Evaluation of the Fatigue Life in Aluminum Alloy Welded Joint by Nonlinear Ultrasonic Testing

Abstract

Fatigue is a common phenomenon in welded structures. Prediction of fatigue life of welded joints in-service is still an unsolved puzzle by the conventional linear ultrasonic testing method. However, the nonlinear ultrasonic waves or the acoustic nonlinear signal can provide clear signs of the accumulative fatigue damage in materials, as reported by a number of researchers. Hence, the nonlinear ultrasonic testing method has revealed a tremendous potential for fatigue damage evaluation. This paper presents a study to characterize the fatigue damage using the analysis of the signal characteristics and a new nonlinear parameter. Based on the very high-cycle fatigue testing results for a 6N01 aluminum alloy welded joint, the relationship between the amplitude of the second-order harmonic and fatigue cycling has been established. The nonlinear ultrasonic system test results show that the amplitude of the second-order harmonic increases at the early fatigue stage, with further increase in cyclic loading until reaching a peak. Metallographic examinations show that a fatigue crack will nucleate in the weld joint in the stage as the amplitude reaches the peak value. Finally, theoretical and experimental results confirm that the amplitude of the second-order harmonic is useful for assessing the fatigue life of a 6N01 aluminum alloy welded joint.

Monitoring Fatigue Damage of Modular Bridge Expansion Joints Using Piezoceramic Transducers

“…Monitoring the fatigue damage of the civil engineering structures has been actively investigated [ 6 , 7 , 8 ]. The current methods for monitoring the fatigue damage mainly include Barkhausen noise measurements [ 9 , 10 , 11 , 12 ], X-ray tomography [ 13 , 14 , 15 , 16 ], metal magnetic memory (MMM) testing method [ 17 , 18 , 19 , 20 , 21 ], acoustic emission (AE) [ 22 , 23 , 24 , 25 ], ultrasonic and nonlinear ultrasonic techniques [ 26 , 27 , 28 , 29 , 30 ], among others. Barkhausen noise measurements were used to evaluate fatigue damage of engineering structural steel structures [ 9 ].…”

“…The acoustic emission (AE) monitoring has been developed as an effective method for the detection, location and monitoring of fatigue damage in the metal structures by monitoring the acoustic signature of the fatigue crack during the opening/closing process [ 22 , 23 ]. The ultrasonic technique is a traditional method used for fatigue damage detection by using ultrasonic transducers [ 26 ] and, the nonlinear ultrasonic techniques, that have higher detection accuracy, are also commonly used [ 27 , 28 , 29 , 30 ]. Though strain based on methods have been used to monitor fatigue crack in welds [ 31 ], recent years have seen the development of strain based smart skin for fatigue crack detection [ 32 , 33 ].…”