Page 419 - Biaxial Multiaxial Fatigue and Fracture

Cyclic Behaviour of a Duplex Stainless Steel Under Multiaxial Loading: Experiments and Modelling 403

EXPERIMENTAL PROCEDURE
In order to characterize the behaviour of the steel studied under complex cyclic loading,
tension-compression tests and tension-compressiodtorsion tests were carried out on INSTRON
servohydraulic machines. Specimens and grips were designed to avoid any play between the
grips and the specimen when the load reverses [29]. A drawing of the specimens is given in
Fig. 2. Earlier investigations with both geometries 1291 have shown the specimens to be well
suitable for axial and torsional deformation studies.

Fig. 2. Specimen geometries: (a) for tension-compression tests, (b) for biaxial tests.

A biaxial extensometer clipped on the specimen measured axial strain E and distortion y.
Axial stress G and shear stress z were calculated from load and torque measured by a load cell,
using the assumption of thin-walled tubes. Equivalent stress ceq and equivalent plastic strain
E' were defined by von Mises equivalence for tensiodtorsion loading as :
eq