Brandt, Robert
2 results
Now showing 1 - 2 of 2
- Some of the metrics are blocked by yourconsent settings
Publication Access status: Open Access , Influence of residual stresses on the crack initiation and short crack propagation in a martensitic spring steelThe crack initiation and short crack propagation in a martensitic spring steel were investigated by means of in-situ fatigue testing. Shot peened samples as well as untreated samples were exposed to uniaxial alternating stress to analyze the impact of compressive residual stresses. The early fatigue damage started in both sample conditions with the formation of slip bands, which subsequently served as crack initiation sites. Most of the slip bands and, correspondingly, most of the short fatigue cracks initiated at or close to prior austenite grain boundaries. The observed crack density of the emerging network of short cracks increased with the number of cycles and with increasing applied stress amplitudes. Furthermore, the prior austenite grain boundaries acted as obstacles to short crack propagation in both sample conditions. Compressive residual stresses enhanced the fatigue strength, and it is assumed that this beneficial effect was due to a delayed transition from short crack propagation to long crack propagation and a shift of the crack initiation site from the sample surface to the sample interior.Source Type:Article2 18 - Some of the metrics are blocked by yourconsent settings
Publication Access status: Metadata only , Torsional fatigue behaviour and damage mechanisms of martensitic spring steel in the HCF regimeThis study investigates the fatigue behaviour and damage mechanisms of the martensitic spring steel SAE 9254, with emphasis on short crack propagation. Shear stress-controlled torsional fatigue tests are performed at stress ratio R = -1 and test frequency f = 79 Hz using structure-sensitive measurement techniques to detect the relevant damage mechanisms. An in-situ torsional fatigue testing device is applied for shear-controlled fatigue tests at two amplitudes of the torsion angle using R = –1 and f = 5 Hz, and the microstructural-dependent short crack propagation path is documented by means of confocal laser microscopy and electron backscattering analysis. It is found that the early development of fatigue damage is characterised by the formation of slip bands, which serve as crack initiation sites. In this process, crack initiation occurs preferentially at or near prior austenite grain boundaries. Furthermore, prior austenite grain boundaries were identified as obstacles for the propagation of short cracks, because of the change of the crystallographic orientation leading to an oscillating propagation rate of short cracks. The short crack density ρCD, which is an important parameter for fatigue damage, is rapidly growing with increasing shear stress amplitude ΔτT/2 and reveals a stress type specific behaviour.Source Type:Article4
