Protective liner for helmets and other articles
Embodiments herein employ a novel strategy based on a floating cellular liner that acts as a torsional suspension system to dampen rotational acceleration, such as head acceleration in a helmet, in response to an oblique impact. Specifically, the torsional suspension consists of an anisotropic cellular liner that is at least partially recessed inside a more rigid adjacent shell, relative to which the cellular liner can simultaneously undergo translation and in-plane compression.
1. A protective helmet, comprising:
an anisotropic cellular liner with a compressive stiffness that is lower in-plane than out-of-plane;
a rigid foam liner; and
a barrier layer between the anisotropic cellular liner and the rigid foam liner, wherein the barrier layer prevents penetration of the anisotropic cellular liner into the rigid foam liner,
wherein the anisotropic cellular liner is at least partially recessed in a recess formed in the rigid foam liner, wherein the anisotropic cellular liner and the recess are sized such that the anisotropic cellular liner is confined and retained in the recess of the rigid foam liner by a friction fit, and wherein the barrier layer facilitates relative sliding of the anisotropic cellular liner within the recess of the rigid foam liner and with respect to the rigid foam liner.
2. The protective helmet of claim 1 , wherein the anisotropic cellular liner is comprised of an open cell structure with auxetic properties to allow for spherical deformation of the anisotropic cellular liner without irregular distortion of the anisotropic cellular liner.
3. The protective helmet of claim 1 , wherein the anisotropic cellular liner has an in-plane compressive stiffness and an out-of-plane compressive stiffness, and the in-plane compressive stiffness is at least 50% lower than the out-of-plane compressive stiffness.
4. The protective helmet of claim 1 , wherein the barrier layer comprises a coating, film, or discrete sheet element, and wherein the barrier layer is present only in the recess between the anisotropic cellular liner and the rigid foam liner.
5. The protective helmet of claim 1 , wherein the barrier layer comprises a polymer film.
6. The protective helmet of claim 1 , wherein the rigid foam liner is made of expanded foam.
7. The protective helmet of claim 1 , wherein the rigid foam liner has an inward facing surface and an outward facing surface, and the recess is recessed into the inward facing surface or the outward facing surface of the rigid foam liner.
8. The protective helmet of claim 1 , wherein shear-loading in response to an oblique impact to the protective helmet is at least partially absorbed by in-plane compression of a portion of the anisotropic cellular liner, caused by tangential translation of a portion of the anisotropic cellular liner within the recess of the rigid foam liner.
9. The protective helmet of claim 1 , wherein the rigid foam liner has an inward facing surface and an outward facing surface, and the anisotropic cellular liner is a unitary structure that covers at least 50% of the inward facing surface or outward facing surface of the adjacent liner made of rigid foam.