Angle of twist: For a shaft under torsional loading, the angle through which fixed end of a shaft rotates with respect to the free end is called the angle of twist.
Data acquisition: Data acquisition is a process of digitizing and storing data from any sensor connected to the test system.
Digital controller: The digital controller provides an interface between the computer and the test system. It also contains the feedback loops and aquires data from the transducers.
Elastic material: An elastic material is one which returns to its original shape once the load is removed.
Elastic-plastic torsion: Suppose a shaft is made of ductile material and is subjected to torsional loading. At a particular value of torque known as yield torque, the outer surface yields. As the torque is increased, the outer region of the shaft behaves like a plastic material while the inner core is still linear elastic. This behavior of the shaft can be explained using ‘Elastic-plastic torsion’ theory.
Feedback: The feedback is a signal from a sensor that indicate the current state of the controlled element, e.g. actuator position.
Grip: Grips hold the specimen in place while testing.
Hooke’s law: In a linear elastic body, the stress is directly proportional to the strain. The stresses and strains are related by constants that are solely material property.
Hydraulic Actuator: An actuator is a hydraulically powered device that provides displacement of (or force into) a specimen or structure for testing. The actuators can be linear or rotary.
Hydraulic power supply (HPS): The hydraulic is the mechanical source of high-pressure hydraulic fluid necessary for the test system operation.
Linear actuator: Applies a force or a displacement on the sample to be tested.
Linear elastic material: An elastic material which exhibits a linear relationship between stresses and strains.
Load cell: Load cell is a force transducer used to measure forces and torques.
Load frame: The load frame is the mechanical structure that can react to the force applied to the specimen by the hydraulic actuator. Load frame also provides mounting to other components of the machine.
LVDT (Linear variable differential transformer): LVDT provide an output voltage that is proportional to the displacement of the sample in the test performed.
Maximum torque: It is the maximum torque value reached when a shaft is subjected to torsional loading.
Modulus of rigidity / Shear modulus: The constant relating shear stress and shear strain in a linear elastic material is called shear modulus or modulus of rigidity. Shear modulus is a material property.
Polar moment of inertia: The moment of inertia of a body about an axis perpendicular to plane of its surface is called polar moment of inertia. Hence, polar moment of inertia is a mass distribution property about an axis perpendicular to its surface.
Rotary actuator: Applies a torque or a rotation on the sample to be tested.
RVDT (Rotary variable differential transformer): RVDT provide an output voltage that is proportional to the rotation of the sample in the test performed.
Servomechanism: A servomechanism is a servo where the mechanical device is a part of the feedback loop.
Servovalve: A servovalve regulates the rate and direction the flow of the hydraulic fluid between the hydraulic power supply and the actuator. This flow determines the magnitude of the applied torque or rotation of the actuator.
Tibiotarsus: Limb bone formed by fusion of the end of the long bone (tibia) with the ankle bone (astragalus).
Torsion: Torsion refers to the twisting of a structural member loaded by torque, or twisting couples.
Transducer: It is a device that converts a physical quantity (e.g. force, torque, rotation) to an electrical signal.
Ultimate strength: The maximum value of stress that a material can sustain is called the ultimate strength of the material.
Yield torque: The torque value at which the material of a shaft under torsion undergoes first yield is called yield torque. Yield torque only is defined for ductile materials.