Emissivity is a crucial property in quantitative thermographic testing, a leading technique in nondestructive inspections for exterior wall diagnosis. We propose a method for measuring emissivity that exploits the angle dependence of polarized reflectivity. This approach involves measuring the reflected energy from a heat source near the Brewster angle using an infrared thermographic instrument equipped with an infrared polarizer. However, the emissivity measurements for insulators exhibited significant discrepancies when compared with values obtained via FT-IR, attributable to two main factors: diffuse reflection caused by surface roughness and approximation errors inherent in the simplistic theoretical formula. To address these issues, we applied a correction for specular reflectivity considering surface roughness and refined the theoretical formula by incorporating polarization theory and the extinction coefficient. This enhancement enabled accurate emissivity measurements for ceramic tiles with rough surfaces. Notably, this method only requires a heat source and does not necessitate precise temperature measurements with an infrared thermographic instrument, which is significant since standard instruments used in nondestructive inspections often fail to measure temperature accurately. Additionally, we achieved thermal imaging without background reflection through subtraction image processing, beneficial for field measurements. Consequently, this improved method is highly effective for nondestructive inspections.

This study investigated the effects of artificial defects, introduced via focused ion beam (FIB) processing, on the tensile properties of thin titanium alloy wires (Ti-6Al-4V). Results indicated that the defective wires fractured when the net-section nominal stress reached the ultimate tensile strength of the smooth wires, probably because of localized stress concentrations relaxing due to plastic deformation around the defects. The effect of defects on tensile properties was classified into three regions based on the size of the defect area. In the case of small defects, wires fractured at the smooth area away from the defects where the cross-sectional strength was lower. In this case, the defects minimally affected the tensile properties. This is attributable to variations in the cross-sectional strength of the wire, which resulted in some sections with lower strength as compared with the defect area. In the case of medium-sized defects, the fracture strain decreased gradually as the defect area increased. Finally, in the case of large defects, the fracture strain was extremely small. The boundary between the medium-sized and large defects indicates the transition from plastic deformation to no plastic deformation in the smooth area.

When an elongated columnar shape memory alloy (SMA) element buckles, in some cases it exhibits negative stiffness. This post-buckling negative stiffness can be repeatedly used as SMAs can recover their shape. This property has potential application to passive vibration isolation devices. A previous study on the behavior of convex-tape-shaped Ti-Ni SMA elements found that their properties are superior to those of normal flat-tape-shaped SMA elements. However, a Ti-Ni SMA has a high dependence on environmental temperature. Therefore, this study investigates the effect of cross-sectional curvature on the buckling characteristics of convex-tape-shaped Cu-Al-Mn SMA elements, whose shape memory and mechanical properties are less dependent on environmental temperature than those of a Ti-Ni SMA, using the three-dimensional finite element method and a buckling test. The results show that the post-buckling negative stiffness increases with increasing cross-sectional curvature. This tendency is similar to that for a Ti-Ni SMA, indicating that the buckling characteristics of a Cu-Al-Mn SMA can be designed using methods for a Ti-Ni SMA. Moreover, the lower temperature dependence of a Cu-Al-Mn SMA compared to that of a Ti-Ni SMA makes a Cu-Al-Mn SMA more suitable as a material for vibration isolators.

The demand for printed electronics is increasing with the development of flexible devices. Flexible electric line printed with metal nanoparticle ink is widely used. Electromigration (EM) is a phenomenon in which metal atoms are transported by electron wind under high current density, and it is important to reduce EM damage to improve device reliability. It is already known that EM damage occurs in Ag nanoparticle line not covered with an insulating layer, but EM damage in Ag nanoparticle line covered with an insulating layer has not been investigated. In this study, high-density current loading tests were conducted on Ag nanoparticle line with and without insulating layer to investigate EM damage. Test specimens were fabricated using an inkjet printer, and high-density current loading tests were conducted using a current testing machine to measure the potential drop for a constant current in the line using the four-terminal method. After the test, the surface of the test section was observed using a microscope. Damage occurred on the anode side of the line section of the Ag nanoparticle line with an insulating layer, and decrease in the potential drop was observed in the early stages of the high-current loading test. From the results, it was confirmed that EM damage occurred in the Ag nanoparticle line with an insulating layer as well as in the Ag nanoparticle line without an insulating layer.

