June 1, 2023 By Rheometer Spares Off

The Ultimate Guide to Rubber Testing Methods: Which One is Right for You?

This article outlines 7 major areas of testing for rubber, elastomers and polymers in general, broken down into 30 individual test methods and procedures. For more information on any of the instruments featured in this article, follow this links at the bottom of the page.

Introduction

Testing is a crucial step in the manufacturing process of rubber products. It helps to ensure that the products meet the required standards of quality, safety, and performance. Without proper testing, it’s impossible to know if a product will perform as intended or if it will fail prematurely, potentially causing harm to the end-user.

There are many factors that can affect the performance of rubber products, including the composition of the rubber material, the manufacturing process, and the environmental conditions in which the product will be used. Testing allows manufacturers to identify these factors and make adjustments to improve the quality and performance of the product.

This guide outlines the main areas of rubber testing, covering natural rubber testing, cure and rheological testing, chemical analysis, environmental testing, thermodynamic testing, physical testing and mechanical testing. In each section, further information on specific test methods highlights the testing procedure, the instruments used and the applicable international standards. At the end of the guide, a quick reference table gives a comprehensive overview of all the testing methods featured in this guide.

Natural Rubber Testing

Natural rubber is a product of the Hevea brasiliensis tree that is cultivated throughout parts of Southeast Asia. As a natural product, there are more variants and contaminants present in natural rubber than in synthetic rubber. These variations arise because of habitat, climate and processing conditions. As a result, there can be large inter- and intra-batch differences that must be measured. Typically, the proprietary testing of natural rubber takes place at point of harvest, or at small processing plants soon after. When natural rubber is ready to transport, these test results are used to determine the baseline quality of the product.

NameInstrument/EquipmentMaterialStandards
Percentage DirtRubber Solvent, Sieve, Drying Oven, Weighing ScalesNatural RubberISO 249, ASTM D1278
Percentage AshCrucible, Furnace, Weighing ScalesNatural RubberASTM D1278
Volatile Matter ContentDrying Oven, Weighing ScalesNatural RubberISO 248, ASTM D1278
Dry Rubber ContentDrying Oven, Moisture Content BalanceNatural RubberISO 126
Nitrogen ContentMicro-Dumas Combustion MethodNatural RubberISO 19051, ASTM D1278
Plasticity Retention Index (PRI)PlastimeterNatural RubberISO 2930:2017

Composition Testing

The composition testing of natural rubber involves using rudimentary laboratory equipment to determine the various building blocks and contaminants that make up any typical sample of natural rubber. These simple tests are used to measure the quality of both the rubber and the initial processing procedures that take place soon after harvesting.

Percentage Dirt

The percentage dirt of natural rubber is measured by dissolving a small sample of rubber in a rubber solvent, usually alongside a small amount of peptizer, at 125°C until the rubber has dissolved. This process generally takes about 3 hours. Then, the rubber solution is filtered through a 325-mesh screen. The remains are dried at 100°C and weighed. The percentage dirt is equal to ratio of these remains to the original sample weight.

 

Name: Percentage Dirt 

Instrument/Equipment: Rubber Solvent, Sieve, Drying Oven, Weighing Scales

Test Type: Natural Rubber          

Material: Natural Rubber            

Standards: ISO 249, ASTM D1278

Percentage Ash

The percentage ash of natural rubber is measured by heating a sample of natural rubber inside a crucible within a furnace at 550°C until the contents turn to ash. When ashing is complete, the crucible is cooled and the contents weighed. The percentage ash is equal to the ratio of the ash remains to the original sample weight.

 

Name: Percentage Ash

Instrument/Equipment: Crucible, Furnace, Weighing Scales

Test Type: Natural Rubber

Material: Natural Rubber

Standards: ASTM D1278

Volatile Matter Content

To measure the volatile matter content of natural rubber, the rubber is first prepared on a laboratory mill to achieve sample strips of a maximum width of 2.5mm and maximum thickness of 1.25mm. The natural rubber strips are dried in either a circulating air oven set to 100°C or a desiccator. After warming, the dried samples are weighed and compared to the original sample weight.

                                                            

Name: Volatile Matter Content

Instrument/Equipment: Drying Oven, Weighing Scales

Test Type: Natural Rubber

Material: Natural Rubber

Standards: ISO 248, ASTM D1278

Dry Rubber Content

To calculate the dry rubber content, samples of natural rubber are cut and dried for a pre-determined length of time. Using a moisture content balance, the dry rubber content is calculated as the difference in weight before and after the drying process.

                                                               

Name: Dry Rubber Content

Instrument/Equipment: Drying Oven, Moisture Content Balance

Test Type: Natural Rubber

Material: Natural Rubber

Standards: ISO 126

Nitrogen Content

The nitrogen content of natural rubber is typically measured using the Micro-Dumas combustion method. In this method, the rubber sample is combusted at a high temperature in an oxygen environment. The nitrogen released during this process is separated and measured.

