Abstract: A method for measuring a fiber orientation degree includes: irradiating a sample formed of a composite material containing discontinuous carbon fibers with an X-ray to acquire an X-ray diffraction image; calculating an angle (2?)A of a peak originating from a crystal face of graphite; calculating a correction coefficient ? of a thickness of the sample; calculating an upper limit (2?)B of the peak of the crystal face of graphite; calculating a diffraction sensitivity IC(?) of the peak originating from the crystal face of graphite by correcting an integrating range with the correction coefficient ? and integrating the X-ray diffraction image with respect to a diffraction angle (2?); and calculating a fiber orientation degree Sd(?) by the method of Hermans from the diffraction sensitivity IC(?).

Abstract: A method for producing a preparation for fiber length measurement includes: a preliminary dispersion process of adding fibers and a dispersion medium with a viscosity of 500 Pa·s to 10,000 Pa·s to a sealable container so as to give a concentration of the fibers of 0.1% by mass or less and shaking the container to prepare a preliminary dispersion liquid; a dispensing process of dispensing part of the preliminary dispersion liquid to another sealable container; a dilution process of adding the dispersion medium to the dispensed preliminary dispersion liquid so as to give a concentration of the fibers of 0.005% by mass or less and shaking the container to prepare a dispersion liquid for measuring fiber length; and a casting process of spreading part of the dispersion liquid for measuring fiber length onto a base having light transparency.

Abstract: A method for producing a preparation for fiber length measurement includes: a preliminary dispersion process of adding fibers and a dispersion medium with a viscosity of 500 Pa·s to 10,000 Pa·s to a sealable container so as to give a concentration of the fibers of 0.1% by mass or less and shaking the container to prepare a preliminary dispersion liquid; a dispensing process of dispensing part of the preliminary dispersion liquid to another sealable container; a dilution process of adding the dispersion medium to the dispensed preliminary dispersion liquid so as to give a concentration of the fibers of 0.005% by mass or less and shaking the container to prepare a dispersion liquid for measuring fiber length; and a casting process of spreading part of the dispersion liquid for measuring fiber length onto a base having light transparency.

Abstract: A method for measuring a fiber orientation degree includes: irradiating a sample formed of a composite material containing discontinuous carbon fibers with an X-ray to acquire an X-ray diffraction image; calculating an angle (2?)A of a peak originating from a crystal face of graphite; calculating a correction coefficient ? of a thickness of the sample; calculating an upper limit (2?)B of the peak of the crystal face of graphite; calculating a diffraction sensitivity IC(?) of the peak originating from the crystal face of graphite by correcting an integrating range with the correction coefficient ? and integrating the X-ray diffraction image with respect to a diffraction angle (2?); and calculating a fiber orientation degree Sd(?) by the method of Hermans from the diffraction sensitivity IC(?).

Abstract: A bobbin for superconducting coils, which is made of a fiber-reinforced plastic material containing: (1) a matrix resin; (2) a polyethylene fiber having a negative thermal expansion coefficient in the fiber lengthwise direction, the angle between the polyethylene fiber and the longitudinal axis of the bobbin being in the range of .+-.35.degree. to 90.degree.; and (3) a substance having an elastic modulus higher than that of the polyethylene fiber. The bobbin of the present invention is useful for superconducting coils because it only exhibits a quite low degree of deformation, even when used under external stress at cryogenic temperatures.