Abstract: A fiber-reinforced resin material of tape shape having a thickness of at most 0.2 mm and a width/thickness ratio of from 25 to 200 and comprising a synthetic resin and continuous filaments contained as reinforcing material in the resin, said continuous filaments being aligned in lengthwise direction and said resin densely filling spaces among the filaments.

Abstract: A plurality of ultrasonic transducers or probes are positioned around a region of an object such as a steel tube to be inspected. One of the ultrasonic transducers is energized to emit an ultrasonic beam into the region, and ultrasonic waves reflected from and transmitted through the region in response to the emitted ultrasonic beam are received. Sound pressures are then measured from the reflected and transmitted ultrasonic waves, and an evaluation value is produced by arithmetically dividing the sound pressure of the reflected ultrasonic wave by the sound pressure of the transmitted ultrasonic wave.

Abstract: A core material for a fiber reinforced plastic comprises a glass fiber mat composed of glass fiber bundles and having a bulk density of from 50 to 150 kg/m.sup.3 and a porous material filled in void spaces in the glass fiber mat. The porous material is composed of a mixture of a thermoplastic resin and a filler such as a hollow inorganic filler.The core material is prepared by impregnating a glass fiber mat composed of elongated glass fiber bundles, with a mixture of the filler and a dispersion of the thermoplastic resin in a dispersing medium and their evaporating the dispersing medium from the impregnated glass fiber mat.

Abstract: A reinforcing mat for fiber reinforced plastic material comprises a first layer of longer glass fiber strands which are formed by collecting at least 300 glass fibers and are arranged in a non-directional and curled state and a second layer of shorter glass strands arranged in a non-directional state which has a thickness smaller than said first layer, said glass fiber strands of each layer being bonded with a binder.

Abstract: A glass fiber mat is prepared by piling a strand formed by collecting a number of glass fibers on a conveyor in a non-oriented state by making the strand into contact with a rotating cylinder to throw it; thus forming a mat like layer and piling another strand cutting or without cutting on said mat like layer to be a thin layer and said another strand being drawn from a cake.