Friction Test Method Research Articles

Superior interface adhesion and protective mechanism of room-temperature-curable polymer composite coating on engineering substrates with lower roughness

In view of the technology bottleneck of the adhesion failure of traditional functional protective coatings on the smoother surface of precise parts served in the marine atmosphere, a room-temperature-curable fluoropolymer/polyurethane (denoted as RFP) polymer composite coating of 20–30 μm is prepared on the metal substrates. Static pull-off and dynamic friction test methods are used to evaluate the interface adhesion of the coating. The coating shows superior adhesive strength of 18–24 MPa on a variety of metal substrates with a wide range of surface roughness (Ra = 0.1–1.6 μm). The friction coefficient of the coating surface is about 0.05–0.08, and the wear life is up to 9–12 km/μm. Furthermore, the adhesion strength of the coating remains 12–14 MPa after 1600 h of salt spray while the wear life of the coating keeps 3–9 km/μm after 720 h of salt spray. The influences of surface roughness (Ra), surface free energy (γOxide), surface potential (φOxide) of the metal substrates and the bonding force at substrate-coating interface on the adhesive energy (Eadh.) are discussed, and the mechanism of "physical-chemical-surface" synergetic enhanced interface adhesion is proposed. The RFP coating is used as the intermediate layer for traditional PU and EP coatings to improve their adhesion on smooth aluminum substrate from 1.39 MPa to 17.5 MPa (increased by 1260 %). Thus, the polymer coating has the potential to provide technical support for the development of long-term anticorrosive coating technology for precision components of marine high-tech equipment.

Base friction testing methodology for the deformation of rock masses caused by mining in an open-pit slope

Mining in an open-pit slope results in the deformation and instability of rock masses. Correspondingly, it is difficult to quantify the range of internal rock mass damage completely. In this study, a base friction testing method is proposed for the analysis of mining models in an open-pit slope, and new methodology is proposed which combines digital image correlation (DIC) and particle image velocimetry (PIV) techniques to analyze the entire deformation process. A series of base friction tests is performed to reveal the deformation mechanism of the mining model in an open-pit slope, and findings are compared with those obtained from a mining model without an open-pit slope. The test results showed two different types of damage: staged parabolic-like and progressive trapezoidal-like damages. Moreover, the proposed methodology can obtain the entire displacement and velocity vector distributions (from deformation to damage) inside the slope and convert it into data for visualization. This provides a reference for the evaluation and control of field open-pit slopes in similar conditions.

Frictional Characterization Of Grey Cast Iron Train Brake Block Using A Reduced Scale Dynamometer

The brake block is an important component that serves to slow down and stop the train. The safety of this transportation is very dependent on the reliability of this component. One of the important features of the brake block material is the coefficient of friction. The coefficient of friction of the brake block material must meet and match the requirements. The coefficient of friction of a material is measured using a friction test. Previous studies have shown that the friction coefficient of a material is influenced by braking conditions, namely contact pressure and friction speed. Many friction testing methods have been developed to study the characteristics of friction materials. In contrast to previous studies, in this study, the frictional characteristics of gray cast iron brake blocks were evaluated using a reduced scale dynamometer. The friction test is carried out by pressing the brake block specimen to the surface of the rotating wheel. The specimen size of the brake block and carriage wheels is reduced to 1/4 of the original size. The friction test is carried out at a contact pressure of 0.15, 0.20, 0.25, and 0.30 (MPa) and the friction speeds of 3, 6, 9, and 12 (m/s). The results of this study indicate that the coefficient of friction of the gray cast iron brake block decreases with increasing friction speed and contact pressure.

Investigation of the friction conditions of self-pierce rivets by means of a compression-torsion tribometer

Lightweight design is an effective lever for achieving fuel consumption and emission-oriented goals. Therefore micro-alloyed steels and high-strength aluminium materials are included in the multi-material mix of the car body. In this context self-pierce riveting has become established for joining in body-in-white production. For the dimensioning of the joint, numerical simulation is increasingly being used. In order to make reliable predictions about joint quality, knowledge of the friction in the joining process is necessary and needs to be identified experimentally. In previous investigations, the process parameters in the friction test were not comparable to the joining process. Therefore, a new friction test method is presented in this paper, where the process conditions are comparable between joining and friction testing especially regarding the interface pressure. The local joining process parameters between rivet and sheet are derived numerically. In the framework of the investigations, the influences of the local joining process parameters, like interface pressure, relative velocity and temperature, on the friction are investigated and mapped close to the joining process. Additionally a comparison of different rivet coatings is carried out. The rivet contact to the sheet metal HX340LAD as well with aluminium EN AW-5182 is taken into account.

