Artificial defect material and manufacturing method of FRP structure

An artificial defect material comprising:

• a plurality of layers of prepreg material;
• and
• an intermediate structure,
• wherein the intermediate structure is arranged between at least one pair of always adjacent layers of the prepreg material,
• wherein the intermediate structure has heat resistance at a shaping temperature higher than the room temperature and a property of keeping the shape at the room temperature excluding expansion, when an FRP structure is formed,
• wherein the intermediate structure has a linear expansion coefficient larger than that of the FRP structure by 150×10−6 (1/° C.) or more,
• wherein a shape corresponding to the intermediate structure which has thermally expanded at the shaping temperature is formed between the layers of prepreg material, when the FRP structure is formed, and
• wherein at the room temperature after the shaping of the FRP structure, the intermediate structure thermally shrinks to form a space between the intermediate structure and the layers of prepreg material due to shrinkage difference.