A data-driven identification (DDI) method is developed to evaluate material properties and stress distribution from full-field displacement distributions measured by digital image correlation. It is not possible to obtain stresses directly from strains without assuming constitutive laws, which are often empirical and contain uncertainties. In contrast, the DDI approach enables the computation of reasonable stresses by employing uncertainty-free displacement-strain relations, equilibrium equations, and a distance minimization function. The proposed method is applied to displacement fields of an elastoplastic material obtained through digital image correlation to identify material properties and stress distributions. Results demonstrate that the equivalent stress-strain relationship closely matches the reference value and the appropriate stress distributions are obtained, thereby validating the plausibility of the proposed method.

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An integrated accelerated testing method (Integrated ATM) has been proposed by the authors as a method for evaluating the strength and durability of CFRP and its structures. The strength scatter in the Integrated ATM formulation is expressed by a Weibull distribution, and its shape parameter is independent of the type of load (static, creep, or fatigue) and the environment (time or temperature). Christensen's viscoelastic crack kinetics law, the scientific basis for the Integrated ATM formulation, covers static and creep strength but not fatigue strength. In this study, we used resin-impregnated CFRP strands as unidirectional CFRP and performed numerous fatigue tests at various stress levels to compare the scatter in fatigue strength with the scatter in static strength. The Weibull distributions for both strengths were found to be nearly identical, demonstrating experimentally that the Integrated ATM formulation can be extended to the fatigue strength of unidirectional CFRP. Furthermore, we clarified the characteristics of the scatter in the S-N curve, which shows the relationship between fatigue strength and number of cycles to failure for unidirectional CFRP.

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This study aims to investigate the high-speed impact response, specifically the delamination behavior, of CFRP laminates utilized extensively in aerospace applications. The evaluation of Compression After Impact (CAI) strength, which defines the structural design limit for composite structures, typically relies on conventional low-velocity impact tests (~10 m/s). However, actual high-speed events like bird strikes involve velocities exceeding 250 m/s. We employed a detonation-driven high-speed gas gun to conduct impact tests on CFRP laminates while maintaining a constant kinetic energy of approximately 10 J. By utilizing four different projectile materials (PP, POM, Al, SUS), we achieved a broad velocity range from ~1100 m/s (PP) to ~390 m/s (SUS). Dynamic Mechanical Analysis (DMA) confirmed the viscoelasticity of CFRP, suggesting modulus values around 28.5 GPa across the tested high-speed range. Contrary to expectations based solely on CFRP viscoelasticity, soft X-ray observation of internal damage revealed that the lowest velocity (highest density) projectile, SUS, caused the largest delamination area per unit energy, while high-velocity PP and POM projectiles caused the smallest damage. This phenomenon is primarily attributed to the significant proportion of kinetic energy consumed by the internal energy conversion (melting and deformation) of the low-density polymer projectiles (PP, POM) upon high-speed impact. These findings highlight that the projectile's physical properties critically influence energy transmission and damage assessment in the high-speed impact regime.

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The aim of this paper is to investigate the effect of the hydrolytic degradability of the modification molecules on the initial tensile strength and its hydrolytic degradation of the hybrid interface-controlled HAp/PLA composites. Here, pectin, sodium alginate, and mucin were used as the acid surface modification molecules, and chitosan, arginine (Tokyo Chemical Industry Co., Ltd.), and lysine were used as the basic surface modification molecules, under consideration with the biological affinity. In addition, o-nitrobenzyl alcohol was selected as the photodissociable protecting groups to avoid the chemical reaction between the acid and basic modification molecules. First, the FT-IR measurements for the HAp particles revealed that the surface modification of the HAp particles was successfully achieved. Then, the tensile tests were carried out after the immersion into the pseudo biological environment, for the prepared hybrid interface-controlled HAp/PLA composites. As a result, it can be suggested that the modification molecules possessing the higher water-soluble and higher hydrolytic degradability could achieve both high initial mechanical property and speedy hydrolytic degradability of the hybrid interface-controlled HAp/PLA composites.

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