Microtribological investigations of stick/slip phenomena using a novel oscillatory friction and adhesion tester

A novel friction and adhesion tester bridging the gap between macro- and nanotribology is introduced. A friction and/or adhesion induced deflection of a spring is detected using a high-resolution laser interferometer. Unlike force microscopes, where a sharp tip interacts with the surface, this approach allows two plane substrates to be brought into contact. In this way, the exact tribological analysis of microtechnological devices is possible. Since the tester can be operated in air as well as under high vacuum conditions, the environment can be controlled over a wide range. Using this tester, micro-stick/slip phenomena have been investigated as a function of sliding velocity, surface morphology, normal force and contact area. All experiments presented in this paper were carried out on air. This revised version was published online in June 2006 with corrections to the Cover Date.     

Investigation of bending creep tests. Part I: Effect of residual stress

Bending creep test (based on overhang beam geometry) is investigated by incorporating the important contribution of residual stress. Finite element simulations considering the residual stress is employed to investigate the residual stress behavior of bending creep specimen. We propose several methods to determine the creep parameters directly from the bending creep tests. We considered two cases of residual stress, one is tensile residual stress. The other is compressive residual stress. The present work may shed some light on the influences during bending creep, as well as provide an efficient way to determine material residual stress characteristics.     

A method for estimating the stress distributions on the centre line of an axisymmetric, two-material, cross-weld, creep test specimen

Finite element analyses have been performed for an axisymmetric, two-material, cross-weld, creep test specimen. Stationary-state stress (and strain-rate) results were obtained for various geometries and relative material properties. Using these results, it has been shown that a simple interpolation technique can be used to obtain the stress distributions for any geometry and relative creep properties.     

Occurrence limit of stick‐slip: dimensionless analysis for fundamental design of robust‐stable systems

In most practical mechanical systems, sliding surfaces are utilised under the assumption that they operate smoothly. Stick‐slip motion can therefore be a serious nuisance that interferes with achieving high performance in mechanical systems. The present paper describes the nature of stick‐slip based on an analysis of a 1‐DOF sliding system. The dimensionless parameters controlling the stick‐slip are clarified by deriving the dimensionless forms of the governing equations. For a friction model that considers the dependence of the kinetic friction coefficient on the relative velocity, we find three types of sliding systems with regard to stick‐slip: the unstable system, the stable system and the robust‐stable system. A criterion is proposed for the fundamental design of robust‐stable systems; if a sliding system is robust stable, no matter how large a disturbance is, the energy of the disturbance is dissipated perfectly, and steady sliding without any vibration is ensured. Copyright © 2009 John Wiley & Sons, Ltd.     

Numerical analysis of spiral oil wedge sleeve bearing including cavitation and wall slip effects

The modified Reynolds equation is established on the basis of critical shear stress model, in which the circumferential and axial wall slip of sleeve and journal surface is considered. Cavitation is treated using modified Elrod algorithm that simplifies the solution of modified Reynolds equation in the full‐film region. The modified Reynolds equations considering wall slip and cavitation effect for two‐dimensional sleeve bearing are established. The results show that wall slip decreases oil film pressure, carrying capacity, friction drag and temperature rise but increases end leakage and cavitation region. The obtained results using the mass‐conserving boundary condition are compared with the Reynolds boundary condition. Copyright © 2014 John Wiley & Sons, Ltd.     

Rolling cylinder on an elastic half-plane with harmonic oscillations in normal force and rotational speed. Part I: Solution of the partial slip contact problem

We study the effect of harmonic oscillations during the steady rolling of a cylinder on a plane in partial slip contact conditions in the limit of small oscillations. The solution is an extension of that given in Barber et al. [1] for infinitely large coefficient of friction. Here, the effect of varying normal load and hence contact area is investigated in detail by analyzing the first order variation of the tangential force and the corresponding relative displacements.In particular, the solution is given in terms of an explicit length scale d in the Flamant solution used as a Green function. Appropriate choice of values of d allows to treat both two-dimensional problems and three-dimensional ones having elliptical contact area sufficiently elongated in the direction of the rotation axis.Also, this analysis can be used as starting point for corrugation calculations in railway tracks, where oscillations in time of the normal forces can result in non-uniform wear and hence in amplification of the corrugation.     

