In the manufacturing operation of pressure sensors, autofrettage denotes the process of active ?overload? by subjecting the pressure sensor selectively once or several times to a pressure above the nominal pressure range. This process is applied, to experience maximum stability, in particular 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 regions 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 influence on the structural conditions by means of autofrettage is an integral the main development of the sensor and of the associated manufacturing process. Which pressure the sensor is put through and how often, should be determined individually for each sensor design by means of an elaborate FEM simulation and extensive test series.
Caution ? no experiments of your own! However, it should not be figured every sensor will automatically reap the benefits of subjecting it to autofrettage. Autofrettage can only just be used for ductile materials, but under no circumstances for brittle ones. Last Minute must be scheduled and completed very selectively sufficient reason for great care during the production stages. Ill-considered ?overpressurising? of pressure sensors by laymen who like experimenting will not only damage the sensor permanently, but also bring about dangerous preliminary damage and subsequently possibly in accidents due to fatigue and bursting of the sensor. In this way, an improvement in instrumentation is only going to be achieved, if, by hit or miss.