Complex Shapes Research Articles

Fabricating sandwich composite tubes using a new thermal expansion technique: Materials preparation and energy absorption characteristics

The extensive application of hollow composite structures in engineering increasingly demands innovations in highly efficient and economical manufacturing processes as well as materials to achieve lightweighting and enhance mechanical performance. To address the limitations of traditional molding processes in fabricating hollow composite structures with intricate geometries, this study proposes a novel thermal expansion molding technique. This method eliminates the need to remove the mandrel after molding, making it exceptionally suitable for the molding of foam sandwich composite structures. Leveraging this new technique, lightweight sandwich composite tubes filled with polymethacrylimide (PMI) foam and thermal expansion foam were successfully fabricated. Considering the importance of crashworthiness for automotive applications, detailed experimental studies were conducted to investigate the crushing performance of the sandwich composite tubes prepared using this technology. Experimental results reveal that the synergistic effect between the multi-component materials within the sandwich composite tubes confers surprising energy absorption characteristics and crushing stability to the structure. The sandwich composite tubes prepared by this innovative thermal expansion process exhibit promising prospects as crashworthy structures for automotive lightweighting applications, and this method provides critical inspiration for the fabrication of composite structures with complex shapes.

Mineral Signatures in Oued K’sob River (Algeria): Highlighting Geological Variations and Potential Anthropogenic Impacts

This study examines the mineral composition of sediment samples collected from five distinct zones along the Oued K’sob River in Bordj Bou Arreridj, Algeria using scanning electron microscopy (SEM). The analysis revealed intriguing patterns, the Zone 5 emerged as a distinct outlier, exhibiting significantly lower calcium (29.32% vs. 53.25% in Zone 1) and iron (14.94% vs. 6.31% in Zone 1) content compared to other zones, while displaying a higher silicon content (28.82% vs. 25.27% in Zone 1). This suggests a unique geological origin or specific weathering processes shaping the mineral fingerprint of Zone 5. Interestingly, Zones 1, 2, and 3 displayed a relative consistency in silicon content (around 25%, with pairwise comparisons exceeding p > 0.05), suggesting potential similarities in mineral sources or enrichment mechanisms within their watersheds. However, Zone 4 deviated slightly, showing a higher calcium content (64.18% vs. 29.32% in Zone 5) and lower silicon content (17.99% vs. 28.82% in Zone 5), indicating potential differences in its geological makeup or weathering processes. Furthermore, all zones exhibited trace amounts of elements like lead (Pb) and cadmium (Cd) (ranging from 0.76% to 2.16% for Pb and 0.000% to 0.114% for Cd) (Please recheck these values They are very high). This warrants further investigation to understand their potential anthropogenic origins and impact on the river ecosystem. Further investigations incorporating detailed geological surveys, isotopic analyses, and expanded sampling strategies are recommended to gain a more comprehensive understanding of the complex factors shaping the sediment chemistry within the Oued K’sob River system.

Modeling and Simulation of the Aging Behavior of a Zinc Die Casting Alloy

While zinc die-casting alloy Zamak is widely used in vehicles and machines, its solidified state has yet to be thoroughly investigated experimentally or mathematically modeled. The material behavior is characterized by temperature and rate sensitivity, aging, and long-term influences under external loads. Thus, we model the thermo-mechanical behavior of Zamak in the solid state for a temperature range from −40 °C to 85 °C, and the aging state up to one year. The finite strain thermo-viscoplasticity model is derived from an extensive experimental campaign. This campaign involved tension, compression, and torsion tests at various temperatures and aging states. Furthermore, the thermo-physical properties of temperature- and aging-dependent heat capacity and heat conductivity are considered. One significant challenge is related to the multiplicative decompositions of the deformation gradient, which affects strain and stress measures relative to different intermediate configurations. The entire model is implemented into an implicit finite element program and validation examples at more complex parts are provided so that the predicability for complex parts is available, which has not been possible so far. Validation experiments using digital image correlation confirm the accuracy of the thermo-mechanically consistent constitutive equations for complex geometrical shapes. Moroever, validation measures are introduced and applied for a complex geometrical shape of a zinc die casting specimen. This provides a measure of the deformation state for complex components under real operating conditions.

Analysing fluid flow and heat transfer comparatively in flow passage systems: Evaluating thermal impacts and geometric configurations

This research thoroughly examines heat transfer and fluid flow in a passage flow system, highlighting the difficulties posed by different geometric arrangements and temperature conditions that may affect the system's performance. The main aim is to evaluate the impacts of different geometric characteristics on the velocity, pressure, and temperature profiles inside the flow route. These factors encompass cavity dimensions, tube diameter, and input conditions. An inclusive comparison of three different geometric designs at controlled temperatures is conducted using computational fluid dynamics (CFD) simulations. The findings indicate that the optimal geometric parameters improve thermal performance, with certain arrangements displaying improvements in heat transfer rates up to 30 %. In this regard, the higher cavity dimensions and suitable input velocities are exposed as advantages. The first sample exhibited a higher velocity of 0.024 m s-1 due to its simpler geometry and favorable heating conditions, while the third sample demonstrated a higher temperature of 465 K due to its complex cavity shape and multiple heating sources. This study suggests that enhancing efficiency in heat management applications necessitates a strategic design approach for passage flow systems, which must account for flow characteristics and geometric specifications. This research would provide insightful information for designers and engineers looking at enhancing fluid flow systems across a range of industrial applications.

On the suitability of photocuring-assisted DIW for manufacturing complex prosthesis from commercial dental composites

A 3-D printing method to produce dental prostheses of complex shapes from a commercial, photocurable resin-ceramic slurry is developed and optimized. The microstructure, mechanical properties and wear behavior of the resulting material are evaluated and compared with a conventional/control sample and other ceramic-polymer dental composites. Commercial resin-ceramic dental slurries can be successfully extruded and appropriately photocured in a low cost 3-D printing system to produce cost-efficient complex dental parts that could be used in indirect restorations. The printing process does not appreciably introduce defects in the material and the 3-D printed composites exhibit mechanical properties (hardness, elastic modulus) and wear resistance comparable to the control material and analogous, conventional dental composites. The main wear mechanisms under sliding contact against a hard antagonist are plastic deformation at the asperity level and ceramic particle pull-out due to filler/matrix interfacial weakness.Graphical 3-D printing commercial resin-filler slurries creates cost-efficient tooth prostheses with properties akin to conventional dental composites

The use of groups of drones for diagnostics of subsurface objects in the radio range

Diagnostics of objects that are bodies of complex shape can be based on representing their boundaries of such objects (including subsurface ones) in the form of a set of paraboloids. It is shown that the determination of specific geometric characteristics of such paraboloids is ensured through the artificial synthesis of a distributed lens, the individual elements of which are placed on individual unmanned aerial vehicles. Technically, lens synthesis is achieved by changing the phase of radio frequency radiation, carried out using phase shifters. The method is implemented through scanning the object under study by adjusting the effective optical power and its orientation in space. Model calculations are presented that prove the prospects of using the proposed method. Specific examples of radio-electronic circuits that ensure the implementation of the proposed approach are presented. A feature of the phase shifters used is the preliminary detection of the phase of the signal arriving at each of the elements of the distributed lens, and the subsequent introduction of an additional phase difference due to the weighted summation of harmonic signals that are in antiphase.

The Landscape Ecological Quality of Two Different Farm Management Models: Polyculture Agroforestry vs. Conventional

Low-intensity, diversified agricultural land use is needed to counteract the current decline in agrobiodiversity. Landscape ecology tools can support agrobiodiversity assessment efforts by investigating biodiversity-related ecological functions (pattern–process paradigm). In this study, we test a toolkit of landscape ecology analyses to compare different farm management models: polyculture agroforestry (POLY) vs. conventional monoculture crop management (CV). Farm-scale analyses are applied on temperate alluvial sites (Po Plain, Northern Italy), as part of a broader multi-scale analytical approach. We analyze the landscape ecological quality through landscape matrix composition, patch shape complexity, diversity, metastability, and connectivity indices. We assess farm differences through multivariate analyses and t-tests and test a farm classification tool, namely, a scoring system based on the relative contributions of POLY farms, considering their deviation from a local CV baseline. The results showed a separate ecological behavior of the two models. The POLY model showed better performance, with significant positive contributions to the forest and semi-natural component equipment and diversity; agricultural component diversity, metastability; total farm diversity, metastability, connectivity, and circuitry. A reference matrix for the ecological interpretation of the results is provided. Farm classification provides a quick synthesis of such contributions, facilitating farm comparisons. The methodology has a low cost and quickly provides information on ongoing ecological processes resulting from specific farm management practices; it is intended to complement field-scale assessments and could help to meet the need for a partially outcome-based assessment of good farm practice.

Generation of arbitrarily patterned polarizers using 2-photon polymerization

Patterned polarizers are prepared using liquid crystals (LC) doped with a black dichroic dye and in combination with a linear polarizer. The pattern is achieved with a nanostructured LC alignment surface, that is generated using a two-photon polymerization direct laser write (2PP-DLW). This technique creates a pattern of high-resolution grooves in the photoresist at any arbitrary angle. The angle governs the LC orientation at any substrate surface point, determining the transmitted light linear polarization angle. This paper presents the first use of a 2PP-DLW cured positive tone photoresist for dichroic dye-doped LC alignment. Two complementary photoresists have been employed: conventional negative tone SU-8 photoresist and, in this context novel, positive tone S1805 photoresist. The alignment quality of the polarizers has been assessed by analyzing the transmission using an additional polarizer. For SU-8, the resulting grayscale pattern and a contrast ratio (CR) of 14 has measured. The uniformity of the alignment has been measured to be 65% using normalized Shannon entropy (H). For S1805, a CR of 37 was measured, and a uniformity of 63% was obtained. 2PP-DLW allows for shaping complex patterns in submicron dimensions and for the fabrication of arbitrarily patterned polarizers and other LC devices.

Impact of tip curvature and edge rounding on the plasmonic properties of gold nanorods and their silver-coated counterparts.

Colloidal solutions of gold nanorods and silver-coated gold nanorods were prepared. The seeded growth synthesis protocols were improved by adding a flocculation purification step. The resulting populations of pure gold nanorods and Au@Ag core-shell cuboids were characterized by very low dispersion in size and shape. UV-vis-near-infrared absorption measurements were performed on several batches of well-calibrated nano-objects, supported by calculations based on the discrete dipole approximation, allowed to highlight the impact of various morphological features on the optical response. In addition to the well-known effect of the nanorod aspect ratio on the shift of the longitudinal surface plasmon resonance mode, special attention was paid to changing either the rounding of the nanorod end-caps or that of the edges of the coating silver shell. Nanorods and cuboids were modeled as superellipsoids. This approach enabled us to model precisely their complex shapes using just a few simple parameters and analyze the evolution of their extinction spectra as a function of the rounding of their tips and edges. Such nano-objects are widely used for various applications in fields such as biomedical, biosensing, or surface-enhanced Raman spectroscopy, thus making it crucial to precisely assess the impact of each morphological feature for optimizing their performance.

Sacrificial ceramics powders mix for titanium alloys complex shapes production by hybridization of SPS and 3D printing

The production of complex shapes via Spark Plasma Sintering (SPS) is challenging due to intricate die configurations. The “DEFORMINT” approach combines 3D printing with SPS and sacrificial powder to fabricate fully dense shapes. Using the same powder for both the component and sacrificial part avoids distortions, but high costs of titanium alloys like Ti-6Al-4 V are limiting. This study tested a low-cost ceramic powder that mimics Ti-6Al-4 V's behavior, forming a pseudo-isostatic configuration above 1250 K. SPS experiments established a densification model and predicted distortions in a thick cone and a thin, complex turbine blade, showing good correlation with experimental results. The new sacrificial mix does not imply additional deformation and allows the fabrication of turbine blades. The only defect is a 600 μm skin effect at the contact interface.

Wave energy extraction from rigid rectangular compound floating plates

We present a theoretical model to analyse the hydrodynamics of wave energy converters (WECs) comprised of three-dimensional, rigid, floating, compound rectangular plates in the open sea. The hydrodynamic problem is solved by means of Green’s theorem and a free-surface Green’s function. Plate motion is predicted through decomposition into rigid natural modes. We first analyse the case of a single rectangular plate and validate our model against experimental results from physical model tests undertaken in the COAST laboratory at the University of Plymouth. Then we extend our theory to complex shapes and arrays of plates and examine how the geometry, incident wave direction and power take-off (PTO) coefficient affect the response of the platform and the consequent absorbed energy.

Soil organic carbon sequestration can be promoted through the improvement of landscape configuration heterogeneity in typical agricultural regions of northeast China

Landscape heterogeneity is considered a promising option for building resilient and sustainable agroecosystems. Understanding the relationships between farmland soil organic carbon (SOC) and landscape heterogeneity can support soil carbon sequestration and better serve food security and climate change. However, the influence extent and optimal scale of farmland landscape heterogeneity (i.e. landscape composition and landscape configuration heterogeneity) on SOC remains unclear. In this study, we established the relationships between multi-scale landscape heterogeneity and SOC in a typical grain-production county of northeast China. Stepwise regression results showed that when the buffer radius was 2000 m, the interpretation of SOC by landscape heterogeneity was the largest. The effects of landscape composition and landscape configuration on SOC were further decomposed by Variance Partitioning Analysis, and we found that independent interpretation ability of landscape configuration (8%) exceeded landscape composition (7%). The result of soil mapping combined with landscape indexes also showed that landscape configuration contributed more to the increased accuracy. Moreover, we found that correlation between configuration indexes and SOC at the class level was less related than that at the landscape level, among which the two most important indexes were Mean Fractal Dimension Index (FRAC_MN) and Number of Patches (NP). FRAC_MN was even more important than natural factors, indicating the validity of landscape as an indicator of human activities should not be ignored when considering farmland SOC. Overall, the results of this study revealed that the negative effects of agricultural intensification on SOC can be buffered to a certain extent by increasing the complexity of patch shape and reducing the degree of landscape fragmentation at the landscape level, providing hope for the sustainable development in intensive agricultural areas. In addition, due to the scale effect of landscape heterogeneity on farmland SOC, we suggest that decision makers should consider the spatial scale in landscape allocation and planning. This study provides a scientific reference for realizing the balance between grain production and ecological function in intensive agricultural areas.

Improving the Quality of Heat Treatment Using Microwave Heating of Products with a Complex Profile of Hardened Surfaces

The current article provides the results of the study on the improving the procedure of induction heating of products with a curvilinear surface profile by hardening of steam turbine blades surface with a complex helical shape and requiring protection against erosive wear [9, 10] using a universal microwave heating device. A principally new device that uses the effect of the magnetic field's force action has been developed and constructed. That makes possible to provide a high-quality strengthening of product surfaces regardless of their geometric configuration and size. The advantages of thermal treatment technology on such device are substantiated based on the results of metallographic, X-ray structural, and hardness analysis.

Assessing the impact of land use and land cover change on the Densu Delta wetland using Markov chain modeling and artificial neural networks

This study investigates the dynamics of land use and land cover (LULC) changes in the Densu Delta wetlands, a critical ecosystem in Ghana. Here, satellite images spanning from 1998 to 2023 were used to analyse the spatio-temporal patterns of LULC changes and their implications for water bodies, wetlands, vegetations, bare lands and urban areas in the Densu Delta wetland. Employing advanced techniques such as Markov chain modelling and artificial neural networks (ANNs), the research assesses and predicts LULC alterations. Significantly, the largest loss of LULC is observed in the Densu Delta wetland, where wetlands transition to waterbody cover type (14.02 km²). Model validation for 2023 attests to the accuracy of the model, boasting a correctness percentage of 70% and a kappa value of 0.74. In-depth analyses explore regional variations in the Densu Delta wetlands, revealing distinct patterns in the rates of LULC change before and after 2013. Notably, urbanization emerges as a prominent factor post-2013, with urban areas experiencing remarkable rates of change in the wetland. Transition matrices underscore the intricate interplay of different land cover classes over the years. Simulated LULC predictions for 2033 and 2043 highlight the urban land cover type as having the highest positive change, recording approximately 0.39% for the Densu Delta wetland. The wetland land cover in the Densu Delta wetland exhibit negative changes of about −0.52%. The synthesis of LULC data enhances our understanding of the complex interactions shaping these critical ecosystems. This research offers valuable insights for sustainable environmental conservation, emphasizing the pivotal role of informed urban planning policies. It also unveils potential challenges posed by climate change, advocating for a holistic approach to preserve these vital wetland ecosystems.

Laser applications in arts and culture: An example on the construction of tiered umbrellas

Tiered umbrella or in Thai called Chat means a high decoration or decoration of honor, a type of umbrella that is stacked up in layers along a single axis. At present, in Thailand, the tiered umbrellas are seen in three important places including (1) on the top of the pagoda of various temples, (2) inside the ordination hall of temples, and (3) inside the Grand Palace for the king and the royal family. In the past, a tiered umbrella was made from brass because its color was similar to gold. Constructing each set of tiered umbrellas requires a skilled technician and takes a lot of time. At present, laser cutting of metals has been widely used in the production section of the industry. This is due to the advantages of laser cutting that include narrow kerf width, smooth cutting edges, high cutting speed, reduced material waste, no tool wear, and easy automation and manipulation even for complex shapes. In this work, an example for the construction of seven-tiered umbrellas from stainless steel sheets using a high-power CO2 laser was reported. The results show that the total working time for the construction of a seven-tiered umbrella is about 113 h, which is much less time compared to 3–6 months taken by craftsmen. Therefore, this method can preserve the construction of tiered umbrellas in Thailand even though craftsmen are scarce at present.

FFF/FDM 3D-Printed Solid Polymer Electrolytes Based on Acrylonitrile Copolymers for Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) are essential in modern electronics, particularly in portable devices and electric vehicles. However, the limited design flexibility of current battery shapes constrains the development of custom-sized power sources for advanced applications like wearable electronics and medical devices. Additive manufacturing (AM), specifically Fused Filament Fabrication (FFF), presents a promising solution by enabling the creation of batteries with customized shapes. This study explores the use of novel poly(acrylonitrile-co-polyethylene glycol methyl ether acrylate) (poly(AN-co-PEGMEA)) copolymers as solid polymer electrolytes for lithium-ion batteries, optimized for 3D printing using FFF. The copolymers were synthesized with varying AN:PEGMEA ratios, and their physical, thermal, and electrochemical properties were systematically characterized. The study found that a poly(AN-co-PEGMEA) 6:1 copolymer ratio offers an optimal balance between printability and ionic conductivity. The successful extrusion of filaments and subsequent 3D printing of complex shapes demonstrate the potential of these materials for next-generation battery designs. The addition of succinonitrile (SCN) as a plasticizer significantly improved ionic conductivity and lithium cation transference numbers, making these copolymers viable for practical applications. This work highlights the potential of combining polymer chemistry with additive manufacturing to provide new opportunities in lithium-ion battery design and function.

Chloroplasts with clefts and holes: a reassessment of the chloroplast shape using 3D FE-SEM cellular reconstruction of two species of Chlamydomonas.

Chloroplasts are usually considered spheroid organelles, but this is not the only shape of chloroplasts. The chloroplast of Chlamydomonas has been typically described as cup-shaped. However, in old studies, it was also modeled as a complex shape with "perforations" or windows. Here, we reconstructed the cellular architecture of Chlamydomonas reinhardtii and C. applanata using an array tomography system installed on a field emission scanning electron microscope. C. reinhardtii chloroplasts resembled a baseball glove or a cup without a side, featuring numerous large and small holes that may facilitate the transport of metabolites and proteins produced in the Golgi apparatus fitted in the holes. In a lipid-accumulating, high-light condition, the chloroplast volume increased by filling the side cleft with an entire wall. Many accumulated large lipid droplets were accommodated within the chloroplast holes, which could have been considered as "chloroplast lipid droplets." Mitochondrial meshworks surrounded the chloroplast. C. applanata chloroplasts appeared like a folded starfish or a cup with many side clefts and a few holes. There was a single mitochondrion or two that branched in a complex form. Tight contacts of various organelles were also found in C. applanata. These reconstructions illustrate the complexity of chloroplast shape, which necessitates a revised understanding of the localization of lipid droplets and the evolution of chloroplasts: The prevailing image of the spheroid chloroplasts that reminds us of the similarity between chloroplasts and cyanobacteria is no longer tenable.

Features and processes of rock weathering in central Dronning Maud Land, Antarctica

In this study, we have investigated rock weathering phenomena in the central part of Dronning Maud Land, Antarctica. The area is characterized by low mean annual temperatures (−18 °C), strong katabatic winds, and minimal liquid water at the surface. Weathering features, including ventifacts, tafoni, and grus accumulations, are characterized through field observations, rock surface temperature measurements, and microscopic analysis. Abrasion by sand and ice particles transported by strong winds has locally resulted in ridge-shaped ventifacts and rock surfaces with elongated pits, furrows, and grooves. The abrasion-caused features, such as polished facets, keels, and grooves, indicate a northeast-facing wind direction, aligning with the present-day wind regime. The dominant weathering processes in coarse-grained intrusive rocks are oxidation and granular disintegration. Fe-oxidation induces cracking, increasing the porosity and enhancing susceptibility to further weathering. Additionally, temperature fluctuations on rock surfaces caused by solar radiation create thermal stress, which can lead to the formation of microcracks. These microcracks, formed due to thermal expansion, are likely to propagate through subcritical cracking, which is a slow, long-term process. Together, Fe-oxidation, thermal expansion, and subcritical cracking are important mechanisms contributing to long-term weathering and rock decay. Salt weathering, facilitated by snow and ice meltwater, particularly within tafoni, leads to flaking and disintegration of the parent rock. These findings shed light on the complex interactions shaping the geomorphology of central Dronning Maud Land and provide insights into long-term weathering processes operating in Antarctica's extreme environment.

Ti–6Al–4V complex shape production by spark plasma sintering with ceramic–metal sacrificial powder and interface 3D printing

Ti–6Al–4V complex shape production by spark plasma sintering with ceramic–metal sacrificial powder and interface 3D printing

A closed form expression of stress intensity factor for an arbitrarily shaped planar crack in 3-D under tensile loading

A closed-form equation was developed in this work to quantify the stress intensity factor (SIF) along an arbitrarily shaped planar crack under mode-I loading by substituting the ellipse-related parameters in Irwin’s solution with geometry-related parameters fi of the crack. This allowed incorporation of the local crack curvature effect on SIF at each discrete point along the crack front and its relative weighted contribution to SIF of the neighboring crack point i, where either stress concentration or shielding took place, into computation of the SIF distribution along the crack front. Good agreement was obtained between the KI values derived in the current work and previous numerical simulation-based studies. The current method could capture the KI distributions for surface and embedded cracks having the same shape, with their maximum values being consistent with Murakami’s area method. This solution of KI allows for highly efficient calculation of ΔKI for quantification of the 3D growth behaviors of a fatigue crack with a complex shape, paving the way for studying the statistical nature of short fatigue crack growth.