Contents I. Introduction
Acoustic Emission (AE) technique is a highly sensitive diagnostic method enabling cracks to be detected at a very early stage used for structural health monitoring (SHM) [1]. The source of acoustic emission wave is the redistribution of a stress field inside a sample due to a movement of some kind of defect, for example, it could be a crack which can initiate and then propagate. AE is the phenomenon where high-frequency stress waves are generated by a rapid release of energy within a material caused by sources such as initiation or growth either of cracks, material dislocations, and yielding[2]. AE waves can be recorded by means of a sensor and then analyzed to extract information about the source of emission [3]. AE technique is highly sensitive to crack activity and can provide continuous structural health monitoring. The advantage of the AE technique is it’s ability to locate damage that acts as an emission source as soon as it occurs; that is, it enables real-time monitoring of the structure. Another noteworthy advantage is that it is a passive technique; hence, no energy is needed to be supplied to the specimen to receive pulses, unlike other non-destructive methods. Despite the advantages, successful use of AE technique for SHM applications has several challenges; for instance, a number of disguised sources can also imitate AE signals which can dissemble actual damage related signals; hence, it is vital to accurately and automatically sort foreign acoustic emission from damage based acoustic emission [4]. AE sensors are mounted on the structure to detect the damage initiation in real-time. The position of the AE sensor is vital for the effective detection of a crack in a structure. The installation of sensors in a structure for real-time damage detection is a costly affair. Hence, the number of sensors to be used for structural health monitoring needs to be restricted to be as minimum as possible for economy. It is found from the literature survey that most of the studies on optimum AE sensor location for real-time monitoring in steel framed structure, is based on the analytical approach, and no such experimental studies have been established as per the knowledge of the authors[8][9][10][11][12]. In the present study, experimental work is carried out on a prototype steel frame by mounting the sensor on various locations of the structure. Damage is generated by Pencil Lead Break (PLB) using a mechanical pencil. AE events are recorded for all the possible cases in various positions using a single sensor. The recorded time-dependent AE responses are converted to the frequency domain by using Fast Fourier transform (FFT)[5], and all possible sensor locations are compared with respect to the frequency domain data, to find out the effective position for placement of AE sensor.