                                               

Name: Nitrogen Content             

Instrument/Equipment: Micro-Dumas Combustion Method

Test Type: Natural Rubber

Material: Natural Rubber

Standards: ISO 19051, ASTM D1278

Plasticity

The plasticity of natural rubber is measured using a Plastimeter. The plasticity is measured by compressing a small sample under a known load for a set amount of time. An important measurement is the Plasticity Retention Index (PRI), which used to give an indication of the oxidation resistance of raw natural rubber at a specified temperature. In this method, rubber samples are divided into two batches, one of which is tested immediately, the other is aged in oven, typically at 140°C for 30 minutes. The Plasticity Retention Index (PRI) is a ratio of the aged plasticity to its original value, expressed as a percentage.

                                                               

Name: Plasticity Retention Index (PRI)

Instrument/Equipment: Plastimeter

Test Type: Natural Rubber

Material: Natural Rubber

Standards: ISO 2930:2017

 

For more information on the Plastimeter, see the links at the bottom of the article.

Cure/Rheological Testing

One of the most important areas of rubber testing is rheology, where the flow of a material is measured under differing conditions. Broadly speaking, this area of testing involves applying a shearing force to a sample held in a sealed cavity. The flow is determined as a function of the resistance of the material to the applied force. At elevated temperatures, the flow can be measured as the material undergoes the vulcanisation process. Together, cure and rheological testing can be used to determine the flow properties of rubber before, during and after the vulcanisation process. These properties are vital for formula design, mixing, processing and end-user applications.

NameInstrument/EquipmentMaterialStandards
Mooney Viscosity, Stress Relaxation, Scorch TimeMooney ViscometerUncured RubberISO 289, ASTM D1646
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateOscillating Disc Rheometer (ODR)Uncured/Cured RubberISO 3417, ASTM D2084
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateMoving Die Rheometer (MDR)Uncured/Cured RubberISO 6502, ASTM D 5289
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateDynamic Shear Rheometer/Multi-Function Rheometer (MFR)Uncured/Cured RubberISO 6502, ISO 13145, ASTM D5289, ASTM D6048, ASTM D6204, ASTM D6601, ASTM 7605

Mooney Viscosity

The Mooney Viscosity of rubber is a specific measurement of the viscosity of unvulcanised rubber performed on a Mooney Viscometer. The measurement uses its own unique empirical scale, Mooney Units, that is difficult to map to alternative measurement of viscosity that use standard units. In the Mooney Viscometer, an unvulcanised rubber sample is placed above and below a rotor. As the rotor rotates, the resultant resistance of the rubber to the shearing force generates a torque signal that is measured and interpreted to calculate the Mooney Viscosity. The test is performed at an elevated temperature that is less than the ideal curing temperature of the material.

There are two additional tests that can also be performed on a Mooney Viscometer. Stress Relaxation measures the decay in torque after the rotor is stopped abruptly midway through a Mooney Viscosity test. As the sample relaxes, the subsequent decrease in resistant torque is measured as a function of time. Secondly, Scorch Time is used to determine the onset of cure at a given temperature and is interpreted as the time in which a rubber compound can be processed before curing.

 

Name: Mooney Viscosity, Stress Relaxation, Scorch Time

Instrument/Equipment: Mooney Viscometer

Test Type: Cure/Rheological Testing

Material: Uncured Rubber

Standards: ISO 289, ASTM D1646

 

For more information on the Mooney Viscometer, such as the Mooneyline Mooney Viscometer model, see the links at the bottom of the article.

Cure Characteristics

The cure characteristics of rubber are used to measure the process of vulcanisation and its effect on the material properties of the elastomer. It is necessary to understand the vulcanisation process as it affects both how rubber is processed and its material suitability for any given application. The cure characteristics of rubber are measured on a rheometer, or curemeter, that oscillates a sample of rubber between two dies at elevated temperature and pressure.

The primary measurements used for the cure characteristics of rubber include:

 

Torque Curve: This is a graph of torque against time that is divided into three distinct phases. Phase 1 is the used to determine the processability of rubber. Phase 2 describes the curing process of the rubber compound. Phase 3 shows the material properties of the cured rubber.

Viscous Curve: This is a graph of the viscous torque (S”) against time that shows how the viscous component of the rubber compound evolves over time as the rubber undergoes the vulcanisation process.

Tan. Delta: Tan. (Tangent) Delta is used to measure the ratio between the viscous and elastic components of the torque response during the curing process. Tan. Delta is used to represent mechanical energy losses associated with the macromolecular movement of the chains and the polymer phase transitions.

