In artificial leather, which is used in sports as a fiber-reinforced material, the distribution of the fiber family in the tangential plane is more dispersed than that perpendicular to the tangential plane. According to previous studies, its mechanical response is different in the two axisymmetric directions with respect to the main direction of the fiber family. This non-symmetric fiber distribution can significantly affect the mechanical properties of artificial leather, but the currently applied fiber dispersion models cannot accurately describe this anisotropic property. Therefore, we propose a novel anisotropic hyperelasticity constitutive model which describes the mechanical behavior of fiber-reinforced material by using a generalized structure tensor in the form of separated in-plane and out-of-plane fiber distribution and by applying the sine-skewed von Mises distribution function as the in-plane fiber distribution function. Our approach consists of developing a construction form of a generalized structure tensor with non-symmetric components, introducing it into the strain energy function and providing explicit expressions for the corresponding second Piola-Kirchhoff stress tensor and the related elasticity tensor. As specific examples, the distribution and material parameters of the model were identified by fitting fiber distribution data and tensile data, respectively, of artificial leather to the model’s theoretical results. The mechanical behavior of artificial leather specimens under uniaxial extension at various tensile angles was simulated through finite element computations. The differences in mechanical response in two axisymmetric directions about the main direction of the fiber family were captured, breaking through the limitations of the currently applied fiber dispersion models. Moreover, inhomogeneous stress distribution under maximum stretch and inhomogeneous deformation were observed. This constitutive model provides a more accurate method for the description of the mechanical behavior of fiber-reinforced material and provides a theoretical reference for the simulation of the three-dimensional deformation of artificial leather.

Our research group investigated the fundamental equations for simulating the propagation behavior of heat waves, which has been a major issue with the classical Fourier law. We focused on the dual-phase lag (DPL) model introduced by Tzou, and derived a partial differential equation that coupled it with the dynamic thermoelastic equation. Therefore, an exact solution for the one dimensional (1D) bar problem was obtained using the Laplace transform technique. However, it is difficult to obtain an exact solution for more general problems in 3D space. In this study, we analyzed the propagation of heat and stress waves in a 1D bar using discretized equations derived from the finite difference time domain (FDTD) method. We also discussed stability conditions to ensure the accuracy of the FDTD results. The results are as follows: We simulated the propagation of heat and stress waves over time in a 1D bar model and discovered that the wave propagation behavior and its waveform differ significantly based on the combination of relaxation times and coupling terms. Subsequently, we focused on the peak value of the stress wave and investigated the attenuation of the peak value associated with propagation. It was determined that the attenuation increased as the coupling parameter connected between thermo-elastic and heat transfer equations and the two relaxation times in the DPL model increased.

Yttria stabilized tetragonal zirconia polycrystals (Y-TZP) are attractive bone grafting materials for dental and orthopedic applications because of their high strength, high fracture toughness, and excellent biocompatibility. The bioinertness of zirconia makes it suitable for tribological applications such as bone heads. On the other hand, using zirconia as a bone grafting material requires direct bonding ability to living bone. Therefore, attention has been focused on developing surface treatment techniques to directly provide bioactivity to the zirconia surface. Chemical treatment using phosphoric acid has been reported to show excellent apatite-forming ability using simulated body fluid in an in vitro model. Also, it is known that zirconia reacts with water or water vapor and undergoes low-temperature degradation (LTD) accompanied by a phase transformation from tetragonal to monoclinic. However, there is still insufficient research on the degradation behavior of zirconia during phosphoric acid treatment and its effect on bioactivity. This study investigated the osteogenic evaluation employing MC3T3-E1 cells and the LTD behavior of 3Y-TZP after treatment with a phosphoric acid solution. The results revealed the conditions that improve osteogenesis after phosphoric acid treatment. The conditions were, first, excellent cell proliferation and second, a medium contact angle of 40-60°. Also, the decrease in strength with phosphoric acid treatment was limited. Therefore, the possibility of improving osteogenesis was shown by optimizing the phosphoric acid treatment conditions.