Metallic materials are widely employed due to their exceptional mechanical attributes. Plastic deformation is a common issue that influences both the mechanical and electrical properties, with profound implications for the longevity of engineered structures and components. Dislocation density is the core factor in the plastic deformation process. Traditional methods for the evaluation of dislocation density include electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and x-ray diffraction (XRD), requiring meticulous specimen preparation and sophisticated equipment posing challenges for industry-wide fitness-for-service (FFS) monitoring. To address these challenges, a non-contact method to quantitatively evaluate the dislocation density in stainless steel 316L (SUS316L) by employing a microwave reflection method is reported in this study. A dedicated microwave measurement system, coupled with a coaxial line sensor, was used to measure the amplitude of the reflection coefficient of the microwave signal at a constant standoff distance and frequency, closely associated with the electrical resistivity of the SUS316L specimens, a parameter that exhibits variation in response to changes in dislocation density. The results indicate a proportional increase in the amplitude of the microwave signal with higher dislocation density. By establishing a linear correlation, we demonstrate the feasibility of evaluating dislocation density with a minimum detectable difference of 1.824 × 10¹³ m^-2 using the dedicated microwave system under the designed conditions in this study. This approach holds promise for better understanding and monitoring of plastic deformation in metallic materials across various applications.

The jamming transition phenomenon refers to the change in stiffness of a powder as its density changes. As a familiar example, vacuum-packed coffee grounds are hard, but when opened to allow air into the package and the density is reduced, the grounds become softer. Using Ti-Ni shape memory alloys (SMAs) and the jamming transition phenomenon, a variable-stiffness and deformable link was devised and prototyped by Takashima et al. (2022). Although the mechanism worked well, it operated slowly due to the slow shape recovery velocity of the SMA. For practical application of this mechanism, it is necessary to improve the recovery velocity of Ti-Ni SMA. Normally, Ti-Ni SMAs exhibit an austenite to martensite phase transformation; however, Miyazaki and Otsuka (1984) observed that under some conditions, R-phase transformation can occur between these phase transformations. In a previous study, Tanikata et al. (2022) observed that SMAs that show R-phase transformation during shape recovery tend to have higher recovery stress than SMAs that do not show R-phase transformation. Therefore, SMAs that show R-phase transformation during shape recovery are expected to have a high shape recovery velocity. This study investigates the effect of R-phase transformation on the recovery velocity of SMA. From the experimental results, specimens that show R-phase transformation tend to have a higher recovery velocity than specimens that do not show R-phase transformation. However, the mechanism created using materials showing R-phase transformation had a small amount of shape recovery during shape recovery. Thus, we attempted to improve the mechanical properties of the SMA by training. The device using the trained specimen demonstrated increased shape recovery compared to the device using the untrained specimen.

This study investigates the inhibitory effects of high-density pulsed electric current (HDPEC) treatment on fatigue crack initiation in directionally solidified nickel-based superalloy. Experiments were conducted under fully reversed conditions (R = -1) using low-cycle fatigue tests to assess the impact of HDPEC on crack initiation. The distribution of misorientation at different stages before and after crack initiation of untreated and HDPEC-treated samples was analyzed through kernel average misorientation maps by electron backscatter diffraction method. The results demonstrate that the HDPEC treatment significantly delays the initiation life of cracks, extending from approximately 2000 cycles to 5000 cycles. Additionally, the average fatigue life of the samples increased from 3851 cycles to 10881 cycles, more than doubling the fatigue life. Furthermore, the formation of persistent slip markings on the surface of the HDPEC-treated samples was completely suppressed, indicating changes in the persistent slip band’s structure. This phenomenon led to a distinct pattern of crack formation and propagation compared to untreated samples, suggesting that HDPEC treatment effectively alters the pattern of crack initiation and propagation by homogenizing dislocation distribution and alleviating residual stresses caused by cyclic loading. The result confirms the potential of HDPEC technology to enhance the fatigue life of nickel-based superalloys, and underscores the potential for further research in this domain.

