ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

1 Brief Introduction
1.1 This test method includes the evaluation method of the tensile properties of vulcanized thermoset rubber and thermoplastic elastomer. This test method cannot be used to test hard glue and materials with high hardness and low elongation. The test method is as follows:

Method A – Straight bars and dumbbell specimens

Method B — Annular specimen

Note 1 -The results of the two tests are not comparable.

1.2 Units based on SI or non-SI are considered standard units of this standard. Since the value of the results may be different when using different unit systems, the different units should be used separately and not mixed.

1.3 Security

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

2 References
D 1349 Rubber specification — Standard temperature for testing

D 1566 Rubber related terms

D 3182 Rubber specification — Materials, equipment and procedures for the preparation of standard compounds and standard vulcanized test sheets

D 3183 Rubber specification – Preparation of test sheets from finished products

D 4483 Specification for measuring accuracy of standard test methods for rubber and carbon black industrial varieties

2.2 ASTM Accessories

Preparation of annular specimens, method B

2.3 ISO Standards

ISO 37 – Determination of tensile stress-strain properties of vulcanized or thermoplastic rubber

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

3 Terminology
3.1 Definition

3.1.1 Tensile long-term deformation — the residual deformation of the specimen after elongation under certain action, when the action force is relieved, is expressed as a percentage of the original length.

3.1.2 Tearing long deformation — the long deformation measured by attaching the broken dumbbell sample to the cross section.

3.1.3 Tensile force — the maximum force generated in the process of specimen breaking.

3.1.4 Tensile strength — the stress used to stretch the specimen

3.1.5 Constant extension stress — the stress generated when the specimen of regular section is stretched to a specific length.

3.1.6 Thermoplastic elastomer – A material similar to rubber, but unlike ordinary vulcanized rubber, it can be processed and recycled like plastic.

3.1.7 Elongation at break — the elongation rate of the specimen when it breaks during continuous stretching.

3.1.8 Yield point — the point on the stress-strain curve where the velocity of stress change with respect to strain becomes zero and opposite before the final failure of the specimen.

3.1.9 Yield strain — The level of strain at the yield point

3.1.10 Yield stress — The level of stress at the yield point

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

4 Method description
4.1 Test to determine the tensile properties, first cut the sample from the sample material, including sample preparation and test two parts. The shape of the sample can be dumbbell, ring or straight bar, and the section shape is regular.

4.2 Test the tensile strength, fixation stress, yield point and elongation at break without pre-extension of the sample. The determination of tensile strength, fixation stress, yield point and elongation at break of the specimen with regular section is based on the original cross-sectional area of the specimen.

4.3 Long term deformation by stretching and long term deformation by tearing. Measure the deformation of the sample after drawing back according to the specified method.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

5 Key points and applications
5.1 The materials or products involved in this test need to be subjected to tensile force in the actual application process. This test is to determine such tensile characteristics. However, the tensile performance does not directly represent the whole situation of the final use of the product, because the product needs to cover a wide range of potential uses in actual use.

5.2 Tensile properties are related to materials and test conditions (tensile speed, test temperature and humidity, sample geometry, pre-test adjustment, etc.). Therefore, the test results of materials under the same conditions are comparable.

5.3 Test temperature and tensile speed have significant influence on tensile properties, which should be strictly controlled. And the effect varies with the material.

5.4 Tensile long-term deformation represents the residual deformation of the sample. It represents the long-term deformation and partial recovery of the sample after stretching and retraction. Therefore, the stretching and retracting processes (and other test conditions) need to be tightly controlled to ensure that the results are comparable.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

6 Equipment
6.1 Tensile machine — The tensile testing machine shall have an electric drive mechanism to ensure that the separation speed of the sample chuck is constant at 500±50mm/min and the minimum stroke is 750mm(see Note 1). The test machine should have a set of suitable dynamometer and reading recording system to ensure that the measured force deviation is within ±2%. If the range of the testing machine cannot be changed (for example, the pendulum dynamometer), then the deviation of the force measured when the specimen breaks is ±2% of the full range of the dynamometer, and the accuracy of the minimum force measured is 10%. If the dynamometer has an automatic compensation function for the direct measurement of tensile stress, the compensation function for the cross-sectional area of the specimen junction should be turned off during the measurement. The recording device should be fast enough to measure the force and ensure the required accuracy during the whole process of specimen destruction. If the tester does not have a recording device, there should be an indicator to indicate the maximum force during the stretch. Elongation should be measured in the test system with a minimum increment of 10%.

