Page 98 - Biaxial Multiaxial Fatigue and Fracture

BiaxiaVMultiaxial Fatigue and Fracture
Andrea Carpinteri, Manuel de Freitas and Andrea Spagnoli (Eds.)
0 Elsevier Science Ltd. and ESIS. All rights reserved. 83

MULTIAXIAL FATIGUE LIFE ESTIMATIONS FOR 6082-T6 CYLINDRICAL
SPECIMENS UNDER IN-PHASE AND OUT-OF-PHASE BIAXIAL LOADINGS

Luca SUSMEL' and Nicola PETRONE2
'Department of Engineering, University of Ferrara,
Via Saragat 1, 44100 Ferrara, Italy
'Department of Mechanical Engineering, University of Padova,
Via Venezia I, 35131 Padova, Italy

ABSTRACT

Fully reversed bendinghorsion fatigue tests were conducted on 6082-T6 solid cylindrical
specimens under force control. Specimens were subjected to pure bending, pure torsion, in-phase
and out-of-phase bendinghorsion loadings and the investigated fatigue lives ranged between lo4
and 2-106 cycles to failure. The actual strains were measured by means of strain gauges positioned
in correspondence of critical points. Experimental strain measurements highlighted that all the
tests were conduced in pure elastic stress conditions. The material fatigue behaviour was studied
by analysing the cracks pattern due to the considered biaxial loadings. All the tests showed that
crack initiation was always MODE I1 dominated (that is, it occurred on the plain of maximum
shear stress amplitude), whereas the crack propagation was MODE I governed. Just in the
presence of pure torsional loadings cracks grew under MODE I1 loadings. A good correlation with
measured fatigue lives was obtained by applying the Susmel and Lazzarin's criterion valid for
homogeneous and isotropic materials, despite the slight degree of anisotropy showed by the
material.

KEYWORDS
Biaxial fatigue loadings, multiaxial fatigue life prediction, cracking behaviour.

INTRODUCTION

In the most genera1 situations mechanical components are subjected to complex fatigue loadings
that generate multiaxial stress states in correspondence of critical points. During the last 60 years
the problem of multiaxial fatigue assessment has been extensively investigated by researchers in
order to provide engineers with safe methods for the fatigue life prediction in the presence of
complex stress states. The state of the art shows that the problem can be faced by using two
different approaches [l, 21: in the low cycle fatigue ambit (that is, when the damage contribution