Tensile Testing Guide: Procedure, Equipment and Results | United Test

Tensile testing is a fundamental mechanical testing method used by engineers, manufacturers, quality-control departments, and materials researchers around the world. A tensile test, also known as a tension test, applies a controlled uniaxial pulling force to a specimen to evaluate how the material responds under load.

The test can be used to determine important mechanical properties such as tensile strength, yield strength, elastic modulus, elongation, and breaking strength. These results help engineers understand when a material begins to deform permanently, how much force it can withstand, and at what point it will fracture.

Tensile test data is commonly used for material selection, product development, incoming material inspection, production quality control, supplier comparison, and verification against ASTM, ISO, EN, DIN, JIS, or other applicable testing standards.

Why Perform a Tensile Test?

Before a material is selected for a product or structural application, engineers must confirm that it can withstand the mechanical forces it will experience during actual use.

Different applications require different combinations of strength, stiffness, and flexibility. Tire rubber, for example, must be elastic enough to deform repeatedly as the tire moves across uneven road surfaces. A steel fastener, by comparison, must resist high tensile loads without permanently stretching or breaking.

Materials may also experience:

• ·   Static loads applied for a short period

• ·   Long-term constant loads

• ·   Repeated or cyclic loading

• ·   Changes in temperature and humidity

• ·   Exposure to chemicals or corrosive environments

• ·   Sudden changes in operating force

• ·   Deformation during assembly or installation

Tensile testing allows researchers to compare candidate materials and determine whether their mechanical properties are suitable for the intended operating conditions.

The test is equally important in quality assurance. Manufacturers can test incoming raw materials, samples taken from production batches, or finished components to verify that tensile properties remain within specified limits.

Identifying an unsuitable material before it enters production helps reduce the risk of rejected batches, product failure, warranty claims, delivery delays, safety incidents, and damage to the manufacturer’s reputation.

How Does a Tensile Test Work?

A tensile test is normally performed using a universal testing machine, also called a tensile testing machine, tension testing machine, material testing machine, or UTM.

The specimen is secured between an upper and lower grip. The machine then moves one grip away from the other at a controlled rate, gradually increasing the tensile force applied to the specimen.

During the test, the system records data such as:

• ·   Applied force

• ·   Crosshead displacement

• ·   Specimen extension

• ·   Testing time

• ·   Stress

• ·   Strain

Depending on the selected test method, loading may continue until the specimen breaks, reaches a defined extension, exceeds a maximum load, or experiences a specified percentage drop in force.

Testing software uses the recorded force, displacement, strain, and specimen-dimension data to calculate the required mechanical properties and generate the stress-strain curve.

Main Components of a Tensile Testing Machine

A complete tensile testing system normally includes a load frame, force-measurement system, grips or fixtures, control software, and, where required, an extensometer.

1. Load Frame

The load frame provides the mechanical structure needed to apply tensile force to the specimen.

Tensile testing machines may use:

• ·   Single-column frames

• ·   Dual-column tabletop frames

• ·   Dual-column floor-standing frames

• ·   High-capacity hydraulic frames

• ·   Horizontal frames for long specimens

Single-column machines are generally suitable for low-force testing and samples that require longer travel. Dual-column systems provide greater frame stiffness and load capacity for plastics, composites, metals, components, and other medium- or high-force applications.

Hydraulic universal testing machines are commonly selected when testing steel, rebar, structural materials, large fasteners, or other specimens requiring very high tensile force.

Horizontal tensile testing machines are suitable for cables, chains, wire ropes, conductors, insulators, and other long or oversized specimens that cannot be conveniently installed in a vertical machine. United Test supplies electronic, hydraulic, single-column, dual-column, and horizontal universal testing systems for different testing requirements.

2. Load Cell or Force-Measuring System

The load cell measures the tensile force applied to the specimen.

Selecting a suitable load cell is important because an oversized load cell may not provide the required performance at very low forces, while an undersized load cell may be overloaded during the test.

Some United Test electronic universal testing machines support multiple load cells on one frame. This allows the laboratory to use a lower-capacity load cell for small specimens and a higher-capacity load cell for stronger materials without purchasing separate testing machines.

For example, the WDW-10Y, WDW-20Y, and WDW-50Y electronic universal testing machines provide Class 0.5 load accuracy according to ISO 7500-1, with a force-measurement resolution of 1/500,000 of full scale.

3. Grips and Test Fixtures

Grips hold the specimen while tensile force is applied. The correct grip depends on the specimen’s material, shape, thickness, surface condition, and expected breaking load.

