Increase In Normal Load Research Articles

Experimental study of friction coefficient of rocks in high pressure and tight gas reservoirs in Sichuan

The calculation of torque and drag in horizontal wells and extended reach wells is an important element in drilling operations, but determining the value of the friction factor is difficult in the calculation of friction. Sichuan Basin constitutes a special gas reservoir system with high pressure and tight formations. They are favorable for gas production which can be accomplished economically only with horizontal drilling and hydraulic fracturing, and Xujiahe Formation is the focus of the exploration and development. In order to determine the reasonable friction factor for directional well and horizontal well in Xujiahe Formation and complete comprehensive evaluation method, both theoretical study on friction mechanism and experimental investigation on friction factor need to be carried out. A series of experiments are conducted for different lithology (sandstone, sand-mudstone, and mudstone), steel, and lubricants (mud systems). The test results are as follows: lubricants have the most obvious influence on the friction coefficient; the friction-reducing effect of the same lubricant on different friction pairs varies; and lubricants have very different effects on the same friction pair. Under the condition of lubrication with clear water, the friction coefficient of rock increases slightly as the normal load rises. Under lubrication with mud, the change range of the friction coefficient of rock with the increase of normal load is low. Rotation speed has limited impact on the friction coefficient. Under the same test condition, the friction coefficient of sandstone is a little higher in the three kinds of rocks. Through a large number of experimental studies, the value range of the friction coefficient of different kinds of rock in the fifth member in Xujiahe Formation is obtained, providing a scientific basis for the drilling design and the calculation of torque and drag in high pressure and tight formations in Sichuan.

Evaluation of scratch resistance of functionalized graphene oxide/polysiloxane nanocomposite coatings

Abstract Functionalized graphene oxide (FGO) was synthesized with 3-glycidoxy-propyl trimethoxy silane (GPTMS) and subsequently incorporated into polysiloxane coatings to improve the mechanical properties, especially scratch resistance, through the sol-gel and epoxy/amino curing reactions. The surface functionalization of graphene oxide (GO) was evidenced by TEM, FTIR and XPS. FGO was found to have better compatibility and establish stronger interface with polysiloxane matrix than GO based on the observed microstructures using OM and SEM. Nanoindentation, macro scratch and progressive load scratch tests were employed to assess the mechanical performance of FGO/polysiloxane nanocomposite coatings, demonstrating significant improvement in comparison with either the pure polysiloxane or the GO/polysiloxane coatings. A 40% enhancement on microhardness (233 MPa), 83% improvement of scratch resistance (1100 g) and 144% increase in 1st scratch critical normal load (4.88N) are achieved by addition of only 0.75 wt% of FGO. Furthermore, elastic recovery and scratch damage morphology were investigated to provide insight into scratch behavior and reinforcement mechanism.

Influence of the normal load of scratching on cracking and mechanical strength of soda-lime-silica glass

The response of glass to a scratch experiment is first reviewed. Then the influence of the applied load on the microcracking pattern, the apparent friction coefficient, and the strength (post scratch test) are studied and discussed for a soda-lime-silica glass (standard window glass composition). As the normal load increases, the depth of the radial crack seems to stabilize at about 100μm length. Correlatively it is observed that the residual strength of the scratched glass remains at about 40MPa whatever the scratch load above 0.5N. Generally, this work contributes theoretically in the understanding of the existing factor controlling scratch in glasses.

Experimental study on the wear behavior of HVOF sprayed nickel-based coating

Severe wear is a hot issue in the development of petroleum engineering which has attracted many attentions. To address this problem, a nickel-based alloy (NiCrBSiWFeCoC) coating was proposed and prepared using High-velocity oxy-fuel (HVOF) technique. The wear properties of as-sprayed composite coating were studied. The sliding wear experiments of both as-sprayed and uncoated specimens were conducted on a tribometer. The obtained results indicated that the both wear rates increased obviously with the increase in normal load, however, the friction coefficients decreased with the increase in normal load. Based on the comprehensive analyses, it can be concluded that the as-sprayed coating exhibited better wear resistance. Furthermore, the wear behaviors can be investigated by analyzing the worn morphologies. This research can provide insight into the wear prevention in petroleum engineering and decreases the failure of equipments or pipelines.

