Fatigue Crack Paths 2003

C A L C U L A TAENDDE X P E R I M E N TRAELS U L T S

Figure 3 includes some photos of fatigue crack lines. It can be noticed that for most of

the specimens the fatigue crack line is formed in one direction (in macroscopic scale).

Twoexceptions occur, one for pure torsion and one for combined torsion with bending

when the cross correlation coefficient between normal and shear stresses rσ= -0.01 and

for stress ratio λσ=0.97. For these two cases of loading cracks initiate in the plane of

maximumshear stress and then branches and propagates in the plane of maximum

normal stress.

rσ= 1.0, λσ=0.5

rσ= 0.5, λσ=0.54

rσ= -0.01, λσ=0.56

r σ = 1.0, λ σ = 1.0

rσ= 0.5, λσ=0.97

rσ= -0.01, λσ=0.97

Figure 3. The chosen photos of fatigue crack lines

Experimental results of crack lines slope

and calculated values of the critical

expˆα

planes positions

calαˆ are presented in table 2. In the case of weight functions W1, W2

and W3, the calculated angles

cal αˆ describe the angle between the averaged direction of

maximum principal stress σ1 and specimen axis. For weight function W4 angle

)W(ˆ4calα describes an angle between averaged direction of maximumshear stress τ13

and specimen axis.