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What Is a Torsion Test?

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  • Written By: N. Kalu
  • Edited By: A. Joseph
  • Last Modified Date: 23 July 2014
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A torsion test measures the strength of any material against maximum twisting forces. It is an extremely common test used in material mechanics to measure how much of a twist a certain material can withstand before cracking or breaking. This applied pressure is referred to as torque. Materials typically used in the manufacturing industry, such as metal fasteners and beams, are often subject to torsion testing to determine their strength under duress.

There are three broad categories under which a torsion test can take place: failure testing, proof testing and operational testing. Failure testing involves twisting the material until it breaks. Proof testing observes whether a material can bear a certain amount of torque load over a given period of time. Operational testing tests specific products to confirm their elastic limit before going on the market.

It is critical for the results of each torsion test to be recorded. Recording is done through creating a stress-strain diagram with the angle of twist values on the X-axis and the torque values on the Y-axis. Using a torsion testing apparatus, twisting is performed at quarter-degree increments with the torque that it can withstand recorded. The strain corresponds to the twist angle, and the stress corresponds to the the torque measured.

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The elastic limit of any material is the point at which it can no longer return to its original shape or size. The elastic limit determined by a torsion test is equal to the slope of the line from the start of testing to the proportional limit. This relationship was first measured by Sir Robert Hooke in 1678. Hooke's Law states that stress is directly proportional to strain until the proportional limit is reached, at which point the object tested will begin to show signs of stress.

After testing, metal materials are categorized as being either ductile or brittle. Ductile metals such as steel or aluminum have high elastic limits and can withstand a great deal of strain before breaking. Brittle materials such as cast iron and concrete have low elastic limits and do not require much strain before rupturing.

Without performing a torsion test, materials would not be properly vetted before being released for industrial use. It is of paramount importance that the ability for a material to bear a certain amount of twisting is accurately measured. Otherwise, structures and machines that depend on such materials could break down causing instability, work flow interruption or even significant damage and injury.

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Discuss this Article

anon928988
Post 6

@anon35220: Torsion is a bending moment although i understand your confusion.

anon352200
Post 4

I hate that the word "bending" was used in this description of torsion. Twisting, okay. But bending? No way.

epiphany5
Post 3

Great job on explaining what a torsion test is! I think I am going to send this to my wife. She always has questions as to what I do at work, and frankly, you do a better job of explaining it than I do.

Another test that my company does is a fatigue test. This kind of test measures how materials perform under varying levels of stress and strain. We make washers and dryers, so it is important that our products can withstand sudden bursts of pressure applied to them.

Often times, I see that companies only test a portion of their production batch. For instance, only 1 out of every 100 products is tested for torsion and fatigue. While this may not be the cheapest way to do it, I think more frequent testing should occur. Perhaps 1 out of every 50 products should be tested. It is better to be safe than sorry when it comes to making consumer products.

Farah1
Post 2

I am a current civil engineering undergraduate student. My studies have made me very familiar with the different kinds of torsion tests. Thanks for writing this article. It is pretty easy for anyone to understand.

It is good to know that the same tests that I use in my labs are also used in industry. While it is fun to see how much pressure a concrete slab can hold before breaking into pieces, it is good to know that I will be using these same tests outside of college.

YogurtPark
Post 1

Thanks for writing this article, it has a lot of good information in it.

I work for a company that manufactures child playground equipment. It is important that we make products that are safe for children to play on. We also have to consider that adults often use our equipment when playing with their children.

We run a lot of tests to make sure that are equipment can hold up against a lot of pressure. We also do tests to determine how the material properties of our equipment change under extreme weather conditions. It is important that our products are as safe in a snow storm as they would be in a heat wave.

Testing is very important when it comes to materials, so companies should not take it lightly. It is a crucial step in the production process.

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