Designing Load-Dependency of Static Friction of Elastomer Covered with Mesh Sheets

The static friction of compliant elastomers has proven important for industrial applications, including seals, and grips on tools and sports equipment. The design of load-dependent contact state may provide characteristic load-dependent frictional properties beyond that found on conventional rubber surfaces. Here we investigate the static friction, over a wide range of normal loads, between a fat glass surface and polyester meshes adhered on an elastomer surface. At low load the glass is supported only by the mesh members and the static friction is low. As normal load increases, the mesh members tend to dent into the elastomer and at the pore of the mesh the elastomer surface may make contact with the glass. The newly created contact with the elastomer makes the static friction increase with the higher friction coefficient. By tuning the structures, e.g., the aperture ratio, of meshes, we can extend the monotonic load-dependency of static friction of rubbers into the highly nonlinear range.

Behaviour of a plane joint under horizontal cyclic shear loading

This paper describes lab test results of artificial rock-like material samples having a plane joint. Cyclic shear tests were performed under different normal loads and different shear displacement amplitudes. For this purpose, multi-stage normal loading tests (30 kN, 60 kN, 90 kN, 180 kN, 360 kN and 480 kN) with cyclic excitation at frequency of 1.0 Hz and different shear displacement amplitudes (0.5 mm, 1.0 mm, 2.0 mm, 4.0 mm, 5.0 mm, and 8.0 mm) were conducted using the big shear box device GS-1000. Experimental results show, that shear forces increase with the increase of normal forces and quasi-static friction coefficient is larger than dynamic one. With the increase of normal loads, approaching the peak value of shear forces needs larger shear displacements. During each cycle the normal displacements increase and decrease (rotational behavior in every cycle). Peak angle of inclination increases with the increase of normal load. A phase shift between maximum shear displacement and maximum shear force is observed. The corresponding time shift decreases with increasing normal load and increases with increasing shear displacement amplitudes.

EFFECT OF CONTACT PRESSURE ON FRETTING FATIGUE BEHAVIOR UNDER CYCLIC CONTACT LOADING

In this study, the effect of contact pressure on fretting fatigue behavior of Al7075-T6 under cyclic normal contact loading is investigated. It is found that fretting fatigue life for the case of cyclic contact load was significantly less than that for constant contact load at the same axial and contact load levels, particularly for High Cycle Fatigue (HCF) conditions. The results showed that the fretting fatigue life decreased monotonically with the increase in normal contact load for all axial stresses. Examination of the fretting scars was performed using optical microscopy and numerical simulation was carried out using commercial finite element (FE) codes ABAQUS[Formula: see text] and FRANC2D/L[Formula: see text] to calculate the crack propagation life. The crack initiation life was calculated by a combination of numerical and experimental results. Finally, the FE simulation was validated by a comparison between the numerical crack growth rate and the experimental measurement using replica.

Experimental study on ignition mechanisms of wet granulation sulfur caused by friction

It is common to see fire accidents caused by friction during the storage and transportation of wet granulation sulfur. To study the sulfur ignition mechanism under friction conditions, a new rotating test apparatus is developed to reproduce friction scenes at lab scale. A series of experiments are performed under different normal loads. The SEM-EDS and the XRD were utilized to examine the morphologies and compositions of the tested specimens and the friction products. Experimental results show that these two methods are mostly in agreement with each other. The iron-sulfide compounds are produced and the proportion of iron-sulfide compounds is reduced with normal loads increasing, compared to the total number of the friction products. The facts implied by the integration analysis of friction products with the temperature changes of the near friction surface unveil an underlying mechanism that may explain sulfur ignition by friction in real scenarios. The sulfur ignition may be mainly caused by the spontaneous combustion of iron sulfide compounds produced by friction under low normal load with 200N. With the increase of normal loads, the resulting iron-sulfide compounds are decreasing and the high temperature from friction heat begins to play a major role in causing fire.

