A Fracture Mechanics Based Fatigue Life Prediction For Welded Joints Of Square Tubes.pdf

Thin-WalledStructures 21 (1995) 107-120
© 1995 Elsevier Science Limited
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ELSEVIER 0263-8231(94)00028-X
A Fracture Mechanics Based Fatigue Life Prediction
for Welded Joints of Square Tubes
J. M. Ferreira, a A. H. Pereira a & C. M. Branco b
"Dep. Eng. Mec~nica, FCT/UC, University of Coimbra, 3000 Coimbra, Portugal
~CEMUL, Lisbon Institute of Technology, 1096 Lisbon Codex, Portugal
(Received 1 July 1992; accepted 23 May 1994)
ABSTRACT
Square tubes of mild and low alloy steels are extensively used in vehicle
structures and offshore platforms. Despite this fact the fatigue behaviour of
welded nodes of these tubes is not sufficiently known, especially in thin
sections.
The paper presents the results of fatigue life predictions based on frac-
ture mechanics, in non-load carrying T and also load carrying cruciform
joints. The fatigue life prediction models include crack initiation and crack
propagation. The stress intensity factor formulations were obtained using
the weight function solution for semi-elliptical surface cracks with the
puted using a three-dimensional finite element program.
The prediction results pared with experimental results and a
good agreement was obtained. The tube material was mild steel St 37 (DIN
17100). The loading modes were in-plane three point bending and canti-
lever bending or tension.
1 INTRODUCTION
In vehicle structures and offshore constructions the main structural
elements are made of thin-walled rectangular and square sections. These
types of bine low weight with high values of the bending
and torsion modules. In these structures fatigue failures should be avoided
and therefore an appropriate fatigue design is required.
Research work in the field of static and fatigue behaviour of welded
107
108 J. M. Ferreira, A. H. Pereira, C. M. Branco
rectangular tubes has been carried out by,