Deformation Mechanics of a Non-Linear Hyper-Viscoelastic Porous Material, Part II: Porous Material Micro-Scale Model

Abstract

Foam materials are widely used for energy absorbing applications, and are often addressed in a modeling environment at a macroscopic or continuum level by measuring the mechanical properties, which may be size dependent, and implementing the properties in a continuum-level constitutive model. However, foams are known to exhibit a characteristically low wave speed and an understanding of the deformation mechanics of foams at the micro-scale and dependence on morphology are essential to understand the performance of foam material in impact scenarios. In this study, experimental testing and finite element modeling were used to investigate a viscoelastic polychloroprene closed-cell foam at the cell level, subject to large deformation and high deformation rates. A numerical model was created with solid hexahedral elements and a repeated tetrakaidecahedron cell structure using measured foam cell size and wall thickness, and mechanical properties measured from non-porous polychloroprene. The finite element model predictions were evaluated using experimental compression tests on the foam material at high deformation rates. The enclosed nitrogen in the closed cell foam was modeled using an Arbitrary Lagrange-Eulerian method so that this contribution could be included or removed, and demonstrated the significant effect of the enclosed gas on the mechanical response of the foam. The foam cell dimensions were varied to investigate morphological factors including cell size, cell aspect ratio and cell wall thickness.Increasing wall thickness, decreasing cell size and decreasing the cell aspect ratio resulted in increased material stiffness, with wall thickness having the most significant effect. Investigation of the wave transmission speed demonstrated a low value compared to the constituent materials, which was explained by the path of the stress wave through the foam structure and wave reflections within the cells, attenuating the stress wave. The consequence of this low wave speed was non-uniform deformation of the foam sample demonstrating that the measured mechanical properties of porous foams depend on the sample thickness, an important consideration for foam material testing and characterization.

Development of Ultralight Hybrid Pneumatic Artificial Muscle for Large Contraction and High Payload

“…On the other hand, the hysteresis was extremely large. Several studies focused on foam response to different strain, porosity, and temperature [34][35][36]. In our case, the maximum stress and strain are key parameters for designing the actuator.…”

Polymeric Hopkinson Bar-Confinement Chamber Apparatus to Evaluate Fluid Cavitation

“…The strain gauge signal was amplified (2210B Signal Conditioning Amplifier, Vishay) and data was recorded at a frequency of 2 MHz using a high-speed data acquisition system (BNC-2110, National Instruments). This specific instrumentation has been used in several material studies with this apparatus [69,70]. A biaxial HB-4 apparatus (top) assembly indicating supports, pneumatic system (gas-gun), and chamber mount; and schematic (bottom) indicating steel sphere striker, acrylic incident bar, acrylic confinement chamber, and locations of instrumentation strain gauge (WA-09-120WR-120, Micro-Measurements) was mounted on the chamber to measure the longitudinal and circumferential strains in the chamber during the test, using the same amplifier and data acquisition system noted above.…”

Celebrating 75 Years of the Society for Experimental Mechanics and the Study of Dynamic Behavior of Materials

“…The R. E. Peterson Award is named in his honor, and since 2017 has been the annual SEM best paper award for the Journal of Dynamic Behavior of Materials (JDBM). The R. E. Peterson Award from the inaugural 2015 volume of JDBM was awarded to Christopher Salisbury, Duane Cronin, and Fue-Sang Lien at the 2017 SEM Conference for their work on Deformation Mechanics of a Non-linear Hyper-viscoelastic Porous Material, Parts I&II [80,81].…”