Friction Behavior at the Interface Between Surgical Sutures and Tissues

In the process of surgical suturing, friction phenomena at the interface between sutures and tissues can seriously affect the suturing efficiency. However, few studies have assessed the detailed effects of types of sutures or tissues and stitching parameters on the friction behavior. In this paper, the different factors affecting the friction behaviors between sutures and tissues were studied. The unidirectional sliding wear mode in a line-on-flat configuration was selected to simulate the real surgical suturing by using a UMT-II Micro-Tribometer. Artificial skin, porcine muscle and porcine liver were used as experimental samples. Three different surface morphology and structure sutures: multifilament suture (silk), monofilament suture (prolene) and multifilament suture with coating (vicryl), were investigated in this study. The normal load was from 0.1 to 0.5 N, and the unidirectional sliding (suturing) speed was from 5 to 25 mm/s to simulate the suturing operation. Results showed that the friction coefficient at the suture–tissue interface decreased with the increase in normal load and increased with the increase in suturing speed due to the nonlinear viscoelasticity and deformation hysteresis of the soft tissues. The sutures with monofilament structure or coating could effectively reduce the friction coefficient of the suture–tissue interface. Compared to the artificial skin, the porcine tissues had the lower friction coefficients because of 30% blood and 17% interstitial fluid filled in liver and muscle, respectively, which acted as lubricants and reduced the adhesion friction coefficient of the suture–tissue interface. The results can provide guidance for the surgical suture manufacture and the surgical manipulation skills.

Tribological Characterization of AZ91 and AE42 Magnesium Alloys in Fretting Contact

Fretting wear studies were conducted on AZ91 and AE42 magnesium alloys against steel ball. Average coefficient of friction (COF) remains steady with the increase in running time. However, average coefficient of friction decreases with the increase in normal load and frequency and marginally increases with the increase in amplitude. A constant average coefficient of friction of 0.06 was observed for both AZ91 and AE42 under dry sliding conditions at normal load of 50 N. Wear volume increases linearly with increasing running time. Wear volume first decreases sharply, attains minima, and then increases marginally with the increase in normal load. However, wear volume increases with increasing amplitude and frequency. Higher specific wear rate of 10.5 × 10−6 mm3 N−1·m−1 was observed for AE42, as compared to 4.5 × 10−6 mm3 N−1·m−1 for AZ91. The wear in magnesium alloy was caused by a combination of adhesion, abrasion, oxidation, delamination, and plastic deformation under different fretting conditions.

Effect of adding nanosilica particulate filler on the wear behavior of dental composite

The aim of this study was to fabricate BisGMA based nanosilica filled dental composites and to study the effect of varying nanosilica filler content on their wear characteristics. The composites were developed by varying filler content of silane treated nanosilica from 0 to 9 wt%, into the resin matrix consisting of 51 wt% Bisphenol‐A glycidyl methacrylate, 46.5 wt% Tri‐ethylene glycol dimethacrylate, 0.24 wt% Camphorquinone, 1.5 wt% Butyl hydroxyl toluene and 0.76 wt% Dimethylamino ethyl methacrylate. The hardness was determined using Vickers's micro hardness tester. The two body abrasive wear experiments were performed in the artificial saliva medium as per Taguchi Orthogonal Array and steady state condition by varying parameters such as filler content, normal load, and chewing speed. The finding of results indicated that the wear resistance and hardness were improved with increase in filler fraction. The dental composite filled with 9 wt% of nanosilica filler exhibited maximum hardness (31.4 HV), maximum compression strength (360.5 MPa) and flexural strength (120.5 MPa) and minimum volumetric wear rate. Also, the wear volume increased with the increase in normal load, chewing speed and number of cycles but decreased with the increase in filler content. Statistical significance of each factor as per generalized linear model of Analysis of Variance showed that filler content was the most influencing factor followed by applied normal load, numbers of cycle and chewing speed. Worn surfaces were studied using a scanning electron microscope (SEM) to give an insight into the wear mechanisms. POLYM. COMPOS., 39:E332–E341, 2018. © 2017 Society of Plastics Engineers

