# ОСНОВНЫЕ ПУБЛИКАЦИИ КОЛЛЕКТИВА ЛАБОРАТОРИИ

2020 год

## INTERFEROMETRY OF GAS-PHASE FLOWS DURING SELECTIVE LASER MELTING

Pavel A. Podrabinnik, Alexander E. Shtanko,Roman S. Khmyrov, Andrey D. Korotkov and Andrey V. Gusarov

Applied Sciences

2020

Gas-phase flows occurring in a plume in a processing zone during selective laser melting (SLM) can significantly affect the quality of the process. To further enhance SLM performance, the characteristics of the flows should be considered. In this article, the vapor-gas jet emerging from the laser processing zone was studied. It was visualized by interferometry to evaluate flow velocity, geometry and changes in refractory index depending on laser power. The velocity and pressure fields of the vapor jet and the entrained ambient gas were estimated by mathematical modeling. It was shown that the increase of laser power led to higher jet velocity and greater change in its refractory index. The latter also was used to evaluate the content of metal vapor in the plume and its influence on the absorption of laser radiation.

## MORPHOLOGY OF RANDOM PACKING OF MICRO-PARTICLES AND ITS EFFECT ON THE ABSORPTION OF LASER RADIATION DURING SELECTIVE MELTING OF POWDERS

Kovalev O.B., Gusarov A.V., Belyaev V.V.

International Journal of Engineering Science

2020

The results of analytical and numerical studies of the internal structure of random packed beds of metal micro-particles are presented. To construct packed beds from mono- and polydisperse solid spheres, an algorithm for their random generation based on the discrete element method is used. Analysis of the structure of the packed bed includes the determination of porosity, specific surface area and tortuosity of the pores when changing powder particle sizes. A theoretical conclusion of these structural parameters is proposed in the form of formulas. The data obtained characterize the percolation properties of the granular medium, which affects the propagation and absorption of laser radiation in the volumetric layer of particles. Analysis is made of the influence of the physical properties of particles on the limiting characteristics of the penetration of laser radiation into a packed powder layer; the effects of radiation absorption and scattering in the pore space of a granular medium are estimated. A comparative analysis of approximate analytical and numerical solutions with the data of known experiments is carried out.

## ENTRAINMENT FLOW OF A JET EMERGING INTO A HALF-SPACE WITH THE NO-SLIP BOUNDARY CONDITION

A.V. Gusarov

Physics of Fluids

2020

The current development of micro-scale technologies increases the interest in viscous flows with low and moderate Reynolds numbers. This work theoretically studies the entrainment flow of a viscous jet emerging from a plane wall into a half-space with the objective to understand the conditions where a similarity model can approximate a realistic flow. Two similarity models having analytic solutions are considered: the flow dominated by the momentum flux and the flow dominated by the mass flux. Algorithms are proposed to evaluate the parameters of the similarity models from the mass and momentum balances. Distributions of flow parameters and stresses on the wall are calculated for the similarity models. They are compared with the corresponding distributions obtained by computational fluid dynamics for a more realistic model with a finite size of the jet source and competitive influence of the mass and momentum fluxes. This comparison validates the mass-dominated similarity model at the jet Reynolds number Re ≤ 10 and the momentum-dominated similarity model at Re ≥ 30. The obtained results are applied to the problem of laser evaporation in selective laser melting. It is shown that the theoretically estimated flow velocity corresponds to the experimentally observed one. The theory explains the formation of the experimentally observed denuded zone and its widening by decreasing the ambient gas pressure.

## ANALYTIC SIMILARITY SOLUTIONS OF THE NAVIER-STOKES EQUATIONS FOR A JET IN A HALF SPACE WITH THE NO-SLIP BOUNDARY CONDITION

A.V. Gusarov

Physics of Fluids

2020

We consider steady axisymmetric no-swirl viscous flows in a half space driven by a concentrated force. A method of finding physically meaningful similarity solutions of the Navier–Stokes equations with finite values of mass and momentum fluxes satisfying the no-slip boundary condition is developed. A new one-parameter set of analytic similarity solutions that describes impinging or emerging jets depending on the value of the parameter is found. A unique emerging-jet solution can be found for an arbitrary value of the Reynolds number. The accomplished analysis of momentum balance has resulted in an algorithm to estimate the best parameter of the similarity solution corresponding to the given physical characteristics of the jet source.

S. Terekhina, T. Tarasova, S. Egorov, I. Skornyakov, L. Guillaumat, M.L. Hattali

International Journal of Fatigue – 2020. – Т. 140. – С. 105825.

