Control of fatigue failure mechanisms in multilayer coatings by varying the architectural parameters of an intermetallic interlayer

A multilayer overlay coating system containing an intermediate intermetallic layer (designated 2IML) is an architecture expected to show good fatigue resistance. Experimental characterisation and modelling simulations were carried out to classify the different crack initiation mechanisms occurring during fatigue of this coating system and to reveal how changes in the layer architecture lead to fatigue improvement. Fatigue improvement is achieved by decreasing the IML-Top layer thickness due to the increased surface crack initiation resistance. However subsurface initiation mechanisms inhibit the improvement (dominated by surface initiation mechanism) achieved by locating the IML-Top layer closer to the top surface.

Influence of corrosion on fatigue behaviour of old crane runway steel

Experimental measurements of fatigue properties of old steel used for a crane runway were performed to capture the influence of corrosion on fatigue life of the material. Basquin’s law was used to quantify the fatigue properties of old steel with different cross sections and with different surface of specimens (polished and corroded). The finite element model was prepared to assess and quantify the various stress distribution in specimens with circular and rectangular cross sections. Fracture surfaces of the three kinds of specimens (circular polished, rectangular polished and rectangular corroded) were studied and they showed the surface crack initiation. The following fatigue cracks developed from the surface and expanded into specimen with radiation pattern. Observed crack initiation areas confirmed the ones expected according to stress concentrations.

Simulation of Surface Crack Initiation Induced by Slip Localization and Point Defect Kinetics

Crack initiation along surface persistent slip bands (PSBs) has been widely observed and modelled. Nevertheless, from our knowledge, no physically-based fracture modelling has been proposed and validated with respect to the numerous recent experimental data showing the strong relationship between extrusion and microcrack initiation.

Review on Surface Failure Mode of Metallic Materials in Very High Cycle Fatigue Regime

With higher cleanness upgraded steadily, surface failure of metallic materials in very high cycle fatigue (VHCF) regime beyond 107 cycles has been reported one after another. The occurrence of surface crack initiation to failure in VHCF regime is closely related to the following factors: (i) surface finishing condition of specimen, i.e. whether some grinding scratches, grooves and cavities with a relatively larger size than the subsurface defect exist at the surface of specimen; (ii) type, size, location, distribution and density of metallurgical defects such as inclusion contained in the subsurface of material; (iii) degree of persistent slip band (PSB) deformation induced by surface roughening of specimen, mainly corresponding to the some ductile single-phase metallic materials. Furthermore, the effect of environment such as humidity also accelerates surface crack initiation and propagation in VHCF regime. In the present paper, the authors briefly reviewed surface failure modes of metallic materials in VHCF regime beyond 107 cycles, and analyzed the surface crack initiation and propagation mechanisms from the viewpoints of the fracture mechanics and statistics.