Key Engineering Materials Vol. 664

Abstract: In recent years, experimental tests investigating properties of materials in gigacycle regime have suggested modifications to well-known statistical fatigue life models. Classical fatigue life models based on a single failure mode and by the presence of the fatigue limit, have been integrated by models that can take into account the occurrence of two failure modes (duplex S-N curve).Duplex S-N models involve a number of unknown parameters that must be statistically estimated from experimental data. The present paper proposes a simplified and automated procedure for statistical parameter estimation. The procedure is applied to experimental datasets taken from the literature. Parameter estimation is carried out by applying the Maximum Likelihood Principle and by taking into account the possible presence of runout specimens with unequal number of cycles. The application of the procedure permits to estimate different key material parameters (e.g., the characteristic parameters of transition stress and fatigue limit), as well as to statistically predict the failure mode of each tested specimen.

Abstract: In order to investigate very high cycle fatigue properties of Zr₅₅Al₁₀Ni₅Cu₃₀ bulk amorphous alloy, rotating bending fatigue tests were conducted at room temperature by using 5 different series of Zr₅₅Al₁₀Ni₅Cu₃₀ alloy. The differences of material processing conditions are manufacturer, product year, material size and minimum diameter of specimen. Although all specimens fractured from surface, duplex S-N characteristics were observed for each series of the material. Time strength distributions at N=10⁴ for short life region and at N=10⁷ for long life region were well approximated by normal distribution. The entire S-N property accepting the normalized stress amplitude by the time strength at N=10⁴ or N=10⁷ has shown more clearly duplex S-N characteristics. In addition, P-S-N properties were also estimated from the standard deviation of time strength distributions at N=10⁴ or N=10⁷. Based on the observation of fracture surface by scanning electron microscope (SEM), it is confirmed that every fracture surface was consisting of typical three regions such as multi-facet region, stable crack growth region and instantaneous fracture region.

Abstract: Carbon steel is a kind of metallic material that widely used in construction, machinery, manufacturing and other domains. In the mechanical structure system, long-term cyclic stress may cause the mechanical components failure. In this work, the characteristic of fatigue crack propagate in low carbon steel Q345 and the effect of loading frequency to the fatigue property of Q345 steel were investigated. Meanwhile, the dispersion of high-cycle fatigue of life of the Q345 steel under high fatigue testing frequency was analyzed, and the P-S-N curve with the test data was given out. With the help of infrared camera, temperature rise curve during fatigue test was analyzed to study the thermal dissipation of Q345 steel.

Abstract: The experimental observation of the microstructural deformation behavior of a metastable austenitic stainless steel tested at the real VHCF limit indicates that plastic deformation is localized and accumulated in shear bands and martensite formation occurs at grain boundaries and intersecting shear bands. Based on these observations a microstructure-sensitive model is proposed that accounts for the accumulation of plastic deformation in shear bands (allowing irreversible plastic sliding deformation) and considers nucleation and growth of deformation-induced martensite at intersecting shear bands. The model is numerically solved using the two-dimensional (2-D) boundary element method. By using this method, real simulated 2-D microstructures can be reproduced and the microstructural deformation behavior can be investigated within the microstructural morphology. Results show that simulation of shear band evolution is in good agreement with experimental observations and that prediction of sites of deformation-induced martensite formation is possible in many cases. The analysis of simulated shear stresses in most critical slip systems under the influence of plastic deformation due to microstructural changes contributes to a better understanding of the interaction of plastic deformation in shear bands with deformation-induced martensitic phase transformation in the VHCF regime.

Abstract: Recently, in order to make positively use of the effect of adhesive layer, which works as Build-up edge or Belag on the tool surface during machining operation, there have many investigations on the technique to reduce the wear of cutting tool. However, the mechanism of wear on the rake face is unknown and the reason why the adhesive layer can resist the abrasion is also unclear.This study aims to propose a new crater high-cycle fatigue wear model depending on the tool adhesion model established by the surface cluster on the interface between the Tool-Work Piece. By using this model we can elucidate the mechanism of adhesive layer. When the chip flows on the rake face, the commensurate phase occurs in the surface cluster on the interface, and the surface cluster slides in the similar form of dislocation. At the same time, the strong chemical bonding among the surface clusters becomes the repeat force which can result in the fatigue failure on the tool, and the tool crater wear happens. The energy dissipation process associates with the vibration of cluster, which increases the tool temperature rapidly. Therefore, the crater wear is a damage process on the tool with the high-temperature and high-cycle fatigue.In this study, the mechanism of crater wear when the cemented carbide cut the carbon steel was investigated using the adhesion cluster model, and the crater wear model was proposed to estimate the properties of the adhesive layer.