This study addresses the challenge of reducing variability in permeability measurements for the vacuum-assisted resin transfer molding (VaRTM) process, which is essential for accurately evaluating resin impregnation behavior. Initial evaluations were conducted at two different institutions, comparing permeability in both the 0° and 90° fiber directions of carbon fiber plain-woven fabric to identify key challenges contributing to variability. The comparison revealed significant differences in permeability results due to inconsistencies in experimental settings and measurement methods. Based on these findings, improvements were proposed, including temperature control, adjustment of resin impregnation levels, and standardization of VaRTM settings and measurement methods. These improvements were then applied to the 0° direction under the minimum nesting condition. Results showed that the improved methodology significantly reduced variability, with differences between bottom and area measurements being less than 10%, and an average variability of 17%. This approach effectively minimizes variability in permeability measurements, enhancing the reliability of the VaRTM process.

The objective of this study is to numerically evaluate the cyclic softening behavior and creep-fatigue damage of P91 steel. To achieve this, a damage-coupled inelastic constitutive equation is formulated by coupling the Chaboche-type viscoplastic constitutive equation and the damage evolution equation, and aging stresses are considered with back stresses to describe the cyclic softening behavior of P91. In accordance with the damage mechanics concept, the damage parameter D is incorporated in the inelastic constitutive equation to represent the creep-fatigue damage progress. The discretization equations of the damage-coupled inelastic constitutive equation are derived according to the backward Eulerian method which was proposed by Kulling and Wippler (2006). A creep-fatigue analysis is performed on the one-element model using the developed finite element (FE) analysis software. It was confirmed that the hysteresis loops, stress relaxation curves and creep-fatigue life obtained from the FE analysis are in good agreement with the test results.

The crack growth rate of stress corrosion cracking is influenced by residual stress; therefore, if the three-dimensional residual stress in welded pipes can be accurately evaluated, their remaining service life may be predicted. While welding simulations offer a means of assessing residual stress, but weld joining techniques are known to yield significant individual variations even under similar welding conditions. Consequently, a residual stress evaluation grounded in actual measurement data is essential. A non-destructive method for estimating three-dimensional residual stress distribution in situ employs X-ray Diffraction alongside eigenstrain theory. In this approach, the eigenstrain of the entire structure is derived through inverse analysis of measured surface elastic strain values, with three-dimensional residual stresses subsequently calculated by inputting these estimated eigenstrains into a finite element (FE) model. However, to estimate three-dimensional eigenstrains from two-dimensional surface data, it is necessary to appropriately reduce the number of unknown variables. Function approximation serves as an effective method for this reduction, though its optimization is required, as the accuracy of the estimation depends on the function's shape. Previous studies have typically relied on empirical methods to determine the shape of this function. This study first elucidates, through numerical analysis, the challenges associated with empirically defining the approximate function shape of eigenstrain. Subsequently, a novel method is proposed, approximating the eigenstrain by employing a superposition of Chebyshev polynomials and Gaussian functions and optimizing the function’s shape with relatively few parameters. The proposed method’s effectiveness is demonstrated via numerical analysis, aiming to establish an approach that eliminates reliance on empirical assumptions.

We propose a semi-circular composite rubber arch comprising two rubber materials with differing shear moduli as a novel unit cell structure for self-recovering, energy-dissipating metamaterials by adjusting the stiffness ratio and the boundary position between the materials that the arch achieves tunable stiffness distributions. Through a systematic finite element analysis, we identified four deformation modes: snapping, bending, and two distinct flattening modes. The snapping mode, characterized by load-displacement hysteresis, exhibited significant energy dissipation, while the flattening modes demonstrated stable, continuous deformation suitable for irreversible energy absorption. The programmable nature of energy dissipation was achieved over three orders of magnitude by modifying the stiffness distribution. Our results provide a foundation for designing composite arches with tailored mechanical properties. Arranging these unit cells in periodic configurations could serve as advanced mechanical metamaterials with enhanced energy absorption and application-specific deformation characteristics.

Admittance control is a widely used method for regulating interactions between humans and robots. The admittance controller comprises multiple parameters that can be adjusted to improve the overall system performance. In this study, a novel human-centered approach is presented for the adjustment of admittance parameters in human-robot collaboration. First, a head-mounted display with mixed reality features is integrated into the human-robot collaboration system, which enables the user to interactively adjust the mixed reality components using hand gestures in a real-world space. The admittance parameters are then spatially adjusted based on the configured mixed-reality components, which significantly enhances the task configuration and execution efficiency of the human-robot collaboration system. Subsequently, the admittance parameters are fine-tuned using a human preference-based approach. Specifically, preferential Bayesian optimization is used to optimize parameters based on user preferences without directly evaluating or defining the objective function. Pairwise comparisons of parameter sets by humans are used to build a preference model, which helps efficiently identify the optimal parameter set. The proposed approach is user-friendly and accessible to novice users and requires minimal programming knowledge. Experimental validations and demonstrations were conducted using a 7-degree-of-freedom robot arm, and the results showed the effectiveness of the proposed method in enhancing human-robot collaboration.

