Can I develop constant force (pressure) from piezoelectric crystal applying constant voltage?
Yes, you can, however there is some change (call it creep or drift or relaxation) in the motion, logarithmically decreasing with time adding up to perhaps several perecent over hours. Here is the response to a 60\$\mu\text m\$ motion:
To get macroscopic motion from piezo elements there are a few techniques- such as stacking large number of elements, using mechanical amplification (as in benders) and "walking" or other motor techniques. The latter type of technique does not depend on the piezo to hold position so it will not have the same drift characteristic. Also it's common in high precision applications to close the loop with a feedback sensor.
Obviously you want to know, if the crystal deformation under constant DC voltage stays constant, Of course it's possible that the crystal breaks down with high enough voltage or with high enough external force.
There are some applications which need long time deformation. Examples:
- gas lasers are fine tuned (=the distance between the mirrors is adjusted) for precision measuring purposes by moving a mirror with a piezocrystal.
- mirror tilters for optical systems
Here's a datasheet of a mirror tilter.
The specified frequency range starts from zero Hz, so the deformation can be constant.
I know little about the application of piezo electric sensor and actuators other than their common uses as phono record needles, tweeters, beepers and that I have used them on commercially built ultrasonic cutting presses. They also appear to be used as motors / actuators in camera focusing systems and binocular image stabilisation (where, on my Canon binoculars) they do a super job eliminating hand shake from the image.
Introduction to Piezoelectric Actuators Kenji Uchino, International Center for Actuators and Transducers, Penn State University, may be of some interest to you.
I found the link on Wikipedia's Amplified piezoelectric actuator and this makes the interesting statement:
As classical piezoelectric materials have a strain of 0.1%, it is practically impossible to reach significant stroke without displacement amplification (1 mm displacement would require 1 meter of piezoelectric material). The solution to reach middle range stroke is to use an amplification system.