Page 106 - Biaxial Multiaxial Fatigue and Fracture

Multiaxial Fatigue Life Estimations for 6082-T6 Qlindrical Specimens Under ... 91

Table 2. Experimental results: fully-reversed bending tests.

Specimen a, a,, txllr z~,,,, 6 A Nf2%
Code [MPa] [MPa] [MPa] [MPa] ["I [Cycles]
P5B5 224 -1 4 0 0 0 52990
PlBl 190 0 5 7 0 0 159000
P7B1 188 -1 4 0 0 0 197275
P2B2 180 -4 4 -1 0 0 244403
P8B3 162 0 3 1 0 0 421560
P3B3 165 -2 4 1 0 0 437636
P4B4 145 -1 4 1 0 0 1060730
P6B4 145 -1 4 0 0 0 1235690

Table 3. Experimental results: fully-reversed torsion tests.

Specimen U, Ux,m 'Cxyr Zxy,m 6 A Nf$%
Code [MPa] [MPa] [MPa] [MPa] ["I [Cycles]
P14T2 14 1 138 0 0 9.9 14695
P10T2 18 3 139 0 0 7.7 23052
PllT3 15 1 111 0 0 7.4 67690
P12T3 16 1 111 0 0 6.9 113455
P13T1 13 3 99 0 0 7.6 196555
P9T1 24 0 98 0 0 4.1 449997
P16T4 15 2 86 1 0 5.7 497990
P15T4 15 1 87 0 0 5.8 11OoooO

CRACKING BEHAVIOUR

The complex cracking behaviour showed by the material under complex fatigue loadings was a
consequence of the morphological structure of the studied 6082-T6 generated by the extrusion
manufacturing process. This orientated grains mainly along the extrusion axis and it favoured the
initiation of small cracks evenly distributed on the specimen surface and oriented along the
specimen axis.
Under bending loading, shear crack nucleation was followed by growth on the plane of
maximum principal stress (MODE I growth), independently of the bending stress amplitude levels.
As expected, the crack initiation occurred in correspondence of the maximum bending stress
points, so two different cracks were present on the surface of each specimen.