Experimental Studies On Mechanism Of The Initiation, Propagation Coalescence Of Cracks In Soft And Hard Rock-like Specimens Based On Digital Image Technology

Application of similarity model test and analysis of multi-crevasse rock mass to solve geotechnial problems has realistic engineering significance at this stage. Firstly, according to the physical and mechanical similarity theory, access to relevant information, the ductile and brittle similar material was been found to simulate soft, hard rocks, and then it was used for pouring samples and prefabricatting crcks, after that, uniaxial loading experiments were carried out, Digital Image Correlation—DIC was applied to collect image information during specimens destruction, finally according to the image data and load-displacement data collected during the tests, and analysis of crcack initiation, expansion, coalescence and failure of the specimens, corresponding results has been achieved:(1) Based on the research of the rock-like material, It was decided to use sand and barite powder as the filler, alcohol as the organic slovent, epoxy resin and polyamide as the binding material to simulate soft rock, colophony as the binding material to simulate hard rock to conduct tests.(2) By changing the ratio of the raw materials, it was obtained that changing the content of the raw material obviously influents the mechnical properties of the specimens. With ratio of epoxy resin or colophonyincrising, initiation stress, peak strength and connection stress are also increasing. But, crack initiation and connection mode of the specimens have the consistent performance. It means that changing of contents has no significant effect on the crack initiation and connection type.(3) It can be found from experimental results that geometric condtions of pre-existing flaws have the important influences on the crack coalsecence types in the specimens. The initiation of cracks is caused by the tensile wing cracks. While the coalescence of cracks is mainly controlled by the tensile wing cracks and secondary cracks.(4) By comparing the experimental resutls of ductile and brittle specimens, failure modes of ductile specimens are dominated by the composite tension-shearing cracks. While, failure modes of brittle specimens are controlled by the composite tension-shearing cracks and tensile cracks. It can be observed from the experimental resutls that there are more cracks, especitally surface cracks, occuring in the brittle specimens than those in ductile specimens. Moreover, crack initiaiton stresses and peak stresses of brittle specimens fluctuate a range, which is larger than those of ductile specimens.(5) In this paper, DIC Full-Field Displacement and Strain Analysis was employed to make measurements, collect images, and analyse displacement field and strain field throughout the destruction process of crack specimens. Combined with stress-strain curves of the specimens, it can be found that the trend between the displacement and strain during the destruction process is amost in consistance with the stress-strain curves, and that principal strain diagrams are in high consistance with the process of initiation, propagation, coalescence and failure of macroscopic surface cracks, which verified that this measuring method could connect mesomechanics with macromechanics.