Threaded 101: Tensile Strength
EDUCATIONAL SERIES
Threaded 101: Tensile Strength
Welcome back to our Threaded 101 series! Be sure to read our previous articles on finishes and materials to catch up. This article covers the importance of tensile strength.
Threaded rod’s tensile strength varies depending on the material used to manufacture the rod. As mentioned in Threaded 101: Materials, the material chosen for any project should be based on the requirements of the application. Some applications may require very strong material such as Grade 8 or B7, while others may need a softer, more ductile metal like low carbon.
Tensile Strength
What is Tensile Strength?
A material’s tensile strength is the maximum load it is able to sustain before failing. Tensile strength is also often referred to as ultimate tensile strength.
Think of a rubber band being stretched to its full elasticity and snapping. The tensile strength for threaded rod is the maximum amount of tensile stress the material can withstand before failing. Like a broken rubber band, after a certain amount of stress, threaded rod will break or snap from too much tensile stress.
At AATP, we reference yield strength, which refers to the maximum amount of stress a material can withstand before permanent deformation. Once the specimen becomes permanently deformed, it has exceeded its yield strength.
Typically 85% to 95% of a material’s yield strength, a proof load is used for non-destructive testing. It is a load that a specimen must sustain without evidence of permanent deformation.
In the threaded rod industry, mechanical tests are used to determine tensile strength, yield strength, and other mechanical properties. These tests are performed under controlled methods and gauge the limits of a material while it has a prescribed amount of force applied to it.
          
The above diagram depicts a test specimen being subjected to a tensile load.
             
The above graph shows a typical stress-strain curve of ductile material. The stress labeled as σuts represents the ultimate tensile strength while σys represents the yield strength. The points along the strain axis represent the strain that coincides with the yield strength (εyp), the strain that coincides with the ultimate tensile strength (εu), and the strain that coincides with the fracture of the material (εf).
Conclusion
Materials’ mechanical properties such as tensile and yield strength are important because they ensure safe, high-quality materials. Based on the application, only certain materials may be used because of their tensile strength. However, when designing a joint or system with threaded fasteners, an appropriate safety factor must also be used to calculate the number of fasteners required and the material from which those fasteners should be manufactured.
For further information on this topic feel free to ask in the comments section below or contact one of our experts.