Page 228 - Biaxial Multiaxial Fatigue and Fracture

212 A. VARVANI-FARA HANI

Figure 4 presents an out-of-phase biaxial block fatigue loading at a frequency ratio at2 and
the corresponding largest stress and strain Mohr's circles within a block loading history. A
block loading history contains two GI cycles and one 02 cycle having a phase delay of (~90".
The first reversal of GI cycle loaded from zero level while the 02 cycle is under tensile stress.
At the first cycle, the maximum shear strain and stress ranges were numerically calculated at
10" increments and the largest Mohr's circles have been obtained at 81=90" and 82=270"
angles. Similarly, during the second 01 cycle, the reversals of 01 cycle loaded simultaneously
with the second reversal of 02 cycle. At the second 01 cycle, the largest Mohr's circles were
numerically obtained at 03=450" and 84=630° angles (see Fig. 4).
The proposed fatigue parameter for the first 01 cycle is expressed as:

The proposed fatigue parameter for the second 01 cycle is expressed as:

The total damage in a block loading history is calculated by accumulating the parameter for the
block loading history consisting of two (TI Cycles (Pb=Pls&nd).

Stress Mohr's circles Strain Mohr's circles

<
One block loading history

Fig. 4. Out-of-phase biaxial fatigue stressing (history B3) where two axes are at different
frequencies (-2)