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the sensitivity of frictional characterization of elastomers and elastomeric composites.

by:Top-In     2020-07-28
A wide variety of rubber and elastic composites working in friction
Related field applications.
They differ in composition, structure, processing, design and other variables.
Depending on each of these variables, the physical and mechanical properties of the product can change dramatically.
In order to make the problem more complex, it is difficult to predict the actual application conditions.
Therefore, it is difficult to achieve an accurate description of material performance and product application.
At the same time, however, robust and sensitive fast test methods are still needed to describe elastic behavior, selection, and optimization in a final, effective and inexpensive way suitable for material benchmarking.
As we all know, friction is one of the main factors in any product service behavior when it comes to material contact.
Through a large number of laboratory tests, including standardized and customized design methods, friction phenomena can be described quantitatively.
The poor sensitivity of the test to the application parameters determines the necessity of designing various frictions
Related Methods.
Traditionally, there is a set of friction
Relevant tests designed for each product application.
The study did not provide a detailed review of all products and the corresponding test methods, but it would be interesting to list some just to touch the topic.
The biggest friction
The product involved is the tire, one of the main performance features of the tire is the treadlife.
Therefore, tire development must be able to accurately describe the condition of the worn surface of the tire and the friction properties of the materials involved.
There are a number of ASTM procedures covering the wear and friction measurement of tires.
I. ASTM F 408 (ref. 1)
Determine the friction related parameters such as wet traction, braking coefficient and sliding.
This test method is considered to be \"suitable for research and development purposes and not suitable for regulatory status and specification acceptance because the values obtained do not necessarily agree to compare the level of traction performance with those obtained under different conditions (
Surface, environment, etc. ).
\"This is a good example of testing low sensitivity to input parameters.
Another example of the product working in a friction mode is the conveyor belt, which measures wear and friction differently on the conveyor belt.
Overview of wear-
Resilient materials for mining industry (ref. 2)
Emphasizes the importance of understanding the physical properties of the elastic body through appropriate testing.
One of the many traditional tests is astm d 2228 (ref. 3)
Known as pico wear, it is widely used in the conveyor industry.
Rotate the rubber sample at a controlled speed, time and strength under a loaded carbide cutter and report the amount of wear.
However, it was noted in the pico test that \"even if the test can be used to estimate the relative wear resistance of different rubber compounds, due to the wide variation of surface conditions, no correlation is given or implied between this test and service performance.
\"For the conveyor industry, it has been demonstrated that known standard and custom wear tests generally do not show a correlation with the performance of the conveyor belt on-site because of the low sensitivity to the test parameters (ref. 4).
The last example of a high wear-resistant product is the sole and heel, and a wide variety of standard tests have been developed for the application.
Many footwear wear testing machines have been recommended for many years (ref. 5).
However, there are sensitivity limits for most tests such as environment, surface and sample
Geometric conditions, not related to other tests (ref. 5).
Based on the short review of the existing friction quantification methods described above, it is clear that none of the methods is sufficiently sensitive to satisfy all friction-
Related applications.
The purpose of this imaging work is to propose a material representation method based on some kind of friction contact that simulates the friction properties of rubber and elastic composites.
This test must be sensitive to major field application parameters such as load, speed, or contact media shape, as well as environmental conditions.
The test should be applicable to material benchmarking, rating, selection and cost optimization.
In this paper, we present the only-image method of friction representation.
It points out that there is a certain change in the life of the product in its field.
The process that occurs inside the product is complex and cannot be analyzed and described.
However, some field applications (or input)
Parameters such as load, temperature, media shape. , are known.
Due to the influence of input parameters on the product, the final field attribute parameter (or output)
Such as product performance, strength, wear rate, cost, etc. , are formed.
In order to apply the image-only method to high sensitivity Friction properties, a new dynamic test method is introduced.
The test includes a combination of load and torsion performance.
This study proposes an experimental method to simulate specific contact behavior patterns (ref. 5).
In the test, the contact object is presented as a simple symmetric object (indentors).
All selected indentors are generic-
Purpose grinding point (ref. 6)
It includes stones of different shapes such as spherical shape, cone shape and flat shape.
An example of Indenter geometry is shown in Figure 1. [
Figure 1 slightly]
Indentor is compressed into a fixed sample, defined as a plate of a specific elastic body with a known thickness.
Compression can be controlled by force or displacement.
Apply the torque load to the indenter and record it as a function of angular displacement and compression.
The resistance of the torque is considered due to the friction between the Inprint and the elastic sample in contact with the surface.
Described Test Program (ref. 5)
And by reversing MTS dynamic machines in this study (ref. 7).
