Finite element analysis to determine the role of porosity in dynamic localization and fragmentation: Application to porous microstructures obtained from additively manufactured materials

Abstract

In this paper, we have performed a microstructurally-informed finite element analysis on the effect of porosity on the formation of multiple necks and fragments in ductile thin rings subjected to dynamic expansion. For that purpose, we have characterized by X-ray tomography the porous microstructure of 4 different additively manufactured materials (aluminium alloy AlSi 10 Mg, stainless steel 316L, titanium alloy Ti 6 Al 4 V and Inconel 718L) with initial void volume fractions ranging from ≈ 0.0007% to ≈ 2%, and pore sizes varying between ≈ 6 µm and ≈ 110 µm. Three-dimensional analysis of the tomograms has revealed that the voids generally have nearly spherical shape and quite homogeneous spatial distribution in the bulk of the four materials tested. The pore size distributions quantified from the tomograms have been characterized using a Log-normal statistical function, which has been used in conjunction with a Force Biased Algorithm that replicates the experimentally observed random spatial distribution of the voids, to generate ring expansion finite element models in ABAQUS/Explicit (2016) which include actual porous microstructures representative of the materials tested. We have modeled the materials behavior using von Mises plasticity, and we have carried out finite element calculations for both elastic perfectly-plastic materials, and materials which show strain hardening, strain rate hardening and temperature softening effects. Moreover, we have assumed that fracture occurs when a critical value of effective plastic strain is reached. The finite element calculations have been performed for expansion velocities ranging from 50 m/s to 500 m/s. A key point of this investigation is that we have established individualized correlations between the main features of the porous microstructure (i.e. initial void volume fraction, average void size and maximum void size) and the number of necks and fragments formed in the calculations. In addition, we have brought out the effect of the porous microstrucure and inertia on the distributions of neck and fragment sizes. To the authors' knowledge, this is the first paper ever considering actual porous microstructures to investigate the role of material defects in multiple localization and dynamic fragmentation of ductile metallic materials.

Nanofiber-Textured Organic Semiconductor Films for Field-Effect Ammonia Sensors

“…understanding the adsorption and desorption processes of gases [17][18][19][20], which have never been reported for these porous OSC films [21,22].…”

“…5) The increased active sites originated from the nanofiber texture would not affect original active sites from the membrane surface. 6) both the flat and nanofibertextured films are uniform that homogenization method can be used [17][18][19].…”

The effect of voids shape on hypervelocity cylindrical cavity expansion and shock waves formation in transversely isotropic porous materials

“…Note also that the results presented in this paper are specific for the constitutive framework of Section 2 (which is based on specific evolution laws for the shape of the voids during deformation), in which the material porosity stands for the single damage parameter with no contribution of the voids size, so that the effect of microinertia -local acceleration fields that develop near the pores during dynamic compaction-on the mechanical response of the material is not accounted for (Czarnota et al, 2017(Czarnota et al, , 2020. This is a potential limitation of the self-similar cavity expansion model that shall be further assessed using finite element simulations including the actual porous microstructure of the material (see the recent work of Marvi-Mashhadi et al (2021)). Such calculations are part of a work in progress that will help to elucidate the specific role of voids size distribution on the structure of plastic shock waves in porous metallic materials.…”

Shear band formation in porous thin-walled tubes subjected to dynamic torsion

“…The novelty of the dynamic torsion calculations presented in this paper is that we have included explicitly resolved spherical voids in the finite element model to study the effect of porosity on shear band formation. For that purpose, we have followed the methodology developed by Marvi-Mashhadi et al (2021) and Vishnu et al (2022), importing into ABAQUS the representative porous microstructures of four additive manufactured metals: aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718 (referred to as Al3XY, SS5XY, Ti0.5XY and INC1Z, respectively). The main features of the porous microstructures investigated are reported in Table 2.…”

“…In this paper, we have performed 3D finite element calculations of thin-walled tubes subjected to dynamic twisting to investigate the effect of porous microstructure on the formation of shear localization bands under simple shear conditions. For that purpose, we have incorporated into the finite element model the porous microstructures of four different additive manufactured metals -aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718 -for which the void volume fraction varies from ≈ 0.001% to ≈ 2 %, and the voids size between ≈ 6 μm and ≈ 110 μm (Marvi-Mashhadi et al, 2021). For each microstructure, we have created up to 10 realizations varying the spatial location of the voids and the distribution of voids size.…”