This dissertation first discusses the history of fatigue studies, various theories of fatigue failure and the factors affecting fatigue strength. The fatigue tests on axially loaded fillet weldments and built-up beams of American and European structural steels are reviewed. Since a quenched and tempered constructional alloy steel was used in the test program, all existing fatigue studies of this material are presented next. Review of the literature indicated that prior to the test program described the fatigue specimens used to study longitudinal fillet welds did not realistically simulate prototype conditions. An axially loaded welded specimen is presented that gives a true measure of the fatigue strength of a longitudinal fillet weld. This welded specimen is relatively simple to fabricate and may be tested in any of the modern structural fatigue testing machines. It is shown that this welded specimen simulates the flange-to-web fillet weld in the pure moment region of a built-up beam as well as any welded built-up tension-compression member. Direct similitude is obtained where the stress state is essentially uniaxial tension. As long as the load-strain relationship in the longitudinal fillet weld is the same in the welded specimen as in a built-up beam, the stress spectrum is reproduced. It is shown that the stresses in the remainder of the cross section have no effect on the fatigue strength of the weld. For longitudinal fillet welds under combined stresses (for example, in the shear span of a built-up beam), a hypothesis of fatigue failure is presented. This hypothesis, utilizing the distortion energy failure criterion, predicts the fatigue strength of weldments in a combined stress state if their fatigue strength in uniaxial tension is known. The following factors affecting the service life of most large, cyclically loaded steel structures are considered: maximum stress stress range,surface condition, welding procedure, and moisture in the welding flux. The dissertation shows that the stress range is the most important stress parameter affecting service life. Surface condition and welding procedure have little effect on the fatigue strength of weldments but the presence of moisture in the welding flux carn lower the fatigue strength of a weld.

"A Study of the Fatigue Resistance of Longitudinal Fillet Weldments in Steel," Dissertation Abstracts, v. 25, no. 1, 1964, PhD Dissertation, Lehigh University, 1963.