Study on the effects of transverse ultrasonic vibration on deformation mechanism and mechanical properties of riveted lap joints.

In this paper, a new and special transverse ultrasonic vibration-assisted riveting (TUVR) system is developed to improve the plasticity and qualification of titanium alloy rivets. Comparing with conventional riveting (CR), the formed driven heads by TUVR are not only suffered from the riveting force and hole boundary constrain, but also the acoustic softening and dragging friction force. Consequently, to disclose the deformation mechanism and mechanical properties in driven head, a series of studies were carried out. First, the dimensions of driven head for different amplitudes and roughness were investigated. On this basis, the typical position microstructures in driven head of TUVR and CR were contrastively analyzed. Moreover, the interference sizes of laminates riveted lap joints under CR and TUVR were compared. Finally, the micro-hardness and pull-out strength in joints of two riveting processes were tested, and illustrating the mode and microstructure of failure. Results show that ultrasonic vibration can act as a new and effective auxiliary riveting method, which contributes to achieving plasticity improvement and higher mechanical properties of joints. Although the TUVR has significant effects on the deviation of the driven head, which can be restrained well with a reasonable amplitude and roughness. The grains deformation in typical positions of TUVR is much severer than CR, except in the lower shear band and difficult deformation area. Besides, the uniformity of interference sizes of riveted sample is well improved by TUVR. The experimental results show that the micro-hardness and yield load of TUVR riveted lap joints increase more than 10% and 4%, respectively.