2020

The present paper aims to study the effect of manufacturing build orientation on both flexural quasi-static and fatigue behaviours of semi-crystalline polyamide 6 obtained by Fused Filament Fabrication (FFF), by considering the porosity and surface roughness. The glass transition temperature, melting temperature, and crystallinity degree were measured complementary to understand better the process. Fatigue analysis is here fully described in visco-elastic domain of material. The results highlight that the XZ build orientation is better than the XY one and suggest that porosity plays an important role. The obtained results are also compared with conventional techniques given by the literature review.

Sergey N. Grigoriev , Alexander S. Metel , Tatiana V. Tarasova , Anastasia A. Filatova, , Sergey K. Sundukov, Marina A. Volosova , Anna A. Okunkova, , Yury A. Melnik and Pavel A. Podrabinnik

Metals. -2020.-Т. 10. -№11. –С. 1540

2020

The paper is devoted to researching various post-processing methods that affect surface quality, physical properties, and mechanical properties of laser additively manufactured steel parts. The samples made of two types of anticorrosion steels—20kH13 (DIN 1.4021, X20Cr13, AISI 420) and 12kH18N9T (DIN 1.4541, X10CrNiTi18-10, AISI 321) steels—of martensitic and austenitic class were subjected to cavitation abrasive finishing and vibration tumbling. The roughness parameter Ra was reduced by 4.2 times for the 20kH13 (X20Cr13) sample by cavitation-abrasive finishing when the roughness parameter Ra for 12kH18N9T (X10CrNiTi18-10) sample was reduced by 2.8 times by vibratory tumbling. The factors of cavitation-abrasive finishing were quantitatively evaluated and mathematically supported. The samples after low tempering at 240 ◦C in air, at 680 ◦C in oil, and annealing at 760 ◦C in air were compared with cast samples after quenching at 1030 ◦C and tempering at 240 ◦C in air, 680 ◦C in oil. It was shown that the strength characteristics increased by ~15% for 20kH13 (X20Cr13) steel and ~20% for 12kH18N9T (X10CrNiTi18-10) steel than for traditionally heat-treated cast samples. The wear resistance of 20kH13 (X20Cr13) steel during abrasive wear correlated with measured hardness and decreased with an increase in tempering temperatures.

Terekhina S., Tarasova T., Egorov S., Guillaumat L., Hattali M. L.

The International Journal of Advanced Manufacturing Technology. – 2020. – Т. 111. – №. 1. – С. 93-107.

2020

The present paper describes the influence of both flexure quasi-static and fatigue loading on polyamide 12 (PA12) specimens fabricated by fused filament fabrication (FFF) and selective laser sintering (SLS) processes. Rectangular prisms (ISO 178:2010) of polymer were printed and tested under sinusoidal three-point bending fatigue loading at a frequency of 5 Hz. The differences in porosity, surface roughness, and degree of crystallinity are systematically measured and linked to the mechanical fatigue properties. Fatigue analysis in the visco-elastic domain of the polymer is fully described, from fatigue behavior to energy analysis. Here, we have shown that the fatigue properties of the FFF specimens are found to be higher than those of the SLS specimens, despite their lower degree of crystallinity (more than four times). The presence of pores and their growth during fatigue tests in the sintered PA12 specimen seem to be responsible. The fatigue loss factor analysis shows that at lower stress levels, PA12 material reveals its characteristic slight visco-elastic dissipation and heating as its lifetime was exhausted. Also, the obtained results of additively manufactured PA12 were compared with those of materials obtained by injection molding (IM) and extrusion techniques. The quasi-static flexural properties of PA12 obtained by FFF and SLS processes reveal better characteristics compared to IM and extruded specimens. However, the fatigue properties of the SLS-processed polymer are 24% and 40% less than those of materials obtained by IM and extrusion.

T. Tarasova and A. Filatova

2020 IOP Conf. Ser.: Mater. Sci. Eng. 709 033077

2020

Rational selective laser melting modes have been established for the manufacture of parts from domestic powder of steel grade 20H13. The properties of PR20H13 powder have been studied using the methods of granulometric analysis. The physical and mechanical properties of samples manufactured using rational modes of selective melting have been determined.

S.A. Egorov, T. V. Tarasova and S. M. Terekhina

IOP Conference Series Materials Science and Engineering 971:022006

2020

Additive manufacturing methods make it possible to create complex geometry parts, that cannot be produced by conventional methods. For manufacture of the products, composite polymeric materials can be used, both disperse-filled and filled with short or continuous fibers. Recently, more and more attention has been paid to reinforcing plastics with natural fibers. The study of the manufacturing process of a polymeric composite material filled with continuous natural fibers by the fused filament fabrication is presented