Failure Criteria and Cumulative Damage in Fatigue Under Multi-Axial Stress Conditions

Previous investigations into fatigue under multiaxial stress, and also cumulative damage under uniaxial stress, are discussed in conjunction with the parameters relevant to the present experimental investigation. A biaxial fatigue machine is described which can subject thin wall tubes to combinations of fluctuating internal pressure and either fluctuating longitudinal tension or compression covering the complete ++ and +- stress quadrants. The machine is also provided with independent eight stage programmers in both pressure circuits. Constant amplitude fatigue tests have been carried out on thin wall aluminium alloy (2L65) tubular specimens over the complete ,++ and +- stress quadrants. V, 4 new equation for predicting the fatigue failure of ductile metals under multiaxial stress is proposed based on the maximum range of shear stress modified for the effects of the normal stress acting on the maximum shear stress plane and of anisotropy. ý' This equation is shown to give excellent agreement with all published data on fatigue under uniaxial stress and multiaxial stress viz. combined bending and twisting and thin and thick wall cylinder data. A simplified equation, neglecting the effect of the range of normal stress, is suggested for design purposes. Two level biaxial block programme tests, at constant and two step principal stress ratio, have also been carried out on the same aluminium alloy. The results of these tests are discussed with reference to the cumulative damage theories of. failure developed for the case of uniaxial fatigue stress. A new approach to fatigue anal

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

City University London

Year dc:date.issued

1972

Author dc:creator

• McDiarmid, D.L.

• TA Engineering (General). Civil engineering (General)