Laser Powder Bed Fusion (PBF-LB) is widely used to fabricate complex geometries. However, simple evaluation methods, such as monitoring the warpage of cantilever specimens, are required due to residual stresses generated during the process. In this study, cantilever specimens of Inconel 718 alloy were fabricated by PBF-LB to investigate the relationship between residual stress and warpage. Surface residual stresses were measured using X-ray diffraction. Finite element analysis (FEA) was used to estimate the initial residual stress from the measured warped shapes. The results showed no simple correlation between surface residual stress and maximum deflection. However, under the same volumetric energy density (VED), deflection and residual stress displayed a linear relationship. Further, the through-thickness residual stress distribution, modelled as a fifth-order polynomial, closely matched the experimentally measured deflection. The analysis suggested that the curvature in the stress profile depends on the heat input, characterized by VED. These findings show that cantilever-based warpage measurements can serve as a practical screening method for evaluating residual stress in LPBF parts.

This study aims to clarify the thermal piercing behavior of carbon fiber reinforced thermoplastics (CFRTP) using near-infrared heating. The objective of the proposed thermal piercing method is to suppress stress concentration and strength reduction around the hole compared with conventional mechanical drilling. The materials used for the experiments were carbon fiber reinforced polypropylene (CF/PP) and carbon fiber reinforced polyether ether ketone (CF/PEEK) laminates. Firstly, heating experiments of the laminates were conducted using near-infrared heating and high-frequency induction heating in order to investigate suitable heating methods for thermal piercing. A ring shaped near-infrared heater was used for infrared heating, and a pancake-shaped coil with 2 MHz high-frequency power source was used for induction heating. The results showed that near-infrared heating enabled uniform heating regardless of the stacking sequence of the laminates. Based on these results, thermal piercing machine consisting of near-infrared ring heater, puncture pin, and servo press unit capable of precisely controlling load and displacement was developed. Various experiments revealed the thermal piercing behavior of each laminate and the associated process issues. Furthermore, the damage behavior around the pierced area was evaluated by double-lap tensile shear tests. It was found that the maximum load and toughness of the thermally pierced specimens were improved compared with those of mechanically drilled specimens.

We propose a GaP/Si 4-terminal tandem solar cell. It is shown that its theoretical limit efficiency exceeds 40% under ideal conditions. The use of ZnS as a window layer for the top GaP cell is also proposed, and its suitability is shown from the perspective of band alignment. Furthermore, to resolve the lattice mismatch and adjust the conduction band offset at the interface between window layer and GaP, we also proposed using Zn(Cd,Mg)S, which is lattice-matched to GaP.