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The material properties of heat resistant materials are known to be affected by thermal aging as operating time is accumulated at power plants. In this study, the influence of thermal aging on yield strength, ductility and J-Resistance behavior for Mod.9Cr-1Mo (ASME Grade 91) steel which is a material widely adopted for Generation IV nuclear energy system has been investigated. Service exposed Gr.91 steel materials sampled from a piping system of an ultrasupercritical (USC) plant in Korea with accumulated operation time of 73,716 hours were used for material testing. The test results of the service exposed material were compared with those of the virgin Gr.91 steel. Those test data were compared with the material properties of ASME code and RCC-MRx code that are international elevated temperature design codes. Conservatism of the material properties in design code has been quantified based on the comparison of virgin and service exposed materials.

Carbon fiber reinforced plastics (CFRPs), a composite material, are generally vulnerable to compressive load and impact damage in a direction perpendicular to the surface of the material. In particular, during the operation of an aircraft, impact damages caused by bird collisions or falling tools reduce the strength of the aircraft structure. In this study, after impact damages were applied to CFRP specimens with various impact energies and impactor diameters, the compressive residual strength of the impact-damaged specimen was evaluated by performing a compression test. Furthermore, a prediction model for the compressive residual strength is proposed according to the variation in the impact energy by comparing the test results.

Carbon fiber reinforced plastic (CFRP) composites have high specific stiffness and high specific strength. Therefore, they are increasingly being use, instead of conventional metallic materials in the aviation and automobile industries, where there is a strong demand for lightweight materials. In aircraft, the fuselage is exposed to severe conditions of high temperatures and high humidity. Therefore, it is necessary to estimate the strength of CFRP composites under real conditions from the viewpoint of aircraft safety. In this study, CFRP specimens were immersed in distilled water at 75°C for a long time. Then, tensile tests were performed on these specimens, and the fracture characteristics of the fractured surfaces were analyzed using SEM. A fatigue test was performed on specimens immersed for 300 days with R=0.1, and it was confirmed that the fatigue life deteriorated in immersed specimens compared to specimens that were not immersed.