Effects of Service Condition on Rolling Contact Fatigue Failure Mechanism and Lifetime of Thermal Spray Coatings——A Review

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating’s resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings’ contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings’ contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application.     

Effects of the cutting feed, depth of cut, and workpiece (bore) diameter on the tool wear rate

Most published studies on metal cutting regard the cutting speed as having the greatest influence on tool wear and, thus, tool life, while other parameters and characteristics of the cutting process have not attracted as much attention in this respect. This is because of the existence of a number of contradicting results on the influence of the cutting feed, depth of cut, and workpiece (bore) diameter. The present paper discusses the origin of the aforementioned contradicting results. It argues that, when the optimal cutting temperature is considered, the influence of the aforementioned parameters on tool wear becomes clear and straightforward. The obtained results reveal the true influence of the cutting feed, diameter of the workpiece, and diameter of the hole being bored on the tool wear rate. It was also found that the depth of cut does not have a significant influence on the tool wear rate. The obtained results provide methodological help in the experimental assessment and proper reporting of the tool wear rates studied under different cutting conditions.     

ER exit pathways and the control of proteostasis: Crucial role of the UPR,COPII, and ER-phagy in the secretory pathway

The endoplasmic reticulum (ER) is the site of entry of all proteins that function in the secretory pathway including the extracellular environment. Because it controls the folding of newly synthesized secretory proteins, the ER is indispensable for the maintenance of proteostasis in the secretory pathway. Within the ER and, in part, in post-ER compartments, the quality control of protein folding is under the regulation of the unfolded protein response (UPR) pathways. The UPR strategy is to enhance protein folding, increase the ER degradation pathway of misfolded proteins, and allow the exit from the ER of only correctly folded proteins. The latter is controlled by the multimeric complex COPII, which also provides some of the components for ER-phagy the only route for the disposal of protein aggregates. In this overview, we wish to contribute to the introduction of new perspectives in the study of the mechanisms underlying the control of proteostasis within the secretory pathway.     

Effects of veratrine on skeletal muscle mitochondria: ultrastructural, cytochemical, and morphometrical studies

The alkaloid veratrine is a lipid-soluble neurotoxin, which target voltage-gated Na+ channels for their primary action. Recently, we showed that this alkaloid may cause myonecrosis and evidences suggest mitochondria as one of its cell targets. Herein, we investigate the effects caused by variable concentration of veratrine (250 and 550 microg/mL) on mitochondrial oxygen consumption, respiratory chain enzymes activities, and ultrastructure, combining electron microscopy with cytochemical and biochemical approaches. The results showed different sort of ultrastructural changes, both in isolated and intramuscular mitochondria. Veratrine decreased mitochondrial nicotinamide adenine dinucleotide dehydrogenase (NADH-d), succinic dehydrogenase (SDH), and cytochrome oxidase (COX) activities, significantly and dose-dependently inhibited the state 3 respiration rate, respiratory control ratio (RCR), and ADP/O on isolated rat skeletal muscle mitochondria, whereas state 4 was unaffected. A tendency of increase in mitochondria diameter was seen with 250 microg/mL veratrine. We conclude that the alkaloid would probably act on mitochondrial membrane phospholipid configuration, which would explain the changes observed.     

Effects of Cutting Angles in Ti-6al-4v Milling Process on Surface Integrity: Influence of Roughness and Residual Stresses on Fatigue Limit

□ The influence of the milling process on the fatigue behavior of a titanium alloy was investigated. The effect of cutting conditions such as the cutting angles (axial and radial rake angle) on the surface integrity (roughness and the residual stresses) was observed. The results indicated that the cutting angles have a limited influence on roughness parameters, whereas the effects on residual stresses were greater. A negative axial rake angle induced compressive residual stresses regardless of the radial rake angle. In contrast, a positive axial rake angle combined with negative radial rake angle induced tensile residual stresses. To evaluate the fatigue limit, the four point fatigue tests were carried out. Result showed the fatigue limit is sensitive to the surface integrity. The fatigue limit was also evaluated by analytical method (Arola model). A good correlation was found between the analytical results and the experimental results when cutting angles induced compressive residual stress. However the Arola model was less accurate for tensile residual stress surface condition. To improve the prediction precision, the residual stress was considered as a sensitivity parameter and added to Arola model.     