Polymers and their composites are extensively utilized in the aerospace, energy, and automotive industries due to their lightweight properties, ease of manufacturing, high impact resistance, and other advantages. These materials are crucial for applications where performance and durability under varying environmental conditions are critical. Accurately predicting the viscoelastic behavior of polymers is essential for ensuring their reliability and durability. The time-temperature superposition principle (TTSP) is widely used to predict long-term viscoelastic properties, such as creep and stress relaxation, by making a master curve from short-term experimental data at various temperatures. Despite its widespread application, the molecular mechanisms of TTSP are not fully understood. To approach this issue, molecular dynamics (MD) simulations were employed to investigate TTSP mechanisms at the molecular level. Creep analyses were conducted at various temperatures with both with constant density and pressure using polypropylene as the model polymer to examine the effect of density on TTSP. The purpose of the simulations is to explain the basic mechanisms causing viscoelastic behavior, including the effect of chain interactions, potential energy changes, and free volume changes. The results indicate that the change of free volume has an important role in the formation of the TTSP master curve. Additionally, torsional potential energy is highly responsive to temperature changes, whereas non-bonding potential energy is more influenced by density changes. Furthermore, a linear relationship was found between changes in internal molecular angles (bond angle and torsion angle) and molecular chain structures (kinks and entanglements) with shear creep compliance.

A heat-storage device using the latent heat of the martensitic transformation in Nickel Titanium (NiTi) shape memory alloy (SMA) is proposed. The principle of heat-storage is such that, when a piece of NiTi SMA in the state of fully transformed martensite is in contact with a heat source, the piece would absorb a part of heat as the latent heat associated with the phase change from the martensite to austenite. Since the feasibility study of the device has not yet been given, this article presents the computer simulation of the device by considering the composite of NiTi SMA rods embedded in the block of aluminum. The composite is designed to cool down the temperature of a heat source by being in contact with the aluminum block including SMA rods. The absorption of latent heat is expressed in the equation of the continuous change in the enthalpy, which makes it possible to perform the heat transfer analysis of finite element method (FEM). The enthalpy function is derived from the experimental result of differential scanning calorimeter. The result of FEM exhibits the performance of the proposed heat storage composite quantitatively.

In this paper, based on the virtual fields method (VFM) and displacement measurement using digital image correlation, we propose a method for evaluating the equivalent stress and the equivalent plastic strain relationship and the stress distribution even after the onset of the local necking. The proposed method identifies a piecewise relationship between the equivalent plastic strain and the equivalent stress, resulting in model-independent relationship. The effectiveness of the proposed method is demonstrated by applying it to the simulation data obtained using a finite element method. Results show that the proposed method can identify the piecewise relationship between the equivalent plastic strain and the equivalent stress. In addition, the proposed method is applied to the experimental displacement distributions around notches of a thin high-strength steel plate specimen. Experimental results show that the reasonable post-necking stress-strain relationship together with the stress distributions are obtained using the proposed method.

Multilayered skin, subcutaneous tissue, and skeletal muscle exhibit complex mechanical behavior. Deformation of surrounding tissues affects superficial venous circulation, but the deformation behavior of these tissues has not been determined in relation to skin surface shear. This study investigated the effect of shear on the deformation of soft tissues surrounding superficial veins. Motion analysis of five subjects in their 20s was conducted to quantify the deformation of forearm soft tissues with a cephalic vein of about 3 mm in luminal height by ultrasound video imaging with application of shear to the skin surface. Selected points near the skin surface and the top and bottom of the vein were traced on video images. When the top of the vein was at a depth of 2 mm (four subjects; body mass index (BMI) 17–22), the point near the top of the vein moved by almost the same amount as the point near the skin surface, whereas the point near the bottom of the vein moved by only a small amount (three subjects) or by the same amount as the top of the vein (one subject). In one case where the top of the vein was at a depth of 4 mm (one subject, BMI 26; grade 1 overweight according to the World Health Organization classification), the points near the top and bottom of the vein in the thick subcutaneous tissue moved by half the displacement of the skin surface. Finite element analyses were conducted for typical cases of subcutaneous tissue thickness above the vein. The results reproduced the experimental deformation behaviors, with the exception of substantial sliding below the vein. They indicated that BMI category, venous depth, and the sliding mechanism in subcutaneous tissue determine the motion of the vein and surrounding soft tissues under shear.

