ＮＯＬリング引張試験法の検討

Abstract

The so-called NOL ring test has been usually used as a testing method to measure the longitudinal tensile properties of filament-wound composites; however, it has a disadvantage to accompany an appreciable bending moment occurring at the split in the dee-fixture where the fracture takes place.The authors have proposed an improved ring having a form of race track (RT) with straight parts, as Dow noted prior to us. The tensile tests have been carried out to compare both types of ring specimens of carbon fiber reinforced plastics. They show a remarkable bending effect and a decrease of tensile strength with an increase in thickness.On the other hand, the analytical stress distributions in both types of ring specimens under separation of split-dee fixture are obtained by the finite element method. The correction by the numerical results leads to the nearly equal tensile strength and modulus, and the RT ring specimens are shown to be desirable to have the reliable tensile data with a substantial reduction in bending moment. Furthermore, the nonlinear analysis is done by taking into consideration the changes of ring configuration and of contact location with split-dee during elongation, which explains the nonlinear relation between load and bending strains.