SYMPOSIA PAPER Published: 01 January 1992

Nonproportional Fatigue of Welded Structures


Bending and shearing stresses in many structures are out-of-phase. A typical example is the evaluation of a fixed position in a bridge beam as a moving load crosses it. Traditional fatigue design approaches for welded structural details are generally based on inphase laboratory data. Thus the effect of nonproportional stress histories on the fatigue life of welded structural details is usually not considered. Stress-relieved tube-to-plate weldments were subjected to multiaxial in-phase and out-of-phase stress states using combinations of bending and torsion. The fatigue test results were evaluated using three local stress damage criteria modified for multiaxial loading. Finite element techniques were used to calculate the local stresses and strains. The local shear-stress based approach of Findley provided the best correlation of all test data for the loading paths considered. The unique aspects of nonproportional loading are reflected by the Findley model fatigue damage calculations, and the test data were correlated to within a factor of two. Since the scatter in the experimental data was also a factor of two for identical tests, further improvements in predictive ability are not possible. Also, the predicted direction of fatigue damage for the Findley model coincided with surface cracking characteristics.

Author Information

Siljander, A
University of Illinois at Urbana-Champaign, Urbana, IL
Kurath, P
University of Illinois at Urbana-Champaign, Urbana, IL
Lawrence, FV
University of Illinois at Urbana-Champaign, Urbana, IL
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Developed by Committee: E08
Pages: 319–338
DOI: 10.1520/STP24166S
ISBN-EB: 978-0-8031-5185-7
ISBN-13: 978-0-8031-1423-4