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Category: Rotational Tribology

 

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 mechanical action of the opposite surface1. 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 towards specific wear mechanisms or processes, such as adhesive wear, abrasive wear, surface fatigue, fretting wear and erosive wear2. 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 setups34for 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 conrm 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.

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Wood Wear Testing with Nanovea Tribometer

Wood has been used for thousands of years as a building material for homes, furniture and flooring. It has a combination of natural beauty, durability and restorability, 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 under-stand the comparative performance of three wood finishes.

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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.

 

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.

Abrasion Resistance Of Sandpaper Using Tribometer

Abrasion resistance and the effectiveness of sandpaper is often determined by their abrasion performance under different conditions. The grit size, i.e. the size of the abrasive particles embedded in the sandpaper, determines the wear rate and the scratch size of the material being sanded. Sandpapers of higher grit numbers possess smaller particles, leading to lower sanding speed and finer surface finish. Sandpapers of the same grit number made of different materials can behave differently under the dry or wet condition. Reliable tribological evaluation is needed to ensure that the manufactured sandpapers possess desired abrasion behavior under the application conditions. It allows users to quantitatively compare the wear behaviors of different types of sandpapers in a controlled and monitored manner and to select the best candidate for the target application.

Abrasion Resistance Of Sandpaper Using Tribometer

Industrial Coating Scratch & Wear Evaluation

The wear process of the acrylic urethane floor paints with different topcoats is simulated in a controlled and monitored manner using the Nanovea Tribometer as shown in Fig. 1. Micro scratch testing is used to measure the load required to cause cohesive or adhesive failure to the paint. In this study, we would like to showcase that Nanovea Mechanical Tester and Tribometer are ideal tools for evaluation and quality control of commercial floor and automotive coatings.

Industrial Coating Scratch & Wear Evaluation

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).

Wear Testing Glass With Acoustic Emissions Monitoring

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.

Tribocorrosion Wear Evaluation of Protective Coating

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