In this paper, quasi-static loading tests and fatigue tests are carried out on spot welded joints of mild steel (270MPa class) and ultra-high strength steel (980MPa class) sheets in order to investigate the influence of strength level of base steels on fatigue strength and fracture mechanism of spot welded joints. Under quasi-static loading, a spot welded part is more liable to be a fracture-initiation site in the ultra-high strength steel than in the mild steel, and as a result fracture behavior of the ultra-high strength steel is considerably affected by a spot welded part as compared with that of the mild steel. Although the fatigue strength of spot welded joints is higher in the ultra-high strength steel than in the mild steel in low cycle fatigue regime, the difference in fatigue strength decreases in high cycle fatigue regime and the fatigue limit is almost the same in both steels. Fracture morphology of spot welded joints under cyclic loading depends on the load level in the ultra-high strength steel, but not in the mild steel. From the comparison between S-N curves for spot welded joints and notched base steels, the dependency of fatigue strength of spot welded joints on base steels is attributed to the notch-sensitivity to fatigue strength of the base steels.

SummaryThe direct cell-to-cell transfer of tocopherol between red blood cells (RBCs) was examined. Two kinds of RBCs were provided; 1) Tocopherol-deficient ones showing complete dialuric acid-hemolysis and 2) tocopherol-supplemented ones showing no dialuric acid-hemolysis. The two kinds of RBCs were mixed and incubated with gentle swirling in a buffer solution. If no tocopherol transfer occurred between the two kinds of RBCs in the cell suspensions, hemolysis should not change during incubation because hemolysis is limited only in the -deficient cells in the suspensions. However, it was actually observed that when RBCs with adequate amounts of tocopherol were incubated with tocopherol-deficient RBCs, dialuric acid-induced hemolysis decreased during a 3-h incubation period. Contrarily, when an inadequate amount of tocopherol constitut ing a limiting level for inhibition of hemolysis, exsisted in RBCs which were mixed with -deficient ones, hemolysis increased after incubation. This indicates that tocopherol is transferred from the tocopherol-rich RBCs to the -deficient RBCs. The transfer was greater as the hematocrit of cell suspensions increased. Gum arabic contained in the suspensions inhibited the transfer, while bromelain (a protease which lowers the electric charge on the cell surface) increased it. These findings indicate that the transfer of tocopherol is related to the frequency of collision between cells.

We have proposed the practical torque sensor which utilizes elasticity of harmonic drives. The sensing technique provides joint torque sensing without reducing stiffness of the robot and changing the mechanical structure of the joints. I n this paper, we examine experimentally the characteristics of joint torque control using this torque sensor. Three types of torque control laws are implemented with a one-link arm to find a control method which provides excellent friction reduction and dynamic response in joint torque. The experimental results of joint torque control show that the torque sensor is very useful to compensate the nonlinear friction. Furthermore the torque control is effective to improve the accuracy of the motion control at low velocity and to suppress the vibration caused b y the joint fEexib ility .

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Electro-rheological gel (ERG) is a functional elastomer, which changes its surface adhesive property according to the intensity of electric field. In this study, ERG is applied to multiple-disk brake element to realize both simplification of structure and wide range of controlled brake torque. First, static performance of ERG multiple-disk brake (ERG-MDB) is evaluated experimentally. It is clear that a generated brake torque depends on an electric field and the number of layer of ERG. ERG-MDB with 6 layers shows 5 times brake torque as high as that with 1 layer. Second, considering the dynamical model of the ERG-MDB, dynamic performance is investigated through the forced vibration test. The result shows that dynamic damping and stiffness coefficients are changed widely according to applied electric field.