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

1. Overview
1.1 This test method includes methods for evaluating the tensile properties of vulcanized thermosetting rubber and thermoplastic elastomers. This test method can not be used to test hard glue and materials with high hardness and low elongation. The test method is as follows:

Method A — Straight bar and dumbbell samples

Method B — Annular specimen

Remark 1 -the results of the two tests are incomparable.

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


2 References
D 1349 Rubber specification — Standard test temperature

D 1566 Rubber related terminology

D 3182 Rubber specification — Materials, equipment and procedures for making standard compounds and standard vulcanization test pieces

D 3183 Rubber specification — Preparation of test pieces from finished products

D 4483 Standard test methods for rubber and carbon black industrial species – Specification for measurement accuracy

2.2 ASTM Annex

Preparation of annular specimens, Method B

ISO Standards

ISO 37 – Methods for 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 Definitions

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

3.1.2 Long stretching deformation — The long stretching deformation of the pulled dumbbell sample is closely pressed to the cross section.

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

3.1.4 Tensile strength — the stress used when drawing the sample

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

3.1.6 Thermoplastic elasters — 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 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 the stress change with respect to strain becomes 0 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”

Method Description
4.1 For the test of tensile properties, samples are first cut from the sample material, including two parts: sample preparation and test. The shape of the specimen can be dumbbell, ring or straight bar, and the section shape is regular.

4.2 Determination of 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 for the specimen with normal 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 stretching and shrinking according to the prescribed method.

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

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 properties. However, the tensile properties do not directly represent the whole situation of the final use of the product, because the product needs to cover a wide range of potential use conditions in actual use.

5.2 Tensile properties are dependent on 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 effects on tensile properties, which should be strictly controlled. And the effect varies with different materials.

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 comparable results.

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 500±50mm/min, and the minimum stroke is 750mm(see Note 1). The testing machine should have a 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 measured force when the sample is broken is ±2% of the full range of the dynamometer, and the accuracy of the measured minimum force is 10%. If the dynamometer has an automatic compensation function in the direct measurement of tensile stress, then the compensation function for the cross-sectional area of the specimen 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 failure. If the testing machine does not have a recording device, there should be an indicator to indicate the maximum force value during stretching. 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. In case of doubt, the test should be repeated at a speed of 500mm/min.

6.2 High and low temperature test box — the test box should meet the following requirements:

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

6.2.2 Use 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 high temperature (sample) into 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 transient contact caused by agitation of the surrounding air.

6.2.5 Place the chuck appropriately to facilitate operation in high and low temperature environments. In this way, the dumbbell or straight strip specimens are 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 should be suitable for working at the test temperature, or have good insulation with the test chamber.

6.2.7 Elongation measuring device shall be provided in the test chamber. If a ruler is used to measure the elongation of the specimen scale, the ruler should be placed parallel to the scale close to the path of the chuck movement and can be controlled from outside the test chamber.

6.3 Thickness gauges — Thickness gauges 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 — Use test equipment as described in 6.1 or as shown in Figure 1. The stopwatch or other timing device should have a range greater than 30min, and the measuring accuracy of the ruler or other measuring device for elongation 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 samples

7.1.1 The anisotropy and orientation of the material caused by the flow during preparation and treatment can affect the tensile properties. Therefore, in the preparation of dumbbell or straight bar specimens, under the premise of knowing the calendering direction, the direction of sample cutting should be parallel to the calendering direction. For annular specimens, the orientation characteristics are usually averaged to a certain extent.

7.1.2 Unless otherwise specified, for thermoplastic rubbers or elasteers, specimens shall be cut from injection molded specimens with a thickness of 3.0±0.3mm, and the test results obtained from specimens of other thicknesses shall be comparable. The samples should be two sets of perpendicular and parallel forming flow directions. The size of the test piece or test plate should be able to meet the test requirements.

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

7.1.4 When the sample is used for ordinary tensile test, the failure of the sample generally occurs in the chuck. Therefore, the straight bar specimen is used only when the sample cannot be made of other shapes. For non-destructive stress-strain or material modulus experiments, straight strip specimens should be 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 elongation measurement.

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

Calibration of test equipment
8.1 Calibrate the test machine according to Procedure A of Specification E 4 for dynamometers of measuring precision type, and calibrate one or more force points according to the 7 and 18 test of specification E 4. For pendulum dynamometers, 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 clamping 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 with a known weight on the hook, so that a certain mass can be temporarily applied to the lower fixture of the sample (see Note 2).

8.1.5 Turn on the fixture movement monitoring device and keep it running until the weight is free to hang on the sample in the ordinary test.

8.1.6 If a disc or ruler (or equivalent tester for stress compensation) does not indicate force values within the specified accuracy, the equipment should be effectively checked for faults (e.g. friction on 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, the testing machine is calibrated to know that the weight is 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 testing, they should also be used in calibration. Friction is checked by mounting a ratchet.

