A Novel Technique for the Determination of Long-Term Fatigue Behavior of Brazed Joints

The design of high-strength joints becomes increasingly important for a wide field of industrial applications, e.g. automobile components. Recent fatigue studies of brazed joints focus on the Woehler lifetime and are limited at a standardized number of cycles of 2*10⁶. In most cases the test procedure and cycle limit have to be enhanced to guarantee a comprehensive understanding of basic fatigue mechanisms at service-relevant fatigue lifetimes.

In this regard, this study presents the detailed long-term fatigue assessment of austenitic stainless steel AISI 304 brazed with BNi-2 at 1050°C. Therefore, the joining connections were cyclically tested under stress control until a maximum of 10⁷ cycles and characterized by plastic strain measurements. Additional physical measurements, e.g. temperature increases due to plastic deformation processes, were performed for a systematic investigation of their cyclic deformation behavior and a comprehensive understanding of basic fatigue mechanisms. The measured quantities are directly influenced by deformation-induced changes and represent the actual fatigue state, leading to basic data for fatigue life predictions approaches.