Note 1 — If the tensile speed used is 1000±100mm/min, it should be indicated in the test report. If in doubt, the test should be rerun at a speed of 500mm/min.

6.2 High and low temperature test chamber – The test chamber shall meet the following requirements:

6.2.1 In the test chamber, there should be a heat flow around the position of the chuck and shaft, the surround speed is 1 to 2m/s, and the temperature should be kept within the range of 2℃ of the required temperature deviation.

6.2.2 Apply the calibrated temperature measuring device to measure the actual temperature near the chuck and shaft.

6.2.3 The test chamber shall have an exhaust ventilation device to discharge the gas released in the high temperature (sample) to the atmosphere.

6.2.4 Before the test, the sample should be placed vertically near the chuck and shaft for adjustment. Specimens should not be in contact with each other or with the walls of the test chamber except for momentary contact caused by agitation of the surrounding air.

6.2.5 Place the chuck appropriately to facilitate operation in high and low temperature environment. In this way, the dumbbell or straight strip specimen is placed into the chuck for as short a time as possible to reduce the temperature change of the test chamber.

6.2.6 The dynamometer shall be suitable for working at the test temperature or be well insulated from the test chamber.

6.2.7 The test chamber shall be equipped with elongation measuring device. If a ruler is used to measure the elongation of the sample scale, the ruler should be placed parallel to the scale close to the path of the chuck and can be controlled from outside the test chamber.

6.3 Thickness Gauge — The thickness gauge shall meet the requirements of Specification D 3767(Method A). For annular specimens, see Article 14.10 of this test method.

6.4 Measurement of tensile long-term deformation — using test equipment as described in 6.1 or as shown in Figure 1. The measuring range of stopwatch or other timing device should be greater than 30min, and the measuring accuracy of ruler or other measuring device should be within 1%.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

7 Selection of samples
7.1 The following points should be considered when selecting the sample

7.1.1 During preparation and treatment, the anisotropy and orientation of the material caused by the flow can affect the tensile properties. Therefore, in the preparation of dumbbell or straight strip specimens, on the premise of knowing the calendering direction, the direction of sample cutting should be parallel to the calendering direction. For annular specimens, it is usually made a certain average of the orientation characteristics.

7.1.2 For thermoplastic rubber or elastomer, samples shall be cut from injection molded samples with a thickness of 3.0±0.3mm, and the test results obtained from samples with other thicknesses shall be comparable, unless otherwise specified. Samples should be perpendicular and parallel to the forming flow direction of two groups. The size of the test piece or plate should meet the test requirements.

7.1.3 The elongation of annular specimens can be measured by the separation of collets, but the elongation distribution on the radius and width of specimens is inconsistent. To reduce this effect, the sample width should be less than the diameter of the annular sample.

7.1.4 In the ordinary tensile test with small straight strip specimens, the failure of the specimens generally occurs in the chuck. Therefore, only when the sample can not be made of other shapes of the sample to use the straight sample. For non-destructive stress-strain or material modulus tests, straight strip specimens are used.

7.1.4 The size of the sample depends on the requirements of the material, the test equipment and the sample used for the test. For materials with low elongation at break, longer specimens can be used to improve the accuracy of measuring elongation.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

8 Calibration of test equipment
8.1 Calibrate the tester according to Procedure A of Specification E 4 for measuring precision type dynamometers, and calibrate one or more force points according to section 7 and 18 of specification E 4. For the pendulum dynamometer, follow the following steps to calibrate:

8.1.1 Put one end of the dumbbell sample into the chuck of the test machine.

8.1.2 Remove the lower chuck from the testing machine, that is to say, the gripping mechanism of the sample is on the upper chuck of the testing machine.

8.1.3 Install a hook on the lower chuck to hold the lower end of the sample

8.1.4 Hang a weight of known weight to the hook, so that a certain mass can be temporarily applied to the lower fixture of the specimen (see Note 2).

8.1.5 Open the monitoring device for jig movement, and keep it running continuously until the weight is free to hang on the sample in the ordinary test.

8.1.6 If the disc or ruler (or the equivalent of a stress compensator) does not indicate the force value within the specified accuracy, the equipment shall be effectively checked for faults (e.g. friction of shafts or other moving parts). It should be determined that the mass of the lower chuck and hook is also taken into account.

8.1.7 After the friction and other faults of the testing machine are eliminated, calibrate the testing machine to know that the weights are measured at three points at about 10, 20 and 50% of the full scale of the testing machine. If ratchets and spines are used in normal tests, they should also be used in school. Friction is checked by installing a ratchet.

