Universal Journal of Materials Science 3(4): 62-69, 2015 http://www.hrpub.org DOI: 10.13189/ujms.2015.030402 Calibration of Acoustic Emission System for Materials Characterization S. V. Ranganayakulu 1 , B.Samrat Goud 1 , P V Sastry 2,* , B. Ramesh Kumar 3 1 Centre for Non Destructive Evaluation, Guru Nanak Institutions Technical Campus, India 2 R&D Division, Bharat Heavy Electricals Limited, India 3 Prototype VV &Pellet Injector Division, Institute for Plasma Research, India Copyright © 2015 by authors, all rights reserved. Authors agree that this article remains permanently open access under the terms of the Creative Commons Attribution License 4.0 International License Abstract Acoustic Emission (AE) is one of the versatile tools to study the materials and associated defects non-destructively under dynamic or static stress load conditions. The experiments planned to study Acoustic Emission system have to be calibrated with various resonant frequency band sensors and stress levels appropriately. This practice covers requirements for the calibration of acoustic emission sensors. The calibration yields the frequency response of a sensor to acoustic waves of the type which normally comes upon in acoustic emission work. The source producing the signal is used for the calibration that increases on the same surface of the test block as the sensor under testing. The calibration represents primarily of the sensor sensitivity to Rayleigh waves. The sensitivity of the sensor is determined for excitation within the range of 1000 KHz to 1KHz. The sensitivity value is usually determined at frequency approximately 1 KHz apart. The AE sources are generally from high intensity stress zones, cracks or defects in the materials under mechanical loads. The acoustic sound signals generated in the dynamic load conditions like burst or continuous emissions must be correlated with parameters such as velocity, time and displacement within the testing system. AE - 4 Channel Acoustic Emission Detection System (procured from Physical Acoustic Corporation, USA) with various frequency band sensors covering wide range is used in this study for the calibration procedure establishment. AE sensors are arranged in vector and matrix mode for signal analysis through AE parameters. In order to deduce physical description of AE sources from recorded waveforms, a well characterized and calibrated AE sensor is required for study of signal analysis. The present paper reports the estimation of the physical quantity measured by the sensor i.e., velocity of material under test. Subsequently, AE source is used for sound signal to travel in the material such that velocity of the material is calculated by manual displacement and time mode. Calibration of sensors is evaluated by shear velocity and experimental standardization studied by the arrangement of different kinds of sensors namely - R6ά, WS ά, PK15I and PK6I. The calibration procedure and standardization for testing of the materials is established and reported. Keywords AE Parameters, Sensors, Calibration, Standardization 1. Introduction Acoustic Emission technique is emerging as a powerful tool for Non - destructive evaluation [1,2] . AE is defined as the phenomenon; where elastic waves are generated by rapid release of energy from localized sources like places of transient relaxation of stress and strain fields. We can analyze AE signals and detect the location of discontinuities [3]. When experiment is being conducted we can face some difficulties which are caused by couplant that are used, by repeatability of emitted sound waves, force and load effect etc. These problems can be reduced but the major problem is sensitivity of sensors. Without good sensitivity of sensors we cannot get correct signals. Obviously, this may affect our conclusion of studies. Hence we have to calibrate the sensors which we are using for experimental studies prior to the conduct of experimental studies. We can start the testing after calibration and standardizing. ASTM E1106 outlines a method for primary calibration of AE sensor [4]. Here we followed Hue Nelson Shoe Method (pencil led breaking) for calibration and standardization of AE sensors. AE inspection is extremely sensitive compared to the other more familiar NDT methods [5,6]. If ideal conditions are met for each method the minimum detectable crack size for UT, RT and ECT methods is about 0.50 mm whereas AE can detect crack growth of the order of 25 microns. This corresponds to micro crack growth of the order of less than 10 microns. 1.1. AE Sensors An Acoustic Emission Sensor converts the mechanical energy carried by the elastic wave into an electrical signal; the sensor is termed as transducer. The transducer most often used in AE applications is the piezoelectric transducer. This choice has been dictated by the ease with which it may be built, its inherently high sensitivity and ruggedness allows its