Experimental Research of Dry Friction in "Alumina Ceramics - Quartz Glass" Pair

Results of an experimental research of friction coefficient in alumina ceramics - quartz glass friction pair are presented. The research with pin on disc test configuration using SRV-III test machine was carried out at loads from 10 to 1000 N, constant sliding velocities 5 mm/s; ambient temperature 23°C and relative humidity 30%. The obtained results reveal that in general, friction coefficient for alumina ceramics - quartz glass pair decreases with the increase in normal load. It is shown that the obtained friction coefficients values at the normal force from 100 to 1000 N for the given experimental conditions can be used to pre-estimate the interference fits in alumina ceramics - quartz glass friction pairs.

Prediction of sliding speed and normal force effects on friction and wear rate evolution in a dry oscillating-fretting PTFE/Ti-6Al-4V contact

Dry fretting wear tests were performed on a semicrystalline polytetrafluoroethylene PTFE cylinder rubbing on a flat Ti-6Al-4V surface at room temperature. Various sliding speeds and normal loads were imposed for test durations from 5×104 to 106 cycles. The purpose of the investigation was to evaluate how sliding speed and normal load influence friction and wear rate evolution for gross slip fretting-reciprocating sliding conditions. Analysis confirmed an initial transient regime related to the progressive formation of a PTFE transfer film on the titanium counterface, followed by a linear steady-state wear regime. Focusing on the steady-state wear regime, a rising staircase evolution versus sliding speed was observed for both friction and Archard's wear rate. This continuous “sigmoid” wear rate evolution was related to friction heating, inducing transition from micro to macro surface-ploughing wear damage. In addition, a discontinuous cracking wear component was observed from a threshold sliding speed (vth=12mm/s), due to friction-induced thermal activation of the crystalline phase transition then the principal transition (associated with the glass transition) of the PTFE polymer. The analysis also showed that an increase in normal load induced a parallel reduction in the coefficient of friction and parallel increase in wear rate. These parallel evolutions suggest no direct interaction between sliding speed and normal force. Hence the normal force effect can be analyzed using a (P/Pref)n weight function, where the n exponent quantifies the relative effect of normal load versus friction and PTFE wear rate. These results, which are discussed regarding former research works of Tanaka, are correlated with PTFE thermo-mechanical response, friction thermal considerations and competition between several wear processes. Finally, global wear rate could be formulated, including sigmoid (ploughing wear), bell shape (cracking wear) and weighted (normal force effect) functions. Good correlation between experiments and predictions confirmed the stability of this formulation.

Tribological properties of Fe-Cr-B alloy for sliding boot in coal mining machine under dry sliding condition

PurposeTo improve the wear resistance of the sliding boot, the wear-resistant Fe-21 Wt.% Cr-5 Wt.% B alloy is prepared, and the wear mechanism is studied under dry sliding condition.Design/methodology/approachThe anti-wear Fe-21 Wt.% Cr-5 Wt.% B alloy is prepared by powder metallurgy technique. The tribological behavior of Fe-Cr-B alloy sliding against ASTM 1045 steel pin is studied at 30-60 N and 0.03-0.12 m/s using a reciprocating pin-on-disk tribometer under dry sliding condition. Meanwhile, the ASTM 5140 and 3316 steel are studied as compared samples.FindingsThe friction coefficients of tested specimens increase with the increasing normal load. However, this effect is the opposite in case of different sliding speeds. The specific wear rates increase as the sliding speed and normal load increase. The Fe-Cr-B alloy shows the best tribological properties under the dry sliding condition and the wear mechanism is mainly ploughing.Originality/valueThis wear-resistant Fe-21 Wt.% Cr-5 Wt.% B alloy can replace the traditional materials to process the sliding shoes and improve the service life of coal mining machine.

