Piezoelectric Sensor Frequency Response Calibration for Folding Boxboard Converting
Piezoelectric sensor frequency response calibration prevents amplitude distortion during high speed creasing by matching amplifier cutoff to rule strike transients.
Hopkinson Pressure Bar
Dynamic Impact
High strain rate testing systems measure the mechanical response of packaging materials subjected to rapid impact or compression. Using a hopkinson pressure bar, researchers can subject paper, paperboard, and cushioning foam to forces mimicking those of a severe drop or shipping accident. This apparatus employs elastic waves generated by a striker bar to compress the test specimen between two long metal or polymeric bars.
It determines the dynamic yield strength and energy absorption capacity of the packaging material under extreme conditions.
Stress Measurement
Designers of protective packaging rely on accurate stress-strain data to select the optimal materials for cushioning fragile electronics or medical devices during transport. During a typical test on a hopkinson pressure bar, a gas gun launches a striker bar to impact the incident bar, generating a compressive stress pulse. This pulse travels through the bar to the specimen, where a portion is reflected and a portion is transmitted through to the transmitter bar.
Strain gauges mounted on both bars record these pulses, and the resulting electrical signals are converted into stress, strain, and strain-rate curves for the material. Analyzing these dynamic curves allows packaging engineers to optimize the structural design of corrugated boxes and foam inserts to prevent damage from drop impacts. This high-speed testing provides insights into the failure mechanisms of paperboard during rapid folding and forming operations.
Material Constraint
Geometric and impedance matching requirements limit the types of materials that can be tested with this apparatus. Soft papers and low-density foams require bars made of low-impedance materials, such as acrylic or magnesium, to ensure that the transmitted wave is strong enough to be detected. If the material is too soft or the specimen is incorrectly sized, the stress wave will disperse, resulting in inaccurate measurement data.