Owing to the rapid development of additive manufacturing technology, more precise and complex 3D lattice structures can be manufactured easily. In this study, the brittle fracture toughness of 3D lattice structures was investigated by finite element analysis and experimental bending tests. The existence of singular stress fields in 3D lattice structures is highly dependent on the crack length and the relative density of the lattice cores. In this study, two types of lattice core containing cracks (termed BCC and FBCCZ) were selected as analytical models, and the singular stress field was investigated by observing the change in stress values during fracture. Also, based on our numerical calculation, empirical expressions for the brittle fracture toughness K_IC of both lattice structures were obtained and compared with experimental results. The experimental values of fracture toughness K_IC can be predicted within an error margin of approximately 20% by considering the effective length of the strand and the amount of plastic strain that occurs before fracture.

The effects of initial defects, such as fiber breakage, on the strain measurement of 3D-printed carbon fiber-reinforced plastic (CFRP) are evaluated herein. The generation of defects is difficult to avoid during the 3D printing process of CFRP, resulting in degradation of the tensile strength. However, the effects of these initial defects on the elastic modulus have not been investigated. The elastic modulus is generally determined by performing strain measurements using strain gauges and extensometers, as defined by testing standards. Strain gauges and extensometers are attached to the specimen, and therefore, the measurement is affected by the specimen surface, which contains initial defects. In this study, the effects of initial defects on the strain measurement are examined by performing tensile tests, evaluating the elastic modulus, and comparing the results of the 3D-printed CFRP with those of a homogeneous material, namely aluminum. The elastic modulus is evaluated using strain gauges, extensometers, and digital image correlation (DIC). The strain in homogeneous materials is independent of the strain gauge position, but strain variation is observed in CFRP depending on the position, presumably owing to the defect distribution. Furthermore, the strain obtained from extensometers with longer gauge lengths is also affected by the initial defects. Moreover, the variation is larger for the strain obtained by DIC than that obtained using strain gauges or extensometers. The strain distribution obtained by DIC may be useful for identifying the positions where the effects of initial defects are significant.

In this study, tensile properties including material nonlinearity (viscoplasticity) of carbon fiber-reinforced plastics manufactured by the filament winding method (FW-CFRPs) are experimentally investigated, and numerically analyzed using a three-scale homogenization method. First, tensile tests of FW-CFRPs made of towpregs with carbon fibers and an epoxy resin are conducted using coupon specimens with five kinds of laminate configurations, i.e., [0]₄, [90]₈, [0/90]_2s, [45/-45]_2s and [63/-63]_2s. Based on the stress-strain relationships obtained, tensile properties of the FW-CFRPs and their dependence on the laminate configurations are examined. To analyze such properties, multiscale elastic-viscoplastic analysis of the FW-CFRPs is performed using the three-scale homogenization method developed by the authors. For this, meso-scale unit cells consisting of fiber tows without or with crimps and a micro-scale semiunit cell consisting of the carbon fiber and epoxy are prepared. In addition, material constants of the epoxy are determined by tensile tests of epoxy specimens. Using the unit cells and material constants, multiscale tensile analysis of the FW-CFRPs is conducted. It is shown that the analysis results are in quantitatively good agreement with the experimental results, validating the present analysis method. It is also shown that the existence of crimps in fiber tows causes nonlinear behavior of the [0/90] FW-CFRP, resulting in lower macroscopic stress compared with the case without crimps.

