Abstract
A fatigue life calculation method for structural elements made of D16CzATW aluminium alloyIn the calculating of fatigue life of structural elements the methods based on hypotheses of fatigue damage summation are commonly applied. In using the methods, apart from choice of an appropriate hypothesis, it is necessary to know a loading spectrum which usually constitutes a set of sinusoidal cycles of variable parameters (Sa, Sm), as well as fatigue characteristics in the form of Wöhler fatigue diagram, as a rule. Knowledge of the above mentioned data is low during structural design process as designed material objects and possibility of performing measurements are lacking.Hence in this work a calculation method of fatigue life of structural elements, based on the relations between fatigue life diagrams determined in constant-amplitude conditions (Wöhler diagrams) and those obtained under programmed or random loads, is described. The proposed method was experimentally verified by using results of fatigue tests on structural elements made of D16CzATW aluminium alloy.
Highlights
Lack of a coherent theory of fatigue process of materials including metals and their alloys makes that for engineering applications are used phenomenological hypotheses on summation of damages, whose description can be found a.o. in the monographs [1] and [2]
In the first group of the tests, apart from the monotonic tension test, Wöhler fatigue diagrams have to be determined, as well as the test aimed at determination of value of the power exponent r appearing in the formula (5), has to be performed with the use of plain specimens under random loading conditions
The fact results from the greater spread of results of fatigue life tests of the riveted element which is deemed incommensurably more complex from the point of view of run of fatigue process depending on various factors
Summary
Lack of a coherent theory of fatigue process of materials including metals and their alloys makes that for engineering applications are used phenomenological hypotheses on summation of damages, whose description can be found a.o. in the monographs [1] and [2]. For the calculations with the use of the damage summation hypotheses it is necessary to know operational loads (stresses or strains) given in the form of loading spectra, as well as an appropriate fatigue diagram. Such loading spectra are elaborated by applying the cycle - counting methods described in [7], in order to obtain a set of sinusoidal cycles equivalent, as regards fatigue life, to random loading. The drawbacks of the method have been very clearly felt in structural design process where accurate data on operational loads, material cyclic properties and damage summation hypothesis, are lacking
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