Note 3 — There shall be a device to prevent weights from falling from the test machine.

8.2 A spring can be used for approximate quick calibration.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

9 Test temperature
9.1 Unless otherwise specified, the standard test temperature is 23±2℃. The sample should be adjusted at 23 ° C for at least 3 hours. If the material is affected by humidity, the specimen should be conditioned at 50±5%R.H. for more than 24 hours before the test. If tested at other temperatures, the temperature listed in Specification D 1349 shall be used.

9.2 If the test is conducted at A temperature higher than 23℃, the sample of method A should be preheated for 10±2min; For method B, it should be preheated for 6±2min. Before each test interval, the specimens are placed separately in the test chamber so that all specimens receive the same warm-up time continuously. Preheating tests at high temperatures should be strictly limited to prevent persulfur and thermal aging.

Note 3 — Warning: Among other warnings, use insulated and cold gloves to protect hands from high and low temperatures. A mask should be used during high temperature experiments to prevent the inhalation of toxic gases when the door of the experiment box is opened.

9.3 For low temperature test, the sample should be pre-cooled for at least 10min.

Test method A — Strips and dumbbell specimens

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

10 Equipment
10.1 Cutting Tool — The shape and size of the cutting tool should conform to that shown in Figure 2. The inside of the narrow part of the cutting tool shall be perpendicular to the end face of the cutting tool, and at least 5mm long from the end face of the cutting tool shall be polished. The shape of the cutter should remain unchanged without defect. (See Note 4)

Note 4 — The condition of the cutting tool can be determined by observing the fracture point of the sample. The fractured specimens were removed from the chuck and spliced along the fracture surface to observe whether the failure of the specimens occurred at the same location. If the failure occurs at the same location, the cutter may become blunt, defective, or bent at this location.

10.2 Marking — Two marking lines drawn on the specimen for measuring elongation and strain are called marking (see Note 5). The line marker shall include a flat plate with two bumps parallel to each other. The raised surface (parallel to the surface of the plate) should have a long and narrow plane, and the two faces should be kept in the same plane. The raised plane is 0.05 to 0.08mm wide and at least 15mm long. The Angle between the plate and the bump should be at least 75º. The distance between the centers of the two raised planes should be kept within 1% of the deviation of the required or target distance. A handle shall be included on the back or top of the line marker.

Note 4 — No marking is required if contact extensometers are used.

Ink Marking — Use a flat, hard surface (hardwood, metal, or plastic) to make ink or toner marking. The ink or toner shall be firmly bonded to the specimen, shall not corrode the specimen, and shall contrast with the color of the specimen.

10.4 Collets — The test meter has two collets, one of which is connected to the dynamometer.

10.4.1 The chuck of the test dumbbell sample shall have a self-tightening device to generate constant pressure on the surface of the chuck. With the increase of elongation, the clamping force shall also increase to prevent sliding and make the failure occur in the narrow part of the sample. A constant pneumatic chuck is also suitable. There is a special part in the broken part of the fixture, so that the length of the sample inserted into the fixture is the same and the stress distribution is uniform.

10.4.2 The fixture used for testing straight strip specimens shall have pneumatic fixture, clamp mouth or bolt buckle, so that the clamping force of the fixture can be uniformly applied to the entire width of the sample.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

11 Sample
11.1 Dumbbell specimens — Whenever possible, specimens shall be injection molded or cut from specimens 1.3 to 3.3mm thick. One test method can be used to cut the thickness and size of the specimen (see specification D 3182). The test piece can be made directly or cut and polished from the finished product. If the specimen is prepared directly from the finished product, the surface should not be hard leather or fabric, etc. According to the requirements of Specification D 3183. All specimens should be cut parallel to the length of the specimen unless otherwise specified. If the specimen is prepared according to specification D 3182, its thickness should be 2.0±0.2mm and cut along the orientation of the material. Use a C-type cutter (FIG. 2) with a simple stamping device and ensure smooth cut surface. .

11.1.1 Labeling Dumbbell Specimens — The dumbbell specimens shall be marked as described in 10.2, and the specimens shall not be subject to tension when the lines are marked. The mark should be drawn in the narrow part, equal distance from the center of the specimen and perpendicular to the vertical axis. The distance between the two lines is 25.00±0.25mm for type C and type D samples; Others 50.00±0.5mm

11.1.2 Dumbbell sample thickness measurement — The sample thickness should be measured at three points, one point in the center and two points at both ends of the narrow part. The median of the three values was taken to calculate the cross-sectional area. If the range of the sample thickness is greater than 0.08, the sample is invalid. The width of the sample can be calculated according to the width of the working part of the cutter.

