The residual strength in UD-CFRP was measured after being subjected to constant strain. In order to quantify the strength reduction, the time-dependent variation of interfacial stress-transfer capacity in a single-fiber composite specimen was quantitatively studied using micro-Raman spectroscopy. The analysis originally included a decrease of interfacial frictional stress due to a relaxation of interfacial radial stress and a time-dependency of an interfacial debonding propagation criterion, based on the conventional viscoelastic shear-lag model. The residual strength in UD-CFRP after enduring long-term loading was then analyzed using the global load sharing model with the results of variation of the interfacial property.

No abstract

No abstract

A new fatigue-testing machine was developed to perform high-cycle multiaxial fatigue tests at 50 Hz, in order to reduce testing time. The developed machine can combine bending and torsion loading and perform fatigue tests at a high frequency, under proportional and non-proportional loading conditions, where the principal stress direction changes during a cycle. The proportional loading is cyclic bending loading, and the non-proportional loading is cyclic, combining bending and reversed torsion loading. In this study, the effectiveness of the testing machine was verified by conducting tests under these loading conditions, using specimens of type 490A hot-rolled steel and type 304 stainless steel. The fatigue life linked to bending loading obtained using the new testing machine was slightly extended compared with that obtained using the conventional fatigue-testing machine. The fatigue life derived as a result of a combination of bending and torsion was comparable to that obtained using the conventional fatigue-testing machine, although a fatigue limit reduction of 100 MPa was observed compared to the former study. The feasibility of tests using the developed multiaxial fatigue-testing machine was confirmed.

No abstract