A crack growth criterion in research on cyclic cracking resistance in elevated-plasticity materials
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Existing methods of determining parameter δ have not been widely used in testing because of imperfections. The basis of the proposed method is to estimate features in the strain pattern around a crack vertex that make themselves felt in displacement discontinuity. The method is based on measuring the distances between marks on the side surface. These are used in constructing the increment in the measurement baseline in a loading cycle as a function of the magnitude of the latter, which is extrapolated to zero baseline to determine the true Δδ.
The method has been tested on electrotechnically pure aluminum as a model material with high plasticity. It is found to be possible to use the A6 criterion determined by this method. The linear mechanics of failure does not give an unambiguous description for fatigue failure in aluminum because the crack growth kinetics may be dependent on the crack length. At the same time, the growth rate is unambigously determined by the vertex cyclic opening over a wide range in crack length. In a log-log plot, the kinetic diagram for fatigue failure is described satisfactorily by a straight line, so 6 is recommended as a better criterion for evaluating cyclic cracking resistance in plastic materials.
KeywordsCrack Length Growth Kinetic Plastic Material Pure Aluminum Cyclic Opening
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