Mechanics of Microspheres Reinforced Hollow Microcells

Abstract

Emerging polymeric foams exhibiting unique microstructure of microspherical shells with reinforcing dense microspheres creates a new opportunity for impact-tolerant foam paddings in sport gears applications. This paper describes the static response of reinforced microcell consisting of an outer spherical shell and uniformly distributed microspheres while quantifying the stiffening effect. The distribution of the microspheres is illustrated using the Fourier series, allowing tuning of the reinforcing strategy. Expressions of the external and internal works are derived, whereas the Ritz energy method is adopted to calculate the deformations due to a compressive load distributed over a range of areas. Emphasis is given to the effect of the geometrical attributes of the microcell and the reinforcing microspheres on the resulting deformation response and stiffening effect. The framework is used to investigate the response of several case studies to elucidate the effects of relative radii ratio, reinforcement density, microcell wall thickness, and loading configurations on the stiffness. A new normalized strain energy parameter is introduced to simplify and accelerate the analysis while providing insights on the underpinnings of the observed buckling response. The results strongly suggest the viability of the newly discovered foam microstructure in managing static loads while providing an opportunity to strategically tune the mechanical response using the analytical framework presented herein.

Density‐Dependent Impact Resilience and Auxeticity of Elastomeric Polyurea Foams

“…This group also characterized their polyurea foam variation under quasistatic and dynamic loading while comparing the performance to off-the-shelf foam, demonstrating its mechanical superiority. [5,[26][27][28][29]35] A hallmark character of the polyurea foam produced by Reed et al is the self-reinforcing of the cell walls with polyurea microspheres that self-nucleated during the mixing process. [26,27] Do et al comprehensively studied the microstructure of polyurea foams, [26,27,36,37] demonstrating the mechanisms leading to the nucleation of polyurea microspheres (i.e., precipitation polymerization) and their effect on the overall performance of the foam.…”

“…Thereafter, Youssef et al analytically modeled the effect of the microspheres on the mechanical performance of the unit cell, evidencing the mechanistic contributions of the microspheres on the microcellular structure of polyurea foams. [35] Polyurea foams emerged as a suitable material candidate for impact mitigation application. For example, our groups recently published a series of articles delineating the benefit of density gradation on the biomechanical performance of polyurea foams for orthotic shodding applications.…”

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

“…The present study examines the role of interface adhesive properties on the mechanical response of bilayer density-graded polyurea foam structures. In recent years, polyurea foam has attracted a good amount of interest due to its hierarchical cellular network and semiclosed cellular structure in impact mitigation applications. ,, Polyurea shows an extended plateau area in stress–strain response. , The mechanical characterization of polyurea foams demonstrates a superior characteristic under both quasi-static and dynamic loading conditions. ,, The outstanding mechanical performance of polyurea foam under different loading conditions distinguishes it from other elastomeric cellular solids. , …”

“…9, 32 The mechanical characterization of polyurea foams demonstrates a superior characteristic under both quasi-static and dynamic loading conditions. 9, 32,33 The outstanding mechanical performance of polyurea foam under different loading conditions distinguishes it from other elastomeric cellular solids. 31,34 In this work, two different densities of cross-linked, thermoset semiclosed cell polyurea foams served as the main components of the bilayered functionally graded foam structures.…”

“…9 , 32 The mechanical characterization of polyurea foams demonstrates a superior characteristic under both quasi-static and dynamic loading conditions. 9 , 32 , 33 The outstanding mechanical performance of polyurea foam under different loading conditions distinguishes it from other elastomeric cellular solids. 31 , 34 …”