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AR Category: Rotational Tribology
Continuous Stribeck Curve Measurement using Pin-on-Disk Tribometer
Introduction:
When lubrication is applied to reduce the wear/friction of moving surfaces, the lubrication contact at the interface can shift from several regimes such as Boundary, Mixed and Hydrodynamic Lubrication. The thickness of the fluid film plays a major role in this process, mainly determined by the fluid viscosity, the load applied at the interface and the relative speed between the two surfaces. How the lubrication regimes react to friction is shown in what is called a Stribeck [1-4] curve.
In this study we demonstrate for the first time the ability to measure a continuous Stribeck Curve. Using the Nanovea Tribometer advanced step-less speed control, from 15000 to 0.01 rpm, within 10 minutes the software directly provides a complete Stribeck Curve. The simple initial setup only requires users to select the Exponential Ramp Mode and enter initial and final speeds, rather than having to perform multiple tests or program a stepwise procedure at different speeds requiring data stitching for the conventional Stribeck curve measurements. This advancement provides precise data throughout lubricant regime evaluation and substantially reduces time and cost. The test shows a great potential to be used in different industrial engineering applications.
Lubricating Eye Drop Comparison using the Nanovea T50 Tribometer
Importance of Testing Eye Drop Solutions
Eye drop solutions are used to alleviate symptoms caused by a range of eye problems. For example, they can be used to treat minor eye irritation (e.g. dryness and redness), delay the onset of glaucoma or treat infections. Eye drop solutions sold over-the-counter are mainly used to treat dryness. Their effectiveness in lubricating the eye can be compared and measured with a coefficient of friction test.
Dry eyes can be caused by a wide range of factors, for example, computer eye strain or being outdoors in extreme weather conditions. Good lubricating eye drops help maintain and supplement the moisture on the outer surface of the eyes. This works to alleviate the discomfort, burning or irritation and redness associated with dry eyes. By measuring the coefficient of friction (COF) of an eye drop solution, its lubricating efficiency and how it compares to other solutions can be determined.
Measurement Objective
In this study, the coefficient of friction (COF) of three different lubricating eye drop solutions was measured using the pin-on-disk setup on the Nanovea T50 Tribometer.
Test Procedure and Procedures
A 6mm diameter spherical pin made of alumina was applied to a glass slide with each eye drop solution acting as the lubricant between the two surfaces. The test parameters used for all experiments are summarized in Table 1 below.
Results and Discussion
The maximum, minimum, and average coefficient of friction values for the three different eye drop solutions tested are tabulated in Table 2 below. The COF v. Revolutions graphs for each eye drop solution are depicted in Figures 2-4. The COF during each test remained relatively constant for most of the total test duration. Sample A had the lowest average COF indicating it had the best lubrication properties.
Conclusion
In this study we showcase the capability of the Nanovea T50 Tribometer in measuring the coefficient of friction of three eye drop solutions. Based on these values, we show that Sample A had a lower coefficient of friction and therefore exhibits better lubrication in comparison to the other two samples.
Nanovea Tribometers offers precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modules. It also provides optional high temperature wear, lubrication, and tribo-corrosion modules available in one pre-integrated system. Such versatility allows users to better simulate the real application environment and improve fundamental understanding of the wear mechanism and tribological characteristics of various materials.
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Comparing Abrasion Wear on Denim
Introduction
The form and function of a fabric is determined by its quality and durability. Daily usage of fabrics cause wear and tear on the material, e.g. piling, fuzzing, and discoloration. Subpar fabric quality used for clothing can often lead to consumer dissatisfaction and brand damage.
Attempting to quantify the mechanical properties of fabrics can pose many challenges. The yarn structure and even the factory in which it was produced can result in poor reproducibility of test results. Making it difficult to compare test results from different laboratories. Measuring the wear performance of fabrics is critical to the manufacturers, distributors, and retailers in the textile production chain. A well controlled and reproducible wear resistance measurement is crucial to ensure reliable quality control of the fabric.
