The advent of Material Extrusion (MEX) additive manufacturing for metallic feedstocks presents an opportunity for the cost-effective production of complex austenitic stainless-steel components. However, the widespread adoption of this technology is currently limited by challenges related to porosity, anisotropic shrinkage, and suboptimal interlayer bonding, particularly when utilizing standard parameters derived from polymer processing. This paper presents results of studies focused on the influence of critical printing parameters like specifically nozzle diameter, extrusion temperature, and deposition strategy on the mechanical and microstructural properties of BASF Ultrafuse 316L stainless steel. The study employs a rigorous two-stage experimental design. Stage 1 characterises the limitations of standard processing parameters (0.4 mm nozzle), revealing high porosity and insufficient tensile strength (MPa). Stage 2 implements an optimised strategy utilizing a 0.6 mm nozzle and elevated printing temperatures (250 °C), resulting in an enhancement of mechanical performance, with ultimate tensile strength rising to 483 MPa and elongation at break exceeding 50

This paper presents experimental and numerical results of the mechanical response of body-centered cubic (BCC) lattice structures manufactured with the fused filament fabrication (FFF) method using polyethylene terephthalate glycol (PETG) material. The BCC structures were subjected to uniaxial compression tests using a universal strength machine with three different values of deformation velocities. Moreover, dog-bone specimens were manufactured in three orientations to identify the PETG mechanical properties, which were supplemented with the literature data of PETG tested under compression. Then, the mechanical properties were correlated in the LS-Dyna code using a visco-plastic material model, which was used to numerically reproduce the experimental uniaxial tensile test conditions. The compression tests of BCC were simulated, and the results of experiments and numerical simulations were compared with satisfactory agreement. It was demonstrated that the properties of the 3D printed PETG varied, depending on both the printing direction and the type of applied load condition (compression/tension). Furthermore, the results also show that for the strut-based lattice structures manufactured with the FFF method and PETG material, it is mandatory to consider the above remark while simulating this type of mechanical behavior in a structure. Additionally, the influence of element type and cross section of the struts was also analyzed in this work. Results presented in the paper confirmed that the BCC lattice structures were effective in terms of energy absorption capacity, and they demonstrated long-range plateau deformation force plots.

This study aims to present the results of experimental investigations into the energy absorption characteristics of regular cellular structures with auxetic properties, additively manufactured using the Selective Laser Melting (SLM) technique from Maraging M300 steel. The experimental approach included quasistatic compression tests and high-strain-rate dynamic tests conducted using a drop-weight impact testing apparatus. Additionally, tensile test specimens were fabricated to characterise the mechanical properties of the additively manufactured M300 steel. The experimental results indicate that the proposed cellular topologies exhibit pronounced auxetic behaviour and a high capacity for mechanical energy absorption. These findings contribute to the broader understanding of auxetic structures and their potential applications in energy dissipation and impact-resistant materials.

This paper presents the process of manufacturing mechanical joint components using additive manufacturing (AM) techniques such as Material Extrusion (Fused Deposition Modelling (FDM)), Material Jetting (PolyJet), and Vat Photopolymerization (VAT)/Stereolithography (SLA). Using the PolyJet technique and a photopolymer resin, spline and threaded joint components were produced. For comparative analysis, the threaded joint was also fabricated using FDM and SLA techniques. PLA material was used for the FDM technique, while photopolymer resin was utilized for the SLA process. The components produced underwent a surface analysis to evaluate the accuracy of the dimensions in relation to the nominal dimensions. For the spline connection components, the dimensional deviations recorded by a 3D scanner ranged from −0.11 to +0.18 mm for the shaft and up to 0.24 mm for the sleeve. Measurements of screw and nut diameters showed the highest accuracy for screws produced using the PolyJet technique, while the nuts exhibited the best accuracy when fabricated with the SLA method. The profile of the screw threads using a contour gauge revealed the most accurate thread profile on the screw manufactured with the PolyJet technique.

