In this article we will describe the physical properties of rubber that you will see on a physical property data sheets for elastomers that are tested to ASTM D specifications. I have described what the property is, why it is important, and how you test it. ASTM D and D are used to measure the stiffness modulus of rigidity of a sample while applying torsional force on a specimen chilled to a specific temperature. Lets take a quick look at some forces before we get started on explaining properties. These forces will be applied to the specimen during testing.
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Yield Yield strength rubber psi is the first point where the specimen yields, where the specimen's cross-sectional area begins to contract significantly, or where the strain can increase without increase in the stress. Beryllium  Categories Technical Articles. Teijin Aramid. If you want to promote your products or services in the Engineering ToolBox - please use Google Adwords. I had an application where a very small O-ring with an inside diameter of. Aramid Kevlar or Twaron. It is indicated in Figure 5 as Point 3. The Low Temperature Brittleness test is use to determine the lowest temperature at which a rubber specimen will not exhibit fractures or cracks when subject to a specific impact condition. This is a special molded shape with fabric reinforcement molded in the mid-plane of the sample. After the yield point, ductile metals undergo a period of strain hardening, in which Yield strength rubber psi stress increases again with increasing strain, and they begin to neckas the cross-sectional area of the specimen decreases due Penticton tanning plastic flow.
Typically noted in either pounds per square inch psi or megapascals MPa , tensile strength is the amount of force required to break a rubber specimen.
- Tensile Modulus - or Young's Modulus alt.
- In this article we will describe the physical properties of rubber that you will see on a physical property data sheets for elastomers that are tested to ASTM D specifications.
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Hardness Hardness is the measure of how resistant solid material is when a force is applied. U Nyi Hla Nge - Refresher course and field reference manual for site engineers and inspectors. UTS is not used in the design of ductile static members because design practices dictate the use of the yield stress. Social Profiles. This expansion provides additional sealing capability. Tensile strength is measured with a tensometer.
Yield strength rubber psi. Physical properties of some thermoplastics like ABS, PVC, CPVC, PE, PEX, PB and PVDF
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In this article we will describe the physical properties of rubber that you will see on a physical property data sheets for elastomers that are tested to ASTM D specifications. I have described what the property is, why it is important, and how you test it. ASTM D and D are used to measure the stiffness modulus of rigidity of a sample while applying torsional force on a specimen chilled to a specific temperature.
Lets take a quick look at some forces before we get started on explaining properties. These forces will be applied to the specimen during testing. Being familiar with these will also give you and understanding of the forces that may be applied to the rubber parts while in your application. Lets take a rectangular block of rubber as a specimen.
If you stretch the block, this is tension or tensile force. If you twist the block this is torsional force and if you apply an opposing force to the side on top and opposite side on bottom, this is shear force.
Some of these forces will be applied to the specimen during testing. Hardness is the measure of how resistant solid material is when a force is applied.
There are 3 main type of hardness measurements, scratch, indentation and rebound. We will only be talking about the indentation hardness for elastomers. Indentation hardness is the materials resistance to indentation by an indentor.
Some sealing surfaces may not be totally smooth. The little voids, pits and scratches allow a pathway for fluid or air to escape through. Softer materials tend to flow better into these voids and imperfections on the sealing surface creating a better seal.
On the other hand, harder rubbers will not do this as well but they do resist extrusion cause by high pressures. Also, coefficient of friction is also affected by the hardness of the rubber. Softer rubber has a higher coefficient of friction and harder rubber has a lower coefficient of friction. Coefficient of friction plays a factor when the rubber seal is sealing a part that moves.
The durometer gauge is used to test the hardness of elastomers. Type A is used to test soft rubber materials while Type D is used to test hard rubber and plastic materials. Type M, also for soft materials, was developed to test small specimens, typically O-rings, that do not meet the physical size requirements specified in ASTM D Is is important to know that although each of the hardness scales are graduated from , these scales are not the same. A piece of rubber measuring 90 on a Shore A gauge will read around on a Shore D gauge.
Ultimate tensile strength, or just tensile strength, is the maximum force a material can withstand without fracturing when stretched.
It is the opposite of compressive strength. Have you ever purchased a pair of shoes and they came joined together with a piece of string? Instead of getting a pair of scissors, did you opted to test your physical strength against the tensile strength of the string and try to break it by pulling on it? If the string has a low tensile strength you should be able to pull and break the string easily. If it has a high tensile strength it will be much harder to break by pulling.
Are you starting to understand tensile strength? Tensile strength is an indication of how strong a compound is. Any time you have an application where you are pulling on the part, tensile strength is important to know.
