Density‐Dependent Impact Resilience and Auxeticity of Elastomeric Polyurea Foams

Abstract

This research investigates the dynamic response of a novel polyurea foam with different densities by separately submitting samples to single and multiple impacts at different energies ranging from 1.77 to 7.09 J. The impact and transmitted force‐time histories are acquired during the impact events. Deformation of the samples is also recorded using high‐speed photography and analyzed using digital image correlation (DIC) to characterize density‐dependent strain rate and Poisson's ratio. The analyses of the force‐time histories highlight the interrelationship between the incoming impact energy and force characteristics, including amplitude and durations. The experimental results reveal that polyurea foams can absorb nearly 50% of the incoming impact energy irrespective of their density. The dynamic impact efficacy of the foam persists even after sequential impact events are imparted on the same samples, with only a 20% drop in the load‐bearing capacity after seven consecutive impacts. Furthermore, as verified via electron microscopy observations, the higher‐density foam does not exhibit any permanent damage. This high‐density polyurea foam shows reversible auxetic transition at all impact energies considered herein. The outcomes of this research indicate the suitability of polyurea foams for cushioning and impact mitigation applications, especially in repeated biomechanical impact scenarios.

Tuning the Mechanical Behavior of Density-Graded Elastomeric Foam Structures via Interlayer Properties

“…Therefore, the reduction in the stiffness difference in impact loading leads to less intense property gradients across the interlayer, practically attributed to a lower likelihood of damage initiation from the interface. While beyond the scope of the present study, concepts involving the role of adhesive interlayer properties on the damage initiation and evolution in graded foams subjected to repeated impact conditions , would be an interesting topic for future research. In such cases, an optimal interface layer may be identified by taking into account the interplay between mechanical and energy dissipation behaviors as well as the long-term use of foam stacks, especially considering repeated low-rate loading (e.g., for use in a walking shoe midsole) or higher energy impact conditions (e.g., for use as helmet liners).…”

Quasi-Static Mechanical Response of Density-Graded Polyurea Elastomeric Foams

“…In recent years, polyurea foams emerged in the scientific literature as a suitable material candidate for biomechanical impact mitigation applications. ,− Such emphasis was motivated by the contemporary work of Reed et al. , and Ramirez et al, − reporting viable approaches to foam bulk polyurea using spontaneous foaming and heat-activated/controlled foaming methods, respectively. Polyurea is a fascinating class of polymers with several formulations that span the spectrum from linear to cross-linked polymers. − Polyurea, with a specific mixture of diamine and diisocyanate, found favor in the scientific and technological communities for its superior mechanical and thermal properties, including hygrothermal stability, large extensibility, , a broad range of operating temperature, , adhesive properties, − chemical, moisture, and abrasion resistance, and toughness based on its tailored segmental microstructure. − This polyurea formulation was also found to be mildly affected by extended exposure to ultraviolet radiation .…”

Damage protection in fruits: Comparative analysis of the functional morphology of the fruit peels of five Citrus species via quasi-static compression tests

“…Although there is a steady increase in new designs and developments of e.g. polymeric foams with corresponding properties (Koumlis and Lamberson 2019;Youssef et al, 2022), it is still rare to find a commercial, cost-effective, and easy-to-manufacture auxetic product suitable for large-scale fabrication. Nonetheless, material systems with very low or even negative lateral compression offer high potential for applications in impact protection and energy absorption in areas ranging from aerospace applications (Alderson and Alderson 2007) to packaging (Seidel et al, 2010;Li et al, 2019) to protective equipment (Allen et al, 2015;Speck et al, 2018).…”