Note 3 — There should 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 carried out at A temperature higher than 23℃, the sample of method A should be preheated for 10±2min; Method B should be preheated for 6±2min. Before each test interval, the specimens are placed in the test chamber separately, so that all specimens are continuously subjected to the same warm-up time. Preheating tests at high temperatures should be strictly limited to prevent persulphation and thermal aging.

Note 3 — Warning: Among other warnings, use insulated, 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 — Straight bar and dumbbell specimens

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

10 Equipment
10.1 Cutting Knife — The shape and dimensions of the cutting knife shall be as shown in Figure 2. The inside of the narrow part of the cutter shall be perpendicular to the cutter end face and at least 5mm from the cutter end face shall be polished. The shape of the cutter should remain unchanged without defects. (See Note 4)

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

10.2 Marking lines — Two marking lines drawn on the sample to measure elongation and strain are called marking lines (see Note 5). The 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 bulge was at least 75º. The distance between the centers of the two raised planes should be kept within 1% of the required or target distance deviation. A handle shall be included on the back or top of the marker.

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

10.3 Ink Marks — Use a flat, hard surface (hardwood, metal, or plastic) to make ink or toner marks. The ink or toner should be firmly bonded to the sample, not corroding the sample, and contrast with the color of the sample.

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

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

10.4.2 The fixture used for testing straight strip samples shall have pneumatic fixture, clamp mouth or bolt buckle, so that the clamping force of the fixture can be applied evenly 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 should be injection molded or cut from specimens 1.3 to 3.3mm thick. The thickness and size of the specimen can be cut by one test method (see Specification D 3182). The test piece can be made directly or cut and polished from the finished product. If the test piece is prepared directly from the finished product, the surface should not be hard leather or fabric. According to the requirements of specification D 3183. All specimens shall 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 C type cutter (FIG. 2), use a simple stamping device, and ensure the smoothness of the cut surface. .

11.1.1 Labeling Dumbbell Specimens — Dumbbell specimens shall be marked as described in 10.2, and the specimens shall not be subjected to tension when marked. The marking line should be drawn on the narrow part, at the same distance from the center of the sample and perpendicular to the vertical axis. The distance between the two marks is 25.00±0.25mm for type C and type D samples. The other is 50.00±0.5mm

11.1.2 dumbbell sample thickness measurement — The thickness of the sample should be measured at three points, one at the center and two at the ends of the narrow part. The median of the three values is used to calculate the cross-sectional area. If the range of the sample thickness is greater than 0.08, the sample is rejected. 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 strips, small tubes, or fine electrical insulation) can be cut. The specimen should be long enough to fit into the fixture. The marking is made as 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, pay attention to adjust the gripping symmetry of the sample, 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 is 500±50mm/min(see Note 7) unless special requirements are required. Start the testing machine and pay attention to the marking to prevent the influence of parallax. The force values at special elongation and at fracture of the sample were recorded. Elongation can be measured using extensionmeters, automated plotting, or optical tracking systems. The measurement accuracy of elongation at fracture is within 10%. The calculation is given in 13.

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 should be recorded.

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

12.3 Measurement of long-term fracture deformation — After the sample is broken for 10min, the sample should be carefully spliced together to measure the residual deformation within the standard distance, and the calculation is shown in 13

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

13 Calculation
13.1 Strength calculation at any elongation:


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

F(XXX)= stress at specific elongation,MN

A= cross-sectional area of the sample,m2

13.2 Calculation of yield strength


Y(stress)= yield strength,MPa

F(y)= yield force,MN

A= cross-sectional area of the sample,m2

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

13.4 Calculation of tensile strength


TS= tensile strength,MPa

F(BE)= maximum force at fracture,MN

A= cross-sectional area of the sample,m2

13.5 Compute the elongation at any elongation;


E= percentage elongation (distance in scale),%

L= observed distance within the sample standard distance,mm

L(0)= length of the sample’s original marking distance,mm

13.6 Elongation at break is calculated by substituting L at the time of sample fracture into Equation 5.

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

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 samples in the test do not meet the specified measurement.

13.8.2 Special Case 2 — For arbitral tests.

Method B — Annular specimen

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

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

14.1.1 Blade depth retainer — The cylindrical disk in the retainer shall be at least 0.5mm thicker than the thickness of the rubber sheet to be cut. Its diameter should be smaller 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, the upper and lower surfaces parallel to each other, and made of hard polymeric materials (hard glue, polyurethane and polymethyl methacrylate). Holes of about 1.5mm in diameter are distributed at intervals of 6 to 7mm through the center of the plate. All these holes shall communicate with the mold cavity inside to reduce the air pressure used to hold the test piece. Figure 4 is used to hold 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 specimen at the center of the gripper mold cavity.

14.4 Soapy water — Use neutral soapy water to lubricate the knife.

14.5 Rotary cutting — Use a precision rotary machine or other equipment that can provide a speed of at least 30rad/s to cut the test piece. The cutter rotating 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 table — There shall be a table or other device that can be moved along the x-y axis respectively to hold and position the test piece so that the test piece corresponds to the axis of rotation of the rotary cutter.

