Behavior Of Open-cell Foams Research Articles

Macroscopic modeling of open cell foams

AbstractOpen cell foams are widely used in engineering which includes an application in areas, where vibration excitations can act on the structures. Therefore dynamical properties as eigenfrequencies and natural modes are of great interest. We will discuss the description of the dynamic behavior of open cell foams by stochastic macroscopic models. These are based on a computed tomography scan of the foam, which gives access to parameters and the power spectral density needed for the generation of the stochastic process. The simulation results shall be used to get an estimate of the natural frequencies.

A macroscopic model on the dynamic behaviour of open cell foams

AbstractOpen cell foams are widely used in engineering which includes an application in areas, where vibration excitations can act on the structures. Therefore dynamical properties as eigenfrequencies and natural modes are of great interest. Here a modelling approach of the dynamic behaviour of open cell foams by macroscopic stochastic models will be discussed. Based on a 3D computed tomography scan of the foam, statistic and spectral analysis has been carried out to determine the parameters of the stochastic model. Additionally a vibration measurement has been done to provide eigenfrequencies, frequency transfer functions and natural modes of the real foam, which can be compared with the simulation results of the macroscopic model.

Tomography-based analysis of apparent directional spectral emissivity of high-porosity nickel foams

The apparent radiative behaviors of open cell nickel foams and their dependency on textural features and intrinsic optical properties are numerically investigated in the limit of geometrical optics. Five realistic nickel foams with high porosity from 0.87 to 0.97 and pore density from 10 to 40 PPI were used as samples. First, the representations of foams and their microstructures were obtained by using computed tomography and scanning electron microscope techniques. Second, a Backward Monte Carlo method that employed the realistic representations and their intrinsic optical properties facilitated the computation of the apparent directional spectral emissivity. The apparent emissivity and its dependency on textural features and intrinsic optical properties were subsequently investigated based on a specially defined Representative Elementary Volume. It was noted that at pore scale, the non-homogenized apparent emissivity fields can vary according to the local compositions near to the foam surface (solid strut and void space) and the void pore behaves somewhat like a “black cavity” for thermal radiation. For open cell foams composed of low emittance nickel struts, high-porosity cell network may increase the intrinsic emissivity by a maximum of nearly 4 times. A predictive relationship was established that links the homogenized apparent emissivity to the open porosity and the intrinsic emissivity of solid struts. These findings will provide a deeper understanding of both the non-homogenized and homogenized radiative behaviors of open cell foams.

Mechanical Behaviour under Quasi-Static Loading of Open-Cell Foams of 6061-T6 Al Alloys Processed by Pressurized Salt Infiltration Technique

Here, we report the mechanical behaviour of open-cell foams of 6061-T6 Al-alloys under quasi-static loading. The foams were processed by pressurized salt infiltration technique with efficient control over pore size and distribution. Spherical salt beads of NaCl of required size distribution were used as preforms. The molten alloy was infiltrated into the preforms under an inert gas pressure of 2 bar followed by cooling and leaching of the salt pattern in a suitable aqueous medium. The pressurized infiltration process is convenient to overcome the capillary forces arising from the non-wetting conditions between salt beads and molten alloys and offers a versatile and economical route for the production of open-cell foams. The shape, size and distribution of the pores were studied with optical microscope and X-ray computed tomography (X-ray CT). The developed foam samples were cut into required dimensions following ASTM E9-09 standard and their mechanical properties were analyzed under quasi-static compressive loading.

3D Remeshing Simulation of Aluminum Foams Behavior under Static Load

The compression characteristics of open-cell aluminum foams were experimentally and numerically investigated. It is found that the mechanical parameters, such as collapse stress and absorbed energy, are dependent on the porosity of aluminum foams. Three macroscopic models were chose to predict the compression behavior of open-cell foams. During simulation of metal foam compression, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain due to these problems. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental deformation process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred from old to the new one using advanced algorithm.

