New wood forming methods for improving the workability of wood, such as compaction molding or wood forging, have been developed in order to use wood biomass effectively. However, the improvement of the formability and mechanical properties of materials is desired for the practical realization of those wood forming methods. To improve the formability and mechanical properties of materials, it has been reported that steaming is effective. However, the effect of steaming at temperatures lower than 150-160 ℃ has not yet been investigated. In this study, we investigated the hardness of compacted products of woody powder steamed at 130 ℃. Cedar, beech, bamboo and kenaf cores were used as materials, and these materials were steamed for various times. Next, the compaction molding of materials was attempted, and the Vickers hardness and density of the products were measured. The results show that the hardness was increased by steaming when beech, bamboo and kenaf cores were used. In addition, the hardness is proportionally changed with the density for most of the products. On the other hand, in the case of bamboo and kenaf cores, the hardness of products formed from air-dried materials changed, but density remained unchanged. Thus, it was considered that the effect of steaming was greater than that of the density for bamboo and kenaf cores.
A lithium ion battery bank used for electric vehicles is composed of many cells and current-collector tubs, and a large current passes through the tubs from the bank and flow to a motor. Moreover, a joining method for multi-stacked aluminum sheets is required. In this paper, we present a magnetic pulse welding method for five aluminum sheets with four gaps and a measurement method for four collision time signals. The four signals are simultaneously measured with two oscilloscopes. The five sheets used are of same thickness. An experiment is performed on 0.3, 0.5, 0.8 and 1.0mm thickness respectively. The first sheet on a plate coil experiences only an electromagnetic force, but the second sheet on the coil experiences both an electromagnetic force and an impact force by collision with the first sheet. Therefore, the time it takes for the second sheet to collide with the next sheet is always shorter than that for the first sheet. The five aluminum sheets were seam-welded along narrow middle of the coil. In a shearing tension test, five seam-welded sheets of 0.5mm thickness obtained at 3.5 kJ did not come off on four joined interfaces corresponding to the four gaps, but fractured in the five sheets. When all collisions generated in the four gaps are finished within a first wave of electromagnetic force, the five sheets may be strongly joined.
Recently, interest in the global environment has increased demands for strong structural components and lightweight parts. Thus, strengthening high-carbon steel wires is also needed. However, further strengthening is limited by the occurrence of delamination in twisting. The major reasons for the delamination are assumed to be (a) strain aging induced by heat generated and (b) nonuniform deformation in drawing. In this study, (1) cryogenic drawing and/or (2) uniform-deformation drawing schedules were discussed. Cryogenic drawing was realized by holding the wire in a box filled with liquid nitrogen prior to drawing. On the other hand, a uniform-deformation schedule was realized using an optimum combination of die angle and reduction in area per pass. It is found that either cryogenic drawing or uniform-deformation schedule is not effective. It is found, however, that cryogenic drawing with a uniform-deformation schedule, i.e., the combination of the two, is effective for retarding delamination and strengthening high-carbon steel wires.
With the newly developed die life test that simulate actual conditions in cold forging, the effect of the carbide distribution in tool materials is evaluated. Under the short-lived condition of 1x104 cycles or less, the relationship between the maximum carbide size projected to the normal plane to the maximum principal stress in the dangerous volume and fatigue life is revealed. As in high-cycle fatigue, crack initiation from one or a cluster of large carbides, especially multisite cracks, shortens fatigue life. The fracture surface morphology shows no feature of low-cycle plastic fatigue, but shows that of high-cycle fatigue in high-strength steel. The effects of maximum carbide size on fatigue life and fracture surface morphology show the possibility of handling the fracture under the conditions of a high-cycle fatigue fracture. The developed tool life test together with simulation is a potential method of evaluating life of tool materials.