Visualization And Strain Analysis Of The Fracture Process Of Cement-based Materials

As the main load-bearing material,cement-based materials are widely used in engineering fields such as construction,bridges and roads.Therefore,the study of the fracture behavior of cement-based materials is not only an understanding of the fracture theory of the material itself,but also plays a key role in the field of engineering and construction safety.However,due to the intricate internal composition and structure of the cement-based material,even if the structure of the cement-based material is subjected to a simple uniaxial compressive load,its fracture behavior is very complicated.Therefore,we still cannot fully understand the fracture behavior and fracture mechanism of cement-based materials.In addition,the fracture detection of cement-based materials mainly focuses on crack detection and strain detection.However,the current crack detection methods are mostly limited to surface detection and internal local visualization,and it is impossible to intuitively and visually track the micro-fracture process on the entire site and visually.Although there have been studies on the internal fracture process of concrete,the fracture evaluation parameters used in it can still be optimized.The current strain detection method is mainly the surface full field and internal fixed point detection,and it is impossible to detect the full field three-dimensional strain inside the sample.Therefore,in order to more accurately visualize the fracture process of the cement-based material and detect the three-dimensional full-field strain inside the material during the fracture process.This subject uses X-ray computed tomography technology and supporting in-situ loading equipment to track the fracture process of mortar and rubber concrete under uniaxial compression load.Corresponding image processing technology is used for 3D visual tracking and strain detection.The main research findings are as follows:1)XCT in-situ loading technology can perform three-dimensional visualization of the fracture process of cement-based materials.And proposed a crack recognition algorithm based on image processing technology.The algorithm can extract different phases in CT images through gray threshold segmentation,image opening and closing operations and roundness index filtering methods.At the same time,the crack width extracted by the algorithm is usedto compare with the results of scanning electron microscope,and it is found that the crack width extracted by the algorithm is very similar to the result of SEM.2)Based on the two-dimensional and three-dimensional results of image processing,the volume change law of mortar under different loads is analyzed.It can be found that the uniaxial compression of mortar can be divided into compression stage,expansion stage and cracking stage.By comparing the solid phase volume expansion rate with the theoretical expansion rate in the expansion stage,it is found that the expansion rates of the two are relatively close.3)The three-dimensional picture of the internal structure of rubber concrete was obtained by XCT in-situ loading technology,and the spatial distribution and equivalent particle size of the rubber particles inside the rubber concrete sample were extracted.The displacement /strain standard deviation of zero strain data is used to optimize the DVC calculation parameters.Using the DVC technique,the three-dimensional displacement field and three-dimensional strain field inside the rubber concrete under axial load are calculated,and the failure process of the specimen is analyzed by the displacement field and strain field.