Frequency domain analyses of low-velocity impact loading of elastomeric foams

Abstract

Frequency analyses can reveal spectral features otherwise concealed within the time domain data. Such analyses are imperative to gain more insights into the undergoing dynamics in structures and materials, especially those with strong time dependence, such as elastomeric foams. This study aims to extend the applicability to data analysis from low-velocity impact scenarios by transforming into the frequency-domain, concurrently reporting crucial attributes of the dynamic loading and materials properties. Elastomeric polyurea foams with different densities were impacted at four different energies, ranging from 1.71 J to 7.09 J, to simulate low-velocity impact scenarios relevant to dynamic loading at different strain rates. In each impact test, a flattop drop mass was released from a preset height to control the impact velocity and energy while recording the impact and transmitted forces using impactor-mounted and base-mounted force sensors. The time-domain data of the primary impact was transformed into the frequency-domain using fast Fourier analysis. In the transformed domain, impact scenario characteristics, including acceleration and strain rate, and viscoelastic properties, i.e., storage and loss moduli, were extracted and benchmarked to time domain results. The impact characteristics agreed with previous reports based on time domain analysis while revealing the frequency-dependence of the acceleration and strain rate on the foam density and impact energy. The extracted viscoelastic properties were also in reasonable agreement with previously reported properties while consistent with linear viscoelastic principles. The robustness of the demonstrated method unlocks the potential for more in-depth data analysis from other dynamic mechanical experimental setups, including high-velocity impact and shock loading.