Micromechanical approach for the behaviour of open cell foams

The objective of this paper is the prediction of the macroscopic behaviour of open-cell foams in elasticity and viscoelasticity as function of their microstructure by using a micromechanical approach. Open cellular materials are characterised by remarkable mechanical properties with light weight. Such materials are largely used in various applications mainly in energy absorption. Polyurethane foam is used as an application once its microstructure is majorly described by an open-cell foam. Finite Element computations are performed on a unit cell subjected to periodic boundary conditions. Then, a micromechanical model based on Cosserat homogenisation framework is performed to predict the macroscopic elasticity. The linear viscoelastic behaviour is deduced from elastic results by taking advantage of correspondence principle. Finally, the results are confronted to various models developed in literature.

NUMERICAL MODELING OF THE FRACTURE BEHAVIOR OF OPEN CELL FOAMS

The objective of this work is to numerically study the individual and mixed mode fracture behavior of open-cell foams. Three-dimensional tetrakaidecahedron model is adopted and finite element method is employed in analysis. The overall elastic properties of open-cell foams are numerically obtained. Then, modes I, II, III and mixed mode I–II fracture behavior of open-cell foams are numerically predicted respectively, in which both solid/hollow and square/circular strut cross-sections are considered. It is seen that the relationship between the overall critical stress intensity factor and the relative density of foam obeys power law for individual crack problems. Effects of the shape and the topology of strut cross-section are discussed in detail. For mixed mode I–II crack problem, the relationship between KI/KICand KII/KIICis obtained and the effect of the shape of strut cross-section is discussed.

Investigation of the fatigue behavior of open cell foams by a micromechanical 3-D model

This work is concerned with an analysis of fatigue damage accumulation and failure of open cell metal foams. For an efficient numerical analysis, a failure event based simulation procedure is proposed, which considers the failure of individual struts as particular discrete failure events governing the degradation of the foam microstructure during cyclic loading. In a simplifying approach the cyclic stress–strain-response between the discrete failure events is assumed to be independent of time. In conjunction with Miner's rule for the description of the fatigue damage accumulation within the individual struts a numerically efficient computational scheme is obtained, requiring the simulation of only a limited number of cycles. The microscopic results are transferred to the macroscopic level by means of a strain energy based homogenization procedure. In a number of parametric studies on the fatigue behavior of Kelvin foams and a comparison with experimental data, the proposed computational scheme proves to be both accurate and numerically efficient.

Creep/recovery behavior of open‐cell foams

AbstractStatic measurements have been used to predict the dynamic response of ldquo;unboundedrdquo; open‐cell noninked (dry) and inked foam materials. Creep, ec(t), and recovery, er(t), were determined in compression from static and dynamic modes. Force measurements, f(t), and strain decay, e(t), were used to determine the change in creep, δec(t). The change in creep represents the plastic strain, ep1(t=th), and is uniquely defined by the recovery function, er(t=th), where th is the hold time. Creep and recovery results of various classes of foam materials and nonfoam materials were found to fit a master curve of the form Fr(t) =exp[–k′r(th)t] = [er(t) ‐ e00( th)]/[e0 (t = 0) ‐ e00(th)] at a reduced time of k′r(th) t [k′r(th)] C0/(th)a (where Co depends on the material's “dry” or “wet” state), a is a function of the type of material, and em is the permanent set]. These empirical results are applicable to printing ink transfer and print quality. Other important factors of concern are diffusion processes within the polymer matrix and the nature of the polymer (e. g., chemical constitution, porosity, molecular weight, and solubility). © 1995 John Wiley & Sons, Inc.

Mechanical properties and behavior of open cell foams used as cushioning materials

AbstractIt is the purpose of the present publication to show that most of the phenomenological viscoelastic theories developed for bulk polymers can be readily adapted to plastic foams in order to evaluate their mechanical properties. In addition it will be demonstrated how the mechanical properties of open cell plastic foams can be predicted from a few simple compression and relaxation experiments.

Viscoelastic Behavior of Open Cell Foams

Abstract Open-cell foams show abnormally large mechanical damping due to the energy dissipated in forcing air in and out of the foam during a deformation cycle. This pneumatic damping has recently been treated theoretically and experimentally. The dependence upon the test-piece dimensions, the frequency of deformation and the viscosity of the fluid has been shown to be in good agreement with the theoretical predictions. The dominant property of the foam structure is its permeability to fluids. This has also been measured for a number of different foams and related to their structural features by means of a simple model. A review is given of these developments.