Experimental Characterization for Helmet Pads

Abstract

In this study, quasi-static compression and dynamic impact experiments were conducted on helmet pads. Various layers of the foam pad: comfort, stiff and bilayer were tested to characterize their material response. In the compression tests, a piston compressed foam samples at constant velocity. The samples were tested under confined and unconfined conditions. In the dynamic impact experiments, the foam samples were impacted by a rigid projectile. Both the time histories of the force applied to the foam samples and the sample displacement were recorded to calculate the engineering strain and stress in the foam samples. The material stiffness in the impact tests was found to be several times that of the quasi-static tests.

Collapsible fluid-filled fabric shock absorber with constant force

“…Traditional hydraulic shock absorbers are made out of telescoping rigid parts, and thus have a working stroke length of at most half of their total size. Given the inverse relationship between force level and usable stroke length, losing half of the usable stroke length necessitates a doubled force level, thus making existing hydraulic dampers inefficient for use in many space constrained applications (Lamb and Hoshizaki, 2009;Zhang et al, 2017). This paper builds off of the concept of variable area shock absorption (Fanton et al, 2020).…”

“…Solid materials, such as foams and honeycombs are used as compact and compressible energy absorbers for many space-constrained applications, such as personal protective gear (PPE). These solid materials can be designed such that they have a large plateau region in their force displacement curves (Lamb and Hoshizaki, 2009;Zhang et al, 2017); however, the force profiles of these materials only scale weakly with impact velocity (Nagy et al, 1974), thus making them only truly optimal for a narrow range of impact speeds. During compression, a foam or honeycomb will exert a linearly increasing force up to a certain plateau level, at which point the force remains relatively constant until densification around 60%-70% stroke length.…”

“…The presented shock absorber is useful in any spaceconstrained application that requires low force shock absorption, ranging from the automotive industry (Duym, 2000;Mousavi et al, 2017), personal protective gear (Zhang et al, 2017), and manufacturing. Of particular promise are applications in which existing rigid hydraulic shock absorbers are not feasible, for example, implemented within athletic helmets, or integrated within car seat headrests.…”