Fatigue failure of a bar of a twin-screw extruder for plastics

The paper deals with the analysis of the failures regarding one of the bars of a twin screw extruder for plastics and reinforced plastics. The extruder was equipped with an 50 kW electric motor and very soon showed failure problems, always on the same bar, that was substituted many times. The analysis of the material, tensile tests and fractographical observations of some broken bars helped to understand that failures were due to fatigue and to define some design improvements of the bar. In-service strain gauge measurements were executed to assess the actual load acting on the bars and the data were elaborated by using the spectral analysis approach and were used to assess the fatigue strength of the bars.