Understanding the friction behavior of sulfur-terminated diamond-like carbon films under high vacuum by first-principles calculations

Generally, the repulsive force was a key factor account for superlow friction of H or F doped diamond-like carbon (DLC) films under high vacuum. As we known, H or F doped DLC usually exhibited superlow friction under high vacuum. However, the superlow friction of S doped DLC under high vacuum was not found so far. This phenomenon was desirable to be well investigated. In this work, S-terminated diamond interfaces also exhibited strong repulsive force, however, the estimated friction coefficient was variable for S-terminated diamond interfaces. The lowest and largest friction coefficient was about 0.003 and 0.4 respectively, which indicated that the superlow friction of S doped DLC could achieve in theory. In order to well probe the unusual friction behavior of S doped DLC under high vacuum, using first-principles method, the repulsive interaction between sliding surfaces was well investigated in order to understand the unusual friction behavior of S doped DLC films.     

Characterization of prepreg-prepreg and prepreg-tool friction for unidirectional carbon fiber/epoxy prepreg during hot diaphragm forming process

The frictional behaviors of prepreg-prepreg and prepreg-tool play the most important role in hot diaphragm forming and greatly influence the quality of the final product. A new set-up was developed to characterize the frictional behaviors for unidirectional carbon fiber/epoxy prepreg. The effects of temperature, normal force, pulling rate, and relative fiber angles on the frictional behaviors of the prepreg-prepreg and prepreg-tool interface have been investigated. Results of these tests are presented and observations are noted. The results show that the frictional resistance increases with increase in the normal force and the pulling rate, and its variation with the temperature is complicated. The frictional resistance is higher at 90° fiber orientation to the pulling direction than that at 45° and 0°.     

纺织品摩擦时的听觉风格评价的初步研究

为评价不同组织织物的摩擦听觉风格,建立了以刺耳度(C)、顺滑度(S)、响度(L)、沉闷度(D)、喜好度(B)和拟声词描述(O)的主观评价指标。采用语意评定法(SD法)将听觉风格指标各分为5级,并通过对随机抽取的21名合格纺织专业学生进行问卷调查与测试。研究结果表明：在纱线原料、线密度、经密等相同的情况下,织物摩擦听觉风格指标刺耳度(C)与响度(L)成正相关关系,而刺耳度(C)则分别与顺滑度(S)或者喜好度(B)之间存在着一定的负相关关系。听者对于织物摩擦声音的判别,女性的敏锐度明显高于男性。此外,平纹的刺耳度(C)、响度(L)和沉闷度(D)最高,而缎纹的顺滑度(S)和喜好度(B)最高。     

Relationship between Activation Energy of Thermolysis and Friction Sensitivity of Cyclic and Acyclic Nitramines

The knowledge of sensitiveness of an energetic compound to friction stimuli is important to ensure the safety of people and protection of property during shipment. The information on sensitivity to friction is considered very valuable for nitramines, which show relatively higher sensitivity with respect to the other classes of secondary explosives. This study presents a novel general simple model for prediction of the relationship between friction sensitivity and activation energy of thermolysis of cyclic and acyclic nitramines on the basis of their molecular structures. This methodology assumes that friction sensitivity of an energetic compound with general formula C_aH_bN_cO_d can be expressed as a function of activation energy of thermolysis and the contribution of specific molecular structural parameters. For 21 nitramines with different molecular structures, the new correlation has the root mean square and the average standard deviations of 14.2 and 17.8 N, respectively, as compared to experimental values. The proposed new method is also tested for further 8 nitramines containing complex molecular structures, which gives good predictions.     

MODIFICATION OF NYLON-6 WITH POLYORGANOSILOXANE

Nylon-6 has been modified by polyorganosiloxane. It was realized by radical addition of caprolactam to the vinyl group of silicone and anionic polymerization of the monomer in the presence of the silicone macromer. The mechanical properties of the modified plastics are not far from that of the unmodified one whereas its frictional properties are significantly improved.     