Cure Rate: The cure rate is a derived parameter that is essentially a measure of the linear slope of the upward torque curve. The slope is taken between two fixed points, t90 (90% cure time) and ts2 (induction time). The curing rate is an important parameter as it determines the time required to create the crosslinks that define the vulcanisation process.

 

Within the rubber industry, there are three types of rheometer than are most commonly use to test for the cure characteristics of rubber: the Oscillating Disc Rheometer, the Moving Die Rheometer and the Dynamic Shear Rheometer.

Oscillating Disc Rheometer

An Oscillating Disc Rheometer (ODR) uses a disc (rotor) enmeshed between two pieces of rubber. An upper and lower die close to form a sealed testing cavity around the rubber. Under pressure and at an elevated temperature, the rotor oscillates through a fixed angle. During this time, the rubber undergoes a crosslinking process known as vulcanisation, or curing. The resultant resistant torque experienced by the rubber to the shearing force of rotor is recorded and interpreted.

                                                               

Name: Standard Torque Curve, Viscous Curve, Tan. Delta, Cure Rate

Instrument/Equipment: Oscillating Disc Rheometer (ODR)

Test Type: Cure/Rheological Testing

Material: Uncured/Cured Rubber

Standards: ISO 3417, ASTM D2084

 

For more information on the Oscillating Disc Rheometer (ODR), such as the Rheoline Oscillating Disc Rheometer model, see the links at the bottom of the article.

Moving Die Rheometer

The Moving Die Rheometer does not use a rotor, with the oscillation instead being provided by the movement of the die. Without a rotor, only one rubber sample is required. The dies are not flat but have a biconical profile to provide a consistent shearing force throughout the sample. Like an ODR, the oscillation occurs under set pressure and temperature conditions to induce vulcanisation. The resultant reactionary torque experienced by the rubber sample is used to determine the cure characteristics over time.

 

Name: Standard Torque Curve, Viscous Curve, Tan. Delta, Cure Rate

Instrument/Equipment: Moving Die Rheometer (MDR)

Test Type: Cure/Rheological Testing

Material: Uncured/Cured Rubber

Standards: ISO 6502, ASTM D 5289

 

For more information on the Moving Die Rheometer, such as the Rheoline Moving Die Rheometer model, see the links at the bottom of the article.

Dynamic Shear Rheometer

A Dynamic Shear Rheometer is an advanced rheometer that uses the same biconical die assembly as the Moving Die Rheometer (MDR).  With the rubber enclosed between the two dies as before, the Dynamic Shear Rheometer has an extended range of functionality that allows the rubber to be oscillated across a range of amplitudes, frequencies and temperatures. Together, this paints a more detailed picture of the cure properties of rubber and can be used to measure advanced viscoelastic effects.

 

Name: Standard Torque Curve, Viscous Curve, Tan. Delta, Cure Rate

Instrument/Equipment: Dynamic Shear Rheometer/Multi-Function Rheometer (MFR)

Test Type: Cure/Rheological Testing

Material: Uncured/Cured Rubber

Standards: ISO 6502, ISO 13145, ASTM D5289, ASTM D6048, ASTM D6204, ASTM D6601, ASTM 7605

 

For more information on the Dynamic Shear Rheometer, such as the Rheoline Multi-Function Rheometer model, see the links at the bottom of the article.

Chemical Analysis

The chemical analysis of rubber involves using a variety of technique to separate out the chemical building blocks that make up a rubber compound. Sometimes referred to as reverse engineering, chemical analysis is a useful tool to investigate the base polymer, fillers and additives that are present in any given formulation, and how they interact. It is also used to identify any potentially harmful or hazardous substances that exist within a rubber compound.

NameInstrument/EquipmentMaterialStandards
Differential Scanning Calorimetry (DSC)Differential Scanning Calorimeter (DSC)Cured RubberASTM D7426, ASTM D3418
Thermogravimetric Analysis (TGA)TGA AnalyserCured RubberASTM D6370
Fourier Transform Infrared (FTIR) SpectroscopyFourier Transform Infrared (FTIR) SpectrometerCured RubberASTM D3677
ChromatographyGas Chromatography - Mass Spectrometer (GC-MS)Cured Rubber

Differential Scanning Calorimetry (DSC)

Differential Scanning Calorimetry (DSC) is a thermoanalytic technique that aims to detect polymer phase transitions and time-dependent phenomena such as curing. A sample is heated in a chamber alongside a control reference through a set temperature range. The amount of heat (energy) that is needed to raise the temperature of the sample is measured for both the sample and the control reference.  A plot of Heat Flow vs. Temperature is used to reveal distinct peaks and troughs that correspond to phase transitions, such as Glass Transition.

