Frictional properties evaluation

A surface effect (air cushion) vehicle measures 10 ft by 20 ft and weighs 6000 lbf. The air is supplied by a blower mounted on top of the vehicle, which must supply sufficient power to lift the vehicle 1 in. off the ground. Calculate the required blower capacity in scfm (standard cubic feet per minute), and the horsepower of the motor required to drive the blower if it is 80% efficient. Neglect friction, and assume that the air is an ideal gas at 80°F with properties evaluated at an average pressure. 

The thermochemical evaluation of the reactants is the place to start, as discussed in Chapter 2. If the potential energy release is 250 cal/g of substance (1000 J/g) or more, it is necessary to determine initiation properties, such as a sensitivity to impact and friction. Thermochemical evaluation of reaction... 

When a polymer molecule moves in a dilute solution it undergoes frictional interactions with solvent molecules. The nature and effect of these frictional interactions depend upon the size and shape of the polymer molecule. Thus, the chain dimensions of polymer molecules can be evaluated from measurements of their frictional properties [25]. 

The selection of friction parameters in order to determine the above criteria for evaluating the friction properties was based on the analysis and statistical treatment of the data on the regimes of friction units operation where it is beneficial to use self-lubricated polymeric materials. The characteristic operation regimes were found to be in the range of sliding velocities from 0.01 up to 5.0 m/s and loads from... 

Saikko, V. (1993) Wear and friction properties of prosthetic joint materials evaluated on a pin on flat apparatus. Wear, 166, 169-178. 

WUliams, N. D. and HoulUian, M. E (1987), Evaluation of interface friction properties between geosynthetics and soils. Proceedings of the Geosynthetics 87 Conference, Industrial Fabrics Assodation International, St Paul, Minnesota, pp. 616-627. 

Influence of the Duration of Polymer Depo-sition. Using the same microsphere-cantilever assembly throughout, the frictional properties of several PLL(20)-t/[3.5]-PEG(2)-coated SiOa substrates were evaluated as a... 

Williams PF, Iwasaki Y, Ishihara K, Powell GL, Gilbert JA, Nakabayashi N, et al. Evaluation of the frictional properties of an elastomer with enhanced lipid-adsorbing ability. Proc Inst Mech Eng Part H J Eng Med I997 2I I(5) 359-68. 

Frictional properties The Frictorq method consists of characterising the coeficiente of friction between two flat surfaces based on torque evaluation (Lima et al., 2008). The frictional properties of the materials were tested using the Frictorq II. Samples with 84 iran diameter were tested under a conditioned atmosphere. 

Kinetic frictional properties of yam in contact with solid materials are evaluated according to a standardized method. Yam travels with a linear speed of 100 m/ min in contact with a solid with a wrap angle of 3.14 to 6.28 radian. The yam input and output tensions are measured and the coefficient of friction is calculated from Amontons law, according to the following equation ... 

In order to develop the proper dow pattern, knowledge of a material s dow properties is essential. Standard test equipment and procedures for evaluating sohds dow properties are available (6). Direct shear tests, mn to measure a material s friction and cohesive properties, allow determination of hopper wall angles for mass dow and the opening size required to prevent arching. Other devices available to evaluate sohds dowabiUty include biaxial and rotary shear testers. 

Years of development have led to a standardized system for objective evaluation of fabric hand (129). This, the Kawabata evaluation system (KES), consists of four basic testing machines a tensile and shear tester, a bending tester, a compression tester, and a surface tester for measuring friction and surface roughness. To complete the evaluation, fabric weight and thickness are determined. The measurements result in 16 different hand parameters or characteristic values, which have been correlated to appraisals of fabric hand by panels of experts (121). Translation formulas have also been developed based on required levels of each hand property for specific end uses (129). The properties include stiffness, smoothness, and fullness levels as well as the total hand value. In more recent years, abundant research has been documented concerning hand assessment (130—133). 

The above measurements all rely on force and displacement data to evaluate adhesion and mechanical properties. As mentioned in the introduction, a very useful piece of information to have about a nanoscale contact would be its area (or radius). Since the scale of the contacts is below the optical limit, the techniques available are somewhat limited. Electrical resistance has been used in early contact studies on clean metal surfaces [62], but is limited to conducting interfaces. Recently, Enachescu et al. [63] used conductance measurements to examine adhesion in an ideally hard contact (diamond vs. tungsten carbide). In the limit of contact size below the electronic mean free path, but above that of quantized conductance, the contact area scales linearly with contact conductance. They used these measurements to demonstrate that friction was proportional to contact area, and the area vs. load data were best-fit to a DMT model. 

The present model takes into account how capillary, friction and gravity forces affect the flow development. The parameters which influence the flow mechanism are evaluated. In the frame of the quasi-one-dimensional model the theoretical description of the phenomena is based on the assumption of uniform parameter distribution over the cross-section of the liquid and vapor flows. With this approximation, the mass, thermal and momentum equations for the average parameters are used. These equations allow one to determine the velocity, pressure and temperature distributions along the capillary axis, the shape of the interface surface for various geometrical and regime parameters, as well as the influence of physical properties of the liquid and vapor, micro-channel size, initial temperature of the cooling liquid, wall heat flux and gravity on the flow and heat transfer characteristics. 