Boldine provides protective effect against nephrotoxicity induced by cisplatin in Wistar rats: Role of oxidative stress,inflammation and caspase-3

Side effects of cisplatin, especially dose-dependent nephrotoxicity, are major factors limiting its use in cancer.Boldine ((S)-2, 9-dihydroxy-1, 10-dimethoxy-aporphine) is a natural alkaloid known for its strong antioxidant activitypresent in leaves/bark of boldo tree (Peumus boldus Molina), a native tree in Chile. Here, we aimed to investigate thenephroprotective effect of boldine and its underlying mechanisms on cisplatin-induced rat renal injury. Thirty Wistaralbino rats divided into 5 groups (Control, Cis, Bold.40, Cis + Bold.20, Cis + Bold.40 groups) were used. Rats receivedboldine (20 or 40 mg/kg/day), or vehicle (saline) intraperitoneal for 14 days and a single dose cisplatin (7 mg/kg, ip)was applied on the 10th day to induce nephrotoxicity. Rats and kidney tissue were weighed to determine kidneyindex. Blood urea nitrojen (BUN) and creatinine levels, the amount of thiobarbituric acid reactive substances (TBARS,an index of lipid peroxidation), superoxide dismutase (SOD), glutathione peroxidase (GPx) enzyme activities andtumor necrosis factor alpha (TNF-α) levels were measured and histopathologic examination was performed. Induciblenitric oxide synthase (iNOS) and caspase-3 expressions were detected immunohistochemically. Nephrotoxicityinduced by cisplatin was apparent by elevated levels of BUN, creatinine, kidney index, TBARS and TNF-α, anddecreased body weight, SOD and GPx enzyme levels. Pretreatment with boldine protected the renal function at bothboldine doses by fixing the renal damage markers, oxidative stress, caspase-3 and iNOS expression. Histopathologicalfindings supported biochemical findings. Taken together these findings indicate that boldine has promising protectiveeffect against cisplatin nephrotoxicity by improving oxidative stress, inflammation, histopathological alterations andby alleviating caspase 3 expression.     

Effects of Er,Cr:YSGG laser parameters on dentin bond strength and interface morphology

Previous studies have shown the effects of Er,Cr:YSGG laser irradiation on the dentin bond strength; but there are few reports that show the significance of the irradiation with different laser parameters on dentin bond strength and interface morphology. This in‐vitro study attempted to evaluate the microtensile bond strength (μTBS) and interface morphology of resin‐dentin interfaces, either followed by treatment with Er,Cr:YSGG laser irradiation with different parameters or not. The flattened dentin samples of 35 bovine teeth were embedded into acrylic blocks and randomly divided into seven groups according to surface treatments using Er,Cr:YSGG lasers with different parameters: 3 W/20 Hz, 3 W/35 Hz, 3 W/50 Hz, 1.5 W/20 Hz, 1.5 W/35 Hz, 1.5 W/50 Hz, or no laser treatment (n = 5). Composite buildups were done over bonded surfaces and stored in water (24 hours at 37°C). Specimens were sectioned into sticks that were subjected to μTBS testing and observed under FE‐SEM. Control groups (27.70 ± 7.0) showed statistically higher values than laser‐irradiated groups. There were no significant differences among laser groups. Despite that, increasing the pulse frequency yielded slightly higher bond strength. Depending on laser settings, Er,Cr:YSGG laser irradiation caused interfacial gaps and resin tags with wings morphology. With the parameters used in this study, Er,Cr:YSGG laser irradiation promoted morphological changes within resin‐dentin interfaces and negatively influenced the bond strength of adhesive systems. Microsc. Res. Tech. 78:1104–1111, 2015. © 2015 Wiley Periodicals, Inc.     