The underlying principle behind DSC is that energy is required to raise the temperature of a material. The amount of energy needed is determined by the specific heat capacity of the material. At temperatures where phase transitions occur there is a distinct change in the amount of energy required. This is because the energy is used to not only maintain the temperature, but also to facilitate the phase transition. Referenced against a control material, the changes in energy (heat flow) are used to pinpoint the temperatures at which these transitions occur.

 

Name: Differential Scanning Calorimetry (DSC)

Instrument/Equipment: Differential Scanning Calorimeter (DSC)

Test Type: Chemical Analysis

Material: Cured Rubber

Standards: ASTM D7426, ASTM D3418

Thermogravimetric Analysis (TGA)

Thermogravimetric Analysis (TGA) is an alternative thermoanalytic technique that is often used in conjunction with DSC. In both instances, a polymer sample is heated alongside a reference material that used as a control sample. For TGA, the heat flow (energy supplied) is kept steady and the difference between the achieved temperature of the sample and the reference is recorded. When plotted against time, or temperature, this temperature differential reveals points of exothermic or endothermic behaviour that correspond with phase transitions. This contrasts with DSC, whereby the target temperature is reached and the difference between the heat supplied for the sample and reference is recorded.

As TGA and DSC provide similar information about the phase transitions of a material, it is common for one piece of analytic equipment to be able to perform both techniques.

 

Name: Thermogravimetric Analysis (TGA)            

Instrument/Equipment: TGA Analyser

Test Type: Chemical Analysis

Material: Cured Rubber

Standards: ASTM D6370

FTIR

Fourier Transform Infrared (FTIR) Spectroscopy is an analytical technique that measures the infrared absorption spectrum of a sample to determine the base polymer present in a compound. A beam of infrared light is used in conjunction with an interferometer to measure absorption across multiple wavelengths at once. The data is sequenced using Fourier analysis to yield a spectrum that shows how much light is absorbed at each wavelength. This spectrum can be used to identify key information about the composition of a given compound.                  

 

Name: Fourier Transform Infrared Spectroscopy (FTIR)

Instrument/Equipment: Fourier Transform Infrared (FTIR) Spectrometer

Test Type: Chemical Analysis

Material: Cured Rubber

Standards: ASTM D3677

Chromatography

Gas Chromatography-Mass Spectrometry (GC-MS) is a combined analytical technique that is currently regarded as the ‘gold standard’ for substance identification within a test sample. In the first part, Gas Chromatography, a sample is vaporised into an inert gas that carries it into a heated capillary column.  Within the column the sample components travel at different speeds because of their individual chemical and physical properties, alongside their interaction with the column lining. When each component exits the column at different times, they are in turn detected and identified electronically.

In the second part, a Mass Spectrometer is used to capture the downstream chemicals as they exit the column. The next stage is to break these molecules into ionised fragments that can be detected using their mass-to-charge ratio. Used together, these two techniques exceed their individual accuracy and reduce the possibility of error.

 

Name: Chromatography

Instrument/Equipment: Gas Chromatography – Mass Spectrometer (GC-MS)

Test Type: Chemical Analysis     

Material: Cured Rubber

Environmental Testing

The environmental resistance of rubber is used to measure how effective a material is at withstanding various aggressive factors during its lifetime. Many applications involve the exposure of rubber to harsh chemicals and environments where the continued performance of polymers is critical to safety. By testing these factors systematically in a laboratory setting, the material degradation caused by chemical factors can be specified.

NameInstrument/EquipmentMaterialStandards
Ozone ExposureOzone TesterCured RubberASTM D1149
Fluid AgeingAgeing ChamberCured RubberASTM D471
WeatheringQUV Tester, Xenon Arc TesterCured RubberASTM G154, ASTM D4329, ASTM D4587, ISO 4892, ASTM G155-21
FlammabilityOpen Flame TesterCured RubberASTM C1166

Ozone Exposure

Ozone is a toxic gas that attacks any polymer with a double-chain structure, including natural rubber, nitrile rubber and styrene-butadiene rubber (SBR). The ozone gas causes crack propagation that worsens over time. As well as low levels of ozone in the atmosphere, additional acute sources include compressed air systems, fuel lines and proximity to electric motors. For applications where exposure is likely, accelerated ozone ageing helps to characterise the negative effects of ozone gas in a standardised manner.

 

Name: Ozone Exposure

Instrument/Equipment: Ozone Tester

Test Type: Environmental Testing

Material: Cured Rubber

Standards: ASTM D1149

Fluid Ageing

Long-term exposure to fluids can have a detrimental effect on the performance of rubber products. Fluid ageing tests are used to determine the speed and extent of this detrimental effect in a standardised laboratory setting. This data can be used to forecast the service life of rubber products, particularly those that are used in sealing applications. Tests can either be run in real-time or accelerated by applying heat to the test assembly. The most popular choices of testing fluid to measure exposure to are oils, fuels, acids, salt water and inks although any type of fluid can be used.

