Effects of fragments on W-DLC films properties under boundary lubrication condition in the friction system

Abstract Effects of film fragments in the friction system on friction and wear properties of tungsten doped diamond-like carbon films （W-DLC） were studied in the condition of boundary lubrication. It could be observed that the average friction coefficient was increased after introducing film fragments into the friction system, where these film fragments can accelerate the breaking of the extreme thin oil film which could separate two friction surfaces when the system is under boundary lubrication conditions. The increasing friction load can accelerate the friction ehenfieal reaction on the friction interface and lead to the crushing effect on film fragments, which decreased the friction coefficient of friction system. It was also found that the wear width, depth, and volume of the film increased by introducing film fragments and applying great load.

Study on Friction Torque Loading with an Electro-hydraulic Load Simulator

This article, in order to precisely impose friction on aircraft and weapon actuation systems, presents a new friction loading method characteristic of ＂torque-zero velocity＂ switching control with an electro-hydraulic load simulator. As the general Stribeck friction model has little related to static friction, it proposes a ＂torque-zero velocity＂ switcher, in which a zero-velocity controller is developed to load the static friction and a torque controller the kinetic friction. With the help of mathematical modeling, this article designs a ＂torque-zero velocity＂ switching controller and, correspondingly, provides a ＂dual-threshold judgment＂ algorithm. Simulation results indicate that the proposed method can be successfully used to carry out the static and kinetic friction simulation with an electro-hydraulic load simulator.

Robust Control for Static Loading of Electro-hydraulic Load Simulator with Friction Compensation

Load simulator is a key test equipment for aircraft actuation systems in hardware-in-the-loop-simulation. Static loading is an essential function of the load simulator and widely used in the static/dynamic stiffness test of aircraft actuation systems. The tracking performance of the static loading is studied in this paper. Firstly, the nonlinear mathematical models of the hydraulic load simulator are derived, and the feedback linearization method is employed to construct a feed-forward controller to improve the force tracking performance. Considering the effect of the friction, a LuGre model based friction compensation is synthesized, in which the unmeasurable state is estimated by a dual state observer via a controlled learning mechanism to guarantee that the estimation is bounded. The modeling errors are attenuated by a well-designed robust controller with a control accuracy measured by a design parameter. Employing the dual state observer is to capture the different effects of the unmeasured state and hence can improve the friction compensation accuracy. The tracking performance is summarized by a derived theorem. Experimental results are also obtained to verify the high performance nature of the proposed control strategy.

Analysis of blasting damage in adjacent mining excavations

Following a small-scale wedge failure at Yukon Zinc＇s Wolverine Mine in Yukon, Canada, a vibration monitoring program was added to the existing rockbolt pull testing regime. The failure in the 1150 drift occurred after numerous successive blasts in an adjacent tunnel had loosened friction bolts passing through an unmapped fault. Analysis of blasting vibration revealed that support integrity is not compromised unless there is a geological structure to act as a failure plane. The peak particle velocity（PPV） rarely exceeded 250 mm/s with a frequency larger than 50 Hz. As expected, blasting more competent rock resulted in higher PPVs. In such cases, reducing the round length from 3.5 m to 2.0 m was an effective means of limiting potential rock mass and support damage.

An experimental investigation into modeling solids friction for fluidized dense-phase pneumatic transport of powders

Results are presented of an ongoing investigation into modeling friction in fiuidized dense-phase pneumatic transport of bulk solids. Many popular modeling methods of the solids friction use the dimen- sionless solids loading ratio and Froude number. When evaluated under proper scale-up conditions of pipe diameter and length, many of these models have resulted in significant inaccuracy. A technique for modeling solids friction has been developed using a new combination of dimensionless numbers, volu- metric loading ratio and the ratio of particle free settling velocity to superficial conveying air velocity, to replace the solids loading ratio and Froude number. The models developed using the new formalism were evaluated for accuracy and stability under significant scale-up conditions for four different prod- ucts conveyed through four different test rigs （subject to diameter and length scale-up conditions）. The new model considerably improves predictions compared with those obtained using the existing model, especially in the dense-phase region. Whereas the latter yields absolute average relative errors varying between 10% and 86%, the former yielded results with errors from 4% to 20% for a wide range of scale-up conditions. This represents a more reliable and narrower range of prediction that is suitable for industrial scale-up requirements.

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.

Effects of irregularity and initial stresses on the dynamic response of viscoelastic half-space due to a moving load

The present article deals with the stresses developed in an initially stressed irregular viscoelastic half-space clue to a load moving with a constant velocity at a rough free surface. Expressions for normal and shear stresses are obtained in closed form. The substantial effects of influence parameters, viz., depth （from the free surface）, irregularity factor, maximum depth of irregularity, viscoelastic parameter, horizontal and vertical initial stresses, and frictional coefficient, on normal and shear stresses are investigated. Moreover, comparative study is carried out for three different cases of irregularity, viz., rectangular irregularity, parabolic irregulariW and no irregularity, which is manifested through graphs.