We have measured the tensile strengths of bulk YBCO samples using a tensile test machine. We have found that the tensile strength was dramatically enhanced by wrapping the bulk with carbon fibre fabric prior to resin impregnation. We have also characterized the mechanical properties of large-grain YBCO with a diameter of 46 mm using the strain gauges. The electromagnetic stress was imposed on the bulk samples by reducing the external field from 7 T to 0 T at 65 K. The sample without resin was broken during the field-decreasing process with the maximum stress reaching 150 MPa. In contrast, the maximum stress was only 40 MPa for the resin-impregnated sample covered with the carbon fibre fabrics. These results show that wrapping the bulk YBCO sample with the carbon fibre fabrics may have a beneficial effect in stabilizing the mechanical properties in addition to enhancing the tensile strength.
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