Page 308 - Biaxial Multiaxial Fatigue and Fracture

292 T FUKUDA AND H. NISITANI

S20C and S45C. After turning, the specimens were annealed in vacuum at 650°C for one hour,
and were then electropolished to the depth of about 20 p m to remove the surface layer.

EXPERIMENTAL RESULTS AND DISCUSSION
Local normal strain in tensile static test

Figures 3 and 4 show the changes of surface state in the tensile tests of S45C and SC450
materials. The axial direction is the loading direction. It can be seen that square grids are
deformed into nearly rectangular grids due to the axial elongation by tension. The degrees of
their deformations are almost the same, since circumferential grid lines are nearly straight.
Namely, there is not a large difference between the deformations of ferrite and pearlite bands.
Consequently, the strain concentration in tension is small.

n= 1 n= 1.
2 2
3 3

10
10
(a) tg=0% (b) E g= 12%

Fig.3. The changes of surface state in the tensile test of S45C

n= 1 n= 1
2 2
3 3

10
10
(a) E~=O% (b) E g= 12%
Fig.4. The changes of surface state in the tensile test of SC450