Durability and Remaining Useful Fatigue Life Assessment of Welded Joint Using Impedance and Wave Propagation Techniques

All real-life aerospace and machine structures are prone to fatigue, which is the occurrence of localized but progressive damage due to continuous fluctuating stresses. Even if the magnitudes of the fluctuating tensile and compressive stresses are within the limits of the material strength, their alternating nature is responsible for fatigue. Fatigue damage can be monitored by observing changes in the structural stiffness as a function of the number of loading cycles. The problem is more severe if a welded joint is subjected to such fatigue behavior. This paper aims to employ the smart material based electromechancial impedance (EMI) technique to study the welded joint behaviour during cyclic loading for fatigue cracks. Piezoceramic transducers are surface bonded at several distinct locations near the weld and are subjected to actuation, so as to interrogate the joint for the desired frequency range. The interrogation resulted in the prediction of electromechanical admittance signatures. These signatures are then used as indicators to estimate the health/integrity of the welded joint, as changes in these signatures during the cyclic loading period are caused by cracks or damages in the welds. A comparative study is also conducted using strain gauges and guided wave propagation techniques during the period of cyclic loading on the specimen. An attempt has been made to correlate the remaining useful life of the welded joint and statistical indices for various numbers of cycles of load.