Application of microscope camera technique in experiment teaching for freeze-thaw mechanical properties of rock
[Objective]Rock mechanics experiments are an important teaching module that guides students in professional fields,such as geotechnical,hydraulic,and mining engineering,to master the mechanical and engineering properties of rock.However,the traditional experiment teaching of rock mechanics mainly focuses on macroscopic mechanical experiments with conventional instruments and lacks a microscopic perspective.Hence,the microscope camera technique was introduced into the experiment on freeze-thaw mechanical properties of rock to reveal the microscopic mechanism of the freeze-thaw evolution characteristics of macroscopic mechanical properties for rock samples.[Methods]First,macroscopic freeze-thaw deformation and damage experiments were respectively conducted on yellow and green sandstone samples under unidirectional freeze-thaw conditions.Then,the distribution of microscopic pores and fractures on the surfaces of rock samples under freeze-thaw action was observed and filmed by the microscope camera technique,which utilizes a microscope,digital camera,and control software to jointly capture microscopic images.The image capture process can be divided into five steps,including optical path adjustment,target search,image capture,size calibration,and image annotation.Finally,the macroscopic freeze-thaw deformation and damage characteristics of rock samples are analyzed and compared with the distribution characteristics of microscopic fractures.[Results]Under unidirectional freeze-thaw conditions with different freezing temperatures,the freeze-thaw strain of yellow sandstone parallel to the freeze-thaw direction is always greater than the freeze-thaw strain perpendicular to the freeze-thaw direction in each cycle.Moreover,the uniaxial compressive strength and elastic modulus of green sandstone gradually decrease as the cycle number increases.More importantly,after unidirectional freeze-thaw action,the uniaxial compressive strength parallel to the freeze-thaw direction is greater than that perpendicular to the freeze-thaw direction,whereas the elastic modulus perpendicular to the freeze-thaw direction is greater than that parallel to the freeze-thaw direction.The microscopic images show that small pores sporadically distribute on the surfaces of sandstone samples before the freeze-thaw action.However,after unidirectional freeze-thaw action,microcracks with lengths ranging from tens to hundreds of micrometers are generated on the surfaces of samples,and the direction of microcracks is roughly perpendicular to the freeze-thaw direction.Under unidirectional freeze-thaw action,the generation of microcracks is similar to layered damage,and the distribution characteristics of microcracks lead to the differences in freeze-thaw deformation and damage of rock samples along different directions.By introducing the advanced microscope camera technique into the experiment teaching of rock mechanics,students can intuitively understand the macroscopic mechanical properties and microscopic structure evolution characteristics of rocks under the unidirectional freeze-thaw action from both macroscopic and microscopic perspectives.The microscopic mechanism of the macroscopic properties of rocks under unidirectional freeze-thaw conditions was revealed by the microscope camera technique.[Conclusions]Based on the introduction of new instruments,technology,and ideas in rock mechanics experimental teaching,students can further form a better understanding of the connection between macroscopic and microscopic phenomena,as well as the microscopic mechanisms of macroscopic mechanical processes.Moreover,this experiment not only exercises students'abilities in hardware operation,software usage,data processing,and problem analysis but also applies a problem-oriented approach to stimulate their interest in exploring macro-micro connections and cultivate their scientific exploration and practical innovation abilities.
rock mechanicsexperiment teachingmicroscope camera techniquefreeze-thaw mechanical propertiesmicroscopic mechanism
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