11.2 Straight strip specimens — if dumbbells or annular specimens cannot be cut from the sample, straight strip specimens (e.g. narrow bands, small tubes, or fine electrical insulating materials) may be cut. The specimen should be long enough to fit into the fixture. The scale spacing is 11.1.1. To calculate the test cross-sectional area from the tube, the mass, length and density of the tube should be used. The cross-sectional area is calculated as follows:


A= cross-sectional area,cm2

M= mass,g

D= density,g/ cm3

L= length,cm

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

12 Steps
12.1 Determination of tensile stress, tensile strength and yield point — Load the dumbbell sample into the fixture of the testing machine, and pay attention to adjust the symmetry of the sample clamping, so that the tensile force is evenly distributed on the section of the sample. This will avoid overestimation of the tensile force of the specimen. The test speed was 500±50mm/min(see note 7) unless otherwise specified. Start the test machine and pay attention to the line marking to prevent the influence of parallax. The force values at special elongation and at fracture were recorded. Elongation can be measured using an extensiometer, an automatic drawing, or an optical tracking system. The measurement accuracy of elongation at fracture is within 10%. See 13 for the calculation.

Note 8 — If the yield point of the sample is below 20% elongation when the test speed is 500±50mm/min, the test speed can be reduced to 50±5mm/min. If the yield point of the sample is still below 20% elongation, the test speed can be reduced to 5±0.5mm/min. Sample speed shall be recorded.

12.2 Determination of tensile long-term deformation — Load the specimen into the testing machine or device described in 6.1 as shown in Figure 1. Pay attention to adjust the gripping symmetry of the sample so that the tension is evenly distributed on the sample section. The speed of chuck separation should be as constant as possible, so that the time to reach the specified elongation is 15s, and maintain this elongation for 10min. After 10min, the load was released immediately and allowed to recover freely for 10min. After that, the residual deformation within the standard distance was measured with a measurement accuracy of 1% of the original distance. Use a stopwatch to record the time. See 13 for calculation

12.3 Determination of long-term fracture deformation — After the sample is broken for 10min, carefully splice the sample and measure the residual deformation within the standard distance, as shown in 13

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

13 Calculation
13.1 Strength calculation at any elongation:


In the equation

T(XXX)= strength at elongation (XXX)%,MPa

F(XXX)= stress at specific elongation,MN

A= sample cross-sectional area,m2

13.2 Calculation of yield strength


In the equation

Y(stress)= yield strength,MPa

F(y)= yield force,MN

A= sample cross-sectional area,m2

13.3 The evaluated yield point is the point on the stress-strain curve where the velocity of stress change with respect to strain becomes zero and opposite before the final failure of the specimen.

13.4 Calculation of tensile strength


In the equation

TS= tensile strength,MPa

F(BE)= maximum force at break,MN

A= sample cross-sectional area,m2

13.5 Calculate the elongation rate at any elongation;


In the equation

E= percentage elongation (distance in scale),%

L= observed distance within the sample standard distance,mm

L(0)= original scale length of the sample,mm

13.6 Elongation at break is calculated by substituting L when the sample breaks into Equation 5.

13.7 Formula 5 can also be used to calculate the long-term deformation, as long as L in the formula is substituted with the residual deformation after 10min.

13.8 Test results — Test results are expressed as the median of the results of three independent consecutive samples. In two special cases, five samples were tested and the median value of the five samples was reported.

13.8.1 Special Case 1 — When the results of one or two specimens in the test do not meet the specially required measurements.

13.8.2 Special Case 2 — for arbitral trials.

Method B — Annular specimen

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

14 Equipment
14.1 Cutter — Annular cutter is shown in Figure 3. Use a cutting knife to cut an annular specimen from a flat specimen, and install a part of the upper shaft of the cutting knife into a rotary compression device under which the specimen can be fixed to a rubber fixing device.

14.1.1 Blade depth retainer — The cylindrical disc in the retainer shall be at least 0.5mm thicker than the thickness of the rubber sheet to be cut. Its diameter should be less than the inner diameter of the sample, so that the protrusion of the blade can be adjusted from the cutting tool. See Figure 3

14.2 Rubber fixing plate — a device for holding rubber in place during cutting, with top and bottom surfaces parallel to each other, made of hard polymeric materials (hard glue, polyurethane and polymethyl methacrylate). The holes, about 1.5mm in diameter, are distributed 6 to 7mm apart in the center through the plate. All these holes should communicate with the mold cavity inside to reduce the air pressure used to hold the test piece. Figure 4 is used to clamp the standard test piece (about 150×150×2mm) during cutting.