The effect of the variation of the dislocation velocity on the dragging stress of aluminium under cycling loading has been investigated. Hydrogen diffusion around a dislocation was simulated by the finite difference method, and the dragging stress was calculated from the hydrogen distribution. The velocity of the dislocation changed in a sinusoidal manner. The dragging stress depended on the frequency of the sinusoidal velocity variation. In the low-velocity region, the maximum dragging stress decreased with increasing frequency. However, in the mid-velocity region, the maximum dragging stress increased with increasing frequency. The dragging stress did not depend on the frequency in the high-velocity region. A dragging stress model for aluminium with hydrogen under a variable dislocation velocity is proposed. When the frequency is below 0.2 kHz (i.e., in general fatigue tests), the dragging stress–velocity relationship under a constant velocity of the dislocation in the case of aluminium with hydrogen can be used. In the high-velocity region, the dragging stress can be determined using the relationship between the dragging stress and velocity under a constant velocity of the dislocation. The dragging stress under the low-velocity condition can be modelled using an ordinary viscosity model. In the case of actual hydrogen concentration, the dragging stress is thought to be much smaller than 1 MPa.

In this study, a novel carbon fiber reinforced thermoplastics (CFRTP) rod head servo-press thermoforming apparatus using two servo-press units and a ring-type heater in the die was developed. The CFRTP rod head was thermoformed using carbon fiber reinforced polyetheretherketone (CF/PEEK) round rod prepared by thermal pultrusion process. Thermoforming force and displacement during CF/PEEK rod head thermoforming and die clamping force and displacement of the concave die of lower die were controlled individually and precisely by upper and lower servo-press units and were monitored during CF/PEEK rod head thermoforming. Using this apparatus, the shape, dimensions, and density of CF/PEEK rod heads were measured by varying the thermoforming force, head shape (Flat type or Rosette type) and head height, and fiber orientation of the round rod. And the damage behavior was investigated from the load-displacement behavior in head tensile test and cross-sectional images of the heads before and after the test. As a result of thermoforming Flat and Rosette type CF/PEEK rod heads, Rosette type CF/PEEK rod head was more reproducible in head forming. The results of thermoforming by varying the thermoforming force showed that there is an optimal load for the head thermoforming.

Instability-induced patterns with spatially varying dimensions and geometric shapes, or inhomogeneous instability patterns, are ubiquitous in biological structures and have attracted much interest in both fundamental research and engineering applications. However, it remains a challenge to create such patterns using materials with stiffnesses and scales comparable to biological structures. Here, we demonstrate the creation of inhomogeneous instability patterns using film–substrate bilayers of polyacrylamide hydrogels. Swelling of thickness-gradient films on the substrates allows for the coexistence of different instability patterns, including creases and wrinkles, on the surface. The film thickness and the stiffness ratio between the film and substrate are the factors that control the characteristic length of the patterns on the millimeter scale, as well as the switching of the patterns between creases and wrinkles. Furthermore, these patterns can be generated at prescribed local areas on the surface. Our approach to creating inhomogeneous instability patterns on a single surface would help to gain insight into the morphological development of biological patterns and to fabricate bio-inspired functional surfaces.

Laser cladding (LC) is an advantageous surface modification technique. However, in the case of a thin substrate or a large process area to substrate, large thermal distortions could be generated, which can affect the dimensional accuracy of machinery parts. A substrate fixation method in the manufacturing process can mitigate thermal distortion. However, this fixation may induce residual tensile stress in the LC layer. Therefore, a simulation technique is required for scenarios with and without substrate fixation during laser cladding. In this study, models of a cantilevered plate (Cl) and a plate fixed at both ends (Fix) were developed. A 3D coupled thermo-mechanical analysis was performed using the element birth-death technique. Isotropic and kinematic hardening laws were also applied to the Cl and Fix models to compare the simulation results of thermal distortion and residual stress distribution. The Cl model with the isotropic hardening law achieved a higher simulation accuracy, while the model with the kinematic hardening law overestimated the thermal distortion. Conversely, the kinematic hardening law closely matched the experimental results in the Fix model. In addition, the comparison of normal stress–plastic strain diagrams revealed large compressive plastic strains repeatedly induced in the substrate regions below the interface in the Fix model due to substrate fixation during LC. The repeated plastic deformation induced the Bauschinger effect, which increased the simulation accuracy with the kinematic hardening law. These findings are crucial for accurately predicting residual stresses and thermal distortions in LC processes with substrate fixation.

