Abstract
Shrinkage porosities and non-metallic inclusions are common manufacturing process based defects that are present within cast materials. Conventional fatigue design recommendations, such as the FKM guideline (“Forschungskuratorium Maschinenbau”), therefore propose general safety factors for the fatigue assessment of cast structures. In fact, these factors mostly lead to oversized components and do not facilitate a lightweight design process. In this work, the effect of shrinkage porosities on the fatigue strength of defect-afflicted large-scale specimens manufactured from the cast steel G21Mn5 is studied by means of a notch stress intensity factor-based (NSIF-based) generalized Kitagawa diagram. Additionally, the mean stress sensitivity of the material is taken into account and establishes a load stress ratio enhanced diagram. Thereby, the fatigue assessment approach is performed by utilizing the defects sizes taken either from the fracture surface of the tested specimens or from non-destructive X-ray investigations. Additionally, a numerical algorithm invoking cellular automata, which enables the generation of artificial defects, is presented. Conclusively, a comparison to the results of the experimental investigations reveals a sound agreement to the generated spatial pore geometries. To sum up, the generalized Kitagawa diagram, as well as a concept utilizing artificially generated defects, is capable of assessing the local fatigue limit of cast steel G21Mn5 components and features the mapping of imperfection grades to their corresponding fatigue strength limit.
Highlights
Cast steel components are commonly utilized in modern manufacturing processes for complexly shaped structures and demands towards higher strengths
In terms of the fatigue strength assessment, the statistical evaluation in the finite-life region is conducted by application of the common procedure
The mean stress sensitivity approach of the FKM guideline provides a basically matching fatigue assessment relating to the cast G21Mn5 material
Summary
Cast steel components are commonly utilized in modern manufacturing processes for complexly shaped structures and demands towards higher strengths. Despite elaborated efforts in terms of numerical process simulations during component design, casting defects, such as sand inclusions, hot tears and shrinkage porosities, are manufacturing based intrinsic material properties [1]. This is caused by the material’s high shrinkage during cooling and solidification. Despite the use of radiograph standards [2,3,4] for quality assurance, which allow casting defects to be classified according to their accumulation and sizes, into defect and severity grades, it is difficult to attain a conservative estimation of the local strength properties in cast steel components. The influence of shrinkage porosity on the elastic monotonic and fatigue
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