Search Results (118)

This study investigates the dynamic characteristics of three-dimensional (3D) printed acrylonitrile butadiene styrene (ABS) cantilever beams using Experimental Modal Analysis (EMA). The effects of Fused Deposition Modelling (FDM) process parameters—specifically infill pattern, infill density, nozzle size, and raster angle—on the natural frequency, mode shapes, and damping ratio were examined. Although numerous studies have addressed the static mechanical behaviour of FDM parts, there remains a significant gap in understanding how internal structural features and porosity influence their vibrational response. To address this, a total of seventy-two specimens were fabricated with varying parameter combinations, and their dynamic responses were evaluated through frequency response functions (FRFs) obtained via the impact hammer test. Damping characteristics were extracted using the peak-picking (half power) method. Additionally, the influence of internal porosity on damping behaviour was assessed by comparing the actual and theoretical masses of the specimens. The findings indicate that both natural frequencies and damping ratios are strongly influenced by the internal structure of the printed components. In particular, gyroid and cubic infill patterns increased structural stiffness and resulted in higher resonant frequencies, while low infill densities and triangle patterns contributed to enhanced damping capacity. Response Surface Methodology (RSM) was employed to develop mathematical models describing the parameter effects, providing predictive tools for applications sensitive to vibration. The high R² values obtained in the RSM models based on the input variables show that these variables explain the effects of these variables on both natural frequency and damping ratio with high accuracy. The models developed (with R² values up to 0.98) enable the prediction of modal behaviour, providing a valuable design tool for engineers optimizing vibration-sensitive components in fields such as aerospace, automotive, and electronics. Full article

Innovations in additive manufacturing (AM) methods represent a significant advancement in manufacturing technology, opening new avenues for creating objects in various shapes and sizes. Fused deposition modeling (FDM) is a specialized AM technique in which computers build layers upon each other to form a complete 3D object. The feasibility of producing metal parts using these methods has been thoroughly analyzed, but the design process has yet to catch up with manufacturing capabilities. Biodegradable aliphatic polyester PLA is derived from lactic acid. To enhance its strength, PLA is combined with metal particles, resulting in versatile property improvements and applications. While the aesthetic and functional qualities of PLA–metal composite filaments are intriguing, they also present difficulties related to extrusion, equipment wear, and maintaining consistent print quality. These challenges could be mitigated, to some extent, with careful tuning and specialized hardware. However, the inferior mechanical properties of bioresorbable PLA filaments highlight the need for the development of infilled PLA filaments to improve strength and other characteristics. This review discusses the 3D printing of PLA infilled with metal particles, various materials used, and their properties as a matter of interest in AM technology. Additionally, the applications of PLA–metal composites, along with their implications, limitations, and prospects, are comprehensively examined in this article. This sets the stage for the development of high-strength, sustainable materials for use in a range of engineering and technology fields. Full article

In this research, eco-friendly PLA filaments were 3D-printed using FDM. Three geometric shapes with different orders of rotational symmetry were selected to create infill patterns: an equilateral triangle, a square, and a regular hexagon. Additionally, each of these three infill patterns was modified by rotating the basic shape used to form the infill pattern by 0°, 15°, and 30°. The objective of this study was to analyze how the order of rotational symmetry within the infill pattern affects the mechanical properties of the printed specimens. To ensure consistency, infill density was kept as uniform as possible across all samples produced. DMA and tensile tests were performed on the produced specimens. The obtained mean values in the tensile measurements were compared using the Kruskal–Wallis test. Dunn’s test was used for post hoc pairwise multiple comparisons. DMA showed that when comparing different infill patterns, the specimens with an order of rotational symmetry of 3 (triangle) showed the highest modulus of elasticity, and the specimens with a 15° rotation regardless of shape generally had the highest storage modulus. Statistical analysis showed that the maximum force of the infill pattern with an order of rotational symmetry of 3 (triangle) was the least affected by the rotation angle, while the infill pattern with an order of rotational symmetry of 4 (square) and a 0° rotation displayed a significantly higher value of the maximum force than other patterns. The infill pattern with an order of rotational symmetry of 6 (hexagon) was moderately affected by the angle of rotation. Given the numerous infill patterns utilized in FDM, the results of this research offered a new viewpoint and insights into optimizing the mechanical properties of 3D-printed infill patterns. Full article