Common tensile grip configurations include:

• ·   Manual wedge grips

• ·   Hydraulic wedge grips

• ·   Pneumatic grips

• ·   Screw-action grips

• ·   Rubber-coated grips

• ·   Serrated jaw grips

• ·   Rope and yarn grips

• ·   Wire grips

• ·   Film and foil grips

• ·   Belt and webbing grips

• ·   Component-specific fixtures

The gripping surface must provide sufficient holding force without cutting, crushing, or causing premature failure in the specimen.

United Test universal testing machines can be configured with manual, pneumatic, or hydraulic tensile grips, as well as fixtures for peel, tear, shear, puncture, compression, flexural, and other mechanical tests.

4. Extensometer

An extensometer measures the change in the specimen’s gauge length during the test.

Crosshead movement can provide general displacement information, but it also includes movement caused by frame compliance, grip seating, and other parts of the testing system. When accurate strain, elastic modulus, or yield-strength measurements are required, deformation should normally be measured directly on the specimen with an appropriate extensometer.

The extensometer should be selected according to:

• ·   Initial gauge length

• ·   Expected elongation

• ·   Specimen width and thickness

• ·   Test temperature

• ·   Required strain accuracy

• ·   Material stiffness

• ·   Whether the specimen breaks suddenly

United Test tensile testing systems can be configured with extensometers for direct strain measurement. Large-extension options with measuring ranges up to 800 mm are available for selected high-elongation applications.

5. Testing Software and Control System

Testing software controls machine movement, records data, calculates results, displays curves, and generates reports.

Depending on the machine configuration, operators can define:

• ·   Test speed

• ·   Specimen dimensions

• ·   Preload

• ·   Load limits

• ·   Displacement limits

• ·   Strain limits

• ·   Break-detection conditions

• ·   Return position

• ·   Result calculations

• ·   Report format

The FastTest software used with selected United Test electronic universal testing machines can display load-time, load-displacement, displacement-time, stress-strain, and other test curves. Test results can be stored, recalled, compared, reanalyzed, printed, and exported for reporting.

The system also supports curve superposition and batch-test reporting, allowing engineers to compare multiple specimens or production batches more efficiently.

How to Set Up and Perform a Tensile Test

A reliable tensile test requires more than simply placing a specimen in the machine and pressing the start button. The operator must verify that the specimen, machine, grips, load cell, extensometer, and software settings are suitable for the selected test standard.

Even when part of the process is automated, the operator remains responsible for confirming that the test setup is correct.

Step 1: Identify the Applicable Test Standard

The first step is to determine which standard, customer specification, or internal procedure applies to the material.

The test standard may specify:

• ·   Specimen geometry

• ·   Gauge length

• ·   Conditioning requirements

• ·   Testing temperature

• ·   Grip separation

• ·   Test speed

• ·   Strain rate

• ·   Preload

• ·   Extensometer requirements

• ·   Result calculations

• ·   Acceptable failure location

• ·   Reporting format

The test method should be confirmed before selecting the machine configuration or preparing the specimen.

Step 2: Prepare the Specimen

Specimen dimensions vary according to the material and test standard.

Metals and rigid plastics are often tested using reduced-section specimens commonly described as dog-bone or dumbbell specimens. The enlarged ends provide suitable gripping areas, while the narrower central section creates a defined gauge area where deformation and failure should occur.

Films, textiles, rubber, wires, cables, ropes, fasteners, and finished components may require rectangular strips, rings, straight lengths, machined sections, or application-specific specimen shapes.

Before testing, measure and record the required specimen dimensions. Depending on the calculation, these may include:

• ·   Original gauge length

• ·   Width

• ·   Thickness

• ·   Diameter

• ·   Cross-sectional area

• ·   Original distance between gauge marks

Specimens should also be inspected for scratches, incorrect machining, uneven edges, thickness variation, or other defects that could affect the result.

Step 3: Select the Testing Machine and Load Cell

Choose a machine with sufficient load capacity, test space, travel, and frame stiffness for the specimen.

The load cell should be selected so that the expected test force falls within its verified measurement range. For laboratories testing both weak and strong specimens, a machine that supports interchangeable load cells can improve measurement flexibility.

Low-force materials such as films, textiles, fine wires, small components, and some medical products may require a single-column machine or low-capacity load cell.

High-strength metals, rebar, large bolts, structural components, and heavy industrial materials normally require a floor-standing electronic or hydraulic universal testing machine.

Step 4: Install the Correct Grips

Install grips that match the specimen geometry and expected force.

