Superelastic behavior of a ß-type titanium alloy.

The superelasticity of a ß Ti alloy, Ti-7.5Nb-4Mo-2Sn (in atom percent) was evaluated by using loading and unloading cyclic tensile tests under different thermomechanical conditions, and the effects of the plastic deformation, temperature, strain rate and cyclic loading on the superelasticity of the alloy were studied. It is found that, with the applied strain increasing, the stress inducing the reverse martensitic transformation σα″-ß and the strain recovery rate η decreases. The increase of deformation temperature promotes σß-α″, σα″-ß and Δσ, and the temperature dependency of the stresses obeys the Clausius-Clapeyron relation. σß-α″, σα″-ß and Δσ are independent on the strain rate when it is lower than 8.35×10(-4)s(-1). However, when the strain rate is higher than 8.35×10(-4)s(-1), σß-α″ and Δσ increase, but σα″-ß decreased with increasing the strain rate. By cyclic loading and unloading to the maximum strain of 6% at 25°C under the strain rate of 1.67×10(-4)s(-1), the alloy exhibits a improved superelasticity after seventh cycles due to the training effect.

Effect of Grip Force and Training in Unstable Dynamics on Micromanipulation Accuracy.

This paper investigates whether haptic error amplification using unstable dynamics can be used to train accuracy in micromanipulation. A preliminary experiment first examines the possible confounds of visual magnification and grip force. Results show that micromanipulation precision is not affected by grip force in both naive and experienced subjects. On the other hand, precision is increased by visual magnification of up to 10×, but not further for larger magnifications. The main experiment required subjects to perform small-range point-to-point movements in 3D space in an unstable environment which amplified position errors to the straight line between start and end point. After having trained in this environment, subjects performing in the free conditions show an increase in success rate and a decrease in error and its standard deviation relative to the control subjects. This suggests that this technique can improve accuracy and reliability of movements during micromanipulation.