APPLICATION STUDY ON DEFECT DETECTION IN STEEL STRANDS BY USING HIGH-ORDER ULTRASONIC LONGITUDINAL GUIDED WAVES

In order to achieve active health monitoring of steel strands, magnetostrictive transducers fixed on the surface of the structures are applied for the excitation and the reception of high-order ultrasonic longitudinal guided wave modes and proper parameters are optimized for the identification and evaluation of the defects. The sinusoidal tone burst modulated by a Hanning window is used for an exciting high-order ultrasonic longitudinal guided wave mode L(0,2) at 0.86MHz in seven-wire steel strands to detect artificial defects machined in the helical and center wires in two pieces of steel strands separately. The sensitivity of L(0,2) mode to defect detection in different wires of steel strands is analyzed experimentally, and furthermore the effects of the defect depth and the cycles of excitation signals on the amplitudes of received guided wave signals are researched. Experimental results show that the L(0,2) mode at 0.86MHz can be used for the defect detection in the steel strand with the help of magnetostrictive transducers while the mode is more sensitive to the defects in helical wires than in central wires of steel strands, and furthermore the defect characterization can be achieved based on the amplitudes of received echoes. Simultaneously, it is important for the defect detection in steel strands to optimize the cycle number of the excitation signal by using high-order ultrasonic longitudinal guided waves.