Detection of cracks in constructional steel members by means of ultrasound excited thermography

In non-destructive testing of structural elements ultrasound excited thermography offers various fields of application. The most experience is available in testing of CFRP or similar types of composite materials. The available methods have not been fully transferred to massive steel members used in constructional steelwork so far. The idea of ultrasound excitation of structural members is to generate elastic waves that propagate inside the investigated structure. In case of internal failures like cracks the boundary faces move relatively to each other. Rubbing and clapping of crack faces leads to locally restricted heat generation. Investigations on typical heavy load bearing members like plates and girders made of low-carbon steel are presented. Using lockin, sweep and burst approaches the thermal response of cracks at varying ultrasonic frequency and intensity is determined. Ultrasound excited thermography has been attested the capability to develop towards a fail-safe non-destructive test method that clearly visualizes cracks in steel members used in constructional steelwork.