13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Particle simulation of AE statistics and fracture in concrete TPB test Alberto Carpinteri1, Giuseppe Lacidogna1, Stefano Invernizzi1,*, Amedeo Manuello1 1 Department of Structural, Geotechnical and Building Engineering, Politecnico di Torino, 10129, Torino, Italy. * Corresponding author: Stefano.invernizzi@polito.it Abstract We present some experimental results and numerical simulations of acoustic emissions (AE) due to damage propagation in a concrete specimen subjected to the three-point bending (TPB) test. The test is performed under Crack-mouth opening displacement control. Moreover, AE are detected by an eight sensors experimental device, which allows for signal localization and complete storing of the signal wave. The AE cumulative number, the time frequency analysis and the statistical properties of AE time series will be numerically simulated adopting the so-called “particle method strategy”. The method provides the velocity of particles in a set simulating the behavior of a granular system and, therefore, is suitable to model the compressive wave propagation and AE (corresponding to cracking) in a solid body. The localization of AE events is correctly reproduced. In addition, the Gutenberg-Richter statistics of AE events due to cracking, crucial for the evaluation of damage and remaining lifetime, were simulated and result in agreement with the experimental evidences. Keywords Particle method, three-point bending test, acoustic emission, concrete. 1. Introduction Damage and fracture characterizing the bending failure of heterogeneous materials such as concrete are complex processes involving wide ranges of time and length scales, from the micro- to the structural-scale. They are governed by the nucleation, growth and coalescence of microcracks and defects, eventually leading to the final collapse, and to the loss of the classical mechanical parameters, such as nominal strength, dissipated energy density and deformation at failure, as material properties [1]. Furthermore, the collapse mechanism is strongly related to the cracking pattern developing during the loading process. It changes from cracking and crushing, for slender beams, to shear failure characterized by the formation of inclined slip bands for deeper beams. Instrumental and nondestructive investigation methods are currently employed to measure and check the evolution of adverse structural phenomena, such as damage and cracking, and to predict their subsequent developments. The choice of a technique for controlling and monitoring concrete or masonry structures is strictly correlated with the kind of structure to be analyzed and the data to be extracted [2–4]. This study addresses the three point bending test carried out in the laboratory in combination with acoustic emission (AE) monitoring. A similar approach has been already exploited in [5] attempting to link the amount of AE with the structural deflections. In the assessment of structural integrity, the AE technique has proved particularly effective [5-7], in that it makes it possible to estimate the amount of energy released during the fracture process and to obtain information on the criticality of the process underway. Strictly connected to the energy detected by AE is the energy dissipated by the monitored structure. The energy dissipated during crack formation in structures made of quasi-brittle materials plays a fundamental role in the behavior throughout their entire life. Recently, according to fractal concepts, an ad hoc method has been employed to monitor structures by means of the AE technique [8]. The fractal theory takes into account the multiscale character of energy dissipation and the strong size effects associated with it. With this energetic approach, it becomes possible to introduce a useful damage parameter for structural assessment based on a correlation between AE activity in the structure and the corresponding activity recorded on specimens of different sizes, tested to failure by means of pure
RkJQdWJsaXNoZXIy MjM0NDE=