14.3 Air pressure source — A vacuum pump can be used to maintain a suction force of 10kPa on the sample at the center of the gripper mold cavity.

14.4 Soapy Water — Use neutral soapy water to lubricate the cutter.

14.5 Rotary cutting — The test piece can be cut by a precision rotary hole machine or other equipment that can provide at least 30rad/s speed. The cutter rotation device shall be mounted on a horizontal plane with a vertical positioner to support the rotating connecting rod and the shaft used for the cutter. The eccentricity of the rotating shaft should be less than 0.01mm.

14.6 Built-in workbench — There shall be a workbench or other device that can move along the x-y axis respectively for gripping and positioning the test piece so that the test piece corresponds to the rotational axis of the rotating cutter.

14.7 Tensile testing Machine — shall meet the requirements as described in 6.1.

14.8 Test Fixture — The fixture of the annular specimen is shown in Figure 5. The testing machine should be calibrated according to 8 rules.

14.9 Test Chamber — The high and low temperature test chamber shall meet the requirements in 6.2.

14.9.1 The fixture shall not only be suitable for testing at room temperature. However, under special temperature, appropriate lubrication should be used to ensure the lubrication of the rotating shaft.

14.9.2 The dynamometer shall be suitable for use at operating temperature or well insulated from the test chamber.

14.10 Thickness Gauges — Thickness gauges shall comply with the requirements of Specification D 3767(Method A).

14.10.1 The main part of the thickness gauge, a cylindrical upper measuring surface (vertical axis along the vertical direction) at least 12mm high and 15.5±0.5mm in diameter. In order to be suitable for small annular samples, a measuring head with a diameter of 15.5mm is used to measure, and the measurement will not cause the elongation of the sample. The bottom of the cylindrical surface can be cut off half along the center, so that there is no interference when measuring small samples. A curved measuring end can also be used.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

15. Annular specimen

15.1 ASTM Annular specimens — There are two types. Generally, 1-shaped specimens are used

15.1.1 Sample size

Type 1

The inner circumference was 50.0±0.01mm

The inner diameter was 15.92±0.003mm

The radial width was 1.0±0.01mm

Thickness 1.0~3.3mm

Type 2

The inner circumference is 100.0±0.2mm

The inner diameter was 29.8±0.06mm

Radial width 2.0±0.02mm

Thickness 1.0~3.3mm

15.2 ISO Annular specimens — There are two types of specimens, ordinary and small, according to ISO 37, which specifies their specific test procedures.


Inner diameter 44.6±0.2mm

Outer diameter 52.6±0.2mm

Thickness 4.0±0.2mm

Small size

Inner diameter 8.0±0.1mm

Outer diameter 10.0±0.1mm

Thickness 1.0±0.1mm

15.3 Cut the annular sample from the pipe — the diameter wall thickness of the annular sample shall be absolutely the wall thickness of the pipe and shall meet the requirements of the product.

15.4 Preparation of cutting sample — Place the blade in the holder of the cutting tool and adjust the depth of the blade. Place the cutter in the rotary press and adjust the shaft or table so that the bottom of the blade holder is 13mm above the sample holding plate. Shrink the stop for vertical movement of the rotating shaft. This allows the end of the blade holder to penetrate the surface of the plate. Put the sample into the gripper and reduce the pressure of the chamber to 10kPa. Wet the surface of the test piece with neutral soapy water. The cutter should be reduced at a constant speed and then stopped. At this time, the cutter holder should not touch the test piece. Re-adjust the blade depth if necessary. Reset the rotating shaft before the next cutting.

15.5 Preparation method for cutting a sample from a pipe — insert a shaft into the pipe, the diameter of which is slightly larger than the pipe diameter. Put the shaft and tube together on the machine tool. Cut the sample of the required axial thickness from the sample with the blade or cutter on the machine tool. For thin-walled pipes, a cutter with two parallel blades can be used to cut them flat.

15.6 Annular specimen:

15.6.1 Circumference — The inner circumference can be measured with a cone or a gauge. No stress can be used to change the ellipticity of the annular specimen during the measurement. The median perimeter can be based on the inner perimeter, the meridional width and π(3.14).

15.6.2 Radial width — three measuring points are evenly distributed around the circumference of the specimen according to the thickness gauge in 14.10.