 

Name: Fluid Ageing

Instrument/Equipment: Ageing Chamber

Test Type: Environmental Testing

Material: Cured Rubber

Standards: ASTM D471

Weathering

Weathering tests are designed to mimic exposure to natural environmental conditions, such as UV radiation and heat, and measure the material response to these aggressive factors. QUV and Xenon arc testers use accelerated ageing techniques to measure the effects of ultraviolet and visible-wavelength sunlight with additional heat and moisture conditions. By accelerating the exposure, the durability of materials can be determined for years of outdoor exposure over a significantly shorter timeframe.

 

Name: Weathering        

Instrument/Equipment: QUV Tester, Xenon Arc Tester

Test Type: Environmental Testing

Material: Cured Rubber

Standards: ASTM G154, ASTM D4329, ASTM D4587, ISO 4892, ASTM G155-21

Flammability

The flammability of dense and cellular elastomeric gaskets and accessories can effectively be measured using a flame propagation test. A flame propagation test provides crucial test data that can be used to specify the safety of rubber products that are used extensively in construction, industrial applications and consumer goods. The test involves exposing a sample to a continuous open flame for a set interval of time and measuring the lateral propagation of the flame across the material. The Flame Spread Index (FSI) and surface flammability are calculated and used to determine the safety and compliance of any given material.                        

 

Name: Flammability       

Instrument/Equipment: Open Flame Tester

Test Type: Environmental Testing            

Material: Cured Rubber

Standards: ASTM C1166

Thermodynamic Testing

The thermodynamic testing of materials relates to the input of heat into a system and measuring the resultant effect of this energy change on the material. In thermodynamics, the change in temperature of system is represented by the transfer of thermal energy called heat. When the temperature of a system is raised, heat (energy) is applied. When the temperature falls, the heat (energy) of system is removed. These transfers of thermal energy affect material properties such as stiffness, strength and volume. This is because changes in thermal energy of the system influence the amplitude of the atomic or molecular vibrations within the material. At certain temperatures, thermal energy can also trigger phase changes, such as evaporation or freezing, to the constituent molecules present in a material. Together, these effects can greatly alter the performance and longevity of a material. 

NameInstrument/EquipmentMaterialStandards
Heat AgeingAir OvenCured RubberASTM D573
Cold TestingChiller, HammerCured RubberASTM D1329, ASTM D746, ASTM D2137

Heat Ageing

Heat Ageing is used to measure the effects of oxidative and thermal ageing on a material. The physical and chemical properties of a sample are measured before and after exposure to elevated temperatures within an air-circulation environmental chamber for a set interval of time. The ageing can be performed in real-time or accelerated by raising the temperature above the application temperature. The application of thermal energy raises the molecular vibration levels of the rubber while the moisture content decreases. Often, this combination leads to degradation and the eventual failure of the material.

 

Name: Heat Ageing

Instrument/Equipment: Air Oven

Test Type: Thermodynamic Testing

Material: Cured Rubber

Standards: ASTM D573

Cold Testing

Cold Testing is a set of test procedures that are used to study the change in physical and chemical properties of a material when heat (energy) is removed. At low temperatures, the amplitude of the molecular vibrations of the rubber is reduced. This leads to a decrease in elasticity and the material will become more brittle and prone to fracture.

Two popular methods of Cold Testing are Temperature Retraction and Brittleness Point Testing. In the first instance, a sample is fixed at an elongated length at room temperature. Once frozen, the sample is released and the length recorded as a function of time as the sample is acclimatised to ambient temperature. In the second instance, Brittleness Point Testing involves striking a sample with sudden impact at a steadily decreasing temperature until the sample fractures under impact.

 

Name: Cold Testing

Instrument/Equipment: Chiller, Hammer

Test Type: Thermodynamic Testing         

Material: Cured Rubber

Standards: ASTM D1329, ASTM D746, ASTM D2137

Physical Testing

The physical properties of a material relate to the quantitative and qualitative parameters that are used to describe a material in the absence of any external forces or movement. At a basic level, the volume and mass of a sample are both physical properties. There exist many tests specific to industry and application for physical properties. For rubber, polymers and elastomers, further physical tests include hardness, specific gravity and surface analysis.

