Physical testing instruments cover a wide range of techniques for assessing the strength and behavior of materials and components. Although the majority of instruments involve the measurement of linear stresses and strains, there are also many applications that require the accurate measurement of torque and torsion. Although torsion tests may be carried out on some universal test systems that perform a variety of physical tests, we only consider specialized torsion testing machines here. Generally speaking, torsion testers are electromechanical machines that measure two properties: the applied torque and the resultant twisting angle of the sample.

A typical example of a torsion tester application would be to measure the effect of torques on a metal axle. By applying different torques and measuring the response angle, the instrument can build up a profile of the axle’s response under different situations. Also, as with a fatigue tester, the instrument can be configured to measure how the axle’s properties change after being subject to repeated torques, as might occur in an automobile during regular use. Another type of measurement would be to measure the torque required to cause the axle to fail.

The range of applications for these devices is quite wide. Many applications involve structural elements for engineering or architectural purposes, ranging from metal struts and bars to concrete. Testers for such components are generally floor standing models that can apply torques up to many thousand Newton-meters. Other samples, including metal or plastic components of consumer products, can be tested in benchtop units with a smaller torque range. Even within the narrow field of torsion testing, there are some niche applications, such as measuring the torque required to secure a screw or bolt, fatigue testing of implantable medical devices, and analyzing the characteristics of delicate torsion springs. The size and maximum torque of the instrument is one of the main differentiating aspects of systems in this market, and one of the main contributors to the price of the system. Other differentiators include accuracy, precision and the software, which may be able to support many different methods.

Considering only models specifically for torsion testing, the three largest vendors are Instron, MTS Systems and Tinius Olsen. Most of the other major participants in the physical testing market offer solutions for torsion testing, but these are generally housed on universal tester frames, which are not the focus here. However, there are many other participants in the specialized torsion testing market, including Deltalab, Pratt & Whitney, Ratnakar and Test Resources. There are also niche players such as Andilog, which specializes in the testing of springs, and Skidmore-Wilhelm, which makes torque testers for bolts and tools. The total market for torsion testers was about $20 million in 2007, and is forecast to grow in the low single digits.