Dynamic strength of rock with single planar joint under various loading rates at various angles of loads applied

Intact rock-like specimens and specimens that include a single, smooth planar joint at various angles are prepared for split Hopkinson pressure bar（SHPB） testing. A buffer pad between the striker bar and the incident bar of an SHPB apparatus is used to absorb some of the shock energy. This can generate loading rates of 20.2-4627.3 GPa/s, enabling dynamic peak stresses/strengths and associated failure patterns of the specimens to be investigated. The effects of the loading rate and angle of load applied on the dynamic peak stresses/strengths of the specimens are examined. Relevant experimental results demonstrate that the failure pattern of each specimen can be classified as four types： Type A, integrated with or without tiny flake-off; Type B, slide failure; Type C, fracture failure; and Type D, crushing failure. The dynamic peak stresses/strengths of the specimens that have similar failure patterns increase linearly with the loading rate, yielding high correlations that are evident on semi-logarithmic plots. The slope of the failure envelope is the smallest for slide failure, followed by crushing failure, and that of fracture failure is the largest. The magnitude of the plot slope of the dynamic peak stress against the loading rate for the specimens that are still integrated after testing is between that of slide failure and crushing failure. The angle of application has a limited effect on the dynamic peak stresses/strengths of the specimens regardless of the failure pattern, but it affects the bounds of the loading rates that yield each failure pattern, and thus influences the dynamic responses of the single jointed specimen. Slide failure occurs at the lowest loading rate of any failure, but can only occur in single jointed specimen that allows sliding.Crushing failure is typically associated with the largest loading rate, and fracture failure may occur when the loading rate is between the boundaries for slide failure and crushing failure.

Metal magnetic memory signals from surface of low-carbon steel and low-carbon alloyed steel

In order to investigate the regularity of metal magnetic signals of ferromagnetic materials under the effect of applied load, the static tensile test of Q235 steel and 18CrNiWA steel plate specimens were conducted and metal magnetic memory signals of specimens were measured during the test process. The influencing factors of metal magnetic memory signals and the relationship between axial applied load and signals were analyzed. The fracture and microstructure of the specimens were observed. The results show that the magnetic signals corresponding to the measured points change linearly approximately with increasing axial load. The microstructure of Q235 steel is ferrite and perlite, whereas that of 18CrNiWA steel is bainite and low-carbon martensite. The fracture of these two kinds of specimens is ductile rupture; carbon content of specimen materials and dislocation glide give much contribution to the characteristics of magnetic curves.

Effect of applied load on transition behavior of wear mechanism in Cu-15Ni-8Sn alloy under oil lubrication

Tribological behavior of Cu-15Ni-8Sn(mass fraction, %) alloy against GCr15 ring under various loads was investigated on a ring-on-block tester in oil lubrication. The results showed that the wear rate increased slowly from 1.7×10^(-7) to 9.8× 10^(-7) mm^3/mm under the load lower than 300 N, and then increased dramatically to the climax of 216×10^(-7) mm^3/mm under the load over 300 N, which indicated the transition of wear mechanism with the increase of applied load. The wear mechanism mainly was plastic deformation and abrasive wear under the load less than 300 N. As the applied load was more than 300 N, the wear mechanism of Cu-15Ni-8Sn alloy primarily was delamination wear. Besides, the transition can also be confirmed from the different morphologies of worn surface, subsurface and wear debris. It is distinctly indicated that the appearance of flaky debris at the applied load over 300 N may be a critical point for the change of wear mechanism.

Seismic Behavior of Steel Reinforced Ultra High Strength Concrete Column and Reinforced Concrete Beam Connection

To investigate the seismic behavior of connections composed of steel reinforced ultra high strength concrete (SRUHSC) column and reinforced concrete (RC) beam, six interior strong-column-weak-beam connection specimens were tested subjected to reversal cyclic load. Effects of applied axial load ratio and volumetric stirrup ratio on ductility, energy dissipation capacity, strength degradation and rigidity degradation were discussed. It was found that all connection specimens failed in bending in a ductile manner with a beam plastic hinge. The ductility and energy dissipation capacity increased with the decrease of applied axial load ratio or increase of volumetric stirrup ratio. The displacement ductility coefficient and equivalent damping coefficient lay between those of steel reinforced ordinary concrete connection and those of reinforced concrete connection. The applied axial load ratio and volumetric stirrup ratio had less influence on the strength degradation and more influence on the stiffness degradation. The stiffness degraded sharply with the decrease of volumetric stirrup ratio or increase of applied axial load ratio. The experimental results indicate that SRUHSC column and RC beam connection exhibited better seismic performance and can provide reference for engineering application.