The aim of this study is to determine the mechanical behavior of 2D honeycomb cellular structures with deformation initiators subject to quasi-static compression testing. Two different loading directions were studied: in-plane (IP) and out-of-plane (OP). The deformation initiators sought to stabilize the mechanical response by decreasing the initial peak force in the case of OP loading. The samples for testing were made using stainless steel 316L that was 3D-printed using material extrusion (MEX). The method enables fabrication of structures with high mechanical strength and ductility. The findings of the quasi-static compression testing showed that the additional deformation initiators were able to significantly reduce the orthotropy in the mechanical response of honeycomb cellular structures.

Purpose:The paper describes the design concept and findings from technological and initial clinical trials conducted to develop a helmet for non-invasive oxygen therapy using positive pressure, known as hCPAP (Helmet Continuous Positive Airway Pressure).Methods:The study utilized PET-G filament, a recommended material for medical applications, along with the FFF 3D printing technique. Additional technological investigations were performed for the production of fitting components. The authors proposed a parameter identification method for 3D printing, which reduced the time and cost of the study while ensuring high mechanical strength and quality of the manufactured elements.Results:The proposed 3D printing technique facilitated the rapid development of an ad hoc hCPAP device, which was utilized in preclinical testing and treatment of Covid-19 patients, and yielded positive results. Based on the promising outcomes of the preliminary tests, further development of the hCPAP device's current version was pursued.Conclusion:The proposed approach offered a crucial benefit by significantly reducing the time and costs involved in developing customized solutions to aid in the fight against the Covid-19 pandemic.

Abstract Elastomers are widely used in many industries. Their use requires thorough knowledge of their strength and stiffness parameters over a wide temperature range. However, determination of the parameters of such materials is still a challenge. Therefore, the paper presents research methodology allowing determination of the properties of rubber-like materials in a wide range of stretch and temperatures (from +50°C to −25°C) by using the example of styrene-butadiene rubber (SBR) and natural rubber (NR) elastomers. Additionally, two blends, chloroprene rubber/nitrile-butadiene rubber (CR/NBR) and NR/SBR blends, were also considered. Based on physical premises, a polynomial and Arruda–Boyce hyperelastic constitutive models parameters were determined using two different methods, namely curve-fitting and the successive response surface method.

Hyperelastic materials are widely used in many industries. Their use requires thorough knowledge of their strength parameters over a wide temperature range. However, determination of the parameters of hyperelastic materials is still a challenge. Therefore, the paper presents research methodology allowing determination of the properties of hyperelastic materials in a wide range of stretch and temperatures (from +50 degrees C to -25 degrees C) on the example of NBR (nitrile butadiene rubber) and CR (chloroprene rubber) elastomers. On the basis of physical premises, a hyperelastic constitutive model was also modified through introducing an explicit dependence of strain energy on temperature, allowing an accurate reflection of the properties of the tested materials. The material parameters of the adopted strain energy functions for the NBR and CR were determined with R2 not less than 0.999.

An analysis of the main recombination modes in nitrides, based on new method of data treatment is proposed for the determination of the carrier recombination processes in optically excited matter measured by time-resolved photoluminescence (PL). The analysis includes basic recombination modes: nonradiative Shockley-Read-Hall (SRH), radiative and Auger recombination in relation to mono-molecular, bi-molecular, and tri-molecular processes of optical relaxation. The method is based on the introduction of instantaneous PL decay rate r(PL) plotted as a function of the PL intensity or of the time. Such an approach provides deep insight into the time evolution of the recombination of the optically excited semiconductor systems and can be applied to the time evolution of a variety of optically excited systems. The demonstration of its strength is given by the application to III-nitride based systems, including nitride highly doped and semi-insulating thick layers, polar and non-polar multi-quantum wells (MQWs). At low temperatures (5 K), the mono- and bi-molecular processes determine the carrier relaxation, and the tri-molecular Auger recombination contribution is negligible. At room temperature the data indicate an important contribution of Auger processes. It is also shown that asymptotic (low excitation), one-exponential recombination rate has different character depending on the presence of the electric fields across the structure. (C) 2020 Elsevier B.V. All rights reserved.

