Mechanical Properties Of Open-cell Foams Research Articles

Effect of slurry composition on the microstructure and mechanical properties of SS316L open-cell foam

This experimental study systematically examines the effect of slurry composition on the microstructure and mechanical properties of open-cell foams, by altering the binder concentration and powder loading of SS316L slurries used in the template replication foam fabrication. The slurry and foam morphologies were observed by Scanning Electron Microscopy (SEM), whereas the rheological properties of the slurry were obtained using a rotational viscometer and parallel plate rheometer. Foam strut densities were measured by a gas pycnometer, which subsequently allowed for the calculation of foam porosity. The mechanical behaviours of the foams were attained through compression test. Results show that increasing both binder and powder contents lead to an increase in slurry viscosity, foam bulk density, green strut density and mechanical strength. A process window for foam fabrication was also proposed based on macroscopic foam morphology, rheological and mechanical properties, and corrosion behaviour of the resulting SS316L foams. Based on the proposed process window, the binder concentration is suggested to be within 10 vol% and 14 vol% and powder loading within Φ = 0.75 and 0.80. This study demonstrates that the microstructure of foam produced by the template replication method can be well-controlled by optimising the composition of the slurry, which is able to attain a higher compression strength than that in the conventional range of Gibson and Ashby scaling law.

Evaluation of mechanical properties under quasi-static compression of open-cell foams of 6061-T6 Al alloy fabricated by pressurized salt infiltration casting method

We report the mechanical properties of open-cell foams of 6061-T6 Al alloy under quasi-static compression. The open-cell foams were fabricated by a proprietary process of pressurized salt infiltration casting of the molten Al alloy in inert atmosphere using preforms of leachable salt particles. The foam morphology was studied with optical and electron microscopes and X-ray computed tomography (CT), which confirmed the formation of interconnected open-cell structures. Quasi-static compression studies showed monotonic improvement in the strength and elastic properties of the foams with the increase in relative density (ρrel) and cell size. Effects of sample dimension on the mechanical properties of the foams were also studied in detail.

THE RANDOM POROUS STRUCTURE AND MECHANICAL RESPONSE OF LIGHTWEIGHT ALUMINUM FOAMS

ABSTRACTLightweight porous foams have been of particular interest in recent years, since they have a very unique set of properties which can be significantly different from their solid parent materials. These properties arise from their random porous structure which is generated through specialized processing techniques. Their unique structure gives these materials interesting properties which allow them to be used in diverse applications. In particular, highly porous Al foams have been used in aircraft components and sound insulation; however due to the difficulty in processing and the random nature of the foams, they are not well understood and thus have not yet been utilized to their full potential. The objective of this study was to integrate experiments and simulations to determine whether a relationship exists between the relative density (porous density/bulk density) and the mechanical properties of open-cell Al foams. Compression experiments were performed using an Instron Universal Testing Machine (IUTM) on ERG Duocel open-cell Al foams with 5.8% relative density, with compressive loads ranging from 0-6 MPa. Foam models were generated using a combination of an open source code, Voro++, and MATLAB. A Finite Element Method (FEM)-based software, COMSOL Multiphysics 4.3, was used to simulate the mechanical behavior of Al foam structures under compressive loads ranging from 0-2 MPa. From these simulated structures, the maximum von Mises stress, volumetric strain, and other properties were calculated. These simulation results were compared against data from compression experiments. CES EduPack software, a materials design program, was also used to estimate the mechanical properties of open-cell foams for values not available experimentally, and for comparison purposes. This program allowed for accurate prediction of the mechanical properties for a given percent density foam, and also provided a baseline for the Al foam samples tested via the IUTM method. Predicted results from CES EduPack indicate that a 5.8% relative density foam will have a Young’s Modulus of 0.02-0.92 GPa while its compressive strength will be 0.34-3.37 MPa. Overall results revealed a relationship between pores per inch and selected mechanical properties of Al foams. The methods developed in this study can be used to efficiently generate open-cell foam models, and to combine experiments and simulations to calculate structure-property relationships and predict yielding and failure, which may help in the pursuit of simulation-based design of metallic foams. This study can help to improve the current methods of characterizing foams and porous materials, and enhance knowledge about theirproperties for novel applications.

Analysis and simulation of high strain compression of anisotropic open-cell elastic foams

By elongating the regular Kelvin model in one direction and keeping unchanged in the other two directions, the anisotropic model was constructed. Then, the simplified periodic structural cell was obtained according to the periodicity and symmetry of the model in the whole space. Using the half-strut element and elastic deflection theory to analyze the mechanical behavior as were adopted in the previous studies, this paper obtained the theoretical expressions for the compressive stress and strain as well as the corresponding curves in the rise and transverse directions. In addition, the theoretical results were examined by the finite element simulation. Results indicated that the theoretical analysis was very close to the finite element simulation when the strain was not too high, which confirmed the validity of theoretical analysis. At the same time, the anisotropy was shown to have a significant effect on the mechanical properties of open-cell foams. As the anisotropy ratio increased, the compressive stress was improved in the rise direction but dropped in the transverse direction under the same strain.

Mechanical behavior of open-cell metallic foams with dual-size cellular structure

The mechanical properties of open-cell aluminum foams with dual-size cellular structure have been studied experimentally and numerically. Introducing secondary-size cells increases the stiffness and strength of open-cell aluminum foams. The effect of dual-size cellular structure optimization on the mechanical properties of open-cell foams is investigated using finite element analysis. Deformations of uniform-size and dual-size open-cell structures are compared and the mechanism whereby the dual-size cellular structure increases stiffness and strength is discussed.

Mechanical properties of open-cell foam synthetic thoracic vertebrae

This study presents comprehensive morphological and mechanical properties (static, dynamic) of open-cell rigid foams (Pacific Research Laboratories Inc. Vashon, WA) and a synthetic vertebral body derived from each of the foams. Synthetic vertebrae were comprised of a cylindrical open-cell foam core enclosed by a fiberglass resin cortex. The open-cell rigid foam was shown to have similar morphology and porosity as human vertebral cancellous bone, and exhibited a crush or fracture consolidation band typical of open-celled materials and cancellous bone. However, the foam material density was 40% lower than natural cancellous bone resulting in a lower compressive apparent strength and apparent modulus in comparison to human bone. During cyclic, mean compression fatigue tests, the synthetic vertebrae exhibited an initial apparent modulus, progressive modulus reduction, strain accumulation and S-N curve behaviour similar to human and animal vertebral cancellous bone. Synthetic open-cell foam vertebrae offer researchers an alternative to human vertebral bone for static and dynamic biomechanical experiments, including studies examining the effects of cement injection.

Strain-rate effect and micro-structural optimization of cellular metals

An overview is given of the researches at USTC on mechanical properties of cellular metals including aluminum honeycombs and foams. The strain-rate effect and micro-structural optimization of cellular metals are reported. The in-plane quasi-static and dynamic behavior of circular-cell aluminum alloy honeycombs is investigated experimentally. The influence of impact velocity on the localized deformation mode and the plateau stress are found. The strain-rate effect and the cell-size effect on the crushing stress of both open-cell and closed-cell aluminum foams are investigated by an improved Split Hopkinson Pressure Bar method. The results reveal that the structural heterogeneity and irregularity have influence on the strain-rate sensitivity of cellular metals. The effect of multi-size cell mix and silicate-rubber filler on the mechanical properties of open-cell aluminum foams is studied. The results show that it is a possible way to improve the mechanical properties of open-cell foams by mixing multi-size cells and by filling silicate-rubber.