Page 239 - 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. 223

FATIGUE ANALYSIS OF MULTIAXIALLY LOADED COMPONENTS WITH THE
FlE-POSTPROCESSOR FEMFAT-MAX

Christian GAIER and Helmut DANNJ3AUER
ECS - Engineering Center Steyr, Magna Steyr
Steyrer Str. 32, A-4300 St. Valentin, Austria

ABSTRACT

The fatigue behavior of machine components is influenced by a lot of parameters as geometry
(notches), load (static - cyclic - stochastic, proportional - nonproportional), material (ductile -
semiductile - brittle), surface roughness, surface treatment, temperature, etc. At the ECS the
software FEMFAT for fatigue analysis has been developed, which is based on elastic Finite
Elements stress results. It can take those influences into account by generating local synthetic
component S/N-curves. Dynamic material data like fatigue limit for tension-compression,
bending and torsion are taken as input to consider notch effects and the different damaging
effect of normal and shear stress. For nonproportional load an extended method of the well-
known critical plane approach is presented, which has been implemented into the multiaxiality
module FEMFAT-MAX. It can be applied even for triaxial stress states and nonproportional
stochastic loads. But for special multiaxial load situations (bending - torsion with phase shift)
the extended critical plane approach delivers good results only for brittle materials. Results for
ductile materials can be strongly on the unsafe side. Suitable corrections of the local S/N-
curves by introducing a new material parameter is presented to overcome these problems.

KEYWORDS
Fatigue analysis, synthetic S/N-curves, critical plane, multiaxial loads, nonproportional loads,
rotating principal stresses.

INTRODUCTION

With increasing capacities of computers the prediction of the lifetime of components by
numerical methods becomes more and more important in the automotive industry, but also in
other areas of mechanical engineering. The number of testing cycles can be reduced by finding
the crack initiation point with suitable software tools and pre-optimization of components,
which saves time and money. At the ECS the software tool FEMFAT for fatigue analysis has
been developed, which is based on elastic Finite Elements stress results. It can be applied for a
wide range of problems: the assessment of uniaxially and multiaxially loaded components as
well as welding seams and spot joints is possible.