Tensile strength tests determine how much of a pulling force you can apply to an object. You can observe how the object will stretch, and at which points it will show the most flexibility in stretching -- and the least flexibility. After a tensile test ends, researchers will generally create a curve that shows how the object stretches until it reaches failure -- also known as UTS, or "Ultimate Strength." The object will break soon after reaching that point.
Plastics -- Choice of Materials
There are many different grades of plastics that come out of manufacturing plants, each designed for specific applications and to endure specific levels of stress. Once product managers know what their new devices need to be able to do, they can order tensile tests to see what will happen to different grades of plastic under those conditions, so that they can order the grade that combines durability with cost effectiveness.
Plastics: Quality Control
Tensile strength tests within a plastic manufacturing plant help the design engineers maintain levels of quality. By testing enough items from each batch to produce a statistically significant sample, engineers can determine whether or not quality control problems exist in their manufacturing line: products that fail tests they shouldn't have demonstrate a flaw in the system. Pinpointing the spot in the plastic items that fail can help isolate the problem in the production line.
Common thread tensile strength tests place samples into a pulling machine and then move both ends away from each other at a fixed rate of speed, such as 1 foot per second. The purpose of this is to tell how durable the thread will be under different forms of pulling stress. This can also serve as a quality control measure to determine whether the weaving process for the thread is flawed.
Metal: Preventing Catastrophic Events
It's harder to imagine forces pulling on metal than it is to consider the same forces at work on thread, paper or plastic, but when you get into structural design for buildings, gravity, wind and other forces pull on metal with much more force than those other three items would stand. Tensile strength testing for metal will tell you how much a particular alloy will elongate before hitting UTS and how much you can load onto a particular piece of metal before it will lose structural integrity. Knowing these numbers is vital for construction safety -- both during and after the building is completed.