Patent ID: 8506159

Claim:
A method for detecting a defect both on the surface and in the surface layer of a material, comprising the steps of: making a temperature of the surface of the material be changed with time, obtaining thermal image data of the surface of the material using an infrared thermography camera while the surface of the material is changing in temperature, and detecting the defect by calculating Laplacian Δ xy T shown in the right side of the following expression (1) using the following expression (2), where Laplacian Δ xy T represents a variation of heat storage due to heat migration in a sheet thickness direction z of the material, by using a thermal diffusivity α of the material as shown in the left side of the following expression (1), based on the obtained thermal image data T: ( 1 / a ) · ( ∂ T / ∂ t ) - ∂ 2 ⁢ T / ∂ z 2 = Δ xy ⁢ T ( 1 ) Δ xy ⁢ T = 1 4 ⁢ ⁢ h 2 ⁢ { T ⁡ ( x + 1 , y ) + T ⁡ ( x - 1 , y ) + T ⁡ ( x , y + 1 ) + T ⁡ ( x , y - 1 ) - 4 ⁢ ⁢ T ⁡ ( x , y ) } . ( 2 )