The ARES-EVF design (patent pending) is based on the original Meissner concept and elongates the sample within a confined space by expelling the sample with rotary clamps. Instead of the rotary clamps, two cylinders are used to wind up the sample; one cylinder is rotating, the other measuring the force. In order to wind up the sample equally on both sides, the rotating cylinder moves on a circular orbit around the force measuring cylinder while rotating around its own axis at the same time (Figure). Since the force measuring cylinder is fixed in space it can be directly coupled with the torque transducer of the ARES. The full rotation of the mobile cylinder is generated by the ARES actuator. As such the force measurement is decoupled from all the moving parts and consequently friction and inertia contributions are not affecting the material response, namely the force signal.
The ARES transducer measures a torque. The force at the sample can be easily calculated from the measured torque divided by the cylinder radius. The strain rate applied is the velocity at the cylinder, divided by the sample length, which is equivalent to the separation of the center axes of the two cylinders. The velocity is given by the product of the angular rotation speed Ω(t) and the cylinder radius. Since the sample is elongated at both ends, the Hencky rate applied by the actuator is the product of angular rotation speed and cylinder diameter divided by the distance of the two cylinders.
click here for the product note APN002 on EVF technology