Microstructure-Specific Lifetime Prediction Method for Heavy-Section Castings Based on Non-Destructive Measurements During Fatigue Testing

Abstract Heavy-section ductile cast iron components, such as main shafts or planet carriers in modern wind turbines, are produced under complex solidification and cooling conditions that lead to pronounced local variations in microstructure. These variations, governed by the casting process, significantly influence the fatigue strength and are currently compensated for by high safety factors in design. Conventional fatigue testing to determine microstructure-specific S-N curves requires a large number of specimens, which is impractical for heavy castings. This study presents the applicability of MiDAcLife, an accelerated fatigue testing approach that combines load increase tests (LIT) with thermometric monitoring to derive microstructure-specific S-N curves from only a few specimens and, thus, for only a very specific solidification and cooling condition. By analyzing the characteristic temperature response during LIT and applying a Palmgren–Miner-based evaluation, both fatigue strength and finite life regime are estimated. The method is demonstrated on industrially produced austempered ductile cast iron grade 2, heat-treated after sand casting, with casting simulation data used to select specimens of defined solidification modulus. The resulting virtual fatigue data show good agreement with constant amplitude tests. Moreover, it shows reproducibility for similar solidification and cooling conditions and, thus, is proven to be applicable for quality control. Therefore, the presented approach enables targeted, location-specific material characterization directly linked to casting parameters, supporting both component design optimization and quality control in foundry practice.