The specimen must remain securely clamped throughout the test without:

• ·   Slipping

• ·   Rotating

• ·   Being cut by the jaws

• ·   Being crushed at the gripping area

• ·   Breaking prematurely near the grips

Jaw faces may need to be smooth, serrated, rubber-coated, curved, or specially manufactured for the application.

For repetitive testing, pneumatic or hydraulic grips can improve clamping consistency and reduce the time required to load each specimen.

Step 5: Align and Clamp the Specimen

Position the specimen along the loading axis of the machine.

Incorrect alignment introduces bending or off-axis force, which can change the stress distribution and cause the specimen to fail close to the grip rather than within the intended gauge section.

Clamp one end first, confirm alignment, and then secure the opposite end without twisting or preloading the specimen unnecessarily.

For sensitive tests, alignment fixtures or self-aligning grip connections may be used to reduce bending effects.

Step 6: Attach the Extensometer

When direct strain measurement is required, install the extensometer after the specimen has been positioned in the grips.

Confirm that:

• ·   The correct gauge length is used

• ·   Contact points are positioned symmetrically

• ·   The extensometer is not slipping

• ·   The expected elongation is within the measuring range

• ·   The extensometer can be removed safely before specimen break when required

For highly extensible materials, choose an extensometer with sufficient travel to follow the specimen throughout the required portion of the test.

Step 7: Configure the Test Method

Enter the specimen dimensions and required test parameters into the control software.

Typical settings include:

• ·   Test speed

• ·   Strain rate

• ·   Preload

• ·   Gauge length

• ·   Specimen width and thickness

• ·   Break sensitivity

• ·   Maximum force

• ·   Maximum displacement

• ·   Return speed

• ·   Required result calculations

Do not copy parameters from another material unless the same test standard and specimen configuration apply.

Step 8: Zero the Sensors and Start the Test

Before beginning the test:

• ·   Confirm that the load reading is zero

• ·   Confirm that displacement is zeroed correctly

• ·   Check the grip position

• ·   Verify extensometer output

• ·   Confirm emergency-stop operation

• ·   Make sure the specimen area is clear

Once the test begins, the machine applies tensile load at the programmed rate while continuously recording force, extension, displacement, and strain data.

Step 9: Review the Failure and Test Results

After the test, check the failure location and specimen condition before accepting the result.

A break within the gauge section generally indicates that the specimen was loaded correctly. Failure directly at the grip may indicate misalignment, excessive gripping pressure, an unsuitable jaw face, or specimen damage.

The software can then calculate and report the required tensile properties.

Understanding the Stress-Strain Curve

A stress-strain curve shows how a material behaves throughout a tensile test.

Stress represents the applied tensile force divided by the specimen’s original cross-sectional area. Strain represents the change in gauge length relative to the original gauge length.

Different materials produce different curve shapes. A brittle material may show limited deformation before breaking, while a ductile metal may yield and continue to elongate significantly before fracture. Rubber and elastomers can produce large, nonlinear strain values.

The stress-strain curve helps engineers identify several important properties.

Ultimate Tensile Strength

Ultimate tensile strength, or UTS, is the maximum engineering stress reached during the tensile test.

It is not always the same as stress at break. Ductile materials may reach maximum stress and then experience localized necking before final fracture.

Yield Strength

Yield strength is the stress at which a material begins to deform plastically.

Below this point, the material may return approximately to its original dimensions when the force is removed. Beyond the yield region, some permanent deformation remains.

Some materials show a clearly defined yield point. For materials without an obvious transition, an offset method, commonly a 0.2% offset for many metallic materials, may be used when required by the applicable standard.

Elastic Modulus

Elastic modulus, also known as Young’s modulus in a uniaxial tensile test, describes the material’s stiffness in the initial elastic region of the stress-strain curve.

A higher modulus indicates that the material resists elastic deformation more strongly. A lower modulus indicates greater flexibility under the same applied stress.

Accurate modulus measurement normally requires appropriate strain measurement and careful control of alignment, preload, and test speed.

Elongation

Elongation describes how much the specimen stretches during the tensile test.

It may be reported as:

• ·   Extension in millimetres

• ·   Strain

• ·   Percentage elongation

• ·   Elongation at yield

• ·   Elongation at maximum force

• ·   Elongation at break

The correct result depends on the material and applicable testing standard.

Reduction of Area

Reduction of area is commonly used for metallic specimens. It compares the original cross-sectional area with the minimum area at the fracture location after testing.

This result provides additional information about material ductility.

Choosing a United Test Tensile Testing Machine

United Test offers universal testing machines for loads ranging from low-force material testing to high-capacity structural and metal testing.