Place the rubber plate with constant thickness under the rotating indentor.
The thickness of the elastic composite corresponds to the actual thickness of the product.
Indentor presses into the elastic sample in the direction perpendicular to the surface of the sample, down to the selected load level, given according to the axial force, F, or axial displacement ,[DELTA].
After reaching the selected load or displacement and holding it for 10 seconds, indenter rotates in load control mode at the selected speed rate ,[omega]. The load (torque T)Displacement (angle [theta])
And record the time 0. 5 seconds.
Total rotation angle set to 200 [degrees].
Typical results of the test are shown in figure 2.
The maximum torque has a peak value that can be quantified [T. sub. max]and [[theta]. sub. max].
This peak represents the classical static friction resistance, corresponding to the effort required to move a surface from a static position, as described in the literature (
Ref, for example. 8). Values [T. sub. a]
, Shows the torsional resistance of the rotational motion and can be used to quantify the resistance of the classical dynamic friction, or to move one surface to another at a given speed.
Two groups of materials were considered in this study, including four groups of general materials
Rubber for use (1, 2, 3, 4)
Two kinds of elastic composite materials (A, B)
Fabric reinforcement.
Rubber is a mixture based on natural rubber (NR)
Synthetic rubber with different content, with carbon black (CB)fillers.
The composite tested has one and four layers of reinforced polyester and/or nylon fabrics of different densities (figure 3)
, Has a cover rubber compound selected from ordinary general purpose rubber based on synthetic rubber and NR mixture, as well as CB filler. [
Figure 3 slightly]
The sensitivity of the influence of the friction properties of the indentor shape, axial load, test temperature and torsion speed was studied for the selected material, and the results were shown in Figure 4-8. [FIGURES 4-8 OMITTED]
The effect of the Indentor shape represents the impact of different shape objects that touch the product, for example, similar to the impact difference of sharp stones and round stones compressed into sole or dropped on the conveyor belt.
Under the action of axial force, dents in the shape of cone, spherical and flat balls are loaded into representative rubber materials (
NR with sulfur curing system and carbon black filler)and turned 200[degrees]
To it at room temperature (RT).
Reverse resistance (N*mm)
As shown in figure 4.
The shape of the production curve is similar to the traditional trend (as figure 2).
Figure 4a well represents the peak of the maximum torque corresponding to the static friction.
There is a significant difference in torsional resistance generated by different shapes of indentors.
For example, when the axial force is 300 N, the cone indentor makes the material resist the torque at 1,000 N * mm, while the cone indentor produces about 750 N * mm (figure 4a).
The next aspect of the test is to study the effect of the axial load applied on the same representative rubber material.
For example, this test will repeat the effect of stones of various weights falling from the same height on selected materials.
As expected, an increase in the axial load resulted in a significant increase in the torsional resistance of indentors in various shapes.
With the load increasing from 300 N to 700 N, the twist resistance has more than doubled (figure 4).
Interestingly, as the load increases, the resistance level of the material to the indentors of the selected shape changes.
For example, under a lower axial load, the torsional resistance of the material to the spherical indentor is slightly lower than its resistance to the flat ball shape indentor, but the rating is switched under a higher load.
This result shows the importance of correctly selecting laboratory test parameters in order to properly simulate each field application.
In order to simulate the change of ambient temperature in the field application, the influence of temperature on the friction properties of the material was also studied.
For example, the torsional resistance of the same material to flat indentor was tested at room temperature [60 °c]degrees]C and 80[degrees]
C and under axial loads of 300 N, 500 N and 700 N (figure 5).
The torsion resistance of the material decreases with the increase of temperature, which is definitely the result of softening of rubber.
For tapered indentors, the same trend is observed (Figures 6 and 7).
The effect of speed was previously studied using an elastic material (ref. 5)
, Where the torsional values recorded at an axial force of 300 N have a very consistent dependence: the torsional resistance values increase as the speed increases.
In the current work
Effect of changing speed from 1 [degrees]
To 2 per second [degrees]
For a variety of materials, including four rubber compounds, studies are conducted at a higher axial force of 700 N per second (1,2,3 and 4)
Two kinds of elastic composite materials (A and B), (figure 8).
The anti-twisting ranking of rubber compounds has not changed with the increase of speed, and for all test materials, the higher speed is indeed related to higher torque results.
Material benchmark.
The relative rating of any two compounds (benchmarking)
It can depend on the conditions of the test, as stated in 1950 by. Schallamach (ref. 9).
In order to rate and compare materials and products, benchmarking is required.
In this study, by indenting spherical stones at different speeds, four representative rubber compounds and two composites were tested at room temperature and their torsional responses were rated
Figure 8a or 8b).
