Rivet module and joining structure and method using the same

A rivet module for joining at least two sheets of base materials in a solid state, the rivet module comprising:

• i) a shank portion to be mounted on a reciprocal and rotatable joining tool;
• ii) a base material friction portion that is integrally connected to the shank portion and drills through the base materials as the joining tool causes the base material friction portion to be rotated while applying pressure to the base materials;
• and
• iii) a base material fastening portion that is fixedly fitted to the shank portion, supports the base material friction portion, and is fastened to the base materials through a threaded portion including a thread formed on an outer peripheral surface thereof so that the threaded portion is disposed within the base materials,
• wherein a circular cross-sectional diameter of the base material friction portion becomes progressively larger and then smaller from a part connected to the shank portion toward a tip, and the tip is sharpened,
• wherein the base material fastening portion has a hollow space into which the shank portion and the base material friction portion are fitted,
• wherein the hollow space comprises:
• a first portion having a shape corresponding to a cross-section of the shank portion;
• and
• a second portion connected to the first portion and having a shape corresponding to a region where the cross-sectional diameter of the base material friction portion becomes progressively larger,
• wherein the base material friction portion is pulled upward by the joining tool and enters the first portion, and
• wherein the threaded portion of the base material fastening portion is plastically deformed by the base material friction portion, causing a cross-section of the threaded portion to expand outward.