Page 446 - Biaxial Multiaxial Fatigue and Fracture

430 I: ITOH AND I: MIYAZAKI

Fig.6. Strain waves and definition of strain range for some cases.

considered to be described by a combination of strain waves appearing on the I and 11-planes.
In this study, therefore, the strain cycle is counted for each strain wave based on the Rainflow
counting method. According to the counting method, the strain path in Fig.3 is divided into
strain ranges, A&'! and Ae21 on the I-plane and Ad11 and AE~I~ on the II-plane as shown in Fig.5.
As examples, Figure 6 shows the cyclic counting for the strain paths of Case 1, 12 and 7. In
Case 1, a cruciform strain path, where the tension-compression and the reversed torsion strains
are loaded alternately, the principal strain direction is changed by an angle of 45 degrees in the
specimen. In this case, the strain waves on the I and 11-planes have along the full strain path one
cycle of full reversed straining alternately applied to each plane. In Case 12, i.e, for the box
shape straining, one cyclic fully reversed strain wave appears on both the I and the 11-plane with
a strain phase of 90 degrees. In the steps straining of Case 7, the strain path is divided into one
strain range with large amplitude on the I-plane, Ad1, and several strain ranges with relatively
small amplitudes on the 11-plane, Ad11 and AE211. In this case, the strain cycles are counted along
the full strain path as one cycle for A&'[, three for Ad11 and two for respectively.
Table 2 lists for each case the amplitudes of each strain range and their counted cycles for one
complete path. In this table, the strain ranges are normalized by A&!.