Satoru Yoneyama

Background: Evaluation of warpage and residual stress in silicon wafers is essential for semiconductor manufacturing. Conventional warpage measurement requires double-side surface profiling, increasing system complexity and cost. Objective: This study proposes methods to estimate warpage from single-side surface measurements of a horizontally supported wafer, where the measured profile includes both gravitational deflection and intrinsic warpage. Methods: Two approaches are developed to separate deflection from the measured profile. The first estimates deflection by averaging accumulated measurements, assuming wafer-to-wafer warpage randomness. The second exploits the approximate 60-degree symmetry of the deflection distribution to estimate deflection from a single measurement. Results: Compared with the reliable three-point-support inverting method, warpage is identified within approximately 10% using accumulated data and within about 20% using a single measurement. Residual stress is subsequently identified from the estimated warpage using a superposition-based inverse analysis with stress-gradient regularization. The regularization parameter is determined objectively using the Akaike and Bayesian information criteria. Numerical validation and application to measured data demonstrate that plausible residual stress distributions can be obtained from single-side measurements. Conclusions: The proposed method enables warpage and residual stress estimation without double-side inspection, offering simplified instrumentation and reduced cost for silicon wafer evaluation.

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities.

In this study, to discuss the influence of concussion risk from the long-term use of American football helmets on collegiate teams, accident cases during the game are replicated based on game videos by simulations using whole-body numerical models and helmeted finite element human head models. The concussion risks caused by collisions were estimated using the mechanical parameters inside the skull obtained from finite element analyses. In the analyses, the different material properties of helmets identified by free-fall experiments using headform impactor-embedded helmets were used to represent brand-new and long-term-use helmets. After analyzing the five cases, it was observed that wearing a new helmet instead of a long-term-use one resulted in a reduction in the risk of concussion by 1 to 44%. More energy is attenuated by the deformation of the liners of the brand-new helmet, so the energy transferred to the head is smaller than that when wearing the long-term-use helmet. Thus, the long-term use of the helmet reduces its ability to protect the head.