15.6.3 Thickness — When cutting annular specimens, the thickness of the disk from inner circle to outer circle can be measured by thickness gauge according to specification D 3767.

15.6.4 Cross-sectional Area – The cross-sectional area was calculated as the median of three measurements of radial width and thickness. For thin pipe wall samples, the cross-sectional area was calculated using the axial length of the cutter and the wall thickness.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

16 Process
16.1. Determination of tensile stress, tensile strength, elongation at break and yield point of annular specimens — with suitable lubrication of shafts with lubricating fixture, such as mineral oil or silicone oil. Should choose to use the prescribed and no impact on the material. The calculation and adjustment of the initial position of the shaft center of the two fixtures are as follows:



IS= initial distance from the center of the jig shaft,mm

C(TS)= circumference of the sample, for type 1 sample is the inner diameter, for type 2 sample is the diameter,mm

C(SP)= circumference of jig shaft,mm

The test speed was 500±50 mammin (see notes 7 and 8), among other requirements. Start the test machine and record the force and the relative displacement of the two jig shafts. Elongation and stress were recorded at break. The calculation is shown in Section 17,

Note 8 — The test speed was 100±10mm/min using ISO small ring type sample.

16.2 Experiments at non-standard temperatures – Use the test chamber as described in 6.2 and read the warnings in Note 2. For tests above 23 ° C, the sample was preheated at this temperature for 6±2min. For tests below room temperature, the sample should be adjusted at that temperature for at least 10min. The test temperature in D 1349 should be used. The test pieces shall be put into the test chamber separately to meet the requirements of 9.2.

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

17 Calculation
17.1 Except for one important point, the calculation of the stress-strain properties of the ring-shaped specimens is the same as that of the dumbbell or straight strip specimens. When the annular specimen is stretched, the stress distribution of each edge of the annular is not uniform in width (from left to right). The initial inner diameter of the sample is less than the initial outer diameter. Therefore, in the tensile test of the specimen, the stress of the inner test is greater than that of the outer test, which is caused by the difference in the initial size.

17.2 The following options can be used to calculate tensile strength and fracture strength.

17.2.1 Constant elongation stress — use the median circumference of the annular specimen to calculate the elongation. The reason for using the median perimeter is that it corresponds to the average of the edges of the annular specimens.

17.2.2 Elongation at break — The inner perimeter of the annular specimen is used as the basis for the calculation, as it corresponds to the maximum stress at each edge of the specimen. This position is also the starting position of sample failure.

17.3 The constant extension stress is calculated according to Equation 2 in 13.1

17.3.1 The elongation used to determine the force in Equation 2 (13.1) is calculated as follows



E= elongation,%

L= increase in distance between fixtures,mm

MC(TS)= median perimeter of the sample,mm

17.3.2 In Formula 7, the distance between fixtures during fixed extension is calculated by the following formula:


17.4 The yield point is calculated according to Equation 3 in 13.2

17.5 Determine the yield stress according to 13.3. Since the yield stress is used to evaluate the overall properties of the material, the median perimeter is used to calculate.

17.6 Calculate tensile strength according to Equation 4 in 13.4.

17.7 Elongation at break is calculated according to the following equation (see Notes 9 and 10)



E= elongation at break,%

L= increased distance of fixture at break,mm

IC(TS)= initial inner perimeter of the pattern,mm

17.8 The inner perimeter can be used for two types of specimens (see 15.1.1 dimensions). The inner perimeter of type 2 annular specimens is calculated using the inner diameter.

Note 9 — Equations 7 and 8 can be used only when the initial spacing of the fixture is adjusted according to Equation 7.

Note 10 — Caution should be taken when using this method because stresses at elongation slightly below the elongation at break (4 to 5%) may not be calculated when different dimensions are used to calculate 1) constant elongation stress (less than the breaking stress) and 2) elongation at break (see 20.1 and 20.2).

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

18 Reports
18.1 The report shall contain the following contents:

18.1.1 Calculation results based on Section 13 or 17

18.1.2 Sample type and description, according to the 13-section cutter type, in American, homemade or metric units

18.1.3 Experiment date

18.1.4 Test speed

18.1.5 Laboratory temperature and humidity

18.1.6 Test temperature (if not 23±2℃)

18.1.7 If possible, date of vulcanization or/and rubber preparation

ASTM D412-0 Tensile Test Method for Vulcanized Rubber and Thermoplastic Elastomers

19 Accuracy in deviation (omitted)

20 Key Words (Omitted)

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