PSI - Issue 39

Viktor Morozov et al. / Procedia Structural Integrity 39 (2022) 432–440 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Morozov et al. (2020) presented results on the experimental investigation of loading deformation and fracture of PMMA and fluoroplastic under the short pulse loading caused by EEW. Analysis of propagation of the cylindric waves through the samples performed. Microanalysis of fractured surfaces allowed to compare failure paths and reveal key features of deformation processes in the samples. Research by Lukin and Morozov (2010) presents the numerical solution of the crack propagation equation introduced by Morozov (2010). These outcomes are based on a reach basis of experimental data on PMMA samples fracture with EEW achieved with two different techniques of cracks generation and crack velocity estimation. Experimental and simulation outcomes were also compared. For the present study we established following objectives based on a wide range performed by us experiments: • To reveal dependence of crack propagation velocity against amplitude of the applied loading pulse as well as against pulse duration • To reveal dependence of the boundary failure loading amplitude against pulse duration for the wide diapason of durations • To estimate time of relaxation to the stationary propagation mode for cracks of various range 2. Experiments and samples Our experimental studies performed on the high voltage generator granting in “low-voltage” (or “traditional”) configuration voltages in the range of 10..30 kV and in “high-voltage” configuration voltages in the range of 100..300 kV. The difference between these configurations is the following. In the “low-voltage” configuration the capacitor was discharged directly through the wire to be exploded. This caused a damped sine current with a period of ~7.5 µs through the circuit or aperiodic electric pulse. The “high-voltage” configuration, in contrast, was equipped with the forming line granting single electric pulses with a duration of ~100 ns. These pulses caused damped sine current with a period of ~1 µs through the circuit We utilized PMMA and fluoroplastic cylinders and PMMA lameles as testing subjects in our research. During experiments waveforms of electrical current and mechanical pulses were registered with a digital storage oscilloscope. Registration of the mechanical pulses was performed with developed by us wide-band piezo-probe made of lithium iodate ceramics placed on the outer surface of the cylinder sample or on the grain of lamele normal to the loading propagation direction. Loading of the cylinders was performed with two versions of the testing setup (see Fig. 1 and Fig. 2) and granted us a deformation rate in a range of 10 4 ..10 5 1/s utilizing both low- and high-voltage configurations.

Fig. 1. Low-voltage setup for experiments with cylinder samples: autotransformer (1), rectifier (2), charging resistor (3), capacitor (4), discharge switch (5), Rogovskii coli (current registration device) (6), exploding wire (7), sample (8), oscilloscope (9) and piezo probe (10).