Fretting wear behavior of Ti/TiN multilayer film on uranium surface under various displacement amplitudes

Ti/TiN multilayer film was deposited on uranium surface by arc ion plating technique to improve fretting wear behavior. The morphology, structure and element distribution of the film were measured by scanning electric microscopy（SEM）, X-ray diffractometry（XRD） and Auger electron spectroscopy（AES）. Fretting wear tests of uranium and Ti/TiN multilayer film were carried out using pin-on-disc configuration. The fretting tests of uranium and Ti/TiN multilayer film were carried out under normal load of 20 N and various displacement amplitudes ranging from 5 to 100 μm. With the increase of the displacement amplitude, the fretting changed from partial slip regime（PSR） to slip regime（SR）. The coefficient of friction（COF） increased with the increase of displacement amplitude. The results indicated that the displacement amplitude had a strong effect on fretting wear behavior of the film. The damage of the film was very slight when the displacement amplitude was below 20 μm. The observations indicated that the delamination was the main wear mechanism of Ti/TiN multilayer film in PSR. The main wear mechanism of Ti/TiN multilayer film in SR was delamination and abrasive wear.

Experimental investigation on shear strength deterioration at the interface between different rock types under cyclic loading

The shear strength deterioration of bedding planes between different rock types induced by cyclic loading is vital to reasonably evaluate the stability of soft and hard interbedded bedding rock slopes under earthquake;however,rare work has been devoted to this subject due to lack of attention.In this study,experimental investigations on shear strength weakening of discontinuities with different joint wall material(DDJM)under cyclic loading were conducted by taking the interface between siltstone and mudstone in the Shaba slope of Yunnan Province,China as research objects.A total of 99 pairs of similar material samples of DDJM(81 pairs)and discontinuities with identical joint wall material(DIJM)(18 pairs)were fabricated by inserting plates,engraved with typical surface morphology obtained by performing three-dimensional laser scanning on natural DDJMs sampled from field,into mold boxes.Cyclic shear tests were conducted on these samples to study their shear strength changes with the cyclic number considering the effects of normal stress,joint surface morphology,shear displacement amplitude and shear rate.The results indicate that the shear stress vs.shear displacement curves under each shear cycle and the peak shear strength vs.cyclic number curves of the studied DDJMs are between those of DIJMs with siltstone and mudstone,while closer to those of DIJMs with mudstone.The peak shear strengths of DDJMs exhibit an initial rapid decline followed by a gradual decrease with the cyclic number and the decrease rate varies from 6%to 55.9%for samples with varied surface morphology under different testing conditions.The normal stress,joint surface morphology,shear displacement amplitude and shear rate collectively influence the shear strength deterioration of DDJM under cyclic shear loading,with the degree of influence being greater for larger normal stress,rougher surface morphology,larger shear displacement amplitude and faster shear rate.

SCATTERING OF PLANE SH-WAVES ON SEMI-CANYON TOPOGRAPHY OF ARBITRARY SHAPE WITH LINGING IN ANISOTROPIC MEDIA

The purpose of this paper is to use the conforma mapping method[1]to analyzeand evaluate the ground displacement and scattering of incident SH-waves, on thesurface of semi-canyon topography of arbitrary shape with lining in anisotropic media.The problem to be solved can be reduced to the solution of an infinite algebraicequation set by using the method of full-space expansion of Fourier progression Usingthe mapping function and scattering theory to solve problems due to semi-canyon topography with lining is just like mapping the semi-cylindrical canyon of arbitraryshape into a cylindrical canyon in full-space.Moreover,it is far practical inengineering practice.From the computational examples,it is obvious that the variation of displacement amplitudes on the surface near the canyon topography is rather sharp. especially when the freqencies of incident SH-waves increase.

Longitudinal resistance performance of granular ballast beds under cyclic symmetric displacement loading

The longitudinal resistance performance of a granular ballast bed under cyclic symmetric displacement loading was studied based on a full-scale test model of ballast track structures. The change law of the longitudinal resistance characteristics of the ballast bed under variable displacement amplitudes was analyzed. The results show that： the resistance-displacement curves of a granular ballast bed are a set of closed hysteretic curves, indicating obvious energy consumption; a granular ballast bed softens gradually during the cyclic process with constant displacement amplitude, and the residual deformation rate increases nonlinearly with increasing cycle number; the peak value of the longitudinal resistance of lines decreases with increasing cycle number; the cyclic softening of a granular ballast bed is dependent on the displacement amplitude-the higher the displacement, the more severe the cyclic softening will become; after cyclic displacement loading is applied several times, the longitudinal resistance of the bed will degenerate obviously, and the higher the displacement amplitude, the higher the longitudinal resistance attenuation rate of the ballast bed will become.