Papers by Author: Tadashi Nishimura

Abstract: Welding is widely used for construction of many structures. It is well known that residual stress is measured on welded joint. In this paper, a new method for reduction of residual stress using ultrasonic vibration during welding is proposed. Two thin plates are butt-welded. When ultrasonic vibration is used on one plate, tensile residual stress is reduced at center of the bead. Second, ultrasonic vibrations with different frequencies are applied on both plates. In this case, reduction rate of residual stress increases. Next, reduction of tensile residual stress is demonstrated by simulation method using an analytical model with dynamic characteristics of welded joint.

Abstract: Composite materials are used for many structures because of its high strong-to-weight ratio and easy formation. Secondary machining processes such as drilling and sawing are required to assemble and join composite materials to other structures. When composite materials are machined, delamination occurs at adhesive layer between laminated layers. It is well known that it is possible to cut hard metals and to improve precision of machined surface by using ultrasonic vibration. This method is applied to machining composite materials in this paper. Drilling of composite materials is focused on. First, this method is examined experimentally. Next, experimental results are examined by analytical method. Using condition of experiment, prevention of delamination can be demonstrated from the proposed analytical method.