Fatigue Crack Paths 2003

Surface

σ ,ε

1. Subsurface point 2 ath 3 la e

Nf

Surface

Nf= f(Σ(εi/Δε))

ε

Reference points

Critical distance

Nf

Nf= f(εi /Δε)

Surface Critical distance

ε

ε

}

Distance

Surface

Nf

Critical distance

4. Subsurface volume

Surface

Internal energy method

Critical distance

Figure 2. Illustration of subsurface fatigue model types.

S U M M A ORFYT H ES U B S U R F ASCTER A I NP A T HA P P R O A C H

The subsurface strain path model, Shatil and Smith [5], belongs to case 2, Fig. 2 and

uses the following assumptions:

a) A critical high strain path up to a critical depth is numerically calculated.

b) A subsurface multiaxial strain parameter along a critical path is divided into equal

increments, and using the material strain-life relation, the life corresponding to the

average strain from each increment is obtained.

c) Contribution to the fatigue damage process from each increment of strain under the

surface is weighted and assumed to decrease with the distance from the surface.

d) A linear accumulation of the subsurface damage is carried out along a critical path.

The average strain from each increment is calculated as, Fig. 3a: