The Effect of Surface Pit Treatment on Fretting Fatigue Crack Initiation

This paper analyses the effect of surface treatment on fretting fatigue specimen by numerical simulations using Finite Element Analysis.The processed specimen refers to artificially adding a cylindrical pit to its contact surface.Then,the contact radius between the pad and the specimen is controlled by adjusting the radius of the pit.The stress distribution and slip amplitude of the contact surface under different contact geometries are compared.The critical plane approach is used to predict the crack initiation life and to evaluate the effect of processed specimen on its fretting fatigue performance.Both crack initiation life and angle can be predicted by the critical plane approach.Ruiz parameter is used to consider the effect of contact slip.It is shown that the crack initial position is dependent on the tensile stress.For same type of model,three kinds of critical plane parameters and Ruiz method provide very similar position of crack initiation.Moreover,the improved sample is much safer than the flat-specimen.

Metal-Organic Frameworks Offering Tunable Binary Active Sites toward HighlyEfficient Urea Oxidation Electrolysis

Electrocatalytic urea oxidation reaction(UOR)is regarded as an effective yet challenging approach for the degradation of urea in wastewater into harmless N2 and CO_(2).To overcome the sluggish kinetics,catalytically active sites should be rationally designed to maneuver the multiple key steps of intermediate adsorption and desorption.Herein,we demonstrate that metal-organic frameworks(MOFs)can provide an ideal platform for tailoring binary active sites to facilitate the rate-determining steps,achieving remarkable electrocatalytic activity toward UOR.Specifically,the MOF(namely,NiMn_(0.14)-BDC)based on Ni/Mn sites and terephthalic acid(BDC)ligands exhibits a low voltage of 1.317 V to deliver a current density of 10 mA cm^(-2).As a result,a high turnover frequency(TOF)of 0.15 s^(-1) is achieved at a voltage of 1.4 V,which enables a urea degradation rate of 81.87%in 0.33 M urea solution.The combination of experimental characterization with theoretical calculation reveals that the Ni and Mn sites play synergistic roles in maneuvering the evolution of urea molecules and key reaction intermediates during the UOR,while the binary Ni/Mn sites in MOF offer the tunability for electronic structure and d-band center impacting on the intermediate evolution.This work provides important insights into active site design by leveraging MOF platform and represents a solid step toward highly efficient UOR with MOF-based electrocatalysts.