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Rotative or Linear Wear & COF? (A Comprehensive Study Using the Nanovea Tribometer)
Wear is the process of removal and deformation of material on a surface as a result of the mechanical action of the opposite surface. It is influenced by a variety of factors, including unidirectional sliding, rolling, speed, temperature, and many others. The study of wear, tribology, spans many disciplines, from physics and chemistry to mechanical engineering and material science. The complex nature of wear requires isolated studies toward specific wear mechanisms or processes, such as adhesive wear, abrasive wear, surface fatigue, fretting wear, and erosive wear. However, “Industrial Wear” commonly involves multiple wear mechanisms occurring in synergy.
Linear reciprocating and Rotative (Pin on Disk) wear tests are two widely used ASTM-compliant setups for measuring sliding wear behaviors of materials. Since the wear rate value of any wear test method is often used to predict the relative ranking of material combinations, it is extremely important to confirm the repeatability of the wear rate measured using different test setups. This enables users to carefully consider the wear rate value reported in the literature, which is critical in understanding the tribological characteristics of materials.
Wood Wear Test with the Nanovea Tribometer
Importance of Comparing Wood Finish Wear & COF
Wood has been used for thousands of years as a building material for homes, furniture, and flooring. It has a combination of natural beauty, and durability, making it an ideal candidate for flooring. Unlike carpet, hardwood floors keep their color for a long time and can be easily cleaned and maintained, however, being a natural material, most wood flooring requires the application of a surface finish to protect the wood from various kinds of damage such as scuffing and chipping over time. In this study, a Nanovea Tribometer was used to measure the wear rate and coefficient of friction (COF) to better understand the comparative performance of three wood finishes.
The service behavior of a wood species used for flooring is often related to its wear resistance. The change in the individual cellular and fiber structure of different species of wood contributes to their different mechanical and tribological behaviors. Actual service tests of wood as flooring materials are expensive, difficult to duplicate, and require long periods of testing time. As a result, it becomes valuable to develop a simple wear test that can produce reliable, reproducible, and straight forward.
Measurement Objective
In this study, we simulated and compared the wear behaviors of three types of wood to showcase the capability of the Nanovea Tribometer in evaluating the tribological properties of wood in a controlled and monitored manner.
Discussion
Sample Description: Antique Birch Hardwood has a 7-layer aluminum oxide finish, providing everyday wear and tear protection. Courtship Grey Oak, & Santos Mahogany are both laminate flooring types that vary in surface finish and gloss. The Courtship Grey Oak is a slate gray color, EIR finish, and low gloss. On the other hand, Santos Mahogany is a dark burgundy color, prefinished, and high gloss which allows surface scratches and defects to be more easily hidden.
The evolution of COF during the wear tests of the three wood flooring samples are plotted in Fig. 1. The Antique Birch Hardwood, Courtship Grey Oak, & Santos Mahogany samples all showed different COF behavior.
It can be observed in the graph above that Antique Birch Hardwood was the only sample that demonstrated a steady COF for the duration of an entire test. The Courtship Grey Oak’s sharp increase in COF and then gradual decrease could be indicative that the sample’s surface roughness largely contributed to its COF behavior. As the sample wore, the surface roughness decreased and became more homogenous which explains the decrease in COF as the sample surface became smoother from mechanical wear. The COF on Santos Mahogany displays a smooth gradual increase in COF at the beginning of the test and then transitioned abruptly into a choppy COF trend. This could indicate that once the laminate coating started to wear through, the steel ball (counter material) made contact with the wood substrate which wore in a quicker and turbulent manner creating the noisier COF behavior towards the end of the test.
