In this study, we investigated the impact of varying spoke geometries and the number of layers on tire stiffness and stress concentration in NPTs utilizing a linked zig-zag core structure. Through finite element analysis, our numerical simulations revealed that reducing the number of layers in the zig-zag structure leads to a decrease in the maximum von Mises stress. Additionally, the stress concentrations can be minimized by increasing the angle between the beams and the vertical axis. The proposed NPT model demonstrated a reduction in maximum von Mises stress and strain energy by approximately 51.8% and 26.7%, respectively, compared to previously proposed NPT designs.

This study proposes a 3D-printed carbon-fiber-reinforced metamaterial for wideband vibration attenuation. The proposed metamaterial incorporates periodic lever-type mechanisms. Compliant hinges were used to develop the monolithic lever-type mechanisms. A rigid link-torsion spring model was developed to obtain the dispersion curves of the metamaterial. The band gap of this simplified model was identified to estimate the frequency range within which vibration transmission is inhibited. Frequency response and modal analyses were performed using the finite element method. The effects of the continuous carbon fiber placement and compliant hinge shape on the vibration attenuation performance were numerically examined. The proposed lever-type metamaterial was fabricated using a fiber-composite 3D printer, and its vibration transmissibility was measured. A significant reduction in the vibration transmissibility was observed over a wide frequency range around the massindependent antiresonance frequency. The experimentally obtained transmissibility agreed with that obtained by finite element analysis.

The objective of this study was to propose a novel lightweight and affordable structural material that can withstand temperatures in the range of 500°C–1000°C. A processing technology for amorphous SiC fiber (Nicalon or Hi-Nicalon)/Si-CoSi₂ matrix composites with a fiber-matrix interface of film-boiling (FB)-derived carbon (FB-C) was developed. The mechanical properties of the composites were evaluated at room temperature (25°C). The average 4-point bending strength of the Hi-Nicalon/FB-C/Si-CoSi₂ composite was 511 MPa. Fiber pullout and bridging was clearly observed on the fracture surface of the composites. By contrast, the Nicalon/FB-C/Si-CoSi₂ composite exhibited brittle failure, with an average 4-point bending strength of 87 MPa and no fiber pullout was observed in it. The apparent shear strength at the fiber/FB-C interface was evaluated using a fiber bundle pushout test. The test results indicated that the interfacial shear strength of the Nicalon/FB-C interface was approximately 1.7 times higher than that of the Hi-Nicalon/FB-C interface, indicating the stronger adhesion of the former compared with the latter. Thus, the carbon layer formed using the FB method may not be a suitable interface for Nicalon fiber.