Local quasi-static and cyclic deformation behaviour of brazed AISI 304L/BAu-4 joints characterised by digital image correlation

Abstract

For a reliable design of brazed components, the degradation of mechanical properties due to the corrosive attack by aggressive operating environments has to be considered. In this study, the effect of a condensate corrosion, which is performed according to VDA test sheet 230-214 up to 6 weeks, on the mechanical behaviour of brazed AISI 304L/BAu-4 stainless steel joints is investigated. A time-dependent reduction of the tensile and fatigue strength values down to 42% of the as-received condition is determined. As standard strain measurements are not appropriate to characterise the local strain distributions of heterogeneous material systems, the optical digital image correlation technique is used to evaluate the local quasi-static and cyclic deformation behaviour of the 50 μm wide brazing seam. A novel triggered image acquisition enables measurements in fatigue tests at a frequency of 10 Hz. The reduction of the virtual gauge length from 12.5 down to 0.5 mm leads to an increase of the total strain and ratcheting strain values, which is more pronounced for higher stresses and enhanced for pre-corroded brazed joints. For a microstructure-related analysis of the damage processes, scanning electron microscopy was used.