A. Koethe

Bio: A. Koethe is an academic researcher from Leibniz Association. The author has contributed to research in topics: Paris' law & Crack closure. The author has an hindex of 2, co-authored 4 publications receiving 57 citations.

High cycle fatigue behaviour of a multiphase microalloyed medium carbon steel: a comparison between ferrite–pearlite and tempered martensite microstructures

Abstract: To improve toughness and fatigue strength, a mutiphase (ferrite (F)–bainite (B)–martensite (M)) microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing (two-step cooling and annealing (TSCA)) treatment In the present paper, the high cycle fatigue (HCF) response determined in terms of the endurance limit, long crack fatigue threshold (ΔKth), crack closure and fatigue crack growth rate (FCGR) in a material that has a multiphase microstructure is presented and compared with those of the same material with a ferrite–pearlite (F–P) and a tempered martensite (T–M) microstructure obtained by air-cooling (AC) and quenching and tempering (Q&T), respectively Long crack fatigue threshold (ΔKth) and crack closure were evaluated using a dynamic compliance (DYNACOMP) measurement technique The fatigue limit of the F–B–M and the T–M microstructures (∼400 MPa) was greater than that of the F–P microstructure (∼340 MPa) At load ratios less than 05, the threshold for long crack growth was lower for the F–B–M microstructure compared with that of the F–P microstructure This is attributed to the reduced roughness-induced crack closure (RICC) contribution to the threshold in the former multiphase microstructure A quantitative analysis of the near-threshold fracture surfaces validated the above conclusion Fatigue crack growth rate in the Paris regime was found to be independent of the microstructure but dependent on the load ratio

On the fatigue threshold behaviour of two ferrite-pearlite microalloyed steels

Abstract: Long crack fatigue threshold (A K th ) and crack closure behaviour of two thermomechanically processed microalloyed (MA) ferrite-pearlite steels are reported. A K th and crack closure were measured using a dynamic compliance measurement technique. Crack closure was observed at low load ratios (R < 0.5) and the fatigue thresholds decreased with increasing load ratio. In both steels, the closure-free intrinsic threshold (A K eff th ) was found to be independent of the load ratio.

Fatigue crack growth behaviors in hot-rolled low carbon steels: A comparison between ferrite–pearlite and ferrite–bainite microstructures

Abstract: The roles of microstructure types in fatigue crack growth behaviors in ferrite–pearlite steel and ferrite–bainite steel were investigated. The ferrite–bainite dual-phase microstructure was obtained by intermediate heat treatment, conducted on ferrite–pearlite hot-rolled low carbon steel. This paper presents the results from investigation using constant stress-controlled fatigue tests with in-situ scanning electron microscopy (SEM), fatigue crack growth (FCG) rate tests, and fatigue fractography analysis. Microscopy images arrested by in-situ SEM showed that the fatigue crack propagation in F–P steel could become unstable more ealier compared with that in F–B steel. The fatigue cracks in ferrite–pearlite were more tortuous and could propagate more freely than that in ferrite–bainite microstructures. However, frequent crack branching were observed in ferrite–bainite steel and it indicated that the second hard bainite phase effectively retarded the crack propagation. The variation of FCG rate ( da / dN ) with stress intensity factor range (Δ K ) for F–P and F–B steels was discussed within the Paris region. It was shown that FCG rate of F–P steel was higher than that of F–B steel. Moreover, the fatigue fracture surface analysis proved that grain boundaries could also play a role in the resistance of crack propagation.

High cycle fatigue behaviour of a multiphase microalloyed medium carbon steel: a comparison between ferrite–pearlite and tempered martensite microstructures

Abstract: To improve toughness and fatigue strength, a mutiphase (ferrite (F)–bainite (B)–martensite (M)) microstructure was developed in a V-bearing medium carbon microalloyed (MA) steel through a two-step cooling process that was followed by an annealing (two-step cooling and annealing (TSCA)) treatment In the present paper, the high cycle fatigue (HCF) response determined in terms of the endurance limit, long crack fatigue threshold (ΔKth), crack closure and fatigue crack growth rate (FCGR) in a material that has a multiphase microstructure is presented and compared with those of the same material with a ferrite–pearlite (F–P) and a tempered martensite (T–M) microstructure obtained by air-cooling (AC) and quenching and tempering (Q&T), respectively Long crack fatigue threshold (ΔKth) and crack closure were evaluated using a dynamic compliance (DYNACOMP) measurement technique The fatigue limit of the F–B–M and the T–M microstructures (∼400 MPa) was greater than that of the F–P microstructure (∼340 MPa) At load ratios less than 05, the threshold for long crack growth was lower for the F–B–M microstructure compared with that of the F–P microstructure This is attributed to the reduced roughness-induced crack closure (RICC) contribution to the threshold in the former multiphase microstructure A quantitative analysis of the near-threshold fracture surfaces validated the above conclusion Fatigue crack growth rate in the Paris regime was found to be independent of the microstructure but dependent on the load ratio