Abstract
In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe stress ratio dependency of crack-closure-mechanisms. Thus, an extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves.The article presents a generalized dataset to assess the formation of crack-closure-mechanisms of cast steel G21Mn5+N. Numerous crack propagation experiments utilizing single edge notched bending (SENB) sample geometries are conducted, incorporating alternate to tumescent stress ratios. The statistically derived, generalized crack growth resistance curve features the impact of closure effects on the crack propagation rate in a uniform manner. To extend the dataset to arbitrary load ratios, the long-crack threshold approach according to Newman is invoked. The generalized dataset for the cast steel G21Mn5+N is validated by analytical fracture mechanical calculations for the utilized SENB-sample geometries. Incorporating a modified NASGRO equation, a sound correlation of analytical and experimental crack propagation rates is observed. Moreover, the derived master crack propagation resistance curve is implemented as a user-defined script into a numerical crack growth calculation tool and supports a local, node--based numerical crack propagation study as demonstrated for a representative SENB-sample. Concluding, the derived dataset facilitates the calculation of fatigue life of crack-affected cast steel components subjected to arbitrary stress ratios.
Highlights
Cast steel is widely utilized in mechanical engineering applications to manufacture complexly shaped components with comparably high-strength in mass-production
Crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading
An extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves
Summary
Cast steel is widely utilized in mechanical engineering applications to manufacture complexly shaped components with comparably high-strength in mass-production. As the crack transits from short- to long-crack growth, propagation is heavily influenced by the build-up of mechanisms like plasticity- or roughness-induced crack-closure These effects lead to an increase of the fatigue effective threshold stress intensity factor range, described as crack growth resistance curves [3]. This setting depends on microstructural material parameters as well as on the effective stress ratio, an extensive number of crack propagation experiments is required to conduct statistically valid fracture mechanical parameters that enable accurate fatigue life calculations of crack-afflicted cast steel components. This features crack growth simulation studies for plain SENB-samples and supports spatially shaped porosities under multiaxial loading
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