NameInstrument/EquipmentMaterialStandards
HardnessDurometerCured RubberASTM D2240
Specific GravitySpecific Gravity BalanceCured RubberASTM D792
DispersionDispergraderUncured/Cured RubberISO 11345, ASTM D7723-19

Hardness

The hardness of a material is measured by using a relatively harder material to deform the surface using a small indentor. The material and geometry of the indentor and both the duration and amount of force exerted by the indentor are specific to the hardness scale used. As such, hardness is not an intrinsic material property as it always measured in reference to the indentor. For polymers, the Shore scale is used through a total of 12 scales in order of increasing hardness: A, B, C, D, DO, E, M, O, OO, OOO, OOO-S, and R. Each scale uses values from 0 – 100, with higher values indicating a harder material.

 

Name: Hardness

Instrument/Equipment: Durometer

Test Type: Physical Testing         

Material: Cured Rubber

Standards: ASTM D2240

Specific Gravity

The specific gravity, also known as the specific density, of a material is a ratio of the material density to a reference density. For polymers, the reference density is almost always taken for water. Specific gravity is measured using hydrostatic weighing technique. This involves using balance scales to measure first the mass of the sample in air and secondly the mass of the sample in a known quantity of water. A simple equation is used to calculate the specific density of the sample using the two measurements.

 

Name: Specific Gravity

Instrument/Equipment: Specific Gravity Balance

Test Type: Physical Testing

Material: Cured Rubber

Standards: ASTM D792

Dispergrader

A Dispergrader is light reflecting microscope that is used to determine the dispersion of fillers within the rubber mix by taking an image of the rubber surface. When rubber is freshly cut, the surface consists of peaks and valleys, sometimes referred to as nodges. This surface roughness is taken as a measure of the macro-dispersion of fillers such as carbon black and silica. When light is shone onto the surface, areas of undispersed carbon black and silica agglomerates reflect this light back, resulting in a white area on the image. The composition of white and black areas on the image is used to determine the degree of dispersion in the rubber matrix.

 

Name: Dispersion

Instrument/Equipment: Dispergrader

Test Type: Physical Testing

Material: Uncured/Cured Rubber

Standards: ISO 11345, ASTM D7723-19

Mechanical Testing

The mechanical testing of materials centres around the application of forces and measuring the effect in terms of energy, time and motion. The response of materials to applied forces can be used to determine their durability, elasticity and resistance to wear. This is because within a closed system, both forces and energy are conserved. As no material is 100% elastic, the energy applied to a material cannot be stored completely or indefinitely and is instead lost via friction, either internally or externally. By measuring the storage and loss of energy during and after the application of force, the real-life performance and the underlying behaviour mechanism of a material can be deduced.

NameInstrument/EquipmentMaterialStandards
Dynamic Mechanical AnalysisDynamic Mechanical Analyser (DMA)Cured Rubber
Tensile StrengthTensile TesterCured RubberASTM D412
Flex FatigueDeMattia Flex TesterCured RubberASTM D813, ASTM D430
Fatigue To FailureFatigue TesterCured RubberASTM D4482
AbrasionDIN Abrasion TesterCured RubberASTM D5963
AdhesionTensile TesterCured RubberASTM D429
Compression SetCompression Set JigCured RubberASTM D395

DMA

Dynamic Mechanical Analysis (DMA) describes the application of force to a sample in a periodic motion, most commonly a sinusoidal oscillation. The direction of motion can result in either the compression, tension or flexure of the sample. With the driver following a known force profile, a load cell is used to measure the resultant resistant force experienced by the material. Due to the viscoelastic nature of rubber, there will be a phase difference between the force and displacement signals. This phase difference is measured and used to split the signals into elastic and viscous constituent parts. Together, the interplay between energy storage (elasticity) and energy loss (friction/hysteresis) can be expressed quantitatively.

 

Name: Dynamic Mechanical Analysis

Instrument/Equipment: Dynamic Mechanical Analyser (DMA)

Test Type: Mechanical Testing

Material: Cured Rubber

 

For more information on Dynamic Mechanical Analysis, follow the links at the bottom of the article.  

Tensile Tester

A tensile tester is a simple instrument that measures the strength of a material as it is stretched. Samples are usually cut into dumbbell shapes with each end held firmly in vice or pneumatic grips. A tensile tester pulls one end of the sample at a fixed speed either over a set time or distance, or until the sample breaks. During this movement, a load cell records the force experienced by the sample as it is extended. This force profile is used to determine the tensile strength, the maximum force that the material can handle before breaking, and the maximum elongation at break.

 

Name: Tensile Strength

Instrument/Equipment: Tensile Tester 

Test Type: Mechanical Testing  

Material: Cured Rubber

Standards: ASTM D412

Flex Fatigue

In a flex fatigue test, a rubber sample is subjected to repetitive cyclical bending at low stresses for set number of cycles. Often, this is performed at an elevated temperature to further accelerate the fatigue. This ongoing motion initially causes micro-cracks to form in the rubber, which eventually grow and ultimately lead to complete material failure. By studying these cracks and their formation, it is possible to assess the lifetime performance of a product in a variety of environments.

