Influence of internal imperfections on the fatigue resistance of cast steel – testing methodology

Abstract

Tensile fatigue specimen of G20Mn5 and G22NiMoCr5-6 were tested to quantify the influence of internal defects on the fatigue resistance of cast steel components. Defects with varying sizes, geometric shapes and distribution were enforced by influencing the solidification and recorded by computer tomography (CT). Besides the characteristics of the detected cavities, the surrounding fungoid microstructure is classified and evaluated. Later the specimens were tested under cyclic tension and S/N-curves are derived. These data form the basis for extensive numerical simulations of the damage process and the crack growth of every individual specimen. Both processes are affected by the local multiaxial stress states and have their origin in the inside of the specimen. For validation, knowledge of the crack initiation time and propagation properties are essential. Therefore, all specimens respectively the properties of the internal defects are monitored during testing with three different state-of-the-art non-destructive testing (NDT) methods. Background and application of these NDT techniques are described within this paper. Finally, fracture surface analyses show different failure modes and provide further information for model validation.

A Numerically Efficient Method to Assess the Elastic–Plastic Strain Energy Density of Notched and Imperfective Cast Steel Components

“…is studied and it is assumed that this ratio remains valid in the case of non-linear material behaviour. Thus, the elastic-plastic maximum values σij,max,k of the components of σk can be computed according to Equation (16).…”

“…Due to high-volume contraction, these spatial defect structures often reach dimensions of several millimetres [9][10][11][12]. Hence, the fatigue strength of the respective components is significantly affected by the presence of such macroscopic imperfections [13][14][15][16][17].…”

Vereinfachte Bemessung von ermüdungsbeanspruchten Stahlgussbauteilen

“…Deren individuelle geometrische Gestalt wurde mithilfe von Computertomografieaufnahmen (CT) des Fraunhofer IZFP bestimmt [4]. Details zur Versuchstechnik sowie eine umfangreiche Auswertung sind in [5, 32] gegeben.…”

Effect of Surface Finishing State on Fatigue Strength of Cast Aluminium and Steel Alloys

“…Such local microstructural conditions lead to varying shape and degree of porosity, affecting the local acting stress field significantly [ 11 , 12 , 13 ]. This results in a severely limited fatigue strength of imperfective cast components compared to the strength of the ideal, defect free material [ 2 , 14 , 15 , 16 , 17 , 18 , 19 ]. From the point of manufacturing quality, porosity can be subdivided into gas and shrinkage porosity according to [ 20 ] and may be determined either destructively by fractographical inspection or non-destructively via computed tomography (CT) [ 21 , 22 , 23 ].…”