The friction coefficient of Sample 2 is quite different from the other samples this can be attributed to the surface difference. The previous research shows that the friction coefficient of DLC is related to the deposition parameter [29]. In this study, in order to evaluate the surface properties in the same condition, we designed Layer A as the outermost layer for all the multilayer samples. Among all the samples, only the surface of Sample 2 is from Layer B. 

To evaluate wear properties of the PFAM film, the friction after 20 K flying cycles was measured by Yang et al. [28] and Hu et al. [26] as shown in Fig. 9. Each cycle of the takeoff and landing process was performed within 2 min. The existence of the PFAM film has no influence on the normal takeoff and landing of the slider. In the case of 50 ppm and 500 ppm, the PFAM film maintained a low friction at the last cycle in a CSS test. The maximum friction value of the latter is less than 2 g, which is about one-third of that of the bare... 

The various physical methods in use at present involve measurements, respectively, of osmotic pressure, light scattering, sedimentation equilibrium, sedimentation velocity in conjunction with diffusion, or solution viscosity. All except the last mentioned are absolute methods. Each requires extrapolation to infinite dilution for rigorous fulfillment of the requirements of theory. These various physical methods depend basically on evaluation of the thermodynamic properties of the solution (i.e., the change in free energy due to the presence of polymer molecules) or of the kinetic behavior (i.e., frictional coefficient or viscosity increment), or of a combination of the two. Polymer solutions usually exhibit deviations from their limiting infinite dilution behavior at remarkably low concentrations. Hence one is obliged not only to conduct the experiments at low concentrations but also to extrapolate to infinite dilution from measurements made at the lowest experimentally feasible concentrations. 

In principle, the energy dissipation (friction loss) associated with the gas-liquid, gas-wall, and liquid-wall interactions can be evaluated and summed separately. However, even for distributed (nonhomogeneous) flows it is common practice to evaluate the friction loss as a single term, which, however, depends in a complex manner on the nature of the flow and fluid properties in both phases. This is referred to as the homogeneous model ... 

Evaluation of each term in Eq. (15-51) is straightforward, except for the friction factor. One approach is to treat the two-phase mixture as a pseudo-single phase fluid, with appropriate properties. The friction factor is then found from the usual Newtonian methods (Moody diagram, Churchill equation, etc.) using an appropriate Reynolds number ... 

The theoretical prediction of these properties for branched molecules has to take into account the peculiar aspects of these chains. It is possible to obtain these properties as the low gradient Hmits of non-equilibrium averages, calculated from dynamic models. The basic approach to the dynamics of flexible chains is given by the Rouse or the Rouse-Zimm theories [12,13,15,21]. How-ever,both the friction coefficient and the intrinsic viscosity can also be evaluated from equilibrium averages that involve the forces acting on each one of the units. This description is known as the Kirkwood-Riseman (KR) theory [15,71 ]. Thus, the translational friction coefficient, fl, relates the force applied to the center of masses of the molecule and its velocity... 

Fig 3.8 shows the interface shear bond strength, tb, determined from Eq. (3.7), which is not a material constant but varies substantially with embedded fiber length, L. However, to evaluate all the relevant interface properties properly, which include the interface fracture toughness, Gic, the coefficient of friction, p, and the residual clamping stress, qo, it is necessary to obtain experimental results for a full range of L and plot these characteristic fiber stresses as a function of L. More details of the... 

Eqs. (4.140) and (4.150)-(4.152) are used to evaluate the response of the model composites in cyclic loading and the displacements 6 and 8, can be expressed as a function of the alternating stress, Aff, and the number of cycles, N. In experiments, degradation of the interface properties, e.g., the coefficient of friction, p or A(= 2pjfc/a), can also be expressed in terms of the cyclic loading parameters, Aoptical methods (with a microscope) or by means of more complicated instruments (see for example Naaman et al. (1992)) in fiber pull-out. Alternatively, they can be directly determined from the load and load-point displacement records in the case of fiber push-out. 

A number of explosives for various applications have been synthesized, characterized for structural aspects, thermal and explosive properties by us in India and are being evaluated [193-198] for their intended end-use. The evaluation of BTATNB [Structure (2.27)] indicates that it is slightly more thermally stable than PATO [Structure (2.24)] coupled with better insensitivity toward impact and friction [71]. The data on thermal and explosive properties of some aromatic nitrate esters suggest that l,3,5-tris(2-nitroxyethyl nitramino)-2,4,6-trinitrobenzene [Structure (2.54)] is a potential substitute of PETN [193]. An explosive called 2,4,6-tris (3,5 -diamino-2, 4, 6 -trinitrophenylamino)-l,3,5-triazene [designated as PL-1 Structure (2.55)] is a new thermally stable and insensitive explosive which on comparison with TATB suggests that it is slightly inferior to TATB [Structure... 

---