Page 502 - Biaxial Multiaxial Fatigue and Fracture

486 G. SHATIL AND N. ERSOY

where N * are the modified cycles to failure for a particular surface strain range and Nfnis
fD
the number of cycles to failure at a certain depth along the critical path, corresponding to the
average incremental strain En at that depth, Fig. Ib. This model improved life prediction of
axisymmetric notch specimens and consequently was applied to a car component [19].

do dl d2 d3
Depth from the surface
c
(b)

Cycles to Failu; Nf

Fig.1. Subsurface strain and life calculations using the Shatil and Smith model [6]: (a) average
strains and strain increments; and (b) life to failure using the calculated average strain.

More recently, Qilafku et a1 [S, 121 and Bentachfine et a1 [Ill used similar principles to
those suggested by Shatil and Smith [6] to develop a fatigue failure parameter for the HCF
fatigue region using damage accumulation in a local damage process zone. The relative values
of the stress gradient to the surface were integrated along a critical path and this was directly