Antique Birch Hardwood:
Courtship Grey Oak:
Santos Mahogany
Table 2 summarizes the results of the wear track scans and analysis on all wood flooring samples after the wear tests were performed. Detailed information and images for each sample can be seen in Figures 2-7. Based on the Wear Rate comparison between all three samples, we can deduct that Santos Mahogany proved to be less resilient to mechanical wear than the other two samples. Antique Birch Hardwood and Courtship Grey Oak had very similar wear rates although their wear behavior during their tests differed significantly. Antique Birch Hardwood had a gradual and more uniform wear trend while Court-ship Grey Oak showed a shallow and pitted wear track due to the pre-existing surface texture and finish
Conclusion
In this study, we showcased the capacity of Nanovea’s Tribometer in evaluating the coefficient of friction and wear resistance of three types of wood, Antique Birch Hardwood, Courtship Grey Oak, and Santos Mahogany in a controlled and monitored manner. The superior mechanical properties of the Antique Birch Hardwood leads to its better wear resistance. The texture and homogeneity of the wood surface play an important role in the wear behavior. The Courtship Grey Oak surface texture such as gaps or cracks between the wood cell fibers may become the weak spots where the wear initiates and propagates.
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Evaluating Brake Pads with Tribology
Importance of Evaluating Break Pad Performance
Brake pads are composites., a material made up of multiple ingredients, that must be able to satisfy a large number of safety requirements. Ideal brake pads have high coefficient of friction (COF), low wear rate, minimal noise, and remain reliable under varying environments. To ensure the quality of brake pads are able to satisfy their requirements, tribology testing can be used to identify critical specifications.
The importance of the reliability of brake pads is placed very high; the safety of passengers should never be neglected. Therefore, it is key to replicate operating conditions and identify possible points of failure.
With the Nanovea Tribometer, a constant load is applied between a pin, ball, or flat and a constantly moving counter material. The friction between the two material is collected with a stiff load cell, allowing the collection of material properties at different loads and speeds and tested in high temperature, corrosive, or liquid environments.
Measurement Objective
In this study, the coefficient of friction of the brake pads were studied under a continuously increasing temperature environment from room temperature to 700°C. The environmental temperature was raised in-situ until noticeable failure of the brake pad was observed. A thermocouple was attached to the backside of the pin to measure the temperature near the sliding interface.
Test Procedure and Procedures
Results and Discussion
This study focuses mainly on the temperature at which brake pads start to fail. The COF obtained do not represent real-life values; the pin material is not the same as brake rotors. It should also be noted that the temperature data collected is the temperature of the pin and not the sliding interface temperature
At the start of the test (room temperature), the COF between the SS440C pin and brake pad gave a consistent value of approximately 0.2. As the temperature increased, the COF steadily increased and peaked at a value of 0.26 near 350°C. Past 390°C, the COF quickly starts decreasing. The COF began to increase back to 0.2 at 450°C but starts decreasing to a value of 0.05 shortly after.
The temperature at which the brake pads consistently failed is identified at temperatures above 500°C. Past this temperature, the COF was no longer able to retain the starting COF of 0.2.
Conclusion
The brake pads have shown consistent failure at a temperature past 500°C. Its COF of 0.2 slowly rises to a value of 0.26 before dropping down to 0.05 at the end of the test (580°C). The difference between 0.05 and 0.2 is a factor of 4. This means that the normal force at 580°C must be four times greater than at room temperature to achieve the same stopping force!
While not included in this study, the Nanovea Tribometer is also able to conduct testing to observe another important property of brake pads: wear rate. By utilizing our 3D non-contact profilometers, the volume of the wear track can be obtained to calculate how quickly samples wear. Wear testing can be conducted with the Nanovea Tribometer under different test conditions and environments to best simulate operating conditions.
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Wear Testing Glass With Acoustic Emissions Monitoring
The wear behavior of three types of glass (Regular glass, Galaxy S3 glass and Sapphire coated glass) is compared in a controlled and monitored manner using the Nanovea Tribometer equipped with an AE detector. In this study, we would like to show the application of AE detection during wear and its correlation with the evolution of coefficient of friction (COF).
Tribocorrosion Wear Evaluation of Protective Coating
The tribocorrosion process of the DLC coatings on different types of steel substrates is simulated using the Nanovea Tribometer. In this study, we would like to showcase that Nanovea Tribometer equipped with the Tribocorrosion Module is an ideal tool for evaluating the performance of protective coatings used in wear and corrosion environment.
