In the manufacturing operation of pressure sensors, autofrettage denotes the procedure of active ?overload? by subjecting the pressure sensor selectively once or several times to a pressure above the nominal pressure range. This technique is applied, in order to achieve maximum stability, specifically of the zero point, in later operation. Assuming a suitable design of the sensor, autofrettage enables a long time of trouble-free operation of the sensors even at high load cycles reaching the specified overload range, without resulting in zero-point shift or similar effects.
In autofrettage, certain local areas of the sensor, in which during the selective overload the yield point of the sensor material is locally exceeded, become plasticised, resulting in a permanent change of the instrumentation characteristics. This selective effect on the structural conditions by means of autofrettage can be an integral portion of the development of the sensor and of the associated manufacturing process. Which pressure the sensor is subjected to and how often, should be determined individually for each sensor design through an elaborate FEM simulation and extensive test series.
Caution ? no experiments of your own! However, it must not be figured every sensor will automatically reap the benefits of subjecting it to autofrettage. Autofrettage can only just be utilized for ductile materials, but for no reason for brittle ones. Insidious must be scheduled and carried out very selectively sufficient reason for great care through the production stages. Ill-considered ?overpressurising? of pressure sensors by laymen who like experimenting will not only damage the sensor permanently, but also result in dangerous preliminary damage and subsequently possibly in accidents caused by fatigue and bursting of the sensor. In this way, a noticable difference in instrumentation will only be achieved, if, by hit or miss.