Method and device for non-destructively testing a connection point in a component assembly

A device comprising a thermal imaging camera, a positioning means, an inductor and an evaluation control unit, wherein the evaluation control unit performs a method for non-destructively testing a connection point in a component assembly, the connection point comprising a base layer and at least one cover layer, and a connection element with a head and a shaft, the connection point being formed between the shaft of the connection element and the base layer, wherein the cover layer has a thermal conductivity which is greater than that of the base layer and of the connection element, wherein the inductor which is arranged on a component assembly side opposite the thermal imaging camera, the inductor inductively excites the base layer at an excitation time by means of a pulse via an active surface, the method comprising the steps of:

• at a first detection time, capturing a reference image of the connection point via the thermal imaging camera, the head being imaged in said reference image as a head surface;
• at a second detection time, capturing a test image analogous to the reference image, said second detection time occurring after the first detection time and a specified duration after the excitation time;
• defining an analysis region in at least one of the test image and in the reference image, wherein the analysis region at least partly comprises the head surface, and the analysis region is divided into sub-regions of pixels, said sub-regions being assigned a temperature value;
• forming a temperature change value using a rule on the basis of the temperature values of the corresponding sub-regions of the reference and test images;
• on the basis of the temperature change value, forming an “OK” value if the temperature change lies in a pre-defined temperature interval with at least one lower boundary;
• classifying the connection point in that the sum of the sub-regions with an “OK” value is compared with a reference interval with at least one specified lower interval boundary, wherein the connection point is classified as an “OK” connection if the sum lies in the reference interval, otherwise the connection point is classified as a “not OK” connection.