For this paper, the impact behaviors and the damage state of plain-woven CFRP reinforced by spread tow due to falling weight were evaluated. Stress-Strain responses of the CFRP using spread tows were investigated under drop-weight impact loading at room temperature. Three leveled impact energy was applied to the surface of the specimen in the drop-weight test. The peak load and absorbed energy were then compared with those of a conventional one and the experimental results showed that the peak load and absorbed energy of the developed CFRP were higher. A large amount of energy was absorbed due to the propagation of macro cracks and delaminations near the counter surface in the developed CFRP. When reinforced by spread tow its structure absorbs a large amount of energy after the initial stage of impact damage. The SAI (static strength after impact) and the FAI (fatigue life after impact) were also examined and the tensile test results showed that the static strength retention of the developed CFRP was higher than those of a conventional one. The developed CFRP also has long fatigue life under the tension-tension cyclic load after the impact. It was found that it maintained superior mechanical properties compared to the original, even after the material was damaged due to impact, because critical propagation of the debonding was prevented around the warp of thin cloth. This paper concludes that reinforcing with spread tow is effective for improving the mechanical properties of plain-woven CFRP during and after impact loading.

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The ASME Boiler and Pressure Vessel Code (ASME BPVC) Section III, Division 5, Subsection HB, Subpart B provided only one design fatigue curve for Grade 91 steel (Gr.91) at 540 °C (or 1000 °F) in 2019 and earlier versions. To overcome this disadvantage, The ASME Section III Working Group on Creep-Fatigue and Negligible Creep (WG-CFNC) had taken an action to incorporate the temperature-dependent design fatigue curves for Gr. 91 developed by Japan Society of Mechanical Engineers (JSME) into ASME BPVC Section III Division 5. As a result, the temperature dependent design fatigue curves are provided in the 2021 edition of the ASME BPVC. To clear the features of the best-fit fatigue curve equation developed by the JSME, 305 data stored in the database were analyzed. Details of the database and relationship between the best-fit fatigue curve equation and the data including the statistic values and the values of 95% and 99% lower confidence bound calculated by failure probability assessment were clarified through analysis. In addition to the best-fit fatigue curve equation, an equation for dynamic stress-strain response showing the behavior of Gr.91 steel under cyclic loading of is also provided based on the same database. Moreover, some additional available data of fatigue and creep-fatigue tests obtained in Japan are also provided for considering the creep-fatigue damage evaluation under elevated temperature condition.

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