Page 479 - 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. 463

FATIGUE ASSESSMENT OF MECHANICAL COMPONENTS
UNDER COMPLEX MULTIAXIAL LOADING

JosC L.T. SANTOS, M. de FREITAS, B. LI and T.P. TRIG0
Dept. of Mechanical Engineering, Instituto Superior Tkcnico
Av. Rovisco Pais, 1049-001 Lisboa, Portugal

ABSTRACT

This paper addresses an integrated FEM based approach for crack initiation life assessment of
components under complex multiaxial loading. Generally, there are many sources of error in
the computational fatigue damage assessments, including uncertainties in analysing complex
service environments, complex geometries, and lack of usable material information, etc. This
paper is focused in the methodology for handling the effect of non-proportional multiaxial
loading, and in improvements in computational algorithms for reducing the computation time
for fatigue assessments. Since the effective shear stress amplitude is an important parameter for
crack initiation life prediction, the recent approaches on evaluating the effective shear stress
amplitude under comlex loading paths are studied and compared by examples. The MCE
approach developed on the basis of the MCC approach is described in detail, and it is shown
that this approach can be easily implemented as a post-processing step within a commercial
FEM code such as ANSYS. Fatigue assessments of two application examples are shown, using
the computational procedure developed in this research. The predicted fatigue damage contours
are compared for proportional and non-proportional loading cases, it is concluded that the
fatigue critical zone and fatigue damage indicator vary with the combined conditions of
multiaxial fatigue loading. Advanced multiaxial fatigue approaches must be applied for fatigue
assessments of components/structures under complex multiaxial loading conditions, to avoid
unsafe design obtained from the conventional approaches based on the static criteria.

KEYWORDS

Multiaxial fatigue, fatigue damage evaluation, computational durability assessment, fatigue life
prediction.

LNTRODUCTION

Due to the increasing pressure of market competition for light weight design and fuel economy,
computational durability analysis of engineering components/structures is more and more used
in today’s industrial design for reducing prototype testing and shortening the product
development cycle [ 1 I. Since it is widely recognized that about 80% of mechanical/structural
component failures are related to fatigue, structural fatigue life has become the primary concern
in design for durability.