An investigation on the application of a non-destructive optical strain measurement system to fracture toughness testing
AbstractIn the process of materials’ development and optimisation, the determination and analysis of mechanical properties, in particular toughness, have a major importance. This work presents a non-contact and non-destructive strain analysis technique which allows the determination of strain fields and displacements on a surface of interest. In the present study, an optical strain measurement system called ARAMIS has been used. The aim of this work was to verify the capacity of this system in detecting variations of strain and displacements in the vicinity of a crack tip located in two different regions of a welded joint. The system was applied to monitor the surface of fracture toughness test specimens of welded joints. The results from a CMOD clip gauge and from the optical strain analysis system were analysed and compared. Laser-welded samples of API 5L X-65 steel produced using a 25 kW CO2 laser source were prepared and tested in accordance with BS 7448-1997: ‘Fracture Mechanics Toughness Test’. The displacement results generated by the optical strain measurement system agree with those obtained with the standard clip-gauge technique. The results show that this strain measurement technique is a powerful tool for the strain/stress measurements, capable of providing a non-contact full-field strain map of the analysed specimens.