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Ultrasonic plastic welding is a technique for joining thermoplastic parts through the use of frictional heat and deformation heat generated at the interface between the workpiece parts by high frequency mechanical vibration. This paper proposes a method for predicting the dynamic behavior of the contact surfaces of the parts at the beginning of the welding. The method is based on finite element dynamic contact analysis. To validate the proposed method, the predictions of dynamic behavior are compared with the measured data and a proper friction coefficient of the interface between the parts is determined. In addition, the dynamic behavior of the contact surfaces are investigated when the horn is vibrated at two different operating frequencies, 15 and 19 kHz. The results show that the dynamic behavior considerably depends on a friction coefficient. Furthermore, the displacements and elastic strains of the contact surfaces at 15 kHz are larger than those at 19 kHz. This seemingly results in the better quality of weld for 15 kHz operating frequency., 16th Asia Pacific Vibration Conference 24-26 November, 2015 HUST, Hanoi, Vietnam

Mechanical joints such as bolted and spot welded joints are widely used to join plate structures. The existence of contact interface of the joint increases the vibration damping in the structure because the energy dissipation due to friction occurs at the interface. This paper proposes a procedure for calculating the dissipated energy at the interface using finite element static contact analysis. The structure considered consists of three steel plates bolted together where a long plate is sandwiched between two short plates. We use the mode shapes of linear FE model of the joined structure as a distributed displacement loading in the static contact analysis to estimate the damping for each mode. To accurately calculate the dissipated energy, we apply a surface load on the overlap region of the joint along with the distributed displacement and find the necessary value of surface load. To validate the proposed procedure, the modal damping ratios estimated from the dissipated energy with the necessary surface load are compared with the measured damping ratios. The results show when the mode shapes obtained from the linear FE model approximate the actual deformation, the proposed procedure enables to accurately calculate the dissipated energy of the joined plate structure while the surface load on the overlap region is appropriately set. The necessary surface load increases with increasing mode number and varies almost proportionally to the square of the angular frequency.

In this paper, we investigate the damping characteristics for the fundamental and the higher modes in jointed plate structures with partially overlapping interfaces. First, the damping characteristics are experimentally evaluated. Second, the effect of the mode shape on the damping characteristics is examined. Third, the characteristics of energy dissipation due to friction at the interface, which determine the damping characteristics in jointed plates, are analysed. Consequently, we propose a procedure for estimating the energy dissipation at the interface using finite element (FE) analysis. The structure considered in this paper consists of three steel plates bolted together in which a long plate is sandwiched between two short plates. Comparison of the modal damping ratios estimated from the dissipated energy and those measured in modal testing confirms the validity of the proposed estimation procedure. The FE analysis and the experimental results show that the damping characteristics vary depending on the mode, especially for the difference between the symmetric and antisymmetric mode shapes. This is supported by the characteristics of the energy dissipation obtained in the contact analysis of the proposed estimation procedure.

In the previous study, we reported the gene expression for proteins related to the function of 5-hydroxytryptamine (5-HT, serotonin) and elucidated the expression patterns of 5-HT(2) receptor subtypes in mouse osteoblasts. In the present study, we evaluated the possible involvement of 5-HT receptor subtypes and its inactivation system in MC3T3-E1 cells, an osteoblast cell line. DOI, a 5-HT(2A) and 5-HT(2C) receptor selective agonist, as well as 5-HT concentration-dependently increased proliferative activities of MC3T3-E1 cells in their premature period. This effect of 5-HT on cell proliferation were inhibited by ketanserin, a 5-HT(2A) receptor specific antagonist. Moreover, both DOI-induced cell proliferation and phosphorylation of ERK1 and 2 proteins were inhibited by PD98059 and U0126, selective inhibitors of MEK in a concentration-dependent manner. Furthermore, treatment with fluoxetine, a 5-HT specific re-uptake inhibitor which inactivate the function of extracellular 5-HT, significantly increased the proliferative activities of MC3T3-E1 cells in a concentration-dependent manner. Our data indicate that 5-HT fill the role for proliferation of osteoblast cells in their premature period. Notably, 5-HT(2A) receptor may be functionally expressed to regulate mechanisms underlying osteoblast cell proliferation, at least in part, through activation of ERK/MAPK pathways in MC3T3-E1 cells.