A modified tonality and its application to objective evaluation of laser printers noise

Noise in a laser printer is affected by many components, such as spring force, spring constant, and friction coefficient. Objective evaluation of pick up noise is difficult because of background noises, such as operating sound. In particular, pick up noise generated between the friction pad and paper in the process of printing has become an essential aspect of quality evaluation. However, the existing criteria for evaluating pick-up noise have solely relied on subjective human judgments; therefore, there is a need to objectify these criteria. In this paper, the noise index for determining the existence of pick-up noise is established using a modified tonality at just noticeable sound level limit. The study has investigated factors that cause pick-up noise and suggests the substitution of printer components that determine spring constants, spring force, and the quality of friction pads. The proposed noise index is successfully applied to classifying the pick-up noise and mitigating the noise through the optimized design combination of laser printer components.     

A study of contact non-linearities in pin-loaded lugs: Separation,clearance and frictional slipping effects

Pin-loaded lugs with bush fitting are widely encountered in industrial applications to connect parts and transmit loads and motions. Due to their mechanical function, frictional contact inevitably takes place on the pin–bush and lug–pin interfaces, and can lead to non-linear behaviours occurrence under monotonic or periodic loading, such as bush–lug contact separation, pin–bush conforming contact effects in the presence of initial clearance, or bush–lug frictional slipping mechanisms. The aim of this paper is not to present new results of finite element simulations for lugs involving contact with friction but to provide a comprehensive study of those contact non-linearities through a dedicated analytical contact model.     

Modeling of two-phase flow in porous media with heat generation

The main purpose of this work is investigation of coolability of a boiling debris bed. The main governing equations are derived using volume averaging technique. From this technique some specific interfacial areas between phases are appeared and proper relations for modeling these areas are proposed. Using these specific areas, a modification for the Tung/Dhir model in the annular flow regime is proposed. The proposed modification is validated and the agreements with experimental data are good. Finally, governing equations and relations are implemented in the THERMOUS program to model two-phase flow in the debris bed in the axisymmetric cylindrical coordinate. Two typical configurations including flat and mounted beds are considered and the main physical phenomena during boiling of water in the debris bed are studied. Comparing the results with the one-dimensional analysis shows higher specific power of the bed.     

Effects of micro-additions on structures and properties of rapidly solidified Sn-10% Sb alloy

Structure, electrical resistivity, hardness, internal friction and elastic modulus of Sn-10% Sb and Sn₈₉Sb₁₀M₁ (M₁ = Ag, Cu, Zn and Pb) alloys have been investigated. No obvious change on the electrical resistivity value was found at 293 °K of a Sn-10% Sb alloy by adding Zn and Cu, but extreme changes occurred after adding Ag and Pb. The elastic modulus, internal friction, hardness and thermal diffusivity values are greatly affected by adding the micro-additions to a Sn-10% Sb rapidly solidified alloy. It is also interesting to note that Ledbetter's theoretical values of μ/E are in good agreement with the experimental results. The rapidly solidified alloys Sn₉₀Sb₁₀ and Sn₈₉Sb₁₀Ag₁ have good properties as toxic-free lead solder alloys for high-temperature applications and good mechanical properties such as under the hood in the automobile and avionics systems. Also, the rapidly solidified alloys Sn₈₉Sb₁₀Zn₁, Sn₈₉Sb₁₀Cu₁ and Sn₈₉Sb₁₀Pb₁ have good properties as bearing materials.     

Inverse method for estimating shear stress in machining

An inverse method is presented for estimating shear stress in the work material in the region of chip–tool contact along the rake face of the tool during orthogonal machining. The method is motivated by a model of heat generation in the chip, which is based on a two-zone contact model for friction along the rake face, and an estimate of the steady-state flow of heat into the cutting tool. Given an experimentally determined discrete set of steady-state temperature measurements along the rake face of the tool, it is shown how to estimate the corresponding shear stress distribution on the rake face, even when no friction model is specified.