Fracture Toughness of Hollow Glass Microsphere-Filled Iron Matrix Syntactic Foams.

Dirk Lehmhus,Jörg Weise,Attila Szlancsik,Imre Norbert Orbulov

doi:10.3390/ma13112566

Abstract

In this study, iron-based metal matrix syntactic foam (MMSF) containing hollow glass microspheres as filler was investigated with respect to notch sensitivity aspects. The MMSF was produced by means of metal powder injection molding. The notch sensitivity was studied via (i) elastic-plastic fracture mechanics measurements (determination of R-curves based on three-point bending tests) and (ii) Charpy impact tests. In both cases, the samples were machined with two different (U- and V-shaped) notch geometries. The critical J-integral value was determined for both notch types, which resulted in lower fracture toughness values in the case of the V-shaped notches and thus notch sensitivity of the material. This finding can be connected to the characteristics of the deformation zone and the associated stress concentration at the tip of the machined notches. The results were confirmed by Charpy impact tests showing ~30% higher impact energy in the case of the U-shaped notch. The failure modes were investigated by means of scanning electron microscopy. In contrast to the bulk material, the MMSF showed brittle fracture behavior.

Highlights

In the broader spectrum of metallic foams as described, e.g., by Lehmhus et al, syntactic foams occupy positions between purely stochastic foams and designed structures [1]
R-curve-based measurements were performed on the compact tension (CT) samples, and the results showed that the foams with a higher relative density were tougher and failure of the ligament was due to plastic collapse [13]
From the analyses and tests detailed presented above, the following conclusions can be drawn: The fracture toughness of iron-based metal matrix syntactic foam (MMSF) filled with hollow glass spheres was successfully measured for the first time;

Summary

Introduction

In the broader spectrum of metallic foams as described, e.g., by Lehmhus et al, syntactic foams occupy positions between purely stochastic foams and designed structures [1]. In these materials, the size, or at least the size distributions, of hollow fillers are deliberately set, while their relative position can range from arbitrary to ordered. The results include the observation that, as is the case for non-syntactic foams, the tensile strength tends to be (a) lower than the compressive strength and (b) more dependent on the porosity levels This implies that a strengthening role of the syntactic foams’ fillers is predominantly relevant under compressive loading conditions. This interpretation is supported by investigations of materials with a 316L matrix, for which high sintering temperatures

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Results

Conclusion