Fatigue fractures

Fatigue strength determination of ship structural joints

“…It results from many factors among which the following are most important: a) the material fatigue phenomenon itself has been not sufficiently recognized so far due to complex influence, on run of fatigue changes, of such factors as: kind of [5] Unauthenticated Download Date | 5/11/18 6:02 PM material (its structure, mechanical properties, chemical composition), loading mode (its magnitude, effect of mean stresses), structural element geometry, impact of environmental conditions etc [7], b) difficulties in unambiguous determining loads applied to the entire hull structure and its particular elements (zones, joints) as well, both as to load components, their directions and simultaneity of action, c) different state of protective coating in particular ship zones, which may cause different run of phenomena because of a different degree of environmental influence, d) interaction of geometrical, technological and material notches.…”

“…a weld together with micro-defects contained in it), leads to shortening crack initiation phase and this is crack propagation phase which decides on total fatigue life of the element, i.e. Nc ≈ Np [7,8,29,30,31].…”

“…Therefore the information on fatigue crack growth rate in a given material as well as welded joint zones (HAZ, weld -deposited metal) corresponding to it becomes especially important as it makes it possible to classify materials as to its capability of resisting the so called final fatigue under given loading conditions [7] and to determine fatigue life of structural element especially in the limited fatigue life range. The growth rate at a given crack length l, i.e.…”