Fatigue Crack Paths 2003

L2

0

σ = σ

∫

L12

(1)

a,dr

θ

0

where σθ,a was the amplitude of the stress component perpendicular to the direction,

emanating from the notch tip, which experienced the maximumrange of the normal

stress, σ0 was the fully-reversed plain fatigue limit and L was the El Haddad’s short

crack constant defined as [5]:

2

(2)

⎜ ⎜ ⎝ ⎛

⎟ ⎟ ⎞

L

= π Δ

t h K 1

σΔ

⎠

0

The M W ChaMs been applied as:

− τ + τ

(3)

⎜⎝⎛

σ

⎟⎠⎞ τσ

2

τ≤

a

0

0

amax,n

0

where τa and σn,max were the shear stress and the maximumnormal stress relative to the

plane of maximumshear stress amplitude passing through the point positioned along the

notch bisector at a distance from the notch tip equal to L/2. Here σ0 and τ0 were the

fully-reversed plain uniaxial fatigue limit and the fully-reversed plain torsional fatigue

limit, respectively.

In the present paper, stress fields along the

F = force f =displacement

measured crack paths have been studied

FfF

systematically

to form some hypotheses

capable of explaining the reason both methods

work even though the C D Mis based on a mode

γ

I governed fatigue damage, whereas the

β

M W CisMa crack initiation criterion.

r n

E X P E R I M E N TDAELTAILS

a

The material employed in the present study

was BS 040A12 low carbon steel, having the

following mechanical properties:

tensile

w

strength σT=410 MPa, fully-reversed axial

fatigue limit σ0=273 MPa, fully-reversed

torsional fatigue limit τ0=171 MPa and El

Haddad’s short-crack constant L=0.2 mm. In

phase mode I and mode II loadings have been

f

generated by using specimens having

geometries directly derived from the compact

tension-shear specimens [1, 2]. In our samples

Figure 1. Notch geometry and

cracks were substituted for V-shaped notches

symbolism.

having a nominal opening angle of 60°.