Determination of load condition of standard screws during tensile tests using acoustic emission analysis

We examined the acoustic behaviour of screws under applied load to develop an in-process monitoring system for endangered screw connections. To apply load to a screw, a hydraulic tensile testing machine was designed. Signals occurring during tensile tests were digitally recorded and analysed using acoustic emission (AE) technique. We established an increase of the AE-rate at the yield limit and weaker AE-activity during the plastic deformation. The AE-signals contained dominant frequencies in two narrow frequency ranges, namely at 590 kHz and 1010 kHz and therefore we were capable of distinguishing between friction processes in the screw thread and abrupt dislocation processes under load. The significance of the results for in-process monitoring of screws is illustrated