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

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.

Syntactic Iron Foams’ Properties Tailored by Means of Case Hardening via Carburizing or Carbonitriding

“…Concerning crack propagation, some similarities can be found in other investigations concerning high dynamic testing documented in the literature: impact energies measured in Charpy impact tests performed on U-and V-notched samples proved to be one order of magnitude higher for the former type of specimen, irrespective of the shape of the notch. Similar differences were observed in J integral values [43].…”

Cast Iron Parts Obtained in Ceramic Molds Produced by Binder Jetting 3D Printing—Morphological and Mechanical Characterization

“…Figures [8][9][10][11] show the diagrams of variation of the tensile strength, specific deformation, elongation at break and modulus of elasticity depending on the values of maximum forces applied to the 20 samples of gray cast iron with lamellar graphite type EN-GJL-250. and its breaking process resulted in the following characteristics: Maximum force = 22,103.12 (N); Specific deformation = 0.01245 (mm); Tensile strength = 275.34 (MPa); Elongation at break = 1.9 (%); Elasticity Modulus = 37,039.12 (MPa).…”

“…Figures [8][9][10][11] show the diagrams of variation of the tensile strength, specific deformation, elongation at break and modulus of elasticity depending on the values of maximum forces applied to the 20 samples of gray cast iron with lamellar graphite type EN-GJL-250. In the case of the tensile test for test samples made from cast iron with spheroidal graphite type EN-GJS-400-15, the resulting values are given in Table 2.…”

“…Furthermore, the austenitizing temperature has a significant influence on the microstructure and mechanical characteristics of the material [ 8 , 9 ]. Analyzing the fracture zones of the samples by SEM (scanning electron microscopy) provides important information to determine how mechanical characteristics, such as tensile, flexural, or compression are mainly influenced by the type of casting processes of samples [ 10 , 11 , 12 , 13 ].…”

Special Issue ‘Advanced and High Performance Metallic Foams’

“…Besides the conventional compressive tests, advanced materials testing methods such as fracture mechanics, are considered. Lehmhus et al [ 5 ] and Szlancsik et al [ 6 ] studied the fracture toughness of MMSFs containing hollow spheres as filler in different matrices (steel and aluminum) with respect to notch sensitivity. This was studied via (i) elastic-plastic fracture mechanics measurements (determination of R-curves based on three-point bending tests) and (ii) Charpy impact tests.…”