D3.3 - Real-Time Detection and Measurement of Cracks in Fatigue Test Applications

Abstract

The detection of crack initiation and the observation of crack growth are of great importance for evaluating the fracture mechanics and fatigue behavior of mechanical components and structures. The proposed method targets on detection and measurement of cracks on metallic surfaces where initial artificial cracks have been applied to the specimen’s surface prior to dynamic loading in a test rig. Applying a pre-test surface treatment in terms of polishing the investigation area on the specimen enables for highest resolution and accuracy for crack detection and crack length measurement with a resolution in the order better than 0.05mm over a crack length of up to total 10mm and more. The developed measurement system operates in real time during cyclic loading of the test unit within the test application. Load-triggered illumination by high-power LEDs together with load-triggered image acquisition by a high resolution digital camera enables the real-time observation of crack development on the investigated surface area. The implementation of the system on a real time hardware enables the robust measurement of crack lengths on-site and in real-time. The developed system achieves impressive real-time measurement performance for crack detection and crack length estimation, in combination with the advantage of non-contacting operation and highly desired on-site measurement capabilities during dynamic load experiments.