Detecting damaging limits in plastics - by subjecting disc test pieces to increasing pressure cycles and analysing limiting sound emission values

摘要

The damaging limits produced in flat sheet test pieces of various geometrical sizes (partic. in sheets of reinforced/filled plastic materials) by cyclical loads from internal pressures are detected by sound emission analysis. In the process the pressure is increased continuously until a limiting sound emission value is first exceeded; depending upon that value the pressure is then increased in stages from cycle to cycle until the test piece bursts, eacy cycle including phases of release, holding and increase of the pressure. The rupture disc test piece (5) is mounted on the pressure chamber (1) which is fed with water (3) and has a pressure regulator (2). The applied pressure is measured by a sensor (7) and converted to a votlage which is fed to a regulator (8). Deflection in the test piece (5) is measured by another sensor (9); sound emission is measured by a transducer (10). The former is amplified (11) and the sound emission analysed (12); the two functions are fed to a recording evaluator (13). The voltage proportional to the sound emission is passed to the amplifier to the regulator and compared with nominal voltage. By the control circuit the applied pressure is maintained constant during the holding phase. The supply current is from the unit (15). After suitable time has passed the pressure is raised again (6) until the desired voltage is reached for the sound emission. ADVANTAGE - The limits are characterised by a definedLinitial state.