Page 199 - Biaxial Multiaxial Fatigue and Fracture

BiaxiallMultiaxiaI Fatigue and Fracture
Andrea Carpinten, Manuel de Freitas and Andrea Spagnoli (Eds.)
Q Elsevier Science Ltd. and ESIS. All rights reserved. 183

ESTIMATION OF THE FATIGUE LIFE OF HIGH STRENGTH STEEL UNDER
VARIABLE-AMPLITUDE TENSION WITH TORSION:
USE OF THE ENERGY PARAMETER IN THE CRITICAL PLANE

Tadeusz EAGODA', Ewald MACHA', Adam NIESEONY' and Franck MOREL*
1 Technical University of Opole, ul.Mikolajczyka 5, 45-271 Opole, Poland
ENSMA, Futuroscope, France

ABSTRACT

The paper concerns application of the energy parameter, being a sum of the elastic and plastic
strain energy density in the critical plane, for describing experimental data obtained in fatigue
tests of 35NCD16 steel, subjected to constant amplitude tension-compression, torsion and vari-
able amplitude tension-compression, torsion and combined proportional tension with torsion. It
has been shown that the normal strain energy density in the critical plane is a suitable parameter
for correlation of fatigue lives of 35NCD16 steel under considered kinds of loading. The criti-
cal plane is the plane where the normal strain energy density reaches its maximum value.

KEYWORDS

Biaxial fatigue, proportional loading, variable amplitude, fracture plane, energy criterion, life
time

INTRODUCTION

There are three main models of multiaxial fatigue failure criteria applied for reduction of the
complex loading state to the equivalent uniaxial state. They are stress, strain and energy - based
models.
The proposed energy criteria can be classified into three groups, depending on the strain en-
ergy density per cycle, assumed as a damage parameter under multiaxial fatigue [l - 31. They
are:
- criteria based on the elastic strain energy for high-cycle fatigue,
- criteria based on the plastic strain energy for low-cycle fatigue,
- criteria based on the sum of the elastic and plastic strain energy for low- and high-cycle
fatigue.
At present, the criteria including the strain energy density in the critical plane or in the frac-
ture plane become dominating in energy description of multiaxial fatigue. These criteria seem
to be the most promising for future applications. The authors proposed the energy approach to
fatigue life estimation under multiaxial random loading [4 - 91. In the case of uniform stress