This study deals with the free jet from an asymmetrical two-dimensional nozzle whose asymmetry is introduced by a lip attached on one side of the nozzle. Experiments are conducted for three Reynolds numbers; 1000, 3000 and 6000. The aspect ratio of the nozzle exit is fixed at 300, which can be large enough to research the fundamental behaviour of a plane jet. In order to clarify the effect of the lip length, the lip length l varies in a wide range of 0 – 20h, where h denotes the height of the nozzle exit. Then, the authors show such basic characteristics of the jet as mean-velocity and turbulence-intensity profiles at various downstream sections, which suggest a potential in the control of a plane jet especially concerning its deflection angle in far downstream, which vibrates with l. Besides, the authors reveal negligible Reynolds number effects more than 3000, and propose an empirical formula to predict the deflection angle.

Traveling cables are important components for elevators that transmit electricity and control command to elevator car. In recent years, as buildings have become taller, traveling cables have also become longer. So, cables are easily oscillated by building swing caused by wind or earthquake, and vibration remains long time. It causes collision and entanglement with the devises in the hoistway. Normally, travelling cables are composed of wires covered by vinyl sheath and precise modelling is very difficult. In this paper, two modelling strategies especially for damping property of the cable are proposed using Absolute Nodal Coordinate Formulation (ANCF). ANCF is a kind of the finite element method (FEM) and is suitable for the analysis of the large displacement and deformation problems of flexible structures. One strategy is a combination of bending damping and internal viscous damping; the other is combination of viscoelastic damping modelled by the three elements Maxwell model and internal viscous damping. Deriving of the equations of motion with damping became simple by introducing the complementary element coordinate. Experiments were carried out for bending stiffness and damping parameters identification and swing behavior in lateral direction was observed. Simulation studies were conducted, and both strategies were useful in engineering to simulate the behavior of travelling cables.

This study investigated a time-domain method that uses a neural network (NN) to identify three linear parameters such as mass, viscous damping coefficient and spring constant, as well as nonlinear forces of a nonlinear vibration system. In this method, the measured excitation force, acceleration, velocity, and displacement are input to the NN, which learns the force equilibrium between the external force, inertial force, damping force, and nonlinear restoring force, thus identifying the characteristics of the vibration system in an explicit manner. The proposed NN consists of two subnetworks: the linear subnetwork and the nonlinear subnetwork. The nonlinear subnetwork is called a global NN and cooperates with a local NN that extracts linear parameters. The features of the proposed method are: I) linear parameters are intentionally extracted based on the equation of motion, and II) guidelines for setting hyperparameters can be obtained from the behavior of the mean squared error (MSE). In this study, numerical simulations for parameter identification were performed to validate the proposed identification method. The vibration systems investigated were those governed by the Duffing and Van der Pol equations, as well as those in which the restoring force is represented by a sine function. The data obtained by numerically solving the equations of motion were considered as experimental data, and the linear parameters and nonlinear forces were identified to confirm the validity and applicability of the proposed method.

In Japan, where earthquakes occur frequently, aging infrastructure such as bridges, chimneys, power lines and tunnels have become very severe concern. Aging infrastructure is extremely dangerous as it has possibility to collapse due to earthquake shaking. Therefore, it is necessary to find a dangerous point in infrastructures immediately to prevent accident. Inspection was mostly carried out by inspector climbing the attached ladders. However, the inspection climbing the ladder becomes dangerous, because it uses uncertain ladder and unpredictable weather and conditions occur. Based on the situation, the automatic ladder climbing inspection robot that can climb up and down the ladder by using flexible robot arms without giving damage to the ladder was developed in the previous study. The previous flexible robot arm that consists of three Extension type Flexible Pneumatic Actuators (EFPAs) that can extend about 2.5 times from its original length. In this study, as assuming investigations in hazardous environments where toxic / flammable gas exit or inside of a nuclear reactor, a ladder climbing inspection robot with horizontal mobile function was proposed and tested. The theoretical estimation for ladder climbing up motion of the robot based on the analytical model was carried out. As a result, it was confirmed that the tested robot could climb up the ladder, although only slightly. Also, the driving tests using the tested robot for ladder climbing down motion and horizontal mobile motion were also carried out. As a result, it was confirmed that the tested robot could realize both vertical and horizontal movements.