It is important to pay attention to the significant differences between the results of different materials, as the test sensitivity to the properties of the materials is high.
These results illustrate the importance of benchmarking on specific test parameters to avoid misleading results in material rankings.
The role of energy components all previously discussed tests are conducted using force
A controlled axial compression mode that indicates a situation in which the weight of the penetrating object causes contact stress: for example, a conveyor belt carrying rocks.
Deformation is essential in some field applications, such as sealing under fixed compression.
This means that lab tests must be programmed in displacement control mode.
Finally, some applications are arranged by energy factors, such as shock absorbers or installation performance.
For these cases, try to load-
And deformation
Control mode of an energy component
Control the test, and then compare the rated value of the torsional resistance obtained under the load with the rated value of the energy component-Control test.
In the first part of this experiment, as shown in Figure 9, four rubber compounds and two composites were tested at three axial loads at room temperature.
The indentor of the shape of the sphere was loaded into a sample and turned into 200 [degrees]at 1[degrees]
Speed and complete release.
This load was repeated three times at an axial force of 300 N, 500 N and 700 N, a total of 600 [degrees]rotation (200[degrees]
Repeat three times).
As with previous tests, there are significant differences in torque for representative materials.
The total torque rating shows the highest of material 4, followed by 1, 3 and 2.
The torque values of the two composites are very close.
Interestingly, on the charts obtained at a 300 N load, the classical static friction maximum appears significantly compared to the monotonous increased torque at higher loads. [
Figure 9 omitted
The second part of the experiment is to determine the energy composition of each material by running the load
Use the deflection curve of the sphere-shaped indentor at 10 N/sec.
Compression rate at room temperature (figure 10).
Calculate the area under the curve for each material and specify the name of the energy component E (N*mm).
The load corresponding to the three energy components is determined for each material (figure 11). [FIGURE 10-11 OMITTED]
Then repeat the first part of the experiment, but the load applied is not the same for all materials.
In contrast, for each material corresponding to the three energy component levels, the axial force is determined separately: 700 N * mm, 1,000 N * mm, and 1,500 N * mm, as shown in Figure 11.
Figure 12 gives the obtained torque value.
The ranking of the material twist resistance is completely changed, and due to the change of the control mode of the test from the load, compound 3 and composite B now support the highest torque (figure 9)
Energy components (figure 12). However.
Note that some materials seem to maintain their ratings: Compound 2 and composite A, for example, are still at the low end of the level of torsional resistance. [
Figure 12:
This is a valuable note on how important it is to correctly select test control conditions based on the specific field application of the part.
Conclusion a method for material representation for elastic and elastic bodies is proposed and developed
Composite material to emphasize its unique friction properties.
Based on this method, a set of material parameters were selected to quantify the friction properties under complex dynamic loads and environmental conditions.
High sensitivity of the proposed parameters is observed relative to the loading conditions (
Pressure, speed)
Environmental conditions (temperature)
Contact information (
Head of shape)
Material composition (
Different rubber and composite materials).
The sensitivity of the proposed material parameters can be considered as an important feature of the plausible benchmarking possible for specific products and applications of elastic bodies.
Benchmarking can be considered as an accelerated expression method based on elastic selection and optimization of limited information on field performance. References (1. )ASTM F408-94.
Standard Test Method for straight-Wet Traction tires
Braking in advance, use of trailers, ASTM standard annual Manual, Volume 109. 02. (2. )I. R. Sare, J. I. Mardel and A. J.
Hill, \"wear-resistant metals and elastic materials in the mining and mineral processing industries ---
Overview, \"wear, roll. 250, 1, 2001. (3. )ASTM D2228-88.
Standard Test Method for rubber properties-
Wear resistance (Pico Abrader)
Annual Handbook of ASTM standards, Volume 1. 09. 01. (4. )M.
Scherbakov, etc.
Extension of conveyor belt life by increasing wear resistance, Minutes of Meeting of Mining Engineers Association, February 25-27, 2002. (5. )M.
Shelbakov and M. R. Gurvich.
\"A method of friction properties of elastic materials and elastic composites,\" J.
Rubber and plastic, Volume 1
35, 4, October 2003, 335. (6. )
McMaster-Mount grinding point
Carl Supply Corporation ,(2000).
Directory 102, Cleveland, OH, p2,377. (7. )
MTS System Model 810. (2001). www. mts.
Eden Prairie, MN. (8. )ASTM D1894-01.
Standard Test Methods for static and dynamic friction coefficients of plastic films and films, ASTM standard annual Manual, Volume 108. 01. (9. )A. Schallamach.
Friction and wear of rubber wear
1957/1958, 384.
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