Abstract

ABSTRACT :

Concrete may appear as a boring material on a macroscopic level. However, the concrete fracture process exhibits an interesting complex behaviour dominated by disorder, long-range interactions, and long memory in the intensified stress field ahead of the crack tip known as the fracture process zone. The fracture process resulting from such complexity usually generates long-tailed distributions leading to self-organization signifying the emergence of order from the disorder. The existence of self-organization also hints at a universal pattern dominated by simple governing rules, regardless of system configuration. Consequently, entropy can be used as a measure of disorder to quantify the randomness of the probability distributions arising from the system variable. In this study, we propose cumulative distribution functions for acoustic emission features derived from Tsallis’ non-extensive entropy formulation. The Tsallis entropy is well-suited for modeling long-tailed distributions due to its sensitivity to the tail behaviour. Furthermore, the non-linearly interacting multi-scale cracks in the fracture process zone of concrete are inseparable and the whole system cannot be divided into simple sub-systems without tampering with the systemic properties, resulting in non-additivity and non-extensivity.

An experimental investigation was conducted to acquire acoustic emission data from the concrete fracture process. The testing involves three different sizes of notched plain concrete beams under three-point bending subjected to monotonic and fatigue loading. Two features of the AE stress wave, amplitude (magnitude) and inter-event time appear to be correlated with crack size and crack occurrence rate respectively. Distribution functions derived using the Tsallis entropy formulation are then fitted to the experimental data and compared across the beam sizes and loading conditions. The pattern in the collective behavior of entropic indices evaluated from the AE distribution is illustrated to highlight the possibility of self-organization. Monotonic loading controlled by crack mouth opening displacement allows stable crack growth resulting in critical AE distribution parameters that are used as a reference to track the damage evolution under sub-critical fatigue loading.

KEYWORDS : Concrete, Fracture, Fatigue, Acoustic emission, Tsallis Entropy

SPEAKER BIO :

Dr. Nitin Burud is currently working at the University of Surrey as a post-doctoral researcher. He received a doctorate from the Indian Institute of Science, Bangalore, India. His research work focuses on fracture and fatigue in materials, specializing in structural health monitoring applications using statistical data analysis. He worked extensively on acoustic emission techniques for understanding the fracture process in concrete-like cementitious materials. Consequently, his doctoral dissertation is a thematic exploration of acoustic emission data for mechanistic as well as statistical description, diagnosis, and prediction of damage evolution in concrete. Bringing a complexity perspective to understand the fracture process in concrete, and the use of Tsallis entropy as a measure of the complexity, is a central idea of his recent research. Before joining the University of Surrey, he shortly worked as an assistant professor at a deemed university in India. At the University of Surrey, he is investigating the fatigue behavior of a 130-year-old railway bridge through large-scale testing and numerical modeling.