14.7 Tensile testing machine — shall comply with the requirements described in 6.1.

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

14.9 Test chambers — High and low temperature test chambers 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 meet the requirements of Specification D 3767(Method A).

14.10.1 The main components of the thickness gauge, a cylindrical upper measuring surface (longitudinal axis along the vertical direction) at least 12mm high and 15.5±0.5mm in diameter. In order to fit the small annular sample, the measuring head with 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 perimeter is 50.0±0.01mm

The inner diameter was 15.92±0.003mm

The radial width is 1.0±0.01mm

The thickness is 1.0~3.3mm

Type 2

The inner perimeter is 100.0±0.2mm

The inner diameter was 29.8±0.06mm

The radial width is 2.0±0.02mm

The thickness is 1.0~3.3mm

15.2 ISO Annular specimens — Specimens are classified as normal and small according to ISO 37, which specifies their specific test procedures.


The inner diameter is 44.6±0.2mm

The outer diameter is 52.6±0.2mm

The thickness is 4.0±0.2mm

Small size

Inner diameter 8.0±0.1mm

Outer diameter 10.0±0.1mm

The thickness is 1.0±0.1mm

15.3 Cut the annular sample from the pipe — the diameter of the annular sample should be determined by the wall thickness of the pipe and should meet the requirements of the product.

15.4 Preparation of cutting sample — Place the blade in the holder of the cutter 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 stopper with the rotating shaft moving vertically. This allows the end of the blade retainer to penetrate the surface of the plate. The sample was placed into the gripper and the cavity pressure was reduced to 10kPa. Wet the surface of the test piece with neutral soapy water. The cutter should be stopped after reducing the cutter at a constant speed, and the cutter gripper should not touch the test piece at this time. Adjust blade depth if necessary. Reset the shaft before the next cutting.

15.5 Preparation of a sample cut from a tube — A shaft is inserted into the tube, the diameter of which is slightly larger than the diameter of the tube. Place the shaft and tube together on the machine tool. The specimen of the required axial thickness is cut from the sample with the blade or cutter on the machine tool. For thin-walled tubes, when laid flat, a cutter with two parallel blades can be used to cut.

15.6 Annular sample:

15.6.1 Perimeter — The inner perimeter can be measured with a cone or 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, meridional width, and π(3.14).

15.6.2 Radial width — Distribute three measuring points equally on the circumference of the specimen as per the thickness gauge in 14.10.

15.6.3 Thickness — The thickness of the disk from the inner circle to the outer circle can be measured by a thickness meter according to specification D 3767 when cutting annular specimens.

15.6.4 Cross-sectional Area — Cross-sectional area was calculated as the median of three measurements: 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 have 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 axis,mm

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

C(SP)= circumference of the jig shaft,mm

The test speed was 500±50 mamms (see Notes 7 and 8), unless otherwise required. Start the test machine and record the force and the relative displacement of the two jig axes. Elongation and stress were recorded at fracture. The calculations are given in Section 17,

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

16.2 Experiments at non-standard temperatures — Use the test chamber as described in 6.2 and read the warning in Note 2. For tests higher than 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. Test pieces shall be placed in test chambers separately to meet requirement 9.2.

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

17 Calculation
17.1 Except for one important point, the stress-strain properties of the ring specimen are calculated as those of the dumbbell or straight strip specimen. When the annular specimen is stretched, the stress distribution of each edge of the annular specimen is not uniform in width (from left to right). The initial inner diameter of the sample is smaller than the initial outer diameter. Therefore, the stress in the inner test is greater than that in the outer test in the sample stretching, caused by the different initial size.

17.2 The following options are available for calculating tensile and breaking strengths.

17.2.1 Fixed elongation stress — The median perimeter of the annular specimen was used to calculate the elongation. The reason for using the median perimeter is that it corresponds to the average over the edges of the annular specimen.

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 on each edge of the specimen. This position is also the starting position of the 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 the distance between fixtures,mm

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

17.3.2 In Equation 7, the distance between fixtures at fixed extension is calculated using the following equation:

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

17.5 Use 13.3 to determine the yield stress. 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 Formula 4 in 13.4.

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


E= elongation at break,%

L= the increased distance of the fixture at break,mm

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

17.8 The inner perimeter can be used for both 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 only be used if 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 elongations slightly below the elongation at break (4 to 5%) may not be calculated when different sizes are used to calculate 1) fixed 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 Report
18.1 The report should include the following:

18.1.1 Based on the results of 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 Date of experiment

18.1.4 Test speed

18.1.5 Laboratory temperature and humidity

18.1.6 Test temperature (if not 23±2℃)

18.1.7 Date of vulcanization or (and) rubber preparation, if possible

19 Accuracy in deviation (omitted)

20 Key Words (omitted)

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