The main aim of this article is the analysis of the deformation process of regular cell structures under quasi-static load conditions. The methodology used in the presented investigations included a manufacturability study, strength tests of the base material as well as experimental and numerical compression tests of developed regular cellular structures. A regular honeycomb and four variants with gradually changing topologies of different relative density values have been successfully designed and produced in the TPU-Polyflex flexible thermoplastic polyurethane material using the Fused Filament Fabrication (FFF) 3D printing technique. Based on the results of performed technological studies, the most productive and accurate 3D printing parameters for the thermoplastic polyurethane filament were defined. It has been found that the 3D printed Polyflex material is characterised by a very high flexibility (elongation up to 380%) and a non-linear stress-strain relationship. A detailed analysis of the compression process of the structure specimens revealed that buckling and bending were the main mechanisms responsible for the deformation of developed structures. The Finite Element (FE) method and Ls Dyna software were used to conduct computer simulations reflecting the mechanical response of the structural specimens subjected to a quasi-static compression load. The hyperelastic properties of the TPU material were described with the Simplified Rubber Material (SRM) constitutive model. The proposed FE models, as well as assumed initial boundary conditions, were successfully validated. The results obtained from computer simulations agreed well with the data from the experimental compression tests. A linear relationship was found between the relative density and the maximum strain energy value.

Laser Engineered Net Shaping (LENSTM) is currently a promising and developing technique. It allows for shortening the time between the design stage and the manufacturing process. LENS is an alternative to classic metal manufacturing methods, such as casting and plastic working. Moreover, it enables the production of finished spatial structures using different types of metallic powders as starting materials. Using this technology, thin-walled honeycomb structures with four different cell sizes were obtained. The technological parameters of the manufacturing process were selected experimentally, and the initial powder was a spherical Ti6Al4V powder with a particle size of 45–105 µm. The dimensions of the specimens were approximately 40 × 40 × 10 mm, and the wall thickness was approximately 0.7 mm. The geometrical quality and the surface roughness of the manufactured structures were investigated. Due to the high cooling rates occurring during the LENS process, the microstructure for this alloy consists only of the martensitic α’ phase. In order to increase the mechanical parameters, it was necessary to apply post processing heat treatment leading to the creation of a two-phase α + β structure. The main aim of this investigation was to study the energy absorption of additively manufactured regular cellular structures with a honeycomb topology under static and dynamic loading conditions.

The horizontal excitation energy transport in the range of tens of micrometers was measured in high quality homoepitaxial InGaN quantum wells (QWs) with the use of time and space resolved micro-photoluminescence as a function of (i) applied vertical electric field, (ii) temperature, and (iii) linear density of atomic steps. The investigated structure consisted of InGaN QWs inside a p-n junction. The indium content in QWs was designed to be different in defined areas of the sample (due to mastering of different off-cuts and atomic steps density) so that the wells could emit at energies from 2.6 to 2.86 eV. The horizontal transport range was sensitive to the vertical electric field, which means that it could not be just a radiation transfer, but charge carriers must have been involved as well. We found that the transport range decreased for higher slope angles, possibly due to stronger scattering on atomic steps when their linear density became higher. The diffusion coefficients reached 6 cm2/s and due to long lifetime of even 2 μs, the diffusion length was even LD = 30 μm in areas of low off-cut angles. We discuss possible mechanisms of transport and conclude that for such high diffusion constant, the most probable is the excitonic transport. The LD was maximum at 40 K and then decreased significantly with temperature, which was probably caused by thermal dissociation of excitons.

The main aim of the paper is to present the results of experimental investigations on the deformation process of cellular structures with gradient topologies under quasi-static loading conditions. The specimens used in the tests were designed with the use of a hexagon shape of a unit cell with a graded size preserving the equivalent global size and wall thickness dimensions. The manufacturing process of structure samples was realized by two different 3D printing methods: FFF (Fused Filament Fabrication) and SLA (Selective Laser Sintering). Additionally, two types of materials differing with mechanical properties were used to determine the mechanism of structure damage during the deformation process. As a result of the conducted investigations, it was possible to define a relationship between a structure topology and relative density versus energy absorption capacity.