This study constructs a path-following controller (rider model) based on nonlinear model predictive control (NMPC) with steering torque as the control input. By combining this with the dynamics model derived by Hatakeyama et al. (2024), we propose a simulation model that considers the main dynamic characteristics of a motorcycle, such as weave and wobble modes. In particular, the internal model used in NMPC has been simplified to ensure a reasonable response when the simulation time is shorter than the real time. In the path-following controller, the parts that calculate the reference roll angle from the reference path and those that calculate the steering torque input from the reference roll angle are handled separately. These components are constructed as cascade structures of outer and inner loops, respectively. This allows the two loops to appropriately use different sampling periods and prediction horizon settings for NMPC, enabling fast computation. In addition, an optimal NMPC solver can be used for both the outer and inner loops, further enhancing fast computation. In riding simulations involving high speeds and large roll angles, where nonlinearities are stronger, stable responses that are roughly consistent with actual riding were obtained in a simulation time shorter than the assumed time for one lap in actual circuit riding. The developed simulation model can be used as a reliable and practical support tool for motorcycle designing.

This paper presents a laser direct writing method for the fabrication of a laser-induced graphitic carbon (LIGC)/polydimethylsiloxane (PDMS) bimorph thermal microactuator via two-photon polymerization (TPP) and laser-induced graphitization (LIG). The fundamental parameters of femtosecond laser dotting, adopted as the writing mode for LIG, were investigated by observing the carbonized surface of the TPP-written PDMS plate using optical, scanning electron, and Raman microscopies. Subsequently, as a proof of concept for the proposed method, the LIGC/PDMS bimorph thermal microactuator was fabricated by modifying the surface of a PDMS microcantilever with a thickness of 25 μm and a length of 280 μm through femtosecond laser dotting. The directly written LIGC/PDMS bimorph thermal microactuator produced repeatable displacements of approximately 20 μm with the temperature rise of 66 ℃. Furthermore, the LIGC/PDMS bimorph microactuator exhibited a displacement of 27 μm at 10 mW and a response speed of 0.05 s in photothermal heating. The proposed direct writing fabrication method based on TPP and LIG demonstrates potential for advancing the development of PDMS-based bimorph photothermal microrobots.

Numerical simulation methods driven directly from images have advanced considerably. Oshima (2023, 2024) formulated an immersed boundary Navier–Stokes (IB-NS) equation that treats the solid boundary as a parameter called porosity. This method suggests that flow simulation is driven directly by image-based data without generating surface models. However, specific methods for this approach have not yet been proposed and implemented. Therefore, in this study, we applied a primarily filtering-based image processing technique to calculate the level-set of geometry shapes from image luminance values to apply it to the IB-NS. Using this method, a uniform flow analysis around two-dimensional circular, square and triangular cylinder was performed. The root mean square error of the scalar fields (flow velocity and pressure) was used to compare the calculations based on the porosity generated from the numerical model and the filtered calculations, verifying geometry-specific filter effects. Additionally, the streamlines were compared with a good agreement of the velocity fields. These results confirm that consistency was achieved, and the numerical model can be replaced by filtering. Moreover, actual flow simulations were performed using a two-dimensional RGB image and problem specific to using real images was discussed, along with boundary thickness. Finally, we extended the diffusion filter for calculating the level-set to a three-dimensional binarized voxel-based data and found that it can also be applied to three-dimensional voxel-based data. Therefore, physically consistent numerical solutions were obtained stably, proving that the flow simulation can be performed directly from images without the intermediate step of generating surface models.