As the articles relating to the study of 3D printing processes are picking up pace, the question of comparability and repeatability based on the geometry and size of the specimens arises, based on the fact that the widely used extrusion 3D printing processes inherently have a structure that is made up of extruded lines of various shapes and sizes. This study aimed to determine the impact the specimen geometry and size have on the final tensile strength. One of the most widely used engineering materials, chopped carbon-fiber-reinforced nylon was used for this study. The four main specimen groups examined were specimens containing only walls and specimens containing only infill printed with both a 0.4 mm and 0.8 mm nozzle (to determine that the size of the extrusion lines has any effect on the tensile strength with different specimen sizes) achieving a solid body with two different line structures. Contradictory to the initial expectations, the tests showed that the geometry and size of the specimens had not influenced the tensile strength of the specimens in any of the four specimen groups. However, the tests showed that the groups containing only walls were always stronger than their only-infill counterparts and the groups printed with a 0.4 mm nozzle were stronger than the groups printed with a 0.8 mm nozzle. Full article

Three-dimensional printing is promising in the pharmaceutical industry for personalized medicine, on-demand production, tailored drug loading, etc. Pressure-assisted microsyringe (PAM) printing is popular due to its low cost, simple operation, and compatibility with heat-sensitive drugs but is limited by ink formulations lacking the essential characteristics, impacting their performance. This study evaluates inks based on sodium alginate (SA), hydroxypropyl cellulose (HPC H), and hydroxypropyl methylcellulose (HPMC K100 and K4) for PAM 3D printing by analyzing their rheology. The formulations included the model drug Fenofibrate, functional excipients (e.g., mannitol, polyethylene glycol, etc.), and water or water–ethanol mixtures. Pills and thin films as an oral dosage were printed using a 410 μm nozzle, a 10 mm/s speed, a 50% infill density, and a 60 kPa pressure. Among the various formulated inks, only the ink containing 0.8% SA achieved successful prints with the desired shape fidelity, linked to its rheological properties, which were assessed using flow, amplitude sweep, and thixotropy tests. This study concludes that (i) an ink’s rheological properties—viscosity, shear thinning, viscoelasticity, modulus, flow point, recovery, etc.—have to be considered to determine whether it will print well; (ii) printability is independent of the dosage form; and (iii) the optimal inks are viscoelastic solids with specific rheological traits. This research provides insights for developing polymer-based inks for effective PAM 3D printing in pharmaceuticals. Full article

Additive manufacturing (AM) processes, such as Fused Filament Fabrication (FFF), enable the production of lightweight parts with high stiffness-to-weight ratios, making them highly suitable for a wide range of engineering applications. However, ensuring the mechanical reliability of these components, particularly for load-bearing purposes, requires systematic mechanical testing of well-designed specimens to asses their suitability. While the tensile properties of additively manufactured materials have been extensively studied, the compressive behavior of components produced via AM, particularly those made from thermoplastic materials, remains comparatively underexplored and insufficiently characterized in the existing body of research. Among these materials, polylactic acid (PLA)—a biodegradable thermoplastic derived from renewable resources—has gained prominence in AM applications. Recent studies have investigated the compression properties of PLA in reinforced materials; however, the focus has primarily been on solid, semi-solid, or porous specimens. These investigations largely overlook thin-walled structures, which are integral to weight-saving designs and commonly feature in topology-optimized structures. Understanding the mechanical behavior of monolayers, the fundamental building blocks of most AM components, is essential for accurately predicting the overall performance of multilayer structures. Monolayers represent the smallest, most basic structural elements of AM parts, and their properties directly influence the behavior of the final, more complex assemblies. Establishing a methodology that correlates monolayer properties with those of multilayer components could significantly streamline testing procedures. By performing mechanical tests on monolayers, instead of on more intricate multilayer specimens, manufacturