Proficient design of machine elements requires knowledge of contact stresses and deformation, especially when the contact is concentrated, and high stress gradients arise in confined parts of the bulk. Even with time-independent material properties, a general contact solution can only be numerical and relies on spatial discretisation. Consideration of viscoelasticity as a constitutive law for the contacting materials introduces the time parameter in the problem model. The numerical approach brings the advantage of numerical integration that can be performed over both space and time dimensions. The base for the application of superposition of effects to linear viscoelasticity stems from the Boltzmann superposition principle and the Boltzmann-Volterra integral equation. The latter, combined with Green’s functions for a semi-infinite isotropic continuum, facilitates the evaluation of the displacement exhibited by a viscoelastic flat under arbitrary pressure. By considering the contacting bodies as half-spaces, which is standard for concentrated contacts, a numerical solution to the viscoelastic contact problem can be achieved. Within the developed computational procedure, time-dependent material response is incorporated via a creep compliance function, formulated in alignment with classical linear viscoelastic frameworks, such as the Maxwell or Kelvin-Voigt constitutive models. In this paper, a more complex Standard Linear Solid model is employed because it is the simplest unit that can replicate creep, recovery, and stress relaxation. The assembled algorithm was implemented in MATLAB by reusing code previously developed by the same author for elastic contact. The simulations targeted scenarios with monotonic loading: step, ramped, and step followed by ramped down loading. In step loading, the deformation is instantaneous due to the Hookean spring; the initial state is Hertzian (i.e., purely elastic). The viscoelastic material behaves instantaneously as if the Kelvin-Voigt unit were not present. After an initial rapid increase, stabilization of the contact area occurs, with central contact pressure decreasing to accommodate the larger contact radius while maintaining a semi-ellipsoidal profile. Ramped loading exhibits ever-growing contact radii, but pressure appears to shift from semi-ellipsoidal to a uniform central plateau surrounded by a maximum. This is more apparent when the shear modulus of the Hookean spring is greater than that of the one in the Kelvin-Voight unit. Step – ramped down loading proves that load removal does not result in complete recovery of deformation as in the purely elastic case. These results are consistent with the general expectations regarding the viscoelasticity of the SLS, and encourage the use of the advanced MATLAB simulation tool in more complex contact scenarios.
Numerical dynamic response prediction refers to a research-passenger design concept vessel with the following specifications: 44.5m total length, 9.0m breadth, 3.0m height, mono-hull type, 20 km/h top speed, designed for navigation in the Danube River and Black Sea coastal areas, and with a maximum significant wave height of 2.5m. The multi-deck and compartment layout for research laboratories, as well as onboard rooms for crew and passengers, with specific equipment and provisions, necessitates a dynamic analysis for two loading cases with a draught of 1.5 m and 1.7 m. The vessel oscillation response in regular waves is computed using a frequency-domain linear strip approach, and the dynamic response in irregular waves using a statistical short-term approach, with seakeeping criteria assessment. The detailed parametric dynamic response analysis is solved using the eigen DYN_OSC version 2025 program, which includes a wide range of specific navigation parameters. This research predicts navigation operational capabilities of the research passenger vessel.
The growing demand for sustainable and environmentally friendly materials has spurred interest in green synthesis approaches for bioactive compounds. In this study, nano-hydroxyapatite (nHA) was synthesized from fish scale biowaste via a top-down mechanical milling method. Fish scales, a renewable and calcium/phosphate-rich waste product, were first calcined to produce FsHA and then subjected to ball milling to produce nanoscale FsHA particles. The resulting material was characterized using particle size analysis, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). FTIR analysis on ball-milled FsHA revealed the presence of HA peaks together with carbonate absorption bands, confirming the presence of B-type carbonate substitutions, indicating partial replacement of phosphate groups by carbonate ions. The presence of C-H groups indicates the potential for polyethylene (PE) contamination originating from the milling container. XRD analysis revealed a pronounced reduction in crystallinity and peak intensity, consistent with a reduction in crystallite size, lattice distortion, and partial amorphization induced by mechanical stress and carbonate incorporation. TEM and STEM imaging verified particle sizes in the 20–200 nm range but also revealed severe agglomeration and the presence of nanoplastic debris (4–5 nm), generated by abrasion of the PE container during milling. These results highlight the dual influence of milling conditions and container material on the purity, stability, and dispersion of biogenic nHA, emphasizing the importance of careful material selection in preventing unwanted contamination and preserving functionality for biomedical applications.
Surface roughness is a critical parameter that measures the overall surface quality of a machined component. Most surface roughness measurement techniques are usually time-consuming to set up and measure, and require specialized equipment. This study proposes an alternative method for measuring the expected surface roughness on a machined component by utilizing the programming interface of a commercially available Computer-Aided Design (CAD) system. In contrast to the standard CAD models that the manufacturers provide, which usually lack critical geometrical aspects, the proposed algorithm takes into consideration the full geometry of the cutting tool, which influences the surface profile to a great extent. The CAD system utilized is a generic software, namely SolidWorks™. Specifically, the Application Programming Interface (API) and its methods were used to develop the algorithm that can simulate the kinematics of the machining process. The selected process is the external turning. Additionally, the surface profile, topography, as well as standard measurements were generated. All data were acquired with respect to typical machining parameters such as the depth of cut, feed rate, and cutting speed. Finally, to verify the accuracy of the algorithm, a set of nine cutting tests was carried out, under a widely used range of conditions, suggested by the tool manufacturer. Concluding, the experimental and the simulated measurements were compared in terms of the Ra, Rz, and Rt surface roughness values. The increased correlation percentages, exceeding 90% in most cases, proved the validity of the developed algorithm.
The advancements in modern manufacturing technologies have made it possible to create customized, distinctive, and personalized products in single quantities or small batches tailored to the individual needs of customers, a process commonly referred to as "customization." However, this has introduced challenges in effectively planning production activities and manufacturing customized products, as it requires balancing customer demands with manufacturing capabilities. In addition to traditional production methods such as turning and milling, innovative techniques like laser cutting-particularly when coupled with a robotic arm-offer enhanced flexibility for producing specialized custom products and intricate patterns. This ability has contributed to laser cutting’s rise as a competitive and widely supported method in modern manufacturing. A significant challenge in this domain is the dynamic nature of task execution in manufacturing, which can render cutting lines obsolete and often requires modifications at short intervals. These changes are driven by factors such as evolving customer requirements, shifts in materials, and new production orders. As a result, it is crucial to continually assess and implement the necessary adjustments to maintain process efficiency and ensure the smooth execution of planned activities. This article explores the application of laser cutting on various materials, such as tulle, and presents the results obtained. The objective was to develop a cutting technology suitable for manufacturing specific types of ion membranes that meet required quality standards and chemical purity levels. Additionally, an analysis using an Ishikawa diagram was conducted to identify areas for improving the quality of the cutting elements.
