Tensile Testing: What is it?
Tensile tests are used to determine how materials will behave under tension load. In a simple tensile test, a sample is typically pulled to its breaking point to determine the ultimate tensile strength of the material. The amount of force (F) applied to the sample and the elongation (∆L) of the sample are measured throughout the test. Material properties are often expressed in terms of stress (force per unit area, σ) and strain (percent change in length, ε). To obtain stress, the force measurements are divided by the sample’s cross sectional area (σ = F/A). Strain measurements are obtained by dividing the change in length by the initial length of the sample (ε = ∆L/L). These values are then presented on an XY plot called a stress-strain curve. Testing and measuring procedures vary based on the material being tested and its intended application.
ADMET material testing systems perform accurate and reliable tension tests / tensile tests. Our systems are ideal for measuring the tensile properties of metals, plastics, textiles, adhesives, medical devices and many other products and components. As they pull materials apart, ADMET testing machines accurately calculate mechanical properties such as tensile strength, peak load, elongation, tensile modulus, and yield.
How to Perform a Tensile Test
- Universal test machine frame
- Load cell
- Controller and/or indicator
- Proper grips and fixturing to hold your sample
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 capacities. It is important to select a frame which can withstand the amount of force needed to test the sample.
Load cells measure the amount of force being applied to the sample. Like frames, these come in a variety of capacities. Choosing a load cell with a capacity below the required breaking strength will result in the load cell breaking before the sample does. Conversely, a load cell with too high a capacity will lead to test results that may lack the precision desired as resolution of load cells typically goes down to 1%. For example, a 1,000 lb load cell would be far too high a capacity for a sample that breaks under 1 lb of force.
Depending on your system setup, you may need a controller or an indicator. Controllers, as the name implies, control how the test frame behaves during testing, including test speed and displacement. In some situations, an indicator may be all that 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 sample made of metal requires different grips than a stretchy piece of rubber due to how the materials behave as tensile forces are applied. Selecting the correct grips for your application is crucial in achieving accurate results.