In this study, the relationship between the crack growth rate and the effective stress intensity factor range of additive-manufactured aluminum alloy was evaluated. Fatigue crack growth tests were conducted for the as-built, artificial aging, and T6 heat-treated materials. Crack closure was measured, and the essential fatigue crack growth characteristics were evaluated by examining the effective stress intensity factor range. Based on the experimental results, the effects of the heat treatment and building direction on essential fatigue crack growth characteristics were investigated. For the as-built material, Si precipitated with a fine cell structure. Cracks propagated linearly within the cell, and the curve of the crack path was small because of the fine cellular structure. Therefore, the surface roughness of the fracture surface was small, and roughness-induced crack closure was also small. Crack growth resistance did not appear to be affected by the cellular Si structure. For the T6 material, Si precipitated with a spherical particle shape, and the crack path was curved by this Si particle. Therefore, the crack growth rate was lower in the T6 material than in the as-built material in the crack growth rate-effective stress intensity factor relationship. In addition, the surface roughness of the fracture surface was increased by the curve of the crack path. In the crack growth rate-stress intensity factor relationship, the crack growth rate of T6 samples was slower than that of as-built samples because of the increasing crack closure and crack growth resistance. Moreover, the building direction did not affect the essential fatigue crack growth characteristics.

Manual pollination is an arduous task in farming. To provide an alternative to manual pollination, we developed an artificial pollination sprayer for onboard drones. The sprayer was equipped with a pollen sprayer on a gimbal that could be driven horizontally and vertically. Successful pollination was achieved; however, residual vibrations occurred when the gimbal was driven in the experiment. Thus, we proposed experimentally suppressing the vibration phenomenon by altering the design of a control system of rotational speed in further research. Notably, the control system was able to track reference position signals adequately. This study devised a promising method of pollination.

Runaway accidents of gantry cranes (cranes), used for container cargo handling, occur because of wind. To decelerate and stop the cranes that have started to run away, rail brakes that press brake pads to the top of the rails and generate the sliding friction between the pads and the rails have been developed. In this study, we performed an experimental analysis of the behavior of an actual crane when the rail brake operated, to confirm the basic reliability of the simulation analysis method for analyzing the dynamic characteristics of the runaway crane. When the crane was decelerated and stopped using the rail brakes, the displacement and velocity in the traveling direction of the traveling devices at the bottom of the crane and the acceleration in the same direction of the operator cabin and boom end at the top of the crane were measured in the experimental analysis. Additionally, the displacements of the operator cabin and the boom end were obtained from a video image analysis, and the behavior of the whole crane and the upper part of the crane including the operator cabin and the boom end were considered. Under the experimental analysis conditions, it was suggested that the crane structure behaved as follows. When the crane decelerated by the rail brake operation, the crane structure integrally swung in the traveling direction (pitching motion) and deformed forward. After the crane stopped, it behaved by combining the pitching with the swing around the vertical axis (yawing motion). The frequencies of the operation cabin and the boom end in the traveling direction were 0.54 Hz and 0.39 Hz, respectively. The accelerations of the swing of the cabin and boom end after the rail brake operation were also discussed from the perspective of the structural safety of the crane components.