Basics  

Too high operating frequency causing self-heating and thermal breakdown.

The maximum conditions of voltage amplitude and frequency should be determined for the application - e.g. by setting a limit of 100ºC for the actuators during continuous operation.

 

Voltage or current spikes superimposed to the regular signal causing large acceleration forces to the actuator that cannot be completely compensated for by the pre-loading system.

The consequence is a disintegration or delamination of the ceramic structure and failure of the actuator. Drive electronics should include suitable protection so that the piezos does not see such spikes.

 

Uneven loading of stacks.

Often a mechanical preload is not applied evenly on the stack and in such case torsion, tension or excessive high peak stresses can be conveyed to the stack causing local cracks and failure. Always make sure that the loading of the stack is as evenly as possible during all operating conditions.

 

Humidity is a serious piezo killer.

High humidity, e.g. 85%RH is a serious condition, which shorten the life of the actuator. Make sure that humidity level is kept low - best is hermetically sealed applications. Consult Noliac if actuators must work at high humidity.

 

Insufficient preload.

If insufficient preload is applied to the stack then there might be a loss of preload during operating, e.g. if temperature increase or if frequency is high. In such case there may be high tensile stresses in the stacks causing delamination and failure. It is recommended for actuators operated at dynamic conditions that a minimum of 10MPa preload is available during all operating conditions.

 

Loss of polarization.

The piezo electrical property is applied to the component during the polarization process. This is done by applying an electrical field at elevated temperature. The polarization effect can be lost if a negative electrical field is applied, the operating temperature is increased either due to increased temperature of the surroundings or thermal run away or the polarization can be degraded if too high blocking forces is applied.