Equivalent stress concepts for transforming of variable amplitude into constant amplitude loading and consequences for design and durability approval

• Published in: International journal of fatigue 2022-09, Vol.162, p.106949, Article 106949
• Main Authors: Sonsino, C.M., Baumgartner, J., Breitenberger, M.
• Format: Article
• Language: English
• Subjects: Amplitudes; Constant amplitude loading; Cumulative damage; Damage; Design; Durability; Durability approval; Equivalence; Equivalent stress; Fatigue strength; Materials fatigue; Palmgren-Miner rule; Required fatigue strength; Variable amplitude loading
• ISSN: 0142-1123; 1879-3452
• DOI: 10.1016/j.ijfatigue.2022.106949

•Presentation of two methods, modified equivalent stress (MES) and the required fatigue strength (RFS), for durability assessment based on modifications of the Palmgren-Miner hypothesis.•Transformation of a stress or load spectrum into a damage equivalent constant amplitude loading.•The MES-method delivers a damage equivalent stress that depends on the selected position of the Woehler-line.•The RFS-method defines a damage equivalent fictitious Woehler-line indicating the lowest necessary strength quality.•The RFS-method also allows an experimental durability proof for any amplitude-cycle combination. This paper compares two methods for transforming a stress or load spectrum into a damage equivalent constant amplitude loading, i.e. the modified equivalent stress (MES) and the required fatigue strength (RFS) concepts. Because of the common basis, i.e. the modified Palmgren-Miner hypothesis, the resulting MES- and RFS-amplitudes are related to each other, but not equal. The MES-method results in a damage equivalent stress, which depends on the selected position of the Woehler-line. However, the RFS-method delivers a damage equivalent fictitious Woehler-line indicating the lowest necessary strength quality. This line also allows an experimental durability proof for any amplitude-cycle combination along it.