Influence of inclusion type on the very high cycle fatigue properties of 18Ni maraging steel

Nicht verfügbarThe very high cycle fatigue (VHCF) properties of four 18Ni maraging steels were investigated. Ultrasonic fatigue tests were performed on thin sheets with nitrided surfaces at load ratio R = 0.1. Traditional maraging steel containing Ti (material A) showed crack initiation at TiN-inclusions. The elimination of Ti and the increase in Co content (material B) lead to preferential crack initiation at aluminate-inclusions. Aluminate-inclusions are less damaging than TiN-inclusions, and material B shows higher VHCF strength than material A. A further developed maraging steel (material C) with reduced Co content that is compensated for by alloying with Al showed crack initiation at aluminate- as well as at Zr(N,C)-inclusions. Zr(N,C)-inclusions are more damaging than aluminate-inclusions and less damaging than TiN-inclusions. The highest VHCF strength was found for a recently developed alloy with further increased Al content (material D). In addition to inclusion-initiated fracture, this material showed shear mode crack initiation in the nitrided zone at the surface.(VLID)192917

SBML Level 3: an extensible format for the exchange and reuse of biological models

Systems biology has experienced dramatic growth in the number, size, and complexity of computational models. To reproduce simulation results and reuse models, researchers must exchange unambiguous model descriptions. We review the latest edition of the Systems Biology Markup Language (SBML), a format designed for this purpose. A community of modelers and software authors developed SBML Level 3 over the past decade. Its modular form consists of a core suited to representing reaction-based models and packages that extend the core with features suited to other model types including constraint-based models, reaction-diffusion models, logical network models, and rule-based models. The format leverages two decades of SBML and a rich software ecosystem that transformed how systems biologists build and interact with models. More recently, the rise of multiscale models of whole cells and organs, and new data sources such as single-cell measurements and live imaging, has precipitated new ways of integrating data with models. We provide our perspectives on the challenges presented by these developments and how SBML Level 3 provides the foundation needed to support this evolution

Effects of Non-Metallic Inclusions and Mean Stress on Axial and Torsion Very High Cycle Fatigue of SWOSC-V Spring Steel

Inclusion-initiated fracture in high-strength spring steel is studied for axial and torsion very high cycle fatigue (VHCF) loading at load ratios of R = −1, 0.1 and 0.35. Ultrasonic S-N tests are performed with SWOSC-V steel featuring intentionally increased numbers and sizes of non-metallic inclusions. The fatigue limit for axial and torsion loading is considered the threshold for mode I cracks starting at internal inclusions. The influence of inclusion size and Vickers hardness on cyclic strength is well predicted with Murakami and Endo’s area parameter model. In the presence of similarly sized inclusions, stress biaxiality is considered by a ratio of torsion to axial fatigue strength of 0.86. Load ratio sensitivity is accounted for by the factor ((1 − R)/2)α, with α being 0.41 for axial and 0.55 for torsion loading. VHCF properties under torsion loading cannot appropriately be deduced from axial data. In contrast to axial loading, the defect sensitivity for torsion loading increases significantly with superimposed static mean load, and no inclusion-initiated fracture is found at R = −1. Size effects and the stress gradient effective under torsion loading are considered to explain smaller crack initiating inclusions found in torsion ultrasonic fatigue tests

Mean-stress sensitivity of an ultrahigh-strength steel under uniaxial and torsional high and very high cycle fatigue loading

Abstract The influence of load ratio on the high and very high cycle fatigue (VHCF) strength of Ck45M steel processed by thermomechanical rolling integrated direct quenching was investigated. Ultrasonic fatigue tests were performed under uniaxial and torsional loading at load ratios of R = −1, 0.05, 0.3, and 0.5 with smooth specimens and specimens containing artificially introduced defects. Up to 2 × 10⁵ cycles, failure originated from surface aluminate inclusions and pits under both loading conditions. The prevailing fracture mechanisms in the VHCF regime were interior crack initiation under uniaxial loading and surface shear crack initiation under torsional loading. The mean-stress sensitivity and the fatigue strength were evaluated using fracture mechanics approaches. Equal fatigue limits for uniaxial and torsional loading were determined considering the size of crack initiating defects and the appropriate threshold condition for Mode-I crack growth. Furthermore, the mean-stress sensitivity is independent of loading condition and can be expressed by ${\sigma}_{\mathrm{w}}(R)={\left.{\sigma}_{\mathrm{w}}\right|}_{R=-1}\cdotp {\left(\frac{1-R}{2}\right)}^{0.63}$ and ${\tau}_{\mathrm{w}}(R)={\left.{\tau}_{\mathrm{w}}\right|}_{R=-1}\cdotp {\left(\frac{1-R}{2}\right)}^{0.63}$