A tensile bar is a calibrated and molded bar of material used in testing to determine how flexible and strong the material is under pressure. Tensile bars are made by taking samples of the material being tested and configuring them as needed. Then, they are tested under carefully controlled conditions to collect data about the tensile properties of the material in question. This data is comprehensive and detailed, providing a profile of the material that can be used along with other materials testing results to determine its utility.
A tensile bar, once molded, is carefully stressed with a pull test. During the pull test, note is taken of when the material starts to show signs of strain such as deforming, cracking, or fraying. If the bar snaps in half, this is also noted. This data is used to find out how much strength the material could handle before the tensile bar would deform beyond all usability. Tensile bars can be tested with different types of pulling devices, all calibrated to make sure they are exerting uniform pressure.
Multiple tensile bars will be made to repeat the test and prepare results. If the material is too weak or inflexible for the planned application, it may need to be redesigned or abandoned and picked up in the future for another project. As companies conduct materials testing, they created detailed logs on all the materials they produce and these logs can be referenced when materials are needed for a new project, to see if existing products will meet the need.
Some companies make tensile bars and perform this testing, along with other materials testing, on site. Other companies prefer to ship their products out to companies that specialize in testing materials. In some cases, a third party with neutrality may be required by law or the terms of a contract to confirm the safety of materials and develop a comprehensive report on them. In these instances, companies must ship out their products to someone else for evaluation.
A document noting the results of tensile bar testing may show graphics and include photographs of the bars during testing. This information is used to provide a clear demonstration of the type of damage to the material discussed in the report; rather than saying “the bar cracked” at a given pressure, the author of the report can say “cracking, as seen in figure 2.2, occurred.” This provides people reading the report with useful contextual information to understand the results. Additionally, if a product made with the material fails, the results of the tensile bar testing can be consulted to compare the real-world damage with the damage created in the testing conditions.