Gas atomized powder is commonly used for Laser powder bed fusion (L-PBF) additive manufacturing because of its good flowability. On the other hand, water atomized powder is inexpensive and has a great potential for application to middle range manufactured products. In this study, SUS316L water atomized powder was applied to L-PBF additive manufacturing. To solve its poor flowability and excessive spatter, we investigated these problems and modified the additive manufacturing machine. Our test results revealed that a laser energy density of 57.8 J/mm³ is one of the best laser conditions for water atomized powder additive manufacturing. To apply the design for additive manufacturing (DfAM), the mechanical properties and overhang process window were revised. Finally, an extruder die plate with better pellet productivity was designed and produced by using SUS316L water atomized powder. The results showed that, it produced better quality pellets than the original one. From this research, we found that water atomized powder is useful for L-PBF additive manufactured products.

Tensile tests were conducted for notched round-bar specimens to acquire the limit conditions of local failure, which is ductile failure after large local deformation for three types of steel, SGV480, SPV490 and SGV410, for nuclear containment structures. The notch deformation was monitored using a profile projector. The notch’s cross-section radius and the curvature radius of the notched profile were continuously measured by image analysis in the tensile test. From those measurements, the stress and strain at the notch’s cross-section center were determined by Bridgman’s approximate solution and the elastoplastic FEM analysis. The true stress-true strain curve for the elastoplastic FEM was identified a priori by an optimization program that searches for the good curve in the exponential form applicable to large strain regions. No cracks were observed at the notch bottom surface in all specimens until the final rupture. The failure at the notch’s cross-section center was detected from the inflection point of the load-displacement curve. The limit strain diagrams were compared with those of ASME Sec. VIII-2 and its conservatism were discussed. Further, small-size notched round-bar specimens were sampled from the weld joints of SGV480 and SPV490 to determine the limit strain diagrams and true stress-true strain curves of the base metal, HAZ, and weld metal. The limit strain diagrams at each material of the weld joints were as high as or higher than the base metal, except for the weld metal of SPV490. The authors discussed the optical micrographs for fracture surfaces of specimens, the fracture morphology of weld joints, and the modified expression of a limit failure stress index regarded as the stress indication of the limit strain diagram in the high-stress triaxiality region.

In this paper, the large deflection response of a circular mesh tube under pure bending was investigated by using FE analysis. In the previous study[Nakamura, T., Ushijima, K., Evaluation of large deflection response of circular mesh tubes, Transaction of the JSME (in Japanese), Vol. 88, No. 915 (2022)], the effect of the ovalization across the cross-section on the bending response was neglected, but in this study, the influence of cross-sectional flattening on the nonlinear bending moment versus curvature was taken into consideration. There are three reasons for arising the maximum bending moment, but in this paper, we mainly focused on the two mechanisms (the large flattening response in elastic deformation and the plastic yielding behaviour) to the maximum bending moment. Based on our FE analysis, we proposed theoretical equations for predicting the maximum bending moment as a function of tube geometries and material parameters such as Poisson’s ratio and the plastic yielding stress.

The infrared thermoelastic method is considered a promising technology for the non-contact measurement of the stress distribution and fatigue limit of structures. In this method, the stress distribution can be detected based on the temperature variation caused by loading the structure, and the fatigue strength can be estimated from the dissipated energy. Additionally, the minute temperature variations of the structures under cyclic load conditions are evaluated. However, there is a concern that appropriate measurement results cannot be obtained using low-frequency cyclic loads owing to the large influence of heat diffusion. Therefore, the effect of the load frequency was investigated using a thermoelastic finite element (FE) analysis on a gusset welded joint specimen commonly used in welded structures. Furthermore, to simulate the thermoelastic effect, a stress field-temperature field thermoelastic FE analysis technique that calculates the heat transfer of the generated heat and heat absorption generated by decreasing and increasing tensile stress was developed. The calculated stress distribution showed consistency with the thermoelastic stress distribution measured using the infrared ray method, implying that the proposed technique is effective in reproducing the thermoelastic effect. A small gradient of temperature distribution was observed in the case employing a load frequency of 1 Hz; therefore, it is important to consider the influence of the load frequency when applying the thermoelastic method to the stress concentration field.

Tapping screw fabricates the female thread due to plastic deformation during screw rotation. Since the tapping screw skips the preliminary fabrication of female thread, it is widely used for the tightening in the fields of such as electric parts and car parts. However, there is a few theoretical studies for its self-tapping process and loosening proof. In this paper, we have investigated the mechanism of tapping torque and shape of female thread using three-dimensional finite element analysis. In addition to the plastic flow caused by the friction force due to the rotation of male thread, the plastic flow at the top of male thread separated by the up and down directions occurs. That contact at thread top mostly contributes the torque of self-tapping. Also, plastic flow along the lower surface of frank thread separated by the outside and inside radial directions creates the characteristic shape of female thread. The analysis results well reproduce the tapping torque and the shape of female thread. We also investigate the loosening proofs due to shear loading both for tapping screw and normal screw using there-dimensional finite element analysis. The shape of female screw obtained by self-tapping analysis is incorporated into the analysis model. It is found that the loosening proof of the tapping screw is superior to that of normal screw since contact at the top of thread in the lower part of tapping bolt inhibits the thread slip.

