Damage evolution in metals under the loading due to the contact with surface-active liquid

O. Naimark1, M. Bannikov1
1Institute of continuous media mechanics UrB RAS
Abstract
Features of the Rehbinder effect consist in a qualitative change of the development of multi-scale damage kinetics in a deformed sample with presence of surfactants , its influence on the fatigue life of pure iron in gigacycle loading conditions associated with qualitative changes in the role of the surface are discussed. An example of fatigue crack initiation as observed by optical microscopy is shown.Features of the Rehbinder effect consist in a qualitative change of the development of multi-scale damage kinetics in a deformed sample with presence of surfactants (liquid gallium), its influence on the fatigue life of pure iron in gigacycle loading conditions are associated with qualitative changes in the role of the surface. The property of the surface to serve as a "sink" for defects is significantly reduced due to the similarity of the chemical potential of solid and surfactant as a result of "filling-in" incomplete atomic planes that provides an "adiabatic" process of accumulation of the damage in the volume of material. Fatigue tests of iron were carried out on ultrasonic resonant fatigue machine Shimadzu USF-2000 with frequency 20 kHz in the so-called gigacycle fatigue regime when material failure occurs on reaching the number of loading cycles up to 10^9 with very low stress amplitude. Fractured surfaces were analyzed by optical and electronic microscopes to identify the depth of penetration of liquid metal into the fracture area. It is shown that the durability and strength of the material are significantly reduced in the "adiabatic" surface, the region of localization of the defect density is shifted to the surface layer, which is characteristic for "embrittlement" materials in contact with surfactant. Rehbinder effect radically changes the mechanism of crack initiation in gigacycle fatigue regime, which leads to the formation of cracks on the surface of the sample, rather than the volume of the material, which is characteristic of this kind of fatigue failure.
Received: 02 July 2015   Revised: 13 November 2015   Accepted: 15 November 2015
Views: 366   Downloads: 62
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