The electronic universal testing machine range covers configurations from 100 N to 1,000 kN, while United Test hydraulic systems are available in common capacities of 300, 600, 1,000, and 2,000 kN.

Example: WDW-10Y, WDW-20Y and WDW-50Y Specifications

The WDW dual-column electronic universal testing machine is intended for general-purpose tensile, compression, bending, shear, peel, tear, and component testing.

Key specifications include:

These specifications apply to the stated WDW models and should not be treated as standard parameters for every United Test tensile testing machine. The final configuration depends on the material, specimen dimensions, expected force, test standard, required grip, extensometer, and testing environment.

Common Tensile Testing Standards

The correct testing standard depends on the specimen material, form, thickness, and intended result.

Common examples include:

ASTM E8/E8M covers the determination of properties including yield strength, tensile strength, elongation, and reduction of area for metallic materials. ISO 6892-1 specifies tensile testing methods for metallic materials at room temperature.

ASTM D638 is used for tensile-property testing of standard plastic specimens, while ASTM D882 applies to thin plastic films and sheets below 1 mm. The ISO 527 series provides general and material-specific conditions for determining the tensile properties of plastics and plastic composites.

Operators should always check the current edition of the required standard and any customer-specific specification before creating the test method.

Common Causes of Inaccurate Tensile Test Results

Incorrect Specimen Dimensions

Errors in width, thickness, diameter, or gauge length directly affect calculated stress and strain values.

Poor Specimen Alignment

Off-axis loading can introduce bending stress and cause premature failure.

Specimen Slippage

Insufficient clamping force or an unsuitable grip surface may allow the specimen to move during testing.

Excessive Grip Pressure

Overtightening may damage films, plastics, rubber, composites, or soft metals before the test begins.

Incorrect Test Speed

Many materials are sensitive to strain rate. Using the wrong speed can significantly change measured strength, elongation, and modulus.

Using Crosshead Movement as Strain

Crosshead displacement includes deformation from the complete testing system. It may not provide sufficient accuracy for modulus, yield strength, or precise strain measurement.

Inappropriate Load Cell Capacity

A load cell that is much larger than the expected test force may not provide the desired measurement performance in the low-force range.

Incorrect Break Detection

Improper end-of-test settings may cause the machine to stop too early or continue moving after specimen failure.

Environmental Variation

Temperature, humidity, specimen conditioning, and testing environment can affect the behaviour of plastics, rubber, adhesives, textiles, and other sensitive materials.

Frequently Asked Questions

What is the difference between tensile strength and yield strength?

Yield strength indicates when permanent deformation begins. Tensile strength is the maximum engineering stress reached during the test.

A material can therefore begin yielding before it reaches its ultimate tensile strength.

Does every tensile test require an extensometer?

No. Some tests require only maximum force, breaking force, or basic elongation information.

However, an extensometer is normally recommended when accurate strain, elastic modulus, offset yield strength, or elongation over a defined gauge length is required.

Can a universal testing machine perform tests other than tension?

Yes. By changing the grips or fixtures, a United Test universal testing machine can be configured for compression, bending, peel, tear, shear, puncture, friction, and other static mechanical tests.

The machine capacity, available test space, control mode, and fixture design must still be suitable for the application.

Should I choose an electronic or hydraulic tensile testing machine?

Electronic universal testing machines are generally suitable for low-, medium-, and selected high-force applications that require precise speed control, flexible test methods, and detailed data acquisition.

Hydraulic universal testing machines are commonly selected for high-capacity testing of steel, rebar, large fasteners, structural components, and other heavy-duty specimens.

What information is needed to select a tensile testing machine?

To recommend an appropriate system, the testing-machine supplier normally needs:

• ·   Material type

• ·   Specimen shape and dimensions

• ·   Expected maximum force

• ·   Required test standard

• ·   Required test speed

• ·   Expected elongation

• ·   Required test space

• ·   Grip or fixture requirements

• ·   Extensometer requirements

• ·   Testing temperature or environmental conditions

• ·   Required report format

Tensile Testing Solutions from United Test

A reliable tensile test depends on the complete system—not only the maximum load capacity of the machine.

The load frame, load cell, grip design, specimen alignment, extensometer, software settings, test standard, and operator procedure must work together to produce accurate and repeatable results.

United Test supplies single-column, bench-top, dual-column, high-capacity electronic, hydraulic, and horizontal tensile testing systems. Machines can be configured with different load cells, grips, fixtures, extensometers, test spaces, and software functions according to the material and applicable testing standard.

Provide your material type, specimen dimensions, required standard, expected breaking load, and testing objective to receive a suitable tensile testing machine configuration for your laboratory or production quality-control application.