Mattias Lundberg

Residual Stresses in Shot Peened Grey and Compact Iron

Abstract Grey cast iron and compacted graphite iron with a pearlitic matrix are investigated in this study after shot peening using twelve unique combinations of parameters, namely shot size, peening intensity and coverage, followed by residual stress measurements and evaluations. Cylindrical test samples were cut out from heavy truck cylinder heads and polished on the top flat surface to decrease effects from cutting. Residual stresses and the affected depth from the different peening conditions varied between −245 MPa to −565 MPa and from 280 μm to 770 μm in depth. Resultant surface compressive stresses decrease with increasing shot size, peening intensity or coverage whereas the affected depth increases with increasing intensity. The increased affected depth is a result from the increased extent and magnitude of plastic deformation. The compacted graphite iron was more affected by shot peening than the grey cast iron, meaning that the same shot peening parameters resulted in both higher compressive stresses and larger deformation depth.

Fatigue Strength of Machined and Shot Peened Grey Cast Iron

A common opinion is that cast iron, especially grey cast iron, is not as notch sensitive as steel and has therefore not been treated by shot peening to suppress crack initiation. For a heterogeneous material that also is brittle, just like grey cast iron, the shot peening parameters needed to induce beneficial surface residual stresses can be problematic to identify. Fatigue testing under uniaxial loading with an R value of -1, on mechanically polished and shot peened specimens, has been performed to determine the fatigue strength at 107 cycles as well as complete Wöhler-curves. Two different types of specimen geometries were tested, one smooth and one notched specimen having kt equal to 1.05 resp. 1.33. With large shots and high peening intensity (heavy SP) the fatigue strength clearly decreased whereas small shots and low peening intensity (gentle SP) might have lowered the fatigue strength. A short annealing at 285° after gentle shot peening increased the fatigue strength. The results are discussed and explained based on x-ray diffraction (XRD) measurements, i.e. residual stress and full width at half maximum profiles, as well as microstructural investigations using scanning electron microscope (SEM).

3D Residual Stresses in Selective Laser Melted Hastelloy X

3D residual stresses in as manufactured EOS NickelAlloy HX, produced by laser powder bed additive manufacturing, are analysed on the surface closest to the build-plate. Due to the severe thermal gr ...

Shot Peening Induced Plastic Deformation in Cast Iron – Influence of Graphite Morphology*

Abstract Graphite morphology in cast iron strongly affects the mechanical properties such as: Youngs modulus, tensile/compressive strength and cyclic mechanical behaviour. In this study, pearlitic compact graphite iron (CGI) and grey cast iron (GI) have been studied in a scanning electron microscope (SEM) before and after shot peening under different conditions. The plastic deformation behaviour of CGI and GI under different shot peening conditions has been analysed using electron backscattering diffraction (EBSD) and electron contrast channelling imaging (ECCI). EBSD and ECCI revealed that plastic deformation around graphite inclusions depends on the size and shape of the graphite. The different response of CGI and GI to shot peening is explained by the different damping properties of the graphite and the matrix capability for plastic deformation. n