Tension Testing Solutions

What Properties Are Measured?

In a broad sense, strength refers to the ability of a structure to resist loads without failure. Failure may occur by rupture because of excessive stress or may take place owing to excessive deformation. Tensile properties include the resistance of materials to pulling or stretching forces. The amount of force required to break a material and the amount it extends before breaking are the most important properties. For most materials, the initial resistance to force, or modulus, and the point of permanent deformation, are obtained from plots of force against elongation. Analysis of force-elongation or stress-strain curves can convey much about the material being tested, and it can help in predicting its behavior.

• Tensile Strength: the maximum tensile stress which a material is capable of sustaining.  Tensile strength is calculated from the maximum force during a tensile test carried through rupture and the original cross-sectional area of the specimen.  This is vital for applications like cableways in suspension bridges or safety harnesses.
• Yield Strength: The engineering stress at which a material begins to deform permanently. This tells engineers how much a component can be stressed before it loses its original shape—a critical factor in designing everything from propeller blades to bicycle frames.
• Proportional Limit: the greatest stress that a material can sustain without deviation from the proportionality of stress to strain (Hooke’s Law).
• Young’s Modulus (Modulus of Elasticity): The ratio of tensile stress to strain below the proportional limit;  a measure of a material’s stiffness. A high modulus is essential for a rigid component like a machine part, while a lower modulus is needed for flexible items like plastic films or medical tubing.
• Ductility: The ability of a material to deform plastically without fracturing. Measured by total elongation and reduction of area, ductility is key for applications where a material needs to absorb energy, such as a car’s crumple zone.

What Equipment Is Needed For Tensile Testing?

To perform tension testing, you will need the following equipment:

• Universal test machine frame
• Load cell
• Controller and/or indicator
• Proper grips and fixturing to hold your sample
• Extensometer

The universal test machine frame provides the structure and rigidity needed to pull the sample apart at the desired rate. Frames are available in both electromechanical and servo-hydraulic configurations with a wide range of force capacities.

Load cells measure the amount of force being applied to the sample. Like frames, these come in a variety of force capacities. Choosing a load cell with a capacity below the required breaking strength will result in load cell damage. Conversely, a load cell with too high a capacity relative to the maximum force for a test will lead to results that may lack the precision required. As a general rule, measured forces during a test should exceed at least 1% of the force capacity of the load cell. For example, a 1,000 lb load cell would be too high a capacity for a sample that breaks under 10 lb of force.

Depending on your universal test machine frame, you may need a controller or an indicator. Controllers, as the name implies, automatically control the rate of stressing or straining during test. In manually controlled test machine frames, only an indicator is required. Indicators capture and display the test data but do not control the machine.
There are many types of grips and fixtures available for tension testing. Different materials require different fixturing to properly hold them. For instance, a wedge grip with it’s self-tightening design would be used for metal samples but an elastomer that exhibits a high degree of elongation would use a pneumatic vise grip. Selecting the correct grips for your application is crucial in achieving accurate results.

An extensometer is used to measure engineering strain and are used to precisely measure the per unit change in length referred to its original length during a test. Extensometers are required instruments for accurately measuring Yield Strength, Young’s Modulus and ductility. Extensometers are not always necessary, but they are commonly required by published ASTM and ISO standards as they provide more precise strain measurements than a testing machine can otherwise measure. Options include clip-on extensometers for general purpose testing, long travel extensometers for highly elastic materials, and non-contact video extensometers for high-temperature or delicate samples. Each type offers specific advantages depending on the material and test conditions.

Tensile Testing Solutions For You

While many tensile tests follow a published standard, ADMET understands that no two tests are exactly the same. ADMET offers testing machines, controllers, load cells, grips, fixtures, and extensometers that will get the job done regardless of the size of your sample or the complexity of the application. We have an established product line and also the engineering expertise and willingness to work with you to provide engineered-to-order solutions.

In addition, ADMET’s Technical Support and Engineering teams will help you get the most value out of your testing machine. All ADMET machines come with lifetime application support so you can rely on our decades of experience when setting up a new test. If you have an unusual test application, our engineering team will work with you to design a custom testing machine or fixture that fits your unique needs.