During the acquisition of worm gear profile images, the imagery is frequently compromised by Gaussian noise, variations in illumination intensity, and surface contaminants, which critically impair the subsequent extraction of worm gear profile details. To address these challenges, this study introduces an enhanced method for designing a worm gear tooth profile edge-preserving filter aimed at image detail enhancement. To amplify image details, a two-stage guided filtering algorithm is employed, utilizing the original image and the post-threshold segmented image as guide images for separate filtering processes, followed by a fusion step. The fused image undergoes additional edge enhancement through sharpening and contrast improvement via the adjustment of gray-level distribution. Experimental outcomes indicate that, compared to conventional edge-preserving filtering algorithms, the proposed method achieves a 22.45% increase in peak signal-to-noise ratio and a 20.1% improvement in image contrast. The denoised worm gear tooth profile edge image exhibits enhanced feature details while mitigating the impact of surface stains and uneven lighting on edge detection, resulting in clearer and more reliable detection outcomes.

This study investigated the unstable simultaneous whirl of two cylinders in a concentric double rotating cylinder system, with both co- and counter-rotation. The axes of both cylinders were radially elastically supported independently of each other. A fixed (no rotation and no whirl) cylinder was installed outside the outer cylinder concentrically. The three cylinders were assumed to stay parallel to each other, making the gaps between them axially uniform. A theory to analyze the complex eigenvalues of the coupled system of gap flows and motions of cylinders was formulated. An experiment was carried out, in which structural conditions were set to be the same as possible for the inner and outer cylinders. A basic unstable mode was observed in which both cylinders whirled in the same direction and in opposite phases. In counter-rotation, the whirl direction transitioned from the rotation direction of the outer cylinder to that of the inner cylinder with increasing rotational speed of the inner cylinder. The transitions were brought about by replacement of the eigenmode with the minimum damping ratio. With the transition, the frequency changed discontinuously and the decrease in the damping ratio with increasing rotation speed became steep. Under simultaneous two-cylinder whirling, the stable area at combinations of the inner and outer cylinder rotation speeds became narrower than that of only the outer cylinder whirling.

In this study, we present a novel method for determining key parameters essential for evaluating the health of layered structures. Our approach involves pre-assuming the shape of the characteristic matrix of the objects and determining the values of its elements from the frequency response function (FRF). By breaking down the FRF into real and imaginary components, which arise owing to damping effects, all parameters of the equations of motion can be treated as real numbers. We used a three-layered structure and conducted numerical simulations to validate the effectiveness of our proposed method. The results demonstrated the importance of using a damping model that accurately reflects the true damping characteristics, with general viscous damping proving to be the most appropriate assumption for parameter identification. Furthermore, we validated the applicability of our proposed method using experimental data measured from physical equipment. Our findings revealed that using experimental data with minimal measurement noise across a broad frequency spectrum resulted in consistent identification values and reasonable outcomes. However, there may be cases where the resonant peak frequency in the experimental FRF and the reconstructed FRF do not match perfectly. In such scenarios, we recommend modifying the characteristic parameters based on sensitivity analysis to achieve more accurate results.