 

Name: Flex Fatigue

Instrument/Equipment: DeMattia Flex Tester

Test Type: Mechanical Testing  

Material: Cured Rubber

Standards: ASTM D813, ASTM D430

Fatigue To Failure

A fatigue to failure test is any procedure where a repetitive motion is applied to a sample until it breaks. Examples of this repeated motion include sinusoidal oscillation, torsional twisting or singular impact. Most commonly, this motion closely correlates to the end-product intended use. Each sample is tested in turn using the same repetitive motion but with varying amplitude. For each amplitude level, the number of cycles until breakage is recorded. Using this data, a S-N curve can be generated that determines the number of cycles to breakage at any amplitude level.

 

Name: Fatigue To Failure

Instrument/Equipment: Fatigue Tester

Test Type: Mechanical Testing

Material: Cured Rubber

Standards: ASTM D4482

DIN Abrasion Tester

A DIN Abrasion Tester is used to measure the abrasive resistance of rubber as a function of volume loss. A piece of rubber is held against a rotating drum covered in paper of known roughness for a set amount of time. As the drum rotates against the rubber, small particles will gradually wear away, flattening the surface of the sample. After the test, the difference in mass is recorded. Using the density of the rubber, the volume loss of the rubber is calculated. Expressed as a percentage, this volume loss is used to gauge the abrasion resistance of the sample.

 

Name: Abrasion

Instrument/Equipment: DIN Abrasion Tester

Test Type: Mechanical Testing

Material: Cured Rubber

Standards: ASTM D5963

Adhesion Tester

Adhesion tests are used to measure the strength of physical bonding of a rubber-to-rubber or rubber-to-reinforcement interface. In general, a force is applied to pull against the direction of adhesion until the two surfaces debond. Adhesion tests are commonly performed with additional environmental conditions, such as elevated temperature and humidity. Specific test procedures depend upon the shape of each component and the type and direction of bonding. The most common test methods are a butt test, cone test and peel test.

 

Name: Adhesion

Instrument/Equipment: Tensile Tester

Test Type: Mechanical Testing  

Material: Cured Rubber

Standards: ASTM D429

Compression Set

Compression Set is used to measure the ability of a material to return to its original thickness after prolonged exposure to compressive stresses. Using a compression set jig, a sample is held in compression between two plates at a given distance apart at a chosen temperature. After a set amount of time, the sample is released from the jig and allowed to recover at room temperature. The change in thickness is recorded and expressed as the percentage compression set.

 

Name: Compression Set

Instrument/Equipment: Compression Set Jig

Test Type: Mechanical Testing

Material: Cured Rubber

Standards: ASTM D395

Summary Table

Use the summary table below to quickly reference any testing method mentioned in this guide. Look up tests by name or type, instrument, material or international standard.

NameInstrument/EquipmentTest TypeMaterialStandards
Percentage DirtRubber Solvent, Sieve, Drying Oven, Weighing ScalesNatural RubberNatural RubberISO 249, ASTM D1278
Percentage AshCrucible, Furnace, Weighing ScalesNatural RubberNatural RubberASTM D1278
Volatile Matter ContentDrying Oven, Weighing ScalesNatural RubberNatural RubberISO 248, ASTM D1278
Dry Rubber ContentDrying Oven, Moisture Content BalanceNatural RubberNatural RubberISO 126
Nitrogen ContentMicro-Dumas Combustion MethodNatural RubberNatural RubberISO 19051, ASTM D1278
Plasticity Retention Index (PRI)PlastimeterNatural RubberNatural RubberISO 2930:2017
Mooney Viscosity, Stress Relaxation, Scorch TimeMooney ViscometerCure/Rheological TestingUncured RubberISO 289, ASTM D1646
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateOscillating Disc Rheometer (ODR)Cure/Rheological TestingUncured/Cured RubberISO 3417, ASTM D2084
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateMoving Die Rheometer (MDR)Cure/Rheological TestingUncured/Cured RubberISO 6502, ASTM D 5289
Standard Torque Curve, Viscous Curve, Tan. Delta, Cure RateDynamic Shear Rheometer/Multi-Function Rheometer (MFR)Cure/Rheological TestingUncured/Cured RubberISO 6502, ISO 13145, ASTM D5289, ASTM D6048, ASTM D6204, ASTM D6601, ASTM 7605
Differential Scanning Calorimetry (DSC)Differential Scanning Calorimeter (DSC)Chemical AnalysisCured RubberASTM D7426, ASTM D3418
Thermogravimetric Analysis (TGA)TGA AnalyserChemical AnalysisCured RubberASTM D6370
Fourier Transform Infrared (FTIR) SpectroscopyFourier Transform Infrared (FTIR) SpectrometerChemical AnalysisCured RubberASTM D3677
ChromatographyGas Chromatography - Mass Spectrometer (GC-MS)Chemical AnalysisCured Rubber
Ozone ExposureOzone TesterEnvironmental TestingCured RubberASTM D1149
Fluid AgeingAgeing ChamberEnvironmental TestingCured RubberASTM D471
WeatheringQUV Tester, Xenon Arc TesterEnvironmental TestingCured RubberASTM G154, ASTM D4329, ASTM D4587, ISO 4892, ASTM G155-21
FlammabilityOpen Flame TesterEnvironmental TestingCured RubberASTM C1166
Heat AgeingAir OvenThermodynamic TestingCured RubberASTM D573
Cold TestingChiller, HammerThermodynamic TestingCured RubberASTM D1329, ASTM D746, ASTM D2137
HardnessDurometerPhysical TestingCured RubberASTM D2240
Specific GravitySpecific Gravity BalancePhysical TestingCured RubberASTM D792
DispersionDispergraderPhysical TestingUncured/Cured RubberISO 11345, ASTM D7723-19
Dynamic Mechanical AnalysisDynamic Mechanical Analyser (DMA)Mechanical TestingCured Rubber
Tensile StrengthTensile TesterMechanical TestingCured RubberASTM D412
Flex FatigueDeMattia Flex TesterMechanical TestingCured RubberASTM D813, ASTM D430
Fatigue To FailureFatigue TesterMechanical TestingCured RubberASTM D4482
AbrasionDIN Abrasion TesterMechanical TestingCured RubberASTM D5963
AdhesionTensile TesterMechanical TestingCured RubberASTM D429
Compression SetCompression Set JigMechanical TestingCured RubberASTM D395

