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.
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.