Development of a new high-precision friction test platform and experimental study of friction characteristics for pneumatic cylinders

In order to achieve high-precision pneumatic cylinder friction test, this paper proposes a new direct measurement method based on electric cylinder in which the axially acting forces from the compressed air in the two facing pneumatic cylinders cancel each other out and the detected value of the force transducer is just friction. For the sake of the implementation of the method, a new low-cost test method for identifying deadband of proportional directional valve was proposed, and a set of fuzzy PI constant pressure control system was designed to cope with a certain degree of leakage in the chamber. Based on the above, a friction test platform with two pneumatic cylinders facing each other was eventually built to study the influence of pressure, pressure difference, and piston speed on the friction of two commonly used different types of pneumatic cylinders. Through multiple sets of tests, it is found that when the lip seals are used in pairs between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is only related to the sum of the two chamber pressures, but not to the pressure difference between the two chambers. When the O-ring seal is used between the piston and the inner wall of the cylinder, the friction between the piston and the cylinder is related not only to the pressure of the two chambers, but also to the pressure difference between the two chambers. In addition, a series of comparative tests with the traditional single-cylinder friction test method directly demonstrate the effectiveness of the proposed new method.

Measurement of Friction Coefficient by Backward Extrusion with Rotating Die under Severe Warm and Hot Forming Conditions

We have proposed a new friction test method under severe friction conditions. The method applies backward extrusion, which enables us to create high surface pressure, large surface area expansion and a long sliding distance. In addition, die temperature in the actual forging processes can be reproduced. The unique feature of the die set used in this method is a punch rotating at a very slow angular velocity. From the combination of measured load P and torque M, friction coefficients μ of the entire punch contact surface can be calculated. The equation between M/P and μ was derived using FEM analysis. This equation depends on the punch shape, not the flow stress of material. By this method, we measured friction coefficients at 900 ℃-1200 ℃, in which warm and hot forging conditions of steel were reproduced. As a result, we were able to quantitatively evaluate the lubricant combustion temperature, billet antioxidant coating, lubricant spray pressure, and billet initial temperature, which strongly affect friction coefficients.

Determination of Friction Performance of High Friction Surface Treatment Based on Alternative Macrotexture Metric.

Surface friction is currently the most common metric for evaluating the performance of high friction surface treatment (HFST). However, friction test methods such as the locked wheel skid tester (LWST) commonly provide a spot measurement. Large variations may arise in the LWST testing on curves. Based on 21 actual HFST projects, a study was performed to use a macrotexture metric, i.e., the mean profile depth (MPD) to evaluate HFST’s performance and improve its quality control (QC)/quality assurance (QA) procedures. The material properties were presented to understand the aspects of HFST. The method for calculating MPD was modified to account for the variations of macrotexture measurements. A vehicle-based test system was utilized to measure MPD periodically over an 18-month period since HFST installation. Statistical analysis was performed on the MPD measurements to identify the effects of influencing factors. Compared with the friction from LWST, MPD was equally effective in evaluating HFST performance. However, the use of MPD eliminated the errors as arisen in LWST testing and made it possible to detect surface distresses, including aggregate loss, delamination, and cracking. The expected overall MPD may be calculated by combining the MPD measurements made three months after installation at different HFST sites and used as a metric for evaluating HFST performance and QC/QA.

The Bio-Tribological Effect of Poly-Gamma-Glutamic Acid in the Lysozyme-Ionic Contact Lens System.

Feeling comfortable is an important issue for contact lens wearers as contact lenses are worn for an extensive period of time. It has been shown that the in vitro friction coefficient of contact lenses is correlated to the degree of in vivo comfort, thus many studies focus on establishing friction testing methods for investigating the friction coefficient of contact lenses or contact lens care solution. We have previously demonstrated the lubricating property of poly-gamma-glutamic acid (γ-PGA)-containing care solution, and it could reduce the high friction coefficient caused by lysozyme. However, the mechanism of how γ-PGA-containing care solution reduces the lysozyme-induced friction coefficient of contact lenses is unclear. We investigated the bio-tribological effect of γ-PGA on ionic contact lenses in the presence of lysozyme by testing load and velocity variations. The ability to remove lysozyme deposition by γ-PGA and viscosity analysis of γ-PGA-containing care solutions were also investigated to understand the potential mechanism. Our results showed that the friction coefficient of γ-PGA-containing care solution with lysozyme was the lowest in both load and velocity variations, and γ-PGA functions distinctly in the lysozyme-ionic contact lens system. We proposed a model of how γ-PGA could reduce the friction coefficient in these two conditions.