Lubrication of Ceramics by Tribopolymerization: A Designed Experiment to Determine Effects of Monomer Structure,Load, and Speed on Wear

An experimental study of ceramic lubrication by tribopolymerization at high loads and high speeds, using a pin-on-disk (fixed ball-on-flat) machine with alumina-on-alumina, is presented. In order to extend the range of applied loads and sliding velocities beyond those used in previous studies, a three-factor, two-level designed experiment was carried out to determine the effects of monomer structure, load, and speed on wear. Five monomers of widely varying chemical structure were used at one percent concentration in a hydrocarbon carrier fluid, hexadecane. They consisted of (a) one condensation-type monomer, a partial glycol ester of a longchain dimer acid, and (b) four vinyl-type addition monomers. Two levels of load (40 and 160 N) and speed (0.25 and 1.0 m/s) - each varying by a factor of four were used; thus the range of frictional heat generation was 16 to 1.

The results of this study were rather surprising and changed our thinking on the mechanism(s) by which monomers can act to reduce ceramic wear. For example, at low speeds — regardless of load — the monomers used were very effective in reducing wear, with reductions ranging from 44 to 98 percent depending on the monomer and load. However, at high speeds, the monomers were generally ineffective; in some cases, increases in wear were observed. This was unexpected.

Possible explanations for this behavior — including surface temperature effects and tribochemical reactions — are discussed. Results presented on Fourier Transform Infrared (FTIR) Spectroscopy of worn ceramic surfaces and wear debris show that the film-formation from the monomer solutions is complex, involving a combination of aluminum soap formation as well as evidence of oligomer/polymer formation in some cases, notably diallyl phthalate.     

An extract of <i>Hypericum perforatum</i> induces wound healing through inhibitions of Ca²⁺ mobilizations,mitochondrial oxidative stress and cell death in epithelial cells: Involvement of TRPM2 channels

The wound is induced by several mechanical and metabolic factors. In the etiology of the wound recovery,excessive oxidative stress, calcium ion (Ca²⁺) influx, and apoptosis have important roles. Ca²⁺-permeable TRPM2 channel is activated by oxidative stress. Protective roles of Hypericum perforatum extract (HP) on the mechanical nerve injury-induced apoptosis and oxidative toxicity through regulation of TRPM2 in the experimental animals wererecently reported. The potential protective roles in HP treatment were evaluated on the TRPM2-mediated cellularoxidative toxicity in the renal epithelium (MPK) cells. The cells were divided into three groups as control, wound,and wound + HP treatment (75 µM for 72 h). Wound diameters were more importantly decreased in the wound+HPgroup than in the wound group. In addition, the results of laser confocal microscopy analyses indicated protectiveroles of HP and TRPM2 antagonists (N-(p-Amylcinnamoyl) anthranilic acid and 2-aminoethyl diphenylborinate)against the wound-induced increase of Ca²⁺ influx and mitochondrial ROS production. The wound-induced increaseof early (annexin V-FITC) apoptosis and late (propidium iodide) apoptosis were also decreased in the cells by the HPtreatment. In conclusion, HP treatment acted protective effects against wound-mediated oxidative cell toxicity andapoptosis through TRPM2 inhibition. These effects may be attributed to their potent antioxidant effect.     

A Novel Method for Quantitative Determination of Ultra-low Wear Rates of Materials, Part II: Effects of Surface Roughness and Roughness Orientation on Wear

A novel method of measurement of the very low wear-rates of materials in the ultra-mild wear regime, which involves the use of implanted gold as a marker, was used to understand the effects of surface roughness and roughness orientation on wear under reciprocating sliding conditions. AISI 1095 steel coupons with various Vickers hardness values and different surface roughness and roughness orientation relative to the sliding direction were tested under the same sliding conditions. It was found that parallel sliding causes more wear compared with transverse sliding for the harder samples (Vickers hardness (VH); 450 HV, 650 HV and 1000 HV). Furthermore, the average friction coefficient of parallel sliding is also higher than that of transverse sliding for these samples. Severe wear takes place when the samples are too soft (250 HV), resulting in the complete loss of implanted gold. Surface topographic images were taken before and after the wear tests. It was found that parallel sliding dramatically increases the surface roughness, while transverse sliding does not increase the surface roughness for harder samples (450 HV, 650 HV and 1000 HV). For the soft sample (250 HV), the surface roughness increases significantly under parallel or transverse sliding.