Development and characterization of a split Hopkinson pressure bar for testing high shock accelerometers

Abstract

Extreme environments pose significant challenges in the aerospace and defense fields. Prior to equipment deployment, dynamic testing is often conducted to identify potential failure points from high shock. Accelerometers are vital sensors for characterizing system response to transient inputs, such as impact and vibration, faced by atmospheric reentry vehicles or explosive protection equipment. However, accurate data collection is often inhibited by sensor damage or nonlinear response to dynamic inputs. A controlled experimental system capable of recreating extreme conditions is needed to assess sensor limitations and design options prior to full-scale structural testing. Conventionally built for high strain-rate material testing, a Split Hopkinson Pressure Bar uses colinear elastic bar impact to produce high energy, short-duration stress waves. Material samples are sandwiched between elastic bars and dynamic properties are derived from stress waves reflected by or transmitted through the sample. In this work, a modified Hopkinson Pressure Bar was developed to assess accelerometer response to high-energy, dynamic inputs. The modified system consists of a gas gun that propels a short steel striker into a longer steel incident bar, producing a nondispersive stress wave. A single-axis Endevco 7270 piezoresistive accelerometer is mounted on a fly-away structure aligned with the incident bar. The stress wave that reaches the accelerometer creates a shock impulse of similar magnitude and frequency as an explosive test. The Hopkinson Pressure Bar was characterized with a range of input configurations and produces acceleration pulses with amplitudes up to 100,000 g and durations of 0.2 ms. Strain signals were compared to accelerometer output in two mounting configurations over a range of shock levels. There was good agreement between strain-derived acceleration and peak accelerometer accelerations. Experimental system capabilities and limitations are presented alongside current challenges and directions for future research. The setup developed for this research increases sensor and material testing capabilities under extreme environmental conditions.