Numerical Tests Of Three-dimensional Microscopic Model Of Porous Rock Based On CT Digital Image Processing

It is difficult to consider three-dimensional internal meso-structure of rocks in physical and numerical tests because rocks are heterogeneous,opaque and porous materials.Natural rocks contain a large number of mineral particles and defects.These meso-structures can affect the physical and mechanical properties of rocks.Hence it's particularly important to analyze the engineering and mechanical properties of rock from microscopic view.A 3D numerical method was proposed to simulate porous rock failure based on the parallel finite element method.The CT technology was used to scan the rock specimens and obtain the picture layers.The edge detection algorithm,filtering algorithm and 3D matrix mapping method were applied to process the scanned pictures and reconstruct the numerical finite element models of the rock.This modeling method provides an effective way to describe mesoscopic structure.In this way,the 3D numerical Brazilian disk models and direct tensile models were constructed.The effect of pore structure on the failure mechanism and tensile strength of rocks was studied by using the parallel finite element method.This study can help to reveal the effect of pores on macroscopic failure of rocks.The main research work can be summarized as follows.1.Performed CT scan on basalt samples to obtain the CT images.The CT images can accurately reflect the mesoporous structure inside the basalt.The preprocessing of CT images includes cropping,binary processing,and median filtering.The processed images will be used to build numerical models.2.Three-dimensional Brazilian disk numerical models and direct tensile numerical models were constructed based on the RFPA^3D-CT software.The scale of the model can reach 2.8 million units and the fineness of the element can reach 1/3 mm,which indicates that the numerical model can reflect the mesoporous structure of basalt samples.At the same time,digital image processing technique was used to count the porosity of the numerical samples.3.Brazilian split tests and direct tensile tests were performed by using the proposed numerical methods in this research.The numerical results show that:?1?The Brazilian split test results indicate that the pore distribution and porosity had significant influence on crack propagation and tensile strength.The porosity of different numerical samples was calculated by using digital image processing method,and the relationship between the tensile strength and porosity followed an exponential function.The number of the secondary cracks was decreased when the porosity was smaller and pores were sparse.Moreover,the number of the secondary cracks was increased when the porosity increased.?2?The direct tensile test indicates that the initial crack occurs at pore location,and then the tensile crack propagates laterally with the increasing of the load.The pore is an important factor affecting the final morphology of tensile cracks,which results in an indeterminate failure surface position of the rock samples,and the shape of tensile cracks are different in different samples.?3?In Brazilian tests,the samples were split along the loading axis,and the position of the penetrating cracks were fixed.However,for the direct tensile tests,cracks appeared in the weakest areas of the rock samples,resulting in an undefined position of the final failure surface.Therefore,the tensile strength obtained by the direct tensile test can be smaller than the tensile strength obtained by the Brazilian split test.