Effect of friction on corrosion behaviors of AISI 304 and Cr26Mo1 stainless steels in different solutions

The corrosion and tribocorrosion behaviors of AISI 304 austenitic stainless steel and Cr26Mo1 ultrapure high chromium ferrite stainless steel in 3.5 wt.%NaCl and 0.5 mol/L H2SO4 solutions were investigated.Microelectrode electrochemical measurement technology was applied to identify electrochemistry behaviors during tribocorrosion tests in situ.The surface morphologies and compositions of the wear tracks were analyzed by scanning electron microscopy and Raman spectrum.The results showed that compositions of stainless steels,corrosive mediums and applied loads have great influence on tribocorrosion behaviors of stainless steels.Firstly,the corrosion resistance in static state of stainless steels primarily dominates its tribocorrosion behavior;meanwhile,better mechanical properties are in favor of tribocorrosion resistance.Secondly,the corrosion rate is promoted significantly in 3.5%NaCl solution by friction,while the tendency is inconspicuous in 0.5 mol/L H2SO4 solution.Last but not least,passive films on stainless steels can be wiped off by small friction force.With the increase in applied load,the effect of friction converts to forming friction oxide film from removing passivation film,so that a critical load exists below which the friction force can promote the corrosion process extremely.

Impact of chosen force fields and applied load on thin film lubrication

The rapid development of molecular dynamics(MD)simulations,as well as classical and reactive atomic potentials,has enabled tribologists to gain new insights into lubrication performance at the fundamental level.However,the impact of adopted potentials on the rheological properties and tribological performance of hydrocarbons has not been researched adequately.This extensive study analyzed the effects of surface structure,applied load,and force field(FF)on the thin film lubrication of hexadecane.The lubricant film became more solid‐like as the applied load increased.In particular,with increasing applied load,there was an increase in the velocity slip,shear viscosity,and friction.The degree of ordering structure also changed with the applied load but rather insignificantly.It was also significantly dependent on the surface structure.The chosen FFs significantly influenced the lubrication performance,rheological properties,and molecular structure.The adaptive intermolecular reactive empirical bond order(AIREBO)potential resulted in more significant liquid‐like behaviors,and the smallest velocity slip,degree of ordering structure,and shear stress were compared using the optimized potential for liquid simulations of united atoms(OPLS‐UAs),condensed‐phase optimized molecular potential for atomic simulation studies(COMPASS),and ReaxFF.Generally,classical potentials,such as OPLS‐UA and COMPASS,exhibit more solid‐like behavior than reactive potentials do.Furthermore,owing to the solid‐like behavior,the lubricant temperatures obtained from OPLS‐UA and COMPASS were much lower than those obtained from AIREBO and ReaxFF.The increase in shear stress,as well as the decrease in velocity slip with an increase in the surface potential parameterζ,remained conserved for all chosen FFs,thus indicating that the proposed surface potential parameterζfor the COMPASS FF can be verified for a wide range of atomic models.

Effects of Load on Dry Sliding Wear Behavior of Mg–Gd–Zn–Zr Alloys

Dry sliding wear tests on as-cast and T6-treated Mg-3Gd-1Zn-0.4Zr（wt%, GZ31K） and Mg-6Gd-1Zn-0.4Zr（wt%, GZ61K） alloys were performed using a ball-on-disk configuration at room temperature. Friction coefficient and wear rate of the alloys were measured under three different applied loads（50 N, 100 N, and 200 N, respectively）. Worn surface morphologies were analyzed using a scanning electron microscope（SEM） coupled with an energy dispersive spectrometer（EDS）. It is found that the friction coefficient of the alloys decreases with increasing load, except the as-cast GZ61 K. The wear rates of the as-cast Mg-Gd-Zn-Zr alloys increase with the increase of the load. However, the wear rates of the T6-treated Mg-Gd-Zn-Zr alloys first increase because of the participation of a large amount of needle-like precipitates, but then decline due to obvious work hardening. The wear mechanisms of abrasion, plastic deformation, oxidation, adhesion and delamination are detected. Abrasion dominates the wear mechanism under the low load; whereas, adhesion is the main wear mechanism under intermediate load, and plastic deformation has great effect on the wear rate under high applied load.