Type HT-NX series, DI-BSCCO tapes laminated with pre-tensioned nickel alloy foils for reinforcement, have higher strength than the other types of DI-BSCCO tapes. In this research, we measured the effect of cyclic tensile load of up to 105 cycles on the Ic degradation of 4 kinds of HT-NX tapes and a spliced tape by the original fatigue test system. The results indicated that Ic of HT-NX series tapes survive up to 105 cycles, if an applied cyclic maximum stress (stress ratio 0.1) is less than their own static irreversible stress. From observations of the same location of the longitudinal section during fatigue, a local crack from the BSCCO layer penetrating a few fatigued Ag pipes was found, while a crack in the BSCCO layer by static load with the same Ic degradation level was trapped by a Ag pipe. The damage to the Ag pipe is peculiar to the cyclic load.
Fiber reinforced organic composites materials such as GFRP, which consist of glass fiber and epoxy resin, are intended for use as insulating and structural materials for superconducting magnets. In order to maintain the reliability and long-term durability of these insulating materials, the adhesive strength between laminates, or between laminates and the inserted films are important. In the composites, the adhesive strength is defined as the interlaminar shear strength and is one of the most important index of the composites materials. In this experiment, the test was conducted to establish a method to evaluate the interlaminar shear strength of thin-FRP. The shear test method specified by JIS and ASTM does not produce pure shear failure in fiber reinforced plastics, especially thin composites, and it is difficult to obtain accurate interlaminar shear strength. We developed the shear test method where the interlaminar shear strength can be accurately measured using NAL method and notched specimen from different surface. The experiments were performed both at room and nitrogen temperature. Obtained data were compared with those in ASTM method. It was confirmed that the developed method showed satisfactory performance to obtain the interlaminar shear strength.
Attempts have been made to improve the interlaminar shear strength of various FRPs. FRPs were fabricated by changing the matrix resin, reinforcement, and woven structures, which are essential parameters, combined systematically in the FRPs. The mechanical characteristics of the fabricated FRPs were measured at room and liquid nitrogen temperature. It was found that when a coupling agent was added to the matrix resin, the interlaminar shear strength was improved by 6 to 29 % at room temperature, and also by 21 to 58 % at liquid nitrogen temperature. The effect of the additive showed only slight improvement or no change in bending strength and compressive strength. The effects of other parameters were also presented together with the possible mechanisms.
Tensile tests at liquid helium temperature were performed using specimen taken from high purity large grain niobium ingot produced by CBMM. The measured RRR of large grain niobium is 242. The ingot, a diameter of 260 mm, and was sliced by a multi wire saw to 2.8 mm thickness. 5 specimens were cut off from one sliced disk. 3 disks were set in the same phase to obtain the same grain distribution. 3 specimens, each of 5 grain patterns, 15 in total, were used for the tensile testing. We manufactured the tensile testing stand using a cryostat and liquid helium. The measured tensile strength varied from 379 to 808 MPa. The average tensile strength value is 611 MPa, which is 70% of that of fine grain. The tensile strength at room temperature is 84 MPa. The strength becomes high at low temperature like in fine grain niobium. The specimen includes some grains whose strength depends on the crystal orientation, which causes the variation of strength.