Patent ID: 8559018

Claim:
A method of detecting a crack occurrence position comprising: stacking a surface layer formed of a composite material on a surface of a core layer formed of a foam synthetic resin material; providing an arrester portion in an interface region between the surface layer and the core layer to arrest progression of delamination between the surface layer and the core layer; embedding a first optical fiber having a first grating portion inside the arrester portion and along the surface layer such that the first optical fiber constitutes a fiber Bragg grating sensor, the first optical fiber being provided at one end portion of the arrester portion; embedding a second optical fiber having a second grating portion inside the arrester portion and along the surface layer such that the second optical fiber constitutes a fiber Bragg grating sensor, the second optical fiber being provided at a second end portion of the arrester portion; calculating a first distance between the first grating portion and a tip of a crack of the delamination approaching the arrester portion based on a shape of a spectrum of reflected light from the first optical fiber; calculating a second distance between the second grating portion and the tip of the crack based on a shape of a spectrum of reflected light from the second optical fiber; and determining an occurrence position of the crack between the surface layer and the core layer based on the distances.