Experimental Research On The Identification Of Initial Damage Of Concrete Based On Ultrasonic Wave

For mechanical equipment and structural in work in engineer structural, when they are on exterior force, their work appearance can divide into three stages: earlier property degeneration, which insist of physical and chemical ageing and degeneration, beginning and accumulating of damage, which include hole forming and wiping, and fracture and lost utility at last. Among which, beginning and accumulating of damage have extensively studied based on tiny mechanics, damage mechanics and subject contain them. It existed number of data and models to forecasting circulate load-carrying and fracture expand up to final damage on the affection of environment, nevertheless, it is little known that property degeneration and its affection on material long-term behaviors. It is also little research on concrete, which is anisotropic material.In this paper, itmainly involved concrete damage recognition based on experiments, with ultrasonic testing method, ultrasonic digital signal analysis theory, signal fractal analysis theory, damage recognition theory.Firstly, the research status quo and significance of the ultrasonic wave test technique of concrete, signal analysis, spectrum analysis of ultrasonic test and rescaled range analysis (R/S analysis) at home and abroad is presented in this paper, according to the research background and demand. The major work in this paper is put forward on the basis of the research content and the purpose of this paper. Afterwards, a effective method of ultrasonic wave spectrum analysis in concrete is put forward so that the spectral could be expressed correctly while the frequency resolution is enhanced enough, based on the analysis of usual ultrasonic test, the characteristic of the ultrasonic digital signal, especially the characteristic of the propagation of ultrasonic wave and the spectrum analysis of digital signal. Furthermore, the particular demand, principle calculation method and result demonstration of spectral analysis method in this paper is illustrated.Then, according the demand of the experiment, a rational experiment program is designed, and preparation before experiment is fulfilled, the experiment operation is carried out on the basis of experiment program, the concrete test block is put on the pressure test apparatus, and is loaded on constructive press, ultrasonic tested on the concrete test block when they are on each grade load, then the ultrasonic wave signal can get, which is the digital signal we would analysis.At last, the ultrasonic digital signal we get is analyzed, mainly with fast Fourier transform (FFT) linear analysis and rescaled range analysis (R/S) analysis nonlinear analysis. In connection with varying of the corresponding characteristic variable, dominant frequency and fractal dimensions etc, of the ultrasonic wave when graded loaded on concrete block, the characteristic variable is looked for which can describe the process of concrete from earlier property degeneration, beginning and accumulating of damage, to fracture and lost utility at last.