Characterization of the Tensile Behavior of Expanded Polystyrene Foam as a Function of Density and Strain Rate

Abstract

Due to its high energy-absorbing efficiency, [1,2] foam materials are widely used for protection in crush applications. Even though such applications vary in environmental and loading conditions, when it comes to helmet liners, static and dynamic loads are expected during the life cycle of the product. Such loads can be experienced during storage conditions, accidental or impact loads. Despite the stochastic profile of such loads, each foam material is expected to retain its functionality in all environmental conditions to which it will be exposed. For that reason, a range of standards is created to describe the expected performance of these materials when integrated into protective headgear. Out of all the available choices, expanded polystyrene (EPS) is the most preferable of all, for its thermal and moisture resistance, light weight, durability, availability, and cost. This creates a big range of safety applications where it is crucial to be able to accurately predict the behavior of EPS. As reported by Lorna, [3] foams, another term for a cellular solid, are made up of an interconnected network of solid shells which form the edges and faces of cells. These cells can be either closed-or opencelled and are spread as a 3D polyhedral in space. EPS is a rigid and tough, recyclable, closed-cell cellular material. It can undergo a large compressive deformation and absorb energy even at high strain rates. Under compressive loads, energy is dissipated through cell bending, buckling, or fracture. Its large energy-absorbing properties are the result of the plateau that is observed in the characteristic compressive stress strain curve of the material. [4-6] When closed-cell EPS foam is subjected to compressive loading, the entrapped air within the cells is compressed and additional viscous force is generated. Those forces increase with the loading rate, which results in the increase of strain rate sensitivity. [5] 1.1. Constitutive Material Models Foams are multi-phase materials. The gas-phase that is present in foams adds an additional degree of freedom which makes modeling of foams more difficult. There are several models available for various types of foams (rigid, flexible) and loading, but the models are usually limited, which makes the formulation of all the relevant behaviors of the foam difficult. The Maxwell model is a viscoelastic model. [7] It consists of a spring and a damper in series, where elastic response is represented by the spring and the time-dependent response by the damper. The constitutive equation for this model is described by Equation (1)

Assessment of Compressive and Flexural Properties and Stacking Strength of Expanded Polystyrene Boxes: Experimental and Simulation Study

“…ASTM has provided another standard-ASTM D1623: Standard Test Method for Tensile and Tensile Adhesion Properties of Rigid Cellular Plastics [22]-which is supposed to be more appropriate for the material. Zouzias [23] performed lengthy experiments to characterize the tensile behavior of EPS foams of densities ranging from 60-120 kg/m 3 and verified that the tensile strength also rises with the increase of strain rates and density. Apart from fundamental mechanical properties investigation, Ellouze [24] carried out a heat treatment process on EPS foams and enhanced the hardness.…”

Mechanical properties of diamond lattice structures based on main parameters and strain rate

“…Thus, these materials should be modified to achieve an optimal behavior. For foams [40], the control of the density during foaming influences the mechanical properties; in the case of TTPMS structures, volume fraction control is critical.…”

Preparation and properties of expandable epoxy foam prepreg for sandwich composites prepared via thermal expansion molding process

“…Therefore, lightweight expandable foam is vital for the TEMP technology. The epoxy resin is one of the most commonly used matrix in composites 7,8 . Due to simultaneous curing and foaming reaction, epoxy foam with the same system will improve the poor interface mechanical properties of sandwich composites compared to other foam materials 9,10 .…”

“…The epoxy resin is one of the most commonly used matrix in composites. 7,8 Due to simultaneous curing and foaming reaction, epoxy foam with the same system will improve the poor interface mechanical properties of sandwich composites compared to other foam materials. 9,10 Therefore, the preparation and properties of thermal expansion epoxy foam provides essential support for preparing sandwich composites via the TEMP technology.…”