Tribological characteristics of medical gloves in contact with human skin and skin equivalents

The progress in new surface modification techniques towards the manufacture of tailored latex articles is faced with the requirement of new characterization techniques to determine the tribological properties of elastomer surfaces. Thus, the present study aims at the characterization of friction properties of commercially available medical gloves to assess their donning performance. The experimental design of the friction test method involves a linear movement of the glove sample across selected counterpart materials. In the first step, bio-tribological studies with a panel are carried out enabling an objective evaluation of the donning properties of gloves. These results are compared to the coefficient of friction of the gloves against various skin equivalents including polymer based materials, glass and biological tissue. In terms of skin friction, a high correlation between human skin and the biological skin equivalent is obtained. However, in contrast to bio-tribological studies, the friction experiments with biological tissue benefit from high reproducibility and low standard deviation. With the established test method the influence of state-of-the-art surface functionalization processes (chlorination and polymer-based coatings) and lubricants (cornstarch) on the friction properties of medical gloves is investigated in order to evaluate crucial process and surface parameters for low surface friction against human skin.

Optimization of workability technological testing for open-die forging

Developing an open-die forging process for a poor-workability alloy has always been a challenge. This paper presents a rapid method that meets this purpose. A simplified forging test was considered for assessing the limit states of material in open-die forging. It can be employed in industrial forge shops. A V-shaped testing die was designed using finite element (FE) simulation. The V-shape geometry is convenient for strain evaluation. Rectangular blocks will be tested across a wide range of working temperatures. Based on the test results, limit states can be identified. Then friction testing method was optimized. It is also simple comparison test. Both technological tests are suitable for determination of optimized parameters in forging. The risk of material failure can thus be eliminated or minimized.

극지용 도료의 빙마찰 및 빙마모 시험기법 연구

극지용 도료의 빙마찰 및 빙마모 시험기법 연구

Kinematics and kinetics of the shoe during human slips

This paper quantified the heel kinematics and kinetics during human slips with the goal of guiding available coefficient of friction (ACOF) testing methods for footwear and flooring. These values were then compared to the testing parameters recommended for measuring shoe-floor ACOF. Kinematic and kinetic data of thirty-nine subjects who experienced a slip incident were pooled from four similar human slipping studies for this secondary analysis. Vertical ground reaction force (VGRF), center of pressure (COP), shoe-floor angle, side-slip angle, sliding speed and contact time were quantified at slip start (SS) and at the time of peak sliding speed (PSS). Statistical comparisons were used to test if any discrepancies exist between the state of slipping foot and current ACOF testing parameters. The main findings were that the VGRF (26.7 %BW, 179.4 N), shoe-floor angle (22.1°) and contact time (0.02 s) at SS were significantly different from the recommended ACOF testing parameters. Instead, the testing parameters are mostly consistent with the state of the shoe at PSS. We argue that changing the footwear testing parameters to conditions at SS is more appropriate for relating ACOF to conditions of actual slips, including lower vertical forces, larger shoe-floor angles and shorter contact duration.

Effect of Workpiece Surface Topography on Friction in Cold Forging Using Environmentally-Friendly Lubricant

An optimal surface topography for the use of an environmentally friendly lubricant was elucidated, by making a wide combination of surface roughnesses Ra and RSm representing height and frequency of surface asperity, using the wet blast treatment. A forward conical can - backward straight can extruded friction test method proposed by the present authors was used. Coulomb friction coefficient was evaluated using a calibration curve representing the relationship between the surface friction coefficient of the conical punch and the front/back extrusion height of the workpiece. It was found that the surface topography of workpiece largely affects the lubricating property when the friction coefficient is large. Especially, the surface treatment with larger Ra and smaller RSm is effective for improving the friction. Furthermore, the correlation between the friction coefficient and the proposed parameter for the surface topography Ra/RSm was shown to be better than the Ra.