Three-dimensional fractal model of normal contact damping of dry-friction rough surface

According to the influence of the normal contact damping of joint surfaces on the dynamic characteristics of high-precision machinery (machine tool, robot, etc.), in this article, a three-dimensional fractal model of normal contact damping of dry-friction rough joint surfaces based on Hertz theory and fractal theory is established. The three-dimensional surface topography is constructed, according to the modified double variable Weierstrass–Mandelbrot function. The fractal model of strain energy [Formula: see text], dissipated energy [Formula: see text], damping loss factor [Formula: see text], and normal contact damping [Formula: see text] are deduced in detail, and the influence of fractal parameters and dynamic friction coefficient [Formula: see text] on them are simulated. The simulation curves show that strain energy [Formula: see text], dissipated energy [Formula: see text], damping loss factor [Formula: see text], and normal damping [Formula: see text] increase with the increase in the fractal roughness G; the influence of fractal dimension D on [Formula: see text] is more changeable, first [Formula: see text] decreases with the increase in D and then increases. [Formula: see text], [Formula: see text], and [Formula: see text] increase with the increase in D and [Formula: see text], respectively; the effect of [Formula: see text] on [Formula: see text] is not obvious, so simple change in [Formula: see text] has no significant change in [Formula: see text]; a comparative analysis of the theoretical calculation of normal damping and experimental results show that their general trend is consistent, and they increase with the increase in total normal contact load P, the relative error is 5%–25%. The theoretical model can provide reference for the design of normal contact damping of the joint surfaces.

Friction and Wear Behavior of Carbon Fabric-Reinforced Epoxy Composites

Besides intrinsic material properties, weight/energy savings and wear performance play an important role in the selection of materials for any engineering application. The tribological behavior of carbon fabric-reinforced epoxy composites produced by molding technique was investigated using a reciprocating pin-on-plate configuration. It was shown that the wear rate considerably decreased (by a factor of approx. 8) with the introduction of the reinforcing carbon fabric into the epoxy matrix. It was observed that the wear rate of the tested composites increased with an increase in normal load. Moreover, the coefficient of friction for epoxy/steel and composites/steel tribo-pairs was also determined and decreased with increasing load. By means of scanning electron microscopy of the wear tracks, different wear mechanisms such as matrix wear, matrix fatigue and cracking, matrix debris formation for neat epoxy together with fabric/fiber thinning, fabric breakage and fabric/matrix debonding for the reinforced epoxy could be distinguished.

Comparison of tribological properties of HVOF sprayed coatings with different composition

This paper presents the results of a comparative study conducted to compare the friction and wear behavior of five high velocity oxy fuel (HVOF) sprayed coatings sliding against Al2O3 counter body under dry conditions. Single way ball-on-disk tests were performed on NiCrBSi/WC (50/50), NiCr (80/20), WC/Co (88/12), WC/CoCr and Cr3C2/NiCr (75/25) coatings, deposited on stainless steel substrates, under normal load of 5, 15N and sliding speed of 10, 20cm/s. To understand the wear process, detailed XRD and SEM analysis in combination with EDS of the worn coatings were performed. The results show that the most suitable HVOF sprayed coating to prolong the lifetime of components working at high temperature and wear conditions is WC/CoCr coating owing to its lowest friction coefficient and highest wear resistance. It is followed by WC/Co, Cr3C2/NiCr and NiCrBSi/WC. The NiCr coating exhibited the worst performance at all conditions. Wear volume of the coatings generally increased with the increase in both normal load and sliding speed, while WC/CoCr coating is adversely affected from the normal load. Wear rate decreased with decreasing sliding speed and increasing normal load. The coatings were generally worn by abrasion wear, including particle pull-out and scratching. Plastic deformation was also observed on the surface of softer coatings such as NiCr.