Whether your product is designed to break easily or not at all the tensile strength will let you know how the object will react to the tensional forces. A few rubber products that tensile strength are important would be bungee cords, rubber tie downs, drive belts. Some elastomeric compounds, like Silicone, have a low tensile strength making them unsuitable for a dynamic types of seal because they can fracture easily. Tensile strength is measured with a tensometer. A tensometer is special machine that is designed to apply a tensional or compressive force to a specimen, in our case a die cut dumbbell shape, and measure how much force it takes to deform and fracture the specimen.
The force is typically displayed on a stress-strain curve that shows how much force was required to stretch the specimen to deformation and ultimately break. Maximum elongation, with respect to tensile testing, is the measure of how much a specimen stretches before it breaks.
I had an application where a very small O-ring with an inside diameter of. But when we tried to use a fluorocarbon compound several of the O-rings were breaking during installation.
Elongation is measured with a ruler or an extensometer. An extensometer is an electronic ruler that is attached to the tensometer and will measure the extension of the specimen while torsional force is being applied. Another way of measuring elongation is with a regular ruler. To measure the elongation with a ruler, make two bench marks 1 inch a part on the specimen.
This is the Initial Gage Length L o and then measure the distance between the marks just before the specimen breaks.
This is the Final Gage Length L x. While we are using bench marks, let quickly talk about Tensile Set. Tensile Set is the extension remaining after a specimen has been stretched and allowed to relax for a predefined period of time.
Do not mistake Tensile Set with Elasticity. Elasticity is the mechanical property of a material to return to its original shape where Tensile Set is the amount on extension remaining after being stretched.
After stretched it relaxes close to, if not exactly to, its original length. Now take a piece of Teflon and stretch it. It does not return to its original length and it stays in its stretched state. One test we perform in our Q. The O-ring should fairly quickly return close to its original diameter. Often times a seal has to be stretched during installation and the last thing you want to happen is the O-ring stay stretched and not fit which could cause problems during assembly.
Remember the 2 bench marks 1 inch apart on the specimen in the elongation test? Measure the distance between the bench marks. Use the same equation used in the elongation test except the Final Gage Length L x is the final measured distance between the bench marks.
Another way to test without breaking is to stretch the specimen to a specified elongation and hold for 10 minutes. Release the specimen as quickly as possible, making sure not to allow it to snap back, and let sit for 10 minutes. Again, use the same equation used in the elongation test except the Final Gage Length L x is the final measured distance between the bench marks. When performing a Tensile Strength test a plot is made of the stress vs.
This plot is called a stress-strain curve. At any given point on the stress-strain curve we can read the Tangent Modulus. Knowing how easily a material deforms under strain can be important in some applications. An engineer was installing a rubber seal on a door. The rubber he used had high modulus. The door was hard to close because the rubber resisted being deformed.
He then used a compound with low modulus that deformed easily allowing the door to close easily. As stated above, when performing a Tensile Strength test a stress-strain curve is plotted. Yield Point is the force at which the specimen starts to deform permanently. This is the area which the specimen retains its elasticity. When the force is removed in this area the specimen will return to its original shape. After this area the specimen transitions from elastic to plastic behavior.
This means that after the Yield Point, permanent deformation occurs in the specimen and it will no longer return to its original shape. Here is where I am going to throw a curve at you. To summarize the above properties lets take a look at the stress-strain curve that is generated during the Tensile Strength test, see figures 2 and 5. The amount of tensional force required to fracture a specimen. Ultimate Elongation — the amount a specimen deforms by stretching.
Tangent Modulus — Any point on the stress-strain curve. The force at which a material will begin to deform permanently. Hardness — The measure of how resistant solid material is when a force is applied. A measurement showing the extension remaining after a specimen has been stretched and allowed to relax for a predefined period of time.
Tensile Set is not show on the stress-strain curve. Is is a measurement that can be done after a tensile strength test. So far we talked about properties where tension force was applied to the specimen. Some of these properties were tensile strength, elongation, modulus, and yield point. Now lets talk about compression set, compression-deflection and tear resistance, where compressive and sheer forces are applied, as well as weathering, ozone and low temperature resistance. Lets get started with compression set.
The purpose of the compression set test is to measure the ability of the rubber specimen to retain its elastic properties after compressive forces have been applied for a prolonged period of time at elevated temperatures.
When an O-ring is squeezed the rubber has elasticity. It wants to go back to its original shape. This elasticity is how the O-rings seals, especially under low or no pressure. When pressure is applied to the system the O-ring seal pushes against the groove wall opposite the direction of the pressure, forcing it to expand perpendicular to the direction it is being squeezed.