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ÖgeAnalytical and numerical modeling on strengths of aluminum and magnesium micro-lattice structures fabricated via additive manufacturing(Springer, 2024)Bioinspired lattice structures have a wide range of applications in aerospace, automotive, energy, and medical device industries due to their high strength-to-weight ratio. Although experimental and numerical modeling methods have been extensively used to characterize the compressive behavior of lattice structures, an accurate analytical model has great values in material/structure designs and applications. In this study, a new analytical model is developed for two configurations based on limit analysis in the plasticity theory to predict the compressive strengths of micro-lattice structures (MLS). The model is also discussed for determining the amounts of stretching-dominated deformation and bending-dominated deformation. A comparative study is performed between analytical solutions and experimental results of AlSi10Mg (aluminum alloy) and WE43 (magnesium alloy) MLS additively manufactured via selective laser melting (SLM). Finite element simulations using beam elements are conducted to evaluate the accuracy of the analytical solution. Analytical results, finite element simulation results, and the experimental results are in a good agreement with both AlSi10Mg and WE43 MLS. The shear band formation, as a main failure mode of MLS, is also studied and evaluated using the classical Rudnicki–Rice’s criterion, for which a reasonably good accuracy is demonstrated.
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ÖgeProduction, characterization and mechanical behaviors of electrolytic metal-coated light polymeric cylinders for photogravure press applications(Springer, 2024)Since precision engraving is essential for almost any product or application, it is important that the printing system produces smooth and clear prints. In this regard, the rollers are made of steel and polymeric materials. However, light cylinder production is economical, transportation costs are very low, and it provides ease of transportation and distribution for printing houses. However, regional chain orientations and cracks occur in the polymeric material on the conical surfaces of the cylinders with shafts longer than 1 m. Therefore, it is necessary to improve the surface properties of polymeric cylinder. In this study, electrolytic hard chromium (Cr) and soft copper (Cu) metal layers, conductive (Ni and Ag) paint and polyester coating were successfully fabricated on polymeric lightweight cylinders via electroplating, spraying and hand brushing techniques for photogravure press application. At the fabrication stage on the steel base cylinders, polyurethane has been molded by using an injection molding machine. In order to eliminate the porosities, where polyurethane takes place, polyester has been coated on the polymeric cylinder and consequently polyester has been painted with conductive dye to obtain the conductivity. Then Cu and Cr have been coated by using the electroplating method and gravured. At the end of final stage, the process has been completed with coating of Cr on the Cu layer/conductive paint/polyester coating/polyurethane substrate. Phase analysis, microstructures and mechanical properties of the obtained samples have been examined through XRD, SEM–EDS, surface roughness, microhardness, tensile, three-point bending, scratch and wear machines. As a remarkable result of these studies, correlations were established between the quality of the layers and the mechanical properties as innovative scientific approaches, and between the layers produced on an experimental basis and the samples produced on a fabrication basis, they were produced and used in high-quality multilayered architecture to engraving technology and then to the society because of its effectiveness.
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ÖgeFrom material to field test : an improved under sleeper pad model(Springer, 2024)This study aims to determine the stiffness values of under sleeper pad (USP) and rail pad (RP) components to reduce the high-amplitude vibrations that occur in the transition zones of some specific structures such as viaducts in ballasted railways. The conventional method of simulating USPs and RPs as spring–dashpot elements in the Kelvin–Voigt model is inadequate due to the absence of frequency and temperature dependencies in the model. The study proposes a new analytical model that considers USPs and RPs as viscoelastic (VE) materials and integrates them into the ballasted railway superstructure model by adding unit masses avoiding mathematical singularity. The process includes material testing, field measurements, and validation of the proposed model with finite element model analysis. The effect of ambient temperature and material modelling on the superstructure’s dynamic response in the frequency domain is analysed in detail. To account for VE behaviours of the resilient elements, the generalised Maxwell model (GMM) is chosen via unit mass implementation compared to other VE models. The obtained results show that the dynamic response of the railway superstructure is 8–10 times sensitive to temperature variation. This demonstrates how important it is to include the temperature-dependent dynamics of the elastomer material in the model. According to the other results that were obtained, the use of USP in transition zones does not solve the vibration problem radically. Bridge dynamic responses are also sensitive to the mass of the bridge rather than its stiffness.
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ÖgeEffects of particle damper design parameters on the damping performance of laser powder bed fused structures(Springer, 2024)Particle dampers (PD), a passive damping technology, absorb energy from particle-particle and particle-cell wall interactions originating from friction and collision. PDs offer advantages such as design simplicity, low cost, applicability in harsh conditions, and flexibility to be used in a wide frequency band range. Additive manufacturing, specifically the powder bed fusion process, can fabricate structures with integrated PDs in a single printing process, eliminating the need to implement external dampers. However, the dynamic behavior of PDs must be determined to utilize their full potential. In this study, we examined 16 cases of integrated PDs by varying specific parameters including size, number, and locations on the structure to understand the effects of these parameters on the dynamic behavior of the first and second modes of the structure. Modal tests were conducted on additively manufactured samples to extract frequency response functions and calculate modal parameters (natural frequency and damping ratio) using the rational fraction polynomial method, studying the effects of PDs. The results showed that the damping performance of the parts was increased by a factor of up to 10 using body-integrated PDs compared with the fully fused specimen. The effectiveness of body-integrated PDs was shown to be strongly dependent on their volume and location. For instance, the damping generally increased as the volume fraction increased, which also reduced the total weight of the specimens by up to 60 g. Furthermore, the damping performance significantly increased for a specific mode when the PDs were located near the maximum displacement regions.
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ÖgeEvaluation of mechanical properties of additively manufactured beams with lattice structures(American Society of Mechanical Engineers, 2024)The use of lattice structurses is becoming more common day by day. Limitations such as being expensive and time-consuming have led to a search for new solutions in the industry. In light of these limitations, the widespread use of 3D printing technology methods is evaluated. 3D printing technology has advantages in terms of design flexibility, quick prototyping, lightness and the ability to produce complex shapes. 3D printing is used to systematically investigate different geometries in line with the requirements of sustainable product development, leading to the production of auxiliary structures that are both strong and lightweight. This research investigates the mechanical properties of various lattice structures that were previously modelled and analysed through analytical methods in the literature. The samples with five different auxetic structures are manufactured using the Fused Deposition Modelling (FDM) 3D printing technique, with Acrylonitrile Butadiene Styrene (ABS) as the selected material. The manufactured samples are subjected to a three-point bending test to assess their mechanical characteristics, including the flexural modulus, flexural strength, and elongation at break, and the effect of the in-plane geometry on the mechanical behaviour is evaluated.