CT Study On The Concrete-Damage Evolution And Its Application In Numerical Stimulation

The fracture process of Concrete category in the geotechnical materials, a complex non-linear evolution of the material damage, has been one of hot issues and diffcult reasearch in the field of the mechanical, materials and engineering. In the breakdown process of material, it was the manifestations that internal energy accumulation of the initial defects, and micro-crack continually initiating and expanding till the overall instability, which were performed as constant deterioration of mechanical properties in the macroscopic. In this paper, combined with meso-mechanics, the damage mechanics, statistical theory and numerical theory, the process was researched which included the expanding cracks, finally through and the destruction of concrete material by CT technology which is a effective means of observing meso-damage evolution, so that the concrete cracks expanding and damage patterns were analyzed, and the breakdown mechanism of concrete materials was revealed. In this paper research work was summarized as follows:(1)The composition of the portable latest developed CT load equipment the, the technical indicators and their characteristics were introduced detailed. The instrument is the lastest domestic equipment which supports real-time dynamic load for CT test, using which dynamic loadingand particularly dynamic tension test especially could be achieved. And the static and dynamic real-time CT test were carried out using newly developed portable concrete testing machine(2)Studying CT images of concrete materials including static compression, dynamic compression, static tension and dynamic tension and making full use of the CT scans information, various analysis methods of CT image and CT number were put forward for the meso-damage process investigation of concrete materials, and the fracture characteristics of the concrete material in static compression, dynamic compression, static tension and dynamic tension were obtained.(3)Based on CT crack evolution laws, the damage stageof concrete was classified. At the same time,the D-value of the two CT images on the same cross-section in different stress phase were operated, and the low-density of D-value image would determine the crack whose shape was ring or linear.(4)According to the concrete failure stage, the concrete materials were distinctly described to define the safe zone, damage zone and fracture zone of concrete materials, and the CT threshold criteria on the partition was discussed and selected empirically. In this standard, the scanned cross-section of CONC-10 sample was zoned to study the change regulation and the conditions resulting in fractured zones of concrete CT number with loading process on each partition.(5)Using fractal theory, and concrete CT images of static compression and dynamic compression were acted as the research objects to estimate the fractal dimension of different scanning sections CT images in different stress stages, and based on the VB and MATLAB language, the Program of was visually developed. Through changes of fractal dimension, the meso-damage evolution process of concrete materials was analyzed in the static compression and dynamic compression.(6)In This paper, concrete damage constitutive model assembled by previous based on CT tests were summarized, combining the analysis results in this paper, the damage variables and damage constitutive model were further researched. Based on the meso-CT test characterized by Concrete damage evolution, different ways were applied to define different damage variables of concrete material and to establish the corresponding damage evolution equation. Based on the damage evolution equation created as CT change, a constitutive relation was created to assosiate the damage evolution equation based on to the density damage (CT number changes) and the constitutive relation with the degradation of macro mechanical properties.(7)The damage constitutive relation due to CT changes was used to numerical simulation of concrete in static uniaxial compression. Numerical test results of concrete were analyzed detailedly and compared with CT test results. A simple meso constitutive relation was applied to simulate the complex failure phenomena of macro and to provide mechanical basis for improving test design.At the same time, that maked it possible that the numerical method replaces of some tests in a reliable and effective premise.(8)In this paper, the CT scan data was directly acted as start point to carry out the research on three-dimensional reconstruction of images. Three-dimensional concrete meso-structure was reconstructed by using the method of three-dimensional reconstruction of CT image slice applied Matlab and MIMICS to get the real concrete meso-structure.