Defects-dictated tensile properties of selective laser melted Ti-6Al-4V

The generalized means are used as a simple but elegant mixture rule for providing a unified description of the physical properties of polyphase composites in terms of component properties, volume fractions, and microstructures This formula is named as the generalized mixture rule (GMR) Taking porous materials as a special class of two-phase composites in which pores are dispersed within a solid framework, the GMR yields a rigorous expression for the porosity dependence of the mechanical properties Although the GMR is purely mathematical in origin, its connection to the existing theories and its consistence with extensive experimental data suggests that it should have some physical validity as a hypothesis or at least a very handy tool for a general description of the mechanical properties of multiphase materials including porous solids

Porosity dependence of mechanical properties of solid materials

Deduced from empirical and theoretical work, a model is proposed for the rheology of bi- and polyphase rocks based on the rheology of the components, their volume fractions, and their geometrical distribution. The model is formulated for the common case where some minerals deform by crystall plasticity at steady state and others, stronger ones, deform in the vincinity of the brittle-ductile transition.

The rheology of polymineralic rocks — an approach

Analogies between the high-temperature deformation of polyphase rocks and the mechanical behavior of porous powder metal

In this study, the effects of internal pores on the tensile behavior of austenitic stainless steel 316L manufactured with laser powder bed fusion (L-PBF) additive manufacturing (AM) were investigated. Both fully-dense samples and samples with intentional internal pores of varying diameters were fabricated. For each sample with a pore, the internal pore was deliberately fabricated in the center of the cylindrical tensile sample during AM processing. By varying the diameter of the 180 μm-tall initial penny-shaped pores, from 150 to 4800 μm within 6 mm gauge diameter cylindrical samples, the impact of lack-of-fusion, commonly present in AM, as well as the impact of well-defined pores in general, on tensile mechanical properties was studied. To link the pore size and morphology to the mechanical properties, the sizes of the initial pores were evaluated using non-destructive Archimedes measurements, 2D X-ray radiography, 3D X-ray computed tomography, and destructive 2D optical microscopy. Samples with and without the single, penny-shaped pore were subjected to uniaxial tension to evaluate the defect size dependent mechanical properties. The intentional pore began to impact ultimate tensile strength when the pore diameter was 2400 μm, or 16% of the cross-sectional sample area. Elongation to failure was significantly affected when the pore diameter was 1800 μm or 9% of the cross-sectional sample area. This shows that 316L stainless steel manufactured by additive manufacturing is defect-tolerant under uniaxial tension loading.

Characterization of the Effects of Internal Pores on Tensile Properties of Additively Manufactured Austenitic Stainless Steel 316L

A theory that takes into account the stress-concentrating effect of the pores in porous materials is proposed. Upper and lower limits between which the strengths of porous materials must lie are predicted. A pore-sensitivity factor is defined and, assuming that this is proportional to the fractional porosity, an equation is derived which describes the variation in relative strength with porosity content and which empirically can take account of the matrix ductility. The equation is shown to agree well with published experimental data.

Effect of porosity content on the tensile strength of porous materials

Groups of specimens with nominally 4% and 12% porosity have been prepared from fine (−240 + 300), medium (−200 + 240), and coarse (−150 − 200) mesh sieve fractions of Sherritt-Gordon nickel powder by die compaction, preliminary sintering, re-pressing, and finally sintering at 1573K (1300°C). Irrespective of porosity content and the powder fraction from which they were prepared, all specimens exhibited a mixture of rounded and film-like porosity. The film-like porosity was more extensive in the more porous specimens, but in all specimens markedly influenced the fatigue behaviour. The development of persistent film-like porosity is attributed to the botryoidal form of the powder particles. The endurance limits of the less-porous specimens were almost identical, irrespective of the powder fractions from which they were prepared. However, the endurance limits of the more-porous specimens made from the coarse powder fraction were significantly lower than those made from the fine and medium powder fract...

R. Haynes

Papers

Effect of porosity content on the tensile strength of porous materials

Effect of porosity on the fatigue behaviour of sintered precipitated nickel powder