Correlation Modeling between Morphology and Compression Behavior of Closed-Cell Al Foams Based on X-ray Computed Tomography Observations

Girolamo Costanza,Andrea Sili,Fabio Giudice,Maria Elisa Tata

doi:10.3390/met11091370

Abstract

In the last decades, great attention has been focused on the characterization of cellular foams, because of their morphological peculiarities that allow for obtaining effective combinations of structural properties. A predictive analytical model for the compressive behavior of closed-cell Al foams, based on the correlation between the morphology of the cellular structure and its mechanical response, was developed. The cells’ morphology of cylindrical specimens was investigated at different steps of compression by X-ray computed tomography, in order to detect the collapse evolution. The structure, typically inhomogeneous at local level, was represented by developing a global virtual model consisting of homogeneous cells ordered in space, that was fitted on the experimentally detected structure at each deformation step. As a result, the main parameters characterizing the two-dimensional cells morphology (equivalent diameter, circularity), processed by the model, allowed to simulate the whole compression stress–strain curve by enveloping those obtained for each step. The model, fitted on the previous foam, was validated by comparing the simulated stress–strain curve and the corresponding experimental one, detected for similar foams obtained by different powder compositions. The effectiveness in terms of an accurate prediction of the compression response up to the final densification regime has been confirmed.

Highlights

Due to their cellular microstructure, metal foams have attracted considerable interest in several industrial applications for their unique morphological characteristics, which allow for joining in a single material an effective combination of structural properties, and various functional properties [1]
The compressive properties of cellular materials, which can be expressed by some key parameters of the stress–strain curve, such as the elastic modulus, plateau stress, and final deformation values, are important for the mechanical design of Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
The second observation concerns the plateau regime, and in particular what was already highlighted when the typical compressive stress–strain curve for closed-cell foams was introduced (Figure 3, Section 3.1): the complex behavior in the plastic collapse regime is characterized by unstable σpl stress, which tends to rise with increasing strain. This tendency makes it necessary to fit the correlation model between morphology and mechanical behavior according to several compression steps, as the morphological analysis limited to just one compression state, such as the initial state at

Summary

Introduction

Due to their cellular microstructure, metal foams have attracted considerable interest in several industrial applications for their unique morphological characteristics, which allow for joining in a single material an effective combination of structural properties (low density, high capability to absorb energy during deformation), and various functional properties [1]. The field of possible applications has been further expanded by additive manufacturing technologies, which have revealed a marked capability in fabricating structures characterized by almost all types of cell shapes [2]. Uniaxial stress–strain behavior has been investigated extensively [3,4,5], taking strain rate sensitivity into consideration [6,7], and exploiting the advantages of new manufacturing technologies in cellular structures optimization, in order to obtain greater mechanical efficiency without increasing the relative density [8].

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Discussion

Conclusion