Abstract
Stress controlled multiaxial fatigue test was carried out using a hollow cylinder specimen of type 316 stainless steel. A newly developed fatigue testing machine which can apply push-pull loading and reversed torsion loading and inner pressure to the hollow cylinder specimen was employed. 5 types of cyclic loading paths were employed by combining zero to pull axial and hoop stresses: a Pull (only axial stress), an Inner-pressure (only hoop stress), an Equi-biaxial (equi-biaxial stress by axial and hoop stresses), a Square-shape (trapezoidal waveforms of axial and hoop stresses with 90-degree phase difference) and a L-shape (alternately axial stress and hoop stress) loading paths. Since directions of principal stresses are fixed in all the tests, all of the loading paths are classified into ‘proportional loading’. In the Pull, the Inner-pressure and the Equi-biaxial tests, fatigue lives can be correlated on a unique line by a maximum equivalent stress based on von Mises. On the other hand, fatigue lives in the Square-shape and the L-shape tests were reduced comparing with that in the other tests, which was caused by yielding of larger plastic deformation.
Highlights
M any mechanical structures undergo multiaxial loading by diverse force
In the multiaxial fatigue under non-proportional loading in which directions of principal stress and strain are changed in a cycle, it has been reported that fatigue lives are reduced accompanying with additional hardening which depends on both loading path and material [4,5,6,7,8,9,10,11,12,13,14,15,16]
To perform fatigue tests under wider stress ratio range like an equi-biaxial loading path, the testing machine need to be installed an actuator for inner pressure
Summary
M any mechanical structures undergo multiaxial loading by diverse force. The equivalent stress based on von Mises (Mises stress) is generally used in that design for structures under multiaxial loading. In the multiaxial fatigue under non-proportional loading in which directions of principal stress and strain are changed in a cycle, it has been reported that fatigue lives are reduced accompanying with additional hardening which depends on both loading path and material [4,5,6,7,8,9,10,11,12,13,14,15,16]. The most common testing machine for multiaxial fatigue can perform only the push-pull loading and the reverse torsion loading which limits the stress ratio range from 1 to 0. To perform fatigue tests under wider stress ratio range like an equi-biaxial loading path, the testing machine need to be installed an actuator for inner pressure. The testing machine is an electric servo controlled multiaxial fatigue testing machine, which can combine the push-pull and the reversed torsion loads and the cyclic inner pressure. The effect of loading paths on fatigue lives was discussed from the fatigue tests and observation of specimen surface
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