Wire ropes consisting of strands of twisted steel wires have high flexibility and tensile strength, making them suitable for use in machinery and structures such as cranes and elevators. For their strength evaluation, the wire stress and strain should be measured. However, experimental approaches are limited due to the complex twisted structures of such ropes. Herein, we develop a finite element (FE) modeling scheme for the single-twisted Fi(29) strand used in 6 × Fi(29) rope with an independent wire rope core that reproduces the strand stiffness and wire stress. To validate the FE modeling scheme, we conduct tensile, three-point bending, and bending-over-sheave (BOS) tests. As for the tensile test, the stiffness in the axial direction and torque coefficient are reproduced within 10% and 5% accuracies, respectively. The strain of the outer wire of the strand is reproduced within a 20% accuracy. The strain of the core wire exceeds those of the other wires. Their strains vary because the straight core wire has higher stiffness than the helical inner and outer wires. Regarding the three-point bending test, the bending stiffness and the strain of the outer wire are reproduced within 10% and 5% accuracies, respectively. Moreover, findings indicate that theory based on material mechanics overestimates the bending stiffness by 30% due to the squeezed deformation of the cross section caused by the concentrated contact force from the upper jig in the test setup. Each wire undergoes bending deformation, and the core wire has higher strain than the other wires. As in the tensile test, the larger stiffness of the core wire increases the bending strain. As for the BOS test, the strain of the outer wires is reproduced within a 12% accuracy. Each wire is bent on sheaves. The wire stresses in the axial direction are approximately 1750 MPa for the core wire, 1370 MPa for the inner wire, and 1240 MPa for the outer wire. This tendency is similar to that seen in the three-point bending test. Finally, we estimate the wire fatigue life using FE simulation, and the estimated fatigue life is roughly consistent with the experimental result.

This study proposes a mechanical tire model with deduced friction coefficient based on multiscale friction theory. In the proposed model, the contact shape and contact pressure distribution are calculated based on the elliptical contact tire model. In the calculation of longitudinal stress in the adhesion region, not only the longitudinal deformation in length direction owing to the slip ratio, but also the nonlinear deformation in width direction owing to the tread radius are considered. The coefficient of friction in the sliding region is deduced from the viscoelasticity of tread rubber by multiscale friction theory, with contributions from adhesion and hysteresis friction. The validity of theoretical calculation of coefficient of friction was verified by linear friction tests of a rubber piece conducted under two conditions: a dry road surface and a wet road surface with a water film mixed with detergent. It was confirmed that, with appropriate parameter settings, the longitudinal stress distribution in the tire contact plane calculated by the proposed method can reproduce the experimental results by inner drum tire tester better than the classical brush model. The proposed method can be applied to rubber compound design to achieve the desired braking and driving characteristics of tires because it analytically links the longitudinal forces of tire to the viscoelasticity of tread rubber.

Auditory cues can draw individuals’ spatial attention to visual targets and it enables individuals to find visual targets quickly. Some previous studies suggested that auditory cues should be in approximately the same functional field with visual targets (i.e., both events are presented within near field) to obtain quick responses even if in real situations such as driving. However, quantitative angular differences between auditory cues and visual targets are little investigated. This present study aimed to explore the angular differences that can elicit similar responses with auditory cues and visual targets presented from similar directions under workload conditions. Twenty-two participants were asked to perform visual search and tracking tasks simultaneously. The visual targets were at ±20°, ±40°, and ±60° in azimuth as 0° of frontal view with distance of 1.0 m from participants. The auditory cues were presented simultaneously with visual targets from 0°, ±20°, ±40°, and ±60°. The results of the response time analysis using a fitting approach revealed that the auditory cues within 40° from the visual targets could elicit similar responses similar with those when the auditory cues and visual targets were presented from the same direction even if the participants were deprived of their attentional resources by other tasks. When the angular difference between auditory cues and visual targets were larger than 60°, the participants’ spatial attention was drawn to directions different from visual targets. It elicited a delay in finding visual targets because the participants should reallocate their spatial attention to visual targets. These results have meaningful implications for audio-visual user interface designs.