Effect of Normal Load and Velocity on Continuous Sliding Friction and Wear Behavior of Woven Glass Fiber Reinforced Epoxy Composite

The tribological performance of glass epoxy composite under different conditions has been examined. In this study, the effect of normal loads and sliding velocities on the friction and wear behavior of glass fiber reinforced epoxy composite sliding against a steel disc in dry condition is investigated experimentally using a pin on disc type wear and friction monitor. The composite with 60 wt% of woven E glass fiber reinforcement is fabricated in hand lay up technique followed by compression moulding process. The fiber orientation of the composite has been kept perpendicular to the sliding direction. Tests are conducted at normal loads of 5, 10, 20, 30, 40, and 50 N and the sliding velocities of 0.5, 1, 2, and 3 m/s. Friction and wear are influenced by the duration of sliding, normal load, and sliding velocity. The variation of friction coefficient with the change of sliding duration under different conditions has been considered in detail. In general, friction coefficient decreases with the increase of normal load and it increases with the increase of the sliding velocity for all sliding velocities and normal loads respectively. Wear loss increases in respect of increase in normal loads and sliding velocities for all the conditions.

Influences of extrusion temperatures on the wear behavior of magnesium alloy AZ31 fabricated by the extrusion shear process

Abstract The wear resistance of as-cast AZ31 magnesium alloy samples fabricated by extrusion shear (ES) with various preheating temperatures (420, 400, 370 °C) of billets was tested by using pin-on-disc experiments under dry sliding wear conditions. Wear rates and friction coefficient were measured at various sliding frequencies and normal forces. To define the wear mechanism for each tested condition, the worn surfaces were analyzed using scanning electron microscope (SEM) and energy dispersive X-ray spectrometer (EDS). Based on the test results, the wear resistance of the ES-processed samples decreases with drop of the billet temperatures. The friction coefficients and wear rates of the samples with a preheating temperature of 370 °C are lower than those with deformation temperatures of 400 °C and 420 °C. With the increase of normal loads and reciprocating frequencies, the wear mechanism changes from mild wear (adhesion, abrasion and oxidation) to severe wear (delamination, plastic deformation and melting). Therefore, the extrusion methods have significant influences on the wear behaviors of the samples, and the wear resistance of AZ31 magnesium alloy can be improved by ES process.

Wear behaviors and wear mechanisms of wrought magnesium alloy AZ31 fabricated by extrusion-shear

Abstract Extrusion-Shear (ES) process for magnesium alloy is a newly developed plastic deformation technique which combines direct extrusion (DE) with ECAP (equal-channel angular pressing). Grains of ES-processed magnesium alloys can be refined effectively and mechanical properties can be improved, but the tribological properties have not been studied. In this study, the wear behaviors and wear mechanisms of AZ31 magnesium alloy samples produced by direct extrusion (DE) and extrusion-shear (ES) technologies, respectively, have been evaluated by fiction coefficient and wear frequencies obtained from the dry sliding tests conducted at different loads and frequencies by using a high speed dry sliding test machine. SEM and EDS analyses technologies also have been used to analyze the wear surfaces and wear debris in different fiction conditions. Based on the results, the ES-processed samples show a better wear resistance than those prepared by DE process as the ES-process samples show a lower friction coefficient comparing to those fabricated by DE process at the same conditions of loads and wear frequencies. With the increase of normal loads and reciprocating frequencies, the wear mechanism change from mild wear (adhesion, abrasion and oxidation) to severe wear (delamination, plastic deformation and melting). Therefore, the extrusion ways have significant influences on the wear behaviors of the samples and that the wear resistance of AZ31 magnesium alloy can be improved by extrusion-shear.