The present study is conducted to reveal the plastic deformation behaviors of a Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242) alloy sheet with α − β lamellar structure under cyclic tension – compression deformation by using a commercial finite element analysis with homogenization theory and crystal plasticity theory. The geometrically necessary and statistically stored dislocations were considered in the calculation to evaluate the work-hardening behaviors. The results suggest that the mechanical behavior of a Ti-6242 alloy sheet is strongly affected by the activation of slip systems that depend on the relationship of the initial orientation of each phase. Slip transmission had an obvious influence on the stress state around the grain boundary and on the activities of the mezzo- and macroscopic work-hardening behavior of the nominal stress – strain curve with the Bauschinger effect.

The introducing an expensive 3D attitude sensor to a tiny soft actuator with limited bending directions is over-spec and impractical. This paper presents the development of simple and inexpensive attitude measuring sensor for Tetrahedral-shaped Soft Actuator (TSA for short) using three Extension type Flexible Pneumatic Actuators (EFPA for short). The novel sensor consists of a Hall sensor and a ring-shaped magnet. The simple control system that can decrease number of valves is also proposed and tested. As a result, the attitude control of TSA toward six bending and longitudinal directions can be realized. In this paper, the construction and operating principle of the proposed sensor, applications to a posture control of TSA, a simplification of the system and experimental results are described.

In this study, we present a method for determining parameters that are essential for evaluating the health of layered structures. This method uses modal parameters to identify characteristic parameters that can accurately reproduce the measured modal damping ratio. Specifically, the proposed method uses natural frequencies, natural vibration modes, and modal damping ratios identified via an experimental modal analysis to identify characteristic parameters of stiffness and damping matrices whose characteristic matrix shapes are assumed in advance. This study aims to obtain a good representation of the damping characteristics of the system of interest and a good match between the reconstructed and original frequency response functions (FRFs). In the field of architecture, mass is often considered to be known. Hence, this study treats the mass matrix as known. This study takes a three-layer structure as an example, proposes an identification method, and verifies the validity and applicability of the proposed method via numerical simulations and experiments. The results show that it is necessary to adopt a damping model that can reproduce the actual modal damping ratios well and that both damping models employed in the numerical simulations can reproduce the modal damping ratios well. Next, the applicability of the proposed method is verified using experimental data. In practice, it is difficult to completely reproduce measured modal damping ratios. However, the results of this study show that damping characteristics that closely reproduce the measured modal damping ratios can be obtained.

In analyses of multibody systems, a numerical treatment of finite rotation is of key importance due to its mathematical complexity and numerical difficulties. Methods describing the finite rotation are naturally classified into vectorial and non-vectorial parameterizations. In particular, this study addresses a method incorporating a discretization with respected to time into the vectorial parameterizations. It introduces an approximation form for the rotation kinematic compatibility equation which expresses a relation between the angular velocities and the time derivatives of the rotation parameters. The model used herein is based on the fact that the resulting equations are eventually solved by numerical integration techniques. The resulting set of equations of motion for the rotation can be expressed in terms of the incremental angular velocity only. On the other hand, this study employs a scaling method based on a preconditioning technique, since an iteration matrix in the Newton-Raphson method includes higher order terms for the time step size. This remedy is also effective in order to avoid severe ill-condition in numerical integrations for constrained systems with configuration level constraints. In addition, the present models are enhanced by incorporating with the Euler parameters which are often used as singularity free expression for the finite rotation. Then, this study applies the present expressions for the finite rotation to numerical integration methods based on the energy-momentum preserving scheme and the generalized-α scheme. The present numerical models are verified through comparisons with the conventional models based on the standard Newton-Euler equations with the Euler angles in a typical benchmark problem for a simple multibody system. Then, we discuss its performance as the numerical models, such as convergency and computation time.

