Toshiya Nakamura

This study investigated the characteristics of the amorphous material fatigue model proposed by Kurotani et al. concerning the rate/time-dependent material instability and the fatigue damage initiation process. Stress relaxation simulations showed that, in this model, two mechanisms compete, one of which increases the density fluctuations by mechanical deformation and the other decreases them over time. In fatigue simulations, the density fluctuation gradually becomes nonuniform, resulting in damage generation. During this process, the density fluctuations form a band-like pattern in the principal-stress direction, and the equivalent strain forms a pattern along the shear direction. We demonstrated that the model could provide mesoscopic insights into the mechanical properties of amorphous materials.

The interfacial stress between fibers and matrix plays an important role in the durability and damage initiation of carbon fiber reinforced composites. In this study, thermoelastic analysis was performed on a plate containing randomly distributed multiple fibers. Complex stress functions were employed with a semi-numerical method to ensure displacement continuity along the fiber/matrix interface as a boundary condition. The statistical investigation reveals that the stress concentration due to the presence of multiple fibers increases as the fiber density increases, though its deviation decreases. A numerical case study was conducted to discuss the micromechanics of the inherent scatter of material strength. The stress-strength model with Monte-Carlo simulation demonstrated the fracture probability calculation. The uncertainty obtained is partially attributed to the micromechanical stress variation around the fibers.

The objective of this study is to develop a novel aircraft design approach using biomimetics as an alternative to traditional airframes. This approach is primarily inspired by the dragonfly wing, which possesses reinforcement structures composed of cross veins and longitudinal veins. These structures are assumed to regulate deformation and enhance stiffness, respectively. The cross veins were replicated using weighted centroidal Voronoi tessellation (WCVT) based on the out-of-plane displacement of the skin. In contrast, the longitudinal veins were replicated by extracting a centerline from the topology optimization (TO) results on the skin, achieved through image analysis techniques such as binarization and skeletonization. The longitudinal layout effectively reduces compliance by distributing internal loads, utilizing only essential reinforcements on the skin without increasing its mass. The WCVT layout significantly enhances the buckling resistance of the reinforced skin. As a result, the skin reinforced using both cross–longitudinal layouts from TO and WCVT exhibited a buckling load 2.7 times greater while maintaining a lower mass compared to conventional layouts.