Evaluating the factors influencing the friction behavior of paperboard during the deep drawing process

Deep drawing of paperboard with rigid tools and immediate compression has only a small presence in the market for secondary packaging solutions due to a lack of understanding of the physical relations that occur during the forming process. As with other processes that deal with interactions between two solids in contact, the control of the factors that affect friction is important due to friction’s impact on runnability and process reliability. A new friction measurement device was developed to evaluate the factors influencing the friction behavior of paperboard such as under the specific conditions of the deep drawing process, which differ from the standard friction testing methods. The tribocharging of the contacting surfaces, generated during sliding friction, was determined to be a major influence on the dynamic coefficient of friction between paperboard and metal. The same effect could be examined during the deep drawing process. With increased contact temperature due to the heating of the tools, the coefficient of friction decreased significantly, but it remained constant after reaching a certain charging state after several repetitions. Consequently, to avoid ruptures of the wall during the forming process, tools that are in contact with the paperboard should be heated.

Hyaluronan incorporation into model contact lens hydrogels as a built-in lubricant: Effect of hydrogel composition and proteoglycan 4 as a lubricant in solution.

Contact lens friction significantly correlates with subjective comfort. Hyaluronan (HA) and proteoglycan 4 (PRG4) are natural boundary lubricants present in the body. The objective of this study was to assess the effect of crosslinked HA into the bulk of model contact lens materials pHEMA, pHEMA/TRIS, and DMAA/TRIS on surface wettability, protein sorption, and boundary lubricating properties at a material-cornea biointerface, both alone and synergistically with PRG4 in solution. Surface wettability was assessed by water contact angle measurement, protein sorption by lysozyme sorption assay, and boundary lubricating properties using an in vitro friction test method. HA incorporation (HAinc ) increased the surface wettability of all materials, and reduced protein sorption for pHEMA and DMAA/TRIS. HAinc increased friction for pHEMA, and DMAA/TRIS, whereas a decrease was observed for pHEMA/TRIS. A combination of HAinc and PRG4sol had a synergistic effect of reducing friction only for pHEMA/TRIS. This combination had similar friction reduction compared with PRG4sol alone for DMAA/TRIS. These results indicate HA incorporation could be an effective internal wetting agent, antiadhesive, and boundary lubricant for pHEMA/TRIS silicone hydrogels. In conclusion, HA incorporation can reduce friction of hydrogels alone and in combination with PRG4 in solution, though in a hydrogel composition-dependent (e.g., TRIS) manner. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1818-1826, 2018.

Three-Dimensional Shoe Kinematics During Unexpected Slips: Implications for Shoe–Floor Friction Testing

OCCUPATIONAL APPLICATIONS This study described the three-dimensional kinematics of the shoe during slipping and compared them to shoe kinematics specified by standard methods for coefficient of friction testing. At the time of slip initiation, substantially higher sagittal-plane shoe–floor angles and more medial shoe velocity occur than what have previously been reported. These results suggest that standard slip-testing methods should be reexamined so they better align with the state of the shoe when it begins to slip. The incongruence between actual slips and testing methods could lead to shoe designs that perform well during friction testing but are sub-optimal during an actual slip.TECHNICAL ABSTRACT Background: Shoe design is an important component of slip and fall prevention efforts. Evaluating the slip resistance of shoes in a way that is relevant to slipping accidents requires a comprehensive understanding of the shoe biomechanics during slipping. Limitations in previous studies on this topic include omission of kinematics outside the sagittal plane, which may impact coefficient of friction measurements, and the use of multiple slip perturbations, which can lead to kinematic changes due to anticipation and adaptation. Purpose: The purpose of this study was to describe the three-dimensional kinematics of the shoe during unexpected slips to better inform shoe–floor coefficient of friction testing. Methods: Thirteen subjects were exposed to a low friction fluid contaminant while wearing shoes without tread. The sliding speed, direction of sliding, sagittal-plane shoe–floor angle, and frontal plane shoe–floor angle were described at the moment of slip initiation, peak slipping speed (PSS), and 50% of the peak slipping speed (½ PSS). Statistical comparisons assessed whether the kinematics obtained from standard shoe coefficient of friction methods fell within the 95% confidence interval of the measured shoe kinematics at each time point. Results: At least one of the kinematic variables used during standard friction testing methods deviated from the observed kinematics at each time point. Specifically, the central tendency of the observed slips was characterized with a higher sagittal plane shoe angle at slip initiation, a more medial sliding direction at slip initiation, and a higher sliding speed at ½ PSS and PSS than those used during standard shoe friction testing methods. Conclusions: Shoe kinematics in friction testing standards exhibit differences with shoe kinematics during actual slips. Thus, a need exists for revisiting the kinematic conditions used in slip testing based on rigorous biomechanical studies of slipping.