Conclusion

In conclusion, effective rubber testing is essential for ensuring that rubber products meet the required standards of quality, safety, and performance.

This guide outlined the main areas of rubber testing, from natural rubber testing to mechanical testing, with specific details for 30 individual test methods and procedures, including details of the accompanying international test standards. By using a combination of testing methods and following a structured testing process, manufacturers can gain a comprehensive understanding of the physical and mechanical properties of rubber materials.

Further Resources

For further information on any of these instruments, follow the links below to view the full product specifications on the Prescott Instruments website. Alongside these products, Prescott Instruments offer full training and bespoke rubber consultancy to help you get the most out of your laboratory. To get started, view all products and services, or get in touch.

>> Plastimeter

>> Mooneyline Mooney Viscometer

>> Rheoline Moving Die Rheometer

>> Rheoline Multi-Function Rheometer

>> Dynamic Mechanical Analyser (DMA)

 

Rheometer Spares stock a wide range of parts and spares to help run, maintain and optimise your instrument performance. With no minimum order, secure online payment and worldwide delivery, Rheometer Spares is the online destination for rubber testing professionals. Explore all our products and shop now.  

 

For parts, spares and consumables, follow the links below to head to the Rheometer Spares shop:

>> Mooney Viscometer parts & spares

>> Moving Die Rheometer parts & spares

>> All testing

>> All maintenance

 

More Posts From Rheometer Spares

Christmas Closure Notice - Rheometer Spares will be closed from 12pm, Friday 22nd of December until 9am, Tuesday 2nd January 2024. During this time,…
100+ Fun Rubber Facts - Rubber is a fascinating material that has been used for centuries in countless products and industries. From car tyres to…
From Tree to Tyre: The Complete Guide to Natural Rubber - Discover the secrets of natural rubber through our comprehensive guide. Learn about harvesting, processing, quality control, and testing procedures. Get…
Unravelling the Secrets of the Rubber Process Analyser - Are you tired of dealing with inconsistencies in rubber manufacturing? Wish you could uncover the secrets to enhancing quality and…
Malaysia Rubber Board Technology Day – Kuala Lumpur - This September, Rheometer Spares (Prescott Instruments) are attending the Technology Day seminar held by the Malaysia Rubber Board (Lembaga Getah…
The Top 5 Benefits Of Rubber Testing - Rubber testing is a crucial process for manufacturers to ensure that their products meet safety and quality standards. From automotive…
The Ultimate Guide to Rubber Testing Methods: Which One is Right for You? - This article outlines 7 major areas of testing for rubber, elastomers and polymers in general, broken down into 30 individual…
The Coronation Of King Charles III - An additional UK bank holiday is taking place this month to celebrate the Coronation of King Charles III. The Rheometer…
A Beginners Guide to Viscometer and Rheometer Standards - This article outlines the top 20 standards for testing the viscosity and cure of rubber, elastomers and polymers in general,…
Viscometer vs. Rheometer: Understanding the Differences - Looking to understand the key differences between a viscometer and a rheometer? Discover the unique features and benefits of each…