Strength of Dissimilar Metal Bonds and its Nondestructive Evaluation

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Diffusion bonding were carried out with mild steel/nickel and mild steel/titanium in air, and static and fatigue strengths were obtained. The ultrasonic measurement was also carried out to evaluate these strengths and bonding character. Following results were obtained.(1) The shear fracture occurred in static shear test, and the transverse fracture in the thickness direction of the specimen occurred in the fatigue shear test. The shear strength was in proportion to the square of the diameter of the bonded region estimated by the ultrasonic measurement, but no correlation existed between the fatigue life and the estimated diameter. The fatigue limits of the mild steel/Ni and mild steel/Ti diffusion bonds agreed well with that of the steel bonds.(2) The initiation and extension of the fatigue crack in a single specimen of the steel/Ni bonds was monitored nondestructively by using the relation between the echo intensity ratio and the crack depth, which showed the usefulness of the ultrasonic monitoring of the fatigue crack extension.(3) With the steel bonds with grooves, primary and secondary components were derived from spectra of the ultrasonic wave by using the sub-space method, and these components changed with the groove spacing. The shear strength was evaluated with the estimated diameter and the primary and secondary components.(4) In the case of the mild steel/Ti diffusion bonds, the spectrum of the ultrasonic wave reflected from the bonding interface changed with existence of melted layr at the bonding interface. The shear strength was quantitatively evaluated with the ultrasonic paramenters : the estimated diameter and two components derived from the response function of the ultrasonic spectrum by using the sub-space method.