Stiffened composite panels have been widely used in various structures, enhancing the significance of maintaining the structural integrity of joints between the patches and the baseplates. Ultrasonic guided waves are expected to be used for inspection of these panels because of their ability to monitor structural health and inspect inaccessible areas. However, guided waves propagating in anisotropic materials exhibit complex behavior compared to isotropic materials, and geometric and material discontinuities make the signals more complicated. To utilize guided waves to monitor the condition of the joints, we attempt to investigate the guided wave propagation behavior in composite stiffened panels. Mode conversion occurring between the general and stiffened areas is predicted by deriving phase velocity dispersion curves to compare the phase velocities of these areas, and by computing correlation coefficients of displacement profiles to estimate the matching of wave structures. Thereafter, for predicted modes, the amplitude ratio between signals before and after transmitting the stiffened area is estimated by the power flow in each area computed with the acoustic Poynting’s vector.

A novel multiscale simulation scheme for textile composites is proposed, which accurately predicts their mechanical properties. A key aspect of our method is the numerical construction of their representative volume elements by considering the fiber yarn deformations during weaving and molding of textile composites. We found that fiber yarn deformations during weaving and molding can be precisely computed using a novel method for modeling dry yarn mechanical behaviors with beam and solid elements. We validated our proposed method by comparing its mechanical property predictions with the experimental results obtained from tensile, compression, and bending tests of carbon fiber composites. The validation demonstrated that our method can accurately and robustly predict the mechanical properties of a composite by considering fiber yarn deformations during weaving and molding.

The open-hole compressive (OHC) strength is used as a design allowable for aircraft structure designs that use CFRP laminates. In many cases, fillers such as fasteners are inserted into the holed CFRP parts of actual structures. The filled-hole compressive (FHC) strength, which is higher than the OHC strength, has potential as a design allowable for lighter structural designs. However, the FHC strength depends on the gap (clearance) between the CFRP laminate filler and the hole walls, and the mechanisms that cause its value to change are still unclear. This is a significant issue in standardizing test methods and in estimating mechanical joint strengths. In this study, we observed the changes in the FHC strength with changes in the clearance and explored the mechanism causing the increased FHC strength. We confirmed that the FHC strength increased as the clearance decreased. At the same time, we also confirmed that the FHC strength increase was mitigated when the clearance fell below a certain level. We determined that the FHC strength was governed by the transmitted load, which changes with the amount of clearance and with the contact area fracture state of the CFRP laminates.

This paper presents the findings of an experimental investigation into the strength properties of joint adhesives employed in flame-applied surface treatment, a critical process in adhesive bonding techniques. Among the commercial surface treatment techniques, this study focuses on Itro treatment to analyze the silica deposition flame-applied surface treatment method. Dispersed conditions of silica particles on surfaces, tensile strength, and microscopic fractures are observed using focused ion beam and scanned probe microscopy for varying numbers of Itro treatment passes. Adhesive joint strength either improves or remains constant after 1 or 6 Itro treatment passes compared to non-Itro treatment. In contrast, strength decreases after 30 or 60 Itro treatment passes. During Itro treatment, silica particles form a silica layer with a cohesive fracture mode. The strength of the silica layer is estimated to be lower than the interface strength between the adherend and adhesive.