Application of segment-structured tetrahedral amorphous carbon (ta-C) film on soft metal substrate is proposed to improve wear resistance of mechanical parts. It was generally considered that continuous structure ta-C film was effective when applied to hard materials because it could not follow deformation of substrate material and the film tended to delaminate. In contrast, by applying segment structure on ta-C film, tribological properties of ta-C film coated on soft substrate were further improved, and sliding surface exhibited excellent wear resistance even under high sliding loads. Effectiveness of the use of brass substrate in improving wear resistance was demonstrated through large-scale wear resistant test of valve-plate used in oil pump of construction machine. Segment-structured ta-C coated brass valve-plate reduced maximum wear by approximately 80 % as compared with uncoated brass plate.

Transient behaviors of molecular orientation field of nematic liquid crystal (4-n-4’-octylcyanobiphenyl) under shear flows between concentric cylinders have been numerically investigated using the Leslie-Ericksen continuum theory in which the molecular orientation is represented with a unit vector, called the director. As well as the rotation speed of an inner cylinder, the director anchoring conditions at the inner and outer cylinders are chosen as simulation parameters to obtain four different cases of director initial profiles, which are homeotropic, hybrid, planar, and twist cases. After the imposition of the shear flow, the director start rotating within the shear plane, increasing the curvature energy of the director field. When the energy exceeds a certain critical value, the director start escaping from the shear plane, called the out-of-plane behavior. Because the escaping direction (i.e., either +z or -z directions) is the stochastic choice, the director field is randomly separated into the positive and negative out-of-plane regions. Then, the spatially distributed two out-of-plane regions are transformed into line defect structures. The spatial patterns of the out-of-plane regions and the line defect structures strongly depends on the director anchoring conditions, and no patterns are found for the twist case. The evolutions of torques of the inner cylinder is also estimated from the simulation results for four cases, and the oscillatory behavior of the torque is found for the homeotropic case.

The gas engine for the cogeneration system realizes lean combustion by using prechamber ignition. The fuel properties of natural gas are quantified as methane value, and a small amount of H2 and C2-C4 hydrocarbon fuels affect ignition and combustion. Since the reaction rate of hydrogen fuel is known to be faster than that of hydrocarbon fuel, even a small amount of hydrogen fuel can have an effect on combustion. Therefore, in this study, experiments were conducted with hydrogen added to methane using RCEM, which is an experimental apparatus similar to a real machine, to compare the ignition and combustion properties for each amount of hydrogen added. As a result, it was found that the ignition delay time can be predicted by a zero-dimensional calculation, and the jet velocity can be predicted by a one-dimensional calculation, which can be an important finding for the guideline of prechamber design.

Maintenance is one of the important issues in control systems. It is possible to take appropriate measures for maintenance of the control system by detecting change in characteristic of a controlled object. In this paper, three methods are proposed to detect characteristic change of the controlled object by applying the data-driven control FRIT. The method 1 detects the characteristic change of the controlled object based on a P gain value or an I gain value tuned by FRIT. The method 2 retunes parameter values of a reference model that describes desired response defined in FRIT so that the response is fastest within a range where a P gain value or an I gain value does not exceed each upper limit value. Then the characteristic change of the controlled object is detected based on the retuned values. The Method 3 detects the characteristic change of the controlled object by automatically tuning the parameter values of the reference model with maintaining current values for a P gain and an I gain. Performance of the proposed methods was evaluated by applying the methods to a prototyped small heater. An efficiency of the small heater was pseudo-deteriorated by covering a thermocouple with caps of various materials and thicknesses. A relation between the efficiency and the parameter values tuned by the each method at the pseudo-deteriorated condition was approximated by a linear function, and a correlation between the efficiency and the parameter values was evaluated with coefficient of determination. ζs were estimated from each characteristic change detection parameter values with the obtained linear functions, and the errors between the estimated value of ζ and the measured value of ζ were evaluated under two pseudo-deteriorated conditions. The coefficients of determination of the three methods were more than 0.95. The errors were smaller than 4%. It was confirmed that the proposed methods were effective for detecting the characteristic change of the prototyped small heater.

The nylon thread actuator, a type of super coiled polymer actuator, proposed by Haines et al. in 2014 has many useful advantages, including its relatively high power, lightweight, and low cost. Although the fabrication process seems simple, to fabricate such actuators, we must do so by hand because the finished products are not currently for sale. Thus, we are developing fully automated manufacturing equipment for overtwisted-type actuators using Ag-coated sewing machine nylon threads. In this study, we depict the details of a prototype machine and the basic specifications of conductive nylon thread actuators through experiments. This machine has three stepper motors. We found the maximum recommended drive speed of each spindle: the twist spindle with the drive is approximately 32.8 [rad/s] (313 [rpm]), the feeder speed is 37 [mm/min], and the winding speed is 61 [mm/min]. This condition provides steady overtwisted patterns with simply open-loop control, and the measured tension is approximately 20-30 [cN] during twisting, whereas it is approximately 40-50 [cN] during annealing. These processes run continuously for a single long thread; thus, the overall throughput is equal to the winding speed, which is determined by both the desired annealing tension and time.

