In the related art, a resin rivet, which is an example of a fastening rod, has advantages such as easily molding, reducing weight as well as high corrosion resistance, and the resin rivet is widely used for fastening various components such as a synthetic resin product, a leather or a fabric, and a paper product (for example, Patent Document 1).
In the resin rivet, a method of “caulking” the resin rivet by plastic deformation is used, and the resin rivet is able to be prepared separately from a member to be fastened, and thus is suitably applicable to a position at which a boss or a rib integrated with a shaped product is not able to be easily molded.
In general, the resin rivet includes a flat head part, and a body part which is narrower than the head part. When a first member and a second member are fastened by using the resin rivet, a caulking method is used in which the body part is inserted into a first fitting hole provided in the first member and a second fitting hole provided in the second member from the first member side, and in a state where the head part is in contact with the first member, a portion of the body part, protruding from the second member, is plastically deformed into the shape of a curl.
Also, a joined body fastened by caulking in which a protruding substance such as a rib and a boss is provided in advance in a member to be fastened and a tip end of the protruding substance is deformed by heat has high joining strength in a peeling direction. In this joined body, various methods such as using heat and ultrasonic waves are applicable for a heating method at the time of performing the caulking, and thus the joined body is widely used in various industrial fields (Patent Document 2).