This study introduces a primary diagnosis method for multi-layered structures, leveraging response measurements from an additional vibratory system (AVS) installed on each floor. The goal of the proposed method is to identify the location and severity of abnormalities. Drawing from research in the architectural field, a reduction in the stiffness (spring constant) of building walls and columns is treated as an abnormality. The concept behind the proposed method is as follows. An AVS with known characteristics is attached to each floor. When a structure is subjected to base excitation due to slight ground vibration or road traffic, the frequency response function (FRF) of the response of the AVS to the base excitation is measured. Then, the method is used to perform a diagnosis starting from the bottom layer. At this time, abnormalities are diagnosed based on the mass of the multi-layer structure to be diagnosed and the characteristics of the AVS. A key feature of the proposed method is that the diagnosis is not affected by the damping magnitude of the target structure. The method was explained using a three-layered structure as an example, and its validity and applicability were verified through numerical simulations and experiments. Numerical simulations using noise-free FRFs demonstrated that the spring constant was identified with high accuracy under all four abnormal conditions with different levels of abnormality. Experimental validation using FRFs containing actual measurement noise also confirmed that the spring constant was identified well.

This study delves into the effects of the contact configurations on the nonlinear dynamics of rotor-stator contact systems through analytical investigation. In rotating machinery, the occurrence of harmful vibrations known as rubbing has been reported when the rotor and stator come into contact at specific rotational speeds. To prevent this phenomenon, the characteristics must be understood. This study focuses on the contact configurations between the rotor and stator, emphasizing the stator thickness. Therefore, a contact model that considers the effects of these contact configurations has been developed. The contact detection between the rotor and stator is conducted analytically by considering their geometric shapes and orientations. The influence of contact from the stator to the rotor is represented by an external force, calculated using the Kelvin-Voigt model, and an external moment, determined by the working point of the external force along the axial direction. The analysis is centered on an overhung rotor, which is modeled using the finite element method. Through bifurcation analysis, the main behaviors of the rotor-stator contact system are observed by utilizing the proposed contact model, demonstrating the validity of the contact model. The bifurcation diagram reveals that the band in which partial contact motion occurs tends to shift toward higher rotational speeds as the stator thickness increases. This shift is attributed to the stiffening effect caused by the substantial reduction in clearance and the impact of the external moment resulting from consideration of the stator thickness.

This paper presents a numerical solution for the shape design problem in unsteady fluid-structure-interaction (FSI) fields with viscous flow. The FSI analysis uses a strongly coupled approach based on the Arbitrary Lagrange-Eulerian (ALE) method. The shape design problem is formulated as a shape optimization aimed at controlling displacement distribution within a sub-domain of the structural domain. This problem is treated as an inverse problem, where the objective is to minimize the squared error integral between actual and target structural displacement distributions in the sub-domain. The shape gradient for this design problem is theoretically derived using the adjoint variable method and the shape derivative formula. Shape updates are performed using the conventional H¹ gradient method, along with a newly proposed iterative H¹ gradient method, both of which are approaches to solving the shape optimization problem. A numerical analysis program for this shape design problem was developed using FreeFEM. The validity of the proposed method was confirmed through 2D numerical analysis results.

Ground reaction force (GRF) analysis is critical to evaluate gait and running performances. However, installing force plates on the ground surface is costly, and their transportation is challenging owing to weight constraints and restricted measurement areas. This study proposes the method by Extended Kalman filter (EKF) to estimate the three-axis force components in the GRF, utilizing vertical force data from insole sensors, angular velocity, and acceleration data from inertial measurement units (IMUs). Shear forces were calculated using the acceleration in global coordinates, with the equivalent mass calculated by the vertical force and acceleration. The force components were then compensated for sensitivity and interference using a matrix. Moreover, the method was extended to include the center of pressure and unit position vector. The experimental protocol comprised two phases: calibration and measurement, conducted on force plates installed on the ground surface. The error compensation for force components was based on actual gait motion data and the results were compared with the force plates' outputs. The findings confirmed the effectiveness of this method. This method will be expanded to include motion measurements during long-distance walking and outdoor environments.