54.2.3 High Strain Rate Loading High strain rate tensile tests were carried out using a tensile SHPB apparatus, schematic of which is shown in Fig. 54.3. The incident bar, transmitter bar and the striker were made of Maraging steel (VascoMax 300). A compressed air gun was used to accelerate a 350 mm long striker tube towards the pulse inverter shown in Fig. 54.3. A finite length compressive loading pulse is generated in the pulse inverter by this axial impact. This strain pulse reflects from the inverter’s free end as a tensile pulse and propagates along the incident bar towards the specimen. When the tensile stress pulse reaches the specimen, part of it gets transmitted through the specimen into the transmitter bar and the remaining pulse is reflected back into the incident bar due to impedance mismatch. A pair of strain gages, each placed on the incident and transmitter bars was used to record the incident, reflected and transmitted strain signals using a set of Ectron 563H amplifiers and a data Acquisition system (NI PCI-6115) at a sampling rate of 1 MHz. DIC technique was used to measure the specimen strain. Fig. 54.2 Photograph of specimen grips used in SHPB tests Oscilloscope Channel 1 Input Camera TTL Trig In Data Acquisition Camera TTL Trig Out SG Amp Strain gage Strain gages Pulse inverter Transmitter bar Incident bar Specimen Striker tube Trig out Flash lamp Camera v Strain gage for triggering camera Control Laptop Fig. 54.3 Schematic diagram of the tensile split Hopkinson pressure bar 54 High Strain Rate Tensile Behavior of Fiber Metal Laminates 459
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