When exposed to neutrons from cosmic rays, atmospheric nitrogen reacts to produce the radioactive isotope ¹⁴C. Radiocarbon dating of trees is based on the fact that ¹⁴C in wood originates from the atmosphere. However, several studies have investigated the possibility of in-situ ¹⁴C production in wood exposed to cosmic radiation at high altitudes. In this study, a neutron irradiation experiment was conducted on Japanese cedar (Cryptomeria japonica) specimens and the increase in ¹⁴C concentration was measured. In practice, the increase in ¹⁴C could not be measured, as has been reported in previous studies. We also conducted computer simulations using PHITS, assuming the experimental conditions and a standing tree at high altitude. Neither simulation confirmed a sufficient increase in ¹⁴C in the wood. In the simulations of a standing tree, an increase in ¹⁴C equivalent to 0.1 % of the natural ¹⁴C level required approximately 15,000 years of exposure. The increase in ¹⁴C was too small to confirm in-situ production in the tree, even if a sudden neutron increase event occurred. This study reaffirmed that the in-situ production of ¹⁴C in wood was extremely limited based on nuclear reaction simulations and cosmic ray fluxes prediction model, and empirically confirmed the validity of conventional radiocarbon dating.

Self-healing carbon fiber reinforced polymers (CFRPs) containing microencapsulated healing agents have been proposed to improve reliability and environmental issues. However, microcapsules (MCs) would degrade the mechanical properties of self-healing CFRPs due to their low strength and easy aggregation within the complex CFRP structure. Although we have proposed a spread carbon fiber (SCF) reinforced polymer that can suppress the aggregation of MCs, it is difficult to completely control the MC dispersion state. In this study, we used a representative volume element (RVE) modeling approach to investigate the effects of MC dispersion state, volume fraction and diameter on the elastic properties and internal stresses of MC/SCF/EP laminates. A finite element analysis of RVE models with different microstructures was performed, and the elastic properties and stress distributions of the MC/SCF/EP laminates were predicted. To validate the RVE models, the finite element analysis of short-beam shear test for the MC/SCF/EP laminates was performed using the predicted elastic properties from the RVE models and compared with the experimental results. The results show that the elastic properties of the MC/SCF/EP laminates depend on the MC dispersion state and volume fraction. It was also found that the well dispersed MCs in the MC/SCF/EP laminates resulted in the reduction of stress concentration and supported the higher shear stress. In addition, the initial slopes of the analytical and experimental load-displacement curves in the short-beam shear test showed reasonably good agreement. Therefore, the RVE modeling approach in this study is effective for predicting the properties of the MC/SCF/EP laminates and can contribute to microstructural design of the laminates.

To ensure the safety and reliability of a structure, it is necessary to accurately grasp the magnitude and location of the load acting on it. In this study, we proposed a method to identify the load vector and its acting location using the cuckoo optimization method. In the proposed method, the rotation angle measured by a wireless gyro sensor was related with the load vector via a matrix equation. Then, the location where the load acts was estimated using the cuckoo optimization method, and the magnitude of the load was then estimated using a generalized inverse matrix. In order to verify the effectiveness of the load identification method proposed in this study, we attempted to identify the magnitude and location of the acting load for the problem of a beam with fixed ends on which a concentrated load acts, and the problem of a plate with supported ends on which a concentrated load acts. As a result, it was confirmed that the proposed method was able to estimate the magnitude and location of the acting load with high accuracy in both problems.

Thermal barrier coatings (TBCs) are key technologies for protecting and extending the lifespans of high-temperature components in gas turbines and jet engines. During deposition and subsequent exposure to elevated temperatures, TBCs develop residual stresses that significantly influence their durability, particularly under thermal cycling and in terms of delamination life. X-ray elastic constants are critical for evaluating these residual stresses using X-ray diffraction. Although thermal treatment is known to affect the material structure and mechanical properties of TBCs, its effect on X-ray elastic constants remains unclear. In this study, we investigated the influence of thermal treatment on the relationship between X-ray and mechanical elastic constants in TBCs, using bending of three-layered specimens. The X-ray elastic constants of both as-sprayed and thermally treated TBCs were measured and compared with their corresponding mechanical elastic constants. Inelastic behavior was also assessed by evaluating the X-ray secant constants over the elastic region. The as-sprayed TBCs exhibited X-ray elastic constants significantly higher than their mechanical elastic constants, which was attributed to deformation mechanisms involving secondary phases, specifically inter-splat slip deformation and microcrack opening. After thermal treatment, the X-ray elastic constants approached the mechanical elastic constants, indicating a reduction in the effect of secondary phase mechanisms. Additionally, the threshold stress for elasticity was found to be very low. Beyond this threshold, lattice strain remained constant due to continued inter-splat slip and microcrack opening. As a result, the X-ray secant constants over the elastic region were higher than the X-ray elastic constants.