Investigation of failure in different materials using acoustic emission technique

Abstract

To estimate the behaviour of different materials or structures regarding their inherent flaws and defects, there are different methods available within the domain of science and engineering. Nowadays, Non-destructive testing (NDT) is one of the most efficient method available for testing of any structure or equipment or part without damaging actual body of the specimen. Among the various NDT, wave based techniques are assuming importance since the propagation characteristics of the wave change with damage and can be directly related to the damage. Acoustic Emission (AE) technique is one of such passive wave based monitoring technique. Acoustic Emission waves are the elastic waves, generated by rapid release of energy from different sources like cracks initiation, propagation and growth. This technique is very much remarkably sensitive to crack advancement, able to grab the source of damage involves real time monitoring. Though with AE, various advantages exist for analyzing the true nature by localization of cracks within the material, however, there are still some shortcomings associated with AE data recording. In this study, Acoustic emission technique was applied to track the damage progression under varying loading rates in different types of materials such as mild steel, concrete and FRP composites. Mild steel was loaded at 1.5, 4 & 8 mm/min, concrete was load at 0.5, 1 & 1.5 mm/min and FRP composites were loaded at 0.25, 0.5, 1, 1.5 & 2 mm/min. The AE data for mild steel and concrete was recorded using resonant frequency sensors R15α and R3α. For composites, Wideband frequency sensor WDI-AST sensor was used with a frequency range of 100-900 kHz. The amplitude of AE hits and Ib-values analysis was used to quantify damage and to monitor the cracking patterns in all three materials. The recorded value of amplitude of AE hits were in total coherence with the load-time plot wherein major damage was indicated by higher values of amplitude. Ib-value analysis clearly indicated the damage severity in all the materials at all instants from moderate to severe. Ib-value also exhibited distinct curves for all the three materials. For mild steel, a major drop was observed during the yielding of the specimen and Ibvalue remained constant for the rest of loading time. For concrete, there was a continuous fall in the Ib-value indicating that the damage was progressive leading to failure. For composites, the fall was observed after half loading time indicating the damage progression only after certain extent of applied loading.