Nanostructured organic thin films with polarized luminescence are obtained by means of the slow vapor deposition of fuorescent liquid crystalline dipolar molecules on the surface of the rubbed polyamide layer. Based on the polarized photoluminescence measurements, the polarization degree of thin film based on blue-emitting organic liquid crystalline molecules 4-(n-pentyl)-3-chloro-4′′′-trifluoromethoxy-[1,1′, 4′, 1′′, 4′′, 1′′′-quaterphenyl] (M-BLUE) was found to be 29%, and for red-emitting 4-(dicyanomethylene)-2-(4-amylcyclohexyl)-6[4-(dimethylaminostyryl)]-4H-pyran molecule (M-RED) it is as high as 78%. It can be connected with the higher dipole momentum of M-RED molecule (15) than M-BLUE (3.45), and can be ascribed to its higher interaction with polyamide matrix.

The paper presents a methodology investigation of honeycomb cellular structures deformation process in quasi-static compression tests. Two honeycomb topologies with different elementary cells were designed and manufactured from Ti-6Al-4 V alloy powder with the use of Laser Engineered Net Shaping (LENS) system and compressed using a universal strength machine. To simulate the deformation process with LS-Dyna software, the mechanical properties of the material were assessed and correlated. An elasto-visco-plastic material model (Mat_Plasticity_With_Damage) was used for predicting the material behavior. The results of experimental tests and numerical simulations were compared. A reasonable agreement between deformation, failure and force histories was obtained. Additionally, both the topologies were compared for their energy absorption capabilities. The validated numerical modelling with the adopted constitutive model will be used in the further studies to analyze different cellular structures topologies subjected to dynamic loading.

InGaN quantum wells were grown using metalorganic chemical vapor phase epitaxy (vertical and horizontal types of reactors) on stripes made on GaN substrate. The stripe width was 5, 10, 20, 50, and 100 µm and their height was 4 and 1 µm. InGaN wells grown on stripes made in the direction perpendicular to the off-cut had a rough morphology and, therefore, this azimuth of stripes was not further explored. InGaN wells grown on the stripes made in the direction parallel to the GaN substrate off-cut had a step-flow-like morphology. For these samples (grown at low temperatures), we found out that the InGaN growth rate was higher for the narrower stripes. The higher growth rate induces a higher indium incorporation and a longer wavelength emission in photoluminescence measurements. This phenomenon is very clear for the 4 µm high stripes and less pronounced for the shallower 1 µm high stripes. The dependence of the emission wavelength on the stripe width paves a way to multicolor emitters.

The article presents the results of preliminary research into the feasibility of copper-graphene composite application in the production of shaped charge liners in HEAT ammunition from graphene-coated copper grain powders by powder metallurgy techniques. Copper powder grains were coated with graphene with a machine and process developed at the Institute of Precision Mechanics in Warsaw (Poland). The characteristics of the applied powdered materials (including particle size distribution) were determined in this work. The paper discloses the result of graphene identification by Raman spectroscopy. The presence of graphene was confirmed in the processed copper powder. The paper discusses the preparation of copper powder by grinding (refinement) and reduction for consolidation. Powder mixtures of pure copper and graphene powder were applied at different component ratios. P/M compacts and sinters (agglomerates) for the test specimens were made from the proposed mixtures by die pressing and sintering in dissociated ammonia gas. Examples of microstructures and selected test results of material properties are shown for the produced sinters. The paper shows a selection of test results for the copper-graphene composites produced by PPS (Pulse Plasma Sintering) from 100% graphene-coated copper powder. The properties of the produced composite materials were determined, including their density, porosity, and a selection of mechanical properties identified by DSI (Depth Sensing Indentation). It was found that the copper-graphene composite met the primary design criteria applied to shaped charged liners for HEAT munitions. In “traditional” powder metallurgy processes, high-density products can be produced if the composite material features a low content of graphene-coated copper powder; PPS, however, makes the production viable with 100% graphene-coated copper powder.