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Materials and brazed joints for automotive exhaust systems have to resist the corrosive nature of aggressive exhaust gases as well as static and cyclic loads. In the present study, the influence of condensate corrosion according to VDA 230–214, with an ageing duration of up to 6 weeks, on the tensile and fatigue properties of stainless steel AISI 304L and brazed AISI 304L/BNi‐2 joints is investigated. In relation to the as‐received condition, the ultimate tensile strength is decreased down to 58 % and a reduction of the fatigue strength at 2⋅106 cycles down to 22 % is determined for brazed specimens, pre‐corroded for 6 weeks. In contrast to the brazed stainless steel joints, the condensate corrosion does not influence the tensile properties of the AISI 304L base material. Stress concentrations at the corrosion‐dependent circumferential grooves at the brazing seam are evaluated by stress intensity factors, which are well appropriate to characterise the fatigue behaviour depending on the corrosion condition.

Abstract. For mechanical tests of brazed stainless steel joints, the local deformation behaviour within the small area of the brazing seam is a major concern, because local strains cannot be detected with standard mechanical extensometers. The current study allows a fundamental comprehension of the gauge length influence on the strain measurements of brazed joints with smooth and notch-containing surfaces, under quasistatic and cyclic loadings. Therefore, the optical measurement technique of digital image correlation (DIC) is used within tensile and fatigue tests of brazed AISI 304L/BAu-4 joints in an as-received and pre-corroded condition. A triggered image acquisition of the DIC system is successfully applied to evaluate the local ratcheting fatigue behaviour in the area of the brazing seam at a frequency of 10 Hz. The gauge length influence, analysed in the range of 0.5 to 12.5 mm, is more pronounced with increasing tensile and fatigue stresses and is significantly enhanced for notch-containing surfaces. Instrumented load increase tests with strain, electrical, magnetic and temperature measuring techniques have proven to be appropriate to estimate fatigue properties of the brazed joints with a deviation of 4%. Fatigue and corrosion fatigue damage mechanisms are evaluated by using scanning electron microscopy with secondary and back-scattered electron detectors.

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