Ultralow friction between cemented carbide and graphite in water using three-step ring-on-ring friction test

Effect of running-in process on friction behavior of graphite sliding against cemented carbide in deionized water was investigated using a standard tribometer Plint TE92 in a ring-on-ring contact configuration. A stable and ultralow friction coefficient of about 0.003 between graphite and cemented carbide rings was obtained after a three-step friction test method: Step 1 was rapid pre-sliding at standard operating conditions and then the test apparatus was stopped; Step 2 was the accelerated running-in process under higher load and velocity, and the test apparatus was stopped again; The wear particles on the specimen surface were cleaned, and used water was replaced by new water from step 3. According to the measurements of suface microtopography and macrowaviness, surface geometric features in the interface after three-step friction test reached the optimal harmonious state. Variations of friction coefficient with speed and load were also investigated. The ultralow friction mechanism was attributed to the hydrodynamic effect.

軸受鋼の繰返し往復すべり接触における摩擦挙動と表面損傷

Delamination failure is one of the most important engineering issues for rolling contact machine elements. It is known that this failure is intimately related to shear-mode (mode II and mode III) fatigue crack growth. Generally, the shear-mode fatigue crack growth behavior and its threshold condition can be greatly influenced by the crack face interference. Therefore, understanding of the mechanism of friction and surface damage of crack faces is of importance and a new testing method that can examine appropriately these properties is required. In this study, the influences of the cyclic reciprocating sliding contact with micro-scale relative motion on the frictional behavior and the surface damage of a bearing steel were studied under dry condition. As a novel friction and wear testing method, a cyclic ring-on-ring test was conducted by making use of a hydraulic-controlled combined axial and torsional fatigue testing machine. The coefficient of kinetic friction was ranged from 0.4 to 1.0, the average value being about 0.75.

Application of a new, severe-condition friction test method to understand the machining characteristics of Cu–Zn alloys using coated cutting tools

Friction between copper–zinc (brass) alloys and uncoated as well as differently coated carbide tools was investigated by using a recently developed friction test, characterized by high contact forces, temperatures, and relative velocities. The major aim was to analyze the ability of various tool-brass combinations for reducing friction, adhesion and thus tool wear in cutting operations and to understand the existent mechanisms of action. In the first part of the study, the friction conditions between low-leaded brass alloys with varying chemical composition (CuZn38As, CuZn42 and CuZn21Si3P) and uncoated as well as TiB2 and DLC (ta-C) coated carbide tools were analyzed and compared to the high-leaded free-cutting brass CuZn39Pb3. In a second step, materials with almost the same chemical composition were used (CuZn41.5). Hereby, the influence of low lead contents ranging from Pb=0.003–0.19% on friction was analyzed and compared to a high lead content of Pb=1.9%. It can be summarized that significant differences in frictional behavior were determined depending on the material’s chemical composition, microstructure, mechanical properties, lead content, tool coating and relative velocity. Regarding the applied tools, the lowest coefficients of friction and process temperatures were detected when using a DLC (ta-C) coating.

T-shape upsetting–extruding test for evaluating friction conditions during rib–web part forming

Since the deformation features of existing friction testing methods are not as similar as those of the closed die forging process of rib–web parts, the friction conditions evaluated by these methods are not consistent with the actual situation. In this paper, a new friction testing method, the T-shape upsetting–extruding process employing a rectangular blank, is proposed for evaluating the friction conditions during rib–web part forming process. It was found that rib height and the web width are both sensitive to friction conditions. Therefore, the ratio of rib height to web width was chosen as a criterion for friction evaluation. With the utilization of a commercial FEM program, DEFORM, the effects of the geometrical parameters and testing variables on the friction sensitivity were investigated, and the friction conditions between different interfaces were analyzed. In order to verify the proposed method, friction factors of a water-based graphite lubricant measured by three different methods (the proposed one, the ring compression test and the double-cup extrusion test) at 723K were used to simulate the isothermal deformation process of a cross-rib part. The experimental results suggest that the proposed method is more accurate than the other two methods for rib–web part forming process.