, and fringe order is zero. Caustic shadow area belongs to the high strain area, called strain nuclei, where fringe order is the highest. Analyses indicate that micro-fractures occur rarely at the strain gap and always appear initially at area of the high strain (stress). Their locations are finally in the zone between the stress concentration area and the strain gap and exhibit the clusters or groups. However, the major macro fracture (final rupture) started from the strain nuclei (the shadow areas), and then grew quickly towards the strain gaps, which resulte in failure of sample.On the V-shaped structure sample, there are three structure areas: zone A where faults converge, zone B where faults form left-lateral and left-stepping rock bridges, and zone C where faults form right-lateral and left-stepping rock bridges. (1) The result of micro crack locationshows that AE has the features of grouped occurrence in a region and grouped migration. Micro-cracks migrate from zone A to zone B and then to zone C at last. In the initial stage of migration, AE events appear alternatively in the place of original occurrence and the place where they migrate. Analysis of the local b-value by the "accumulated frequency-energy level" relation shows that the b-value of the zone C reduces obviously before the main fracture. (2) Before 66% of the fracture stress, the strains at measuring points becomes large with the increase of stress and there is no special change such as sudden jump, fluctuation, and so on. Later on, the strains at all the measuring points all become large with the increase of the load. In zones A, B and C, the sudden change of strain, i.e., sudden rise and sudden fall, occur consecutively at some measuring points. Such a sudden chang...