For fully reversed strain-controlled experiments, fatigue process consists of crack initiation, small crack growth, and final failure in tension when the strain amplitude is lower than 3.0%.
Fatigue strength and fatigue crack propagation (FCP) characteristic were evaluated and fracture mechanism was discussed on the basis of crack initiation, small crack growth and fracture surface analysis.
Based on the increase in the ultrasonic nonlinearity with fatigue cycling, crack initiation, small fatigue crack growth and fast crack growth regimes have been distinguished during cycling in specimens with different pore sizes tested at various stress amplitudes.
The first, regional model setup is used to investigate the ability of small-scale convection to initiate subduction (see "Subduction initiation by small-scale convection" section).
In this study, we show that subduction initiation by small-scale convection is, however, favoured by a free surface as compared to a vertically fixed, free-slip surface.
The first is a simplistic regional model in 2D Cartesian geometry that is reproduced from a previous study by Solomatov (2004) and intended to characterise subduction initiation by small-scale convection.
A systematic study of failure initiation in small-scale specimens has been performed to assess the effect of size scale on "failure properties" by drawing on the classical analysis of elliptically perforated specimens.
For the study on subduction initiation by small-scale convection enabled by plastic yielding, we therefore present three suites of a simple regional model with either a simple depth-constant yield stress, a depth-dependent yield stress or a more realistic, composite yield stress by superimposing the two previous formulations (see Fig. 1).
Subduction initiation by small-scale convection (after Solomatov 2004) depending on the constant yield stress σ y,const that varies from the dimensional value of (a, d) σ y,const=4.4 MPa (l i d A1 & l i d A4) to (b, e) σ y,const=5.8 MPa (l i d A2 & l i d A5) and (c, f) σ y,const=7.3 MPa (l i d A3 & l i d A6).
Subduction initiation by small-scale convection (after Solomatov 2004) depending on the composite yield stress that is varied between (a, d) σ y,const=7.3 MPa with Δ σ y =0.0045 (l i d C1 & l i d C4), (b, e) σ y,const=8.7 MPa with Δ σ y =0.0054 (l i d C2 & l i d C5) and (c, f) σ y,const=10.2 MPa with Δ σ y =0.0063 (l i d C3 & l i d C6).
This paper deals with the initiation of small cracks in a martensitic steel under low cycle fatigue loading.
