Abstract. Fatigue crack growth in plain concrete specimens subjected to constant amplitude cyclic loading is studied. Acoustic Emission (AE) technique has been used to monitor the fatigue crack propagation. Three different sizes of geometrically similar beam specimens are prepared and are tested under three point bending (TPB) in a closed loop servo-controlled testing machine. The data such as load, displacement and CMOD from the testing of specimen for fatigue are acquired in a data acquisition systems and crack growth is continuously monitored using six AE sensors mounted on the specimen. The CMOD compliances at different cycles are measured from the load-CMOD curves and the equivalent fatigue crack lengths are determined using the compliance calibration curve obtained from FE analysis. AE parameters such as events, counts and absolute energy are used to analyze the crack growth.
The present work is a comparative study of Acoustic Emission (AE) signals observed during three point bending tests of plain and reinforced concrete beam specimens. AE signals were recorded throughout the tests and analyzed using Wavelet Packet Decomposition (WPD). One of the objective of current study is to utilize available spectral information of signals for comparative study of AE from reinforced concrete and plain concrete. A classification method for AE signals based on sub-band energy ratios obtained from WPD is proposed. Also, use of relative sub-band energy distribution as a Acoustic emission signature for concrete is proposed. Differences in AE signals of reinforced and plain concrete are highlighted at sub-band level. It is concluded that yielding of reinforcing steel has contributed in higher sub-bands 78.126-250 kHz of AE signals.
Abstract. Damage quantification of concrete subjected to variable amplitude load is not a simple task. In this study, a procedure is proposed to convert variable amplitude load acting on concrete structures to an equivalent constant amplitude load. The procedure described in this work is developed using an existing fatigue crack propagation model and an energy dissipation model which are both based on the energy approach. Further, the damage incurred by concrete is quantified using damage index, which is obtained by normalizing the cumulative energy dissipated with the total cumulative energy dissipated at the critical crack length of the concrete specimen.
Abstract. This paper presents an experimental study on mixed crack propagation in reinforced concrete beam. The specimen was reinforced with single longitudinal bar of diameter 8mm (percentage=0.66%) with no stirrups. The notch is provided at the quarter span, as it is the region prone for mixed mode crack initiation and propagation. The specimen is tested in three point bending under displacement/stroke control in the closed loop servo controlled hydraulic testing machine. The results of load, displacement, CMOD and strain in the steel are acquired in the data acquisition system. The results were analysed and related failure mechanisms observed in reinforced concrete are cracking, yielding of steel, shear, slippage and de-bonding between steel and concrete. The acoustic emission technique is used for monitoring the crack growth in reinforced concrete beam using six AE-sensors mounted on the specimen. The acoustic emission events location is used to understand the cracking and fracture process in zone of tensile and shear cracking. The AE data of events, amplitude, absolute energy and time are analysed to understand cracking, energy released and fracture processes in opening and mixed modes and to compare them.
Abstract. Debonding of coarse aggregates from the surrounding matrix is considered as a major energy dissipative mechanism which affects the mechanical behavior of cementitious composites like concrete. In the present work, a micromechanical model has been developed to study the effect of debonding on the macroscopic behavior of concrete. Concrete is modeled as a two phase composite and a linear softening law has been used to characterize the interface between the phases. Numerical analysis is carried out to obtain the macroscopic stress-strain behavior under uniaxial tension. A parametric study is conducted to study how the various material properties of the individual phases affect the overall stress-strain behavior of concrete, with special emphasis on the post-peak softening.
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