This study proposed a vibration analysis employing the substructure elimination and binding method to evaluate the bending vibration of beams. Modal analysis is commonly used for vibration analysis. In modal analysis, it is imperative to obtain highly precise results with fewer degrees of freedom. Thus, to reduce the required degrees of freedom, we proposed the substructure change and elimination methods. Because these methods obtain the desired structure by changing or eliminating certain regions of the original structure, these methods necessitate only a superposition of the eigenmodes of the original structure. Despite no major problems in the substructure elimination method, the precision of the substructure change method decreased owing to the non-smoothness of the shear force etc. at the interface. In addition, a recent study revealed the possibility of analyzing the coupled vibration of a beam using the substructure elimination method with fewer degrees of freedom. In this method, both ends of a beam are eliminated and the coupling with the other structures at the new boundaries were formulated. Owing to the eigenfunctions exhibiting phase variations at the new boundaries, arbitrary amplitudes and phases can be expressed with fewer degrees of freedom at the new boundaries. However, beams are often coupled to other structures other than that at their ends. Despite the long-standing establishment of the analysis method for this case, the precision of this conventional method decreases because of the discontinuity or non-smoothness of the shear force etc., similar to the substructure change method. Thus, this study proposed a method to set a virtual elimination region at the interface and bind the two ends of the virtual elimination region. The virtual elimination region smoothly connected the discontinuities and non-smooth points. Further, we proposed an analytical model for this method, and an equation of motion for a minute fraction was formulated. In addition, modal analysis was applied to the derived equation of motion. Furthermore, simulations revealed that the length of the virtual elimination region must be set to three to four times the wavelength of the highest eigenmode of the original beam. Moreover, to investigate the advantage of precision, the simulation results obtained using the proposed method were compared with those obtained without installing the virtual elimination regions based on the exact solutions.

A simplified probabilistic model is newly developed to give equivalent description for a strengthening method using two-layer CFRP plates bonded to base components by adhesion. First, a system of simultaneous differential equations for the shear and vertical stresses acting on the adhesives are derived. In order to reflect the variation of debonding, it is extended to a system of random differential equations by considering the spatially random variations of the adhesive thickness. Then, in order to reduce the degree of freedom of the system for two-layer CFRP plates, a one-layer equivalent model is newly developed to give almost equivalent result on the probabilistic properties associated with debonding of adhesives in two-layer model, where equivalency is achieved from two points of view; one is a mechanical condition and the other is a fine adjustment on probabilistic factors. Finally, numerical examples are shown to validate the proposed equivalent model, in which Monte Carlo method is applied to estimate the probability of debonding. The results indicate that the proposed model can give appropriate estimation for the probability of debonding, only with reasonably reduced computing efforts.

The analysis of joint angles is used to assess gait and running performance. Inertial measurement units (IMUs) are compact, cost-effective devices that can be attached to the body to perform simple motion analysis. However, the use of IMUs necessitates the resolution of two key issues: compensating for drift and mounting errors. The proposed method employs an extended Kalman filter (EKF) to compensate for drift error and position data from a camera to compensate for mounting error. Joint angles are calculated using the data compensated by the EKF. The proposed method calculates two-dimensional joint angles and is suitable for the performance analysis of gait and running. A measurement experiment was conducted with a runner to validate the proposed method. The IMUs were attached at arbitrary positions on body segments and misalignment with body axis, and position markers were attached for the camera-based joint angle calculation. The experimental protocol comprised four phases: static, acceleration (including calibration period), measurement, and deceleration. The compensation of IMUs mounting error was performed using actual motion data during the calibration period measured by the camera. The running velocity in the measurement phase was 25 km/h. The experimental results demonstrated that the drift and mounting errors due to the IMU measurements were corrected. The accuracy of joint angle measurements was demonstrated by comparing the joint angle results obtained with the method using only a camera, showing the effectiveness of proposed method. Although the proposed method uses both IMUs and a camera, the data from the camera are only required for the calibration period, which is a short part of the experiment. Therefore, the method can be used to improve the accuracy of simple IMU measurements and is expected to be expanded to outdoor motion measurements.

A candidate control method for next-generation standing-type omnidirectional personal mobility vehicles involves the user shifting their center of pressure (COP) to steer the vehicle. However, the characteristics of human COP shifts in the forward-backward, left-right, and oblique directions for mobile vehicle applications are not well understood. In this study, we investigated the accuracy of the COP shift direction and the effects of neck and hip rotation on the COP shift in the forward-backward, left-right, and oblique directions. The results show that the foot center of pressure direction almost exactly matched the target COP direction when the target COP shift was in the forward and left-right directions regardless of the rotation of the neck and hips. However, when the target COP direction was the oblique forward direction, the measured foot center of pressure direction was shifted to the left or right. With rotation of the neck and hips, when the target COP direction was backward, there was a difference between the target direction and the actual direction of foot COP movement. This difference was found to depend on the direction of neck and hip rotation (left or right). In addition, an experiment was conducted in which the user manipulated an object that could move in any direction in a virtual space by moving their COP. The results show that when the target COP direction was the oblique forward or backward direction, the object movement direction tended to shift left or right from the target direction at the start of movement, which is related to the accuracy of the COP movement.