In this study, transient analysis of flexible body motion with time-varying length is conducted using dimensionless finite element model (FEM). First, the equation of motion for a flexible body with large deformation, displacement and time-varying length is derived by VFE-ANCF, which variable-domain finite element model (VFE), a model expresses length change, applied to absolute nodal coordinate formulation (ANCF), known as an effective nonlinear finite element method in dynamic flexible body simulation. Then the equation of motion in dimensionless form is derived using dimensionless variables defined by time-varying length of the flexible body as a representative length and a representative time considering the longitudinal frequency of the flexible body. The system is converted into the system that length of flexible body is always constant by using this representative length. So, this method avoids the problems with analysis accuracy and calculation cost when the length becomes shorter and the natural frequency increases. Furthermore, the numerical results clarify the mechanism of flexible body motion with time-varying length.

In this study, we propose a solution to a shape optimization problem for the strength design of porous structures under thermal loading. The homogenization method is used to bridge the macrostructure and the porous microstructures, in which the elastic and thermal expansion tensor are homogenized. The local thermal stress in the porous structure is minimized. By replacing the maximum thermal stress with a Kreisselmeier-Steinhauser function, the difficulty of non-differentiability of maximum stress is avoided. This problem is formulated as a distributed parameter optimization problem subject to an area constraint including the all microstructures. The shape gradient function for this design problem is derived using Lagrange multiplier method, the material derivative methods, which are independently defined for the sub-regions in the macrostructure and the adjoint variable method. The H¹ gradient method is used to determine the optimal shape of the porous unit cell while reducing the objective function and maintaining smooth design boundaries. Effectiveness of the proposed method for minimizing the thermal stress of porous structures is confirmed by the numerical examples.

Ball screws and ball bearings are important mechanical elements in automobiles and machine tools due to their high mechanical transmission efficiency. However, with the spread of electric vehicles, the designs that ensure low noise and high durability are required. Currently, numerical analysis is mainly used to clarify the inner balls motion, but it is necessary to tune simulation models based on knowledge obtained from experiments in order to reproduce the behavior of experimental systems. Moreover, while there are the quantification methods of contact states and rolling motion of steel balls inside the ball screw using mathematical methods, the contact state and the ball motion are only considered in limited circumstances. Therefore, this study aims to extend mathematical methods to clarify the contact state and rolling motion of steel balls and guide grooves inside ball screws in order to contribute to noise reduction and longevity of ball screws. Four arc shapes of a Gothic arc, considering the helix orbit of steel balls and the position and dimensional errors of the steel balls in the contact plane under non-driven and non-loaded conditions of the ball screw, are given as geometric shapes, and the balance and rolling motion of steel balls during ball screw drive are calculated. Next, numerical examples are presented to examine the effects of changes in the arc shape on the revolution and rotation of steel balls and the impact on noise, wear, and lost motion inside the ball screw. Finally, the validity of the mathematical model is demonstrated by comparing the measured values with the theoretical values using a device composed of intersecting straight grooves with a crossing angle.

In the 21st century, as it is important to produce products with high quality, high dignity and high accuracy, mirror-like surface was requested for many products and prats. Therefore, polishing process, lapping process and buffing were performed for mirror-like surface as in the past. However, both polishing process and lapping process need long working time and high cost, and buffing accuracies except surface roughness were very low. Therefore, mirror-like surface turning technology with swift and easy working was developed and evaluated using only one lathe. Surface roughness on the turning was firstly considered for mirror-like surface. Then the simple grinder using polishing for mirror-like surface turning insert was also developed and installed on the turning lathe with linear motor. Cutting property using the proposed technology was evaluated in the several experiments. It is concluded from the results that; (1) The proposed technology can machine mirror-like surface in the turning. Its surface roughness was Rz 0.1μm, (2) The process for mirror-like surface becomes swift and easy working.

We examined the effects of the robotic walker’s dynamic characteristics on postural stability, operating forces, ground reaction forces (GRF), and muscle activity in young healthy adults during sit-to-stand (STS) and sit-to-walk (STW) tasks. All study participants were evaluated under eight conditions where the dynamic characteristics, inertia, damping, and frictional forces were changed during the STW test. We analyzed the effects of the robotic walker’s dynamic characteristics on postural stability, force, and muscle activity during STS and STW tasks. A multiple regression analysis revealed that the robotic walker’s inertia and frictional force altered vastus lateralis loading while standing. Here, inertia increases, and friction is applied as a load. The vastus lateralis muscle was activated due to changes in the center of gravity (COG) acceleration and postural stability resulting from inertia and friction loading. Participants compensated for changes in postural stability associated with loading using medial direction operating forces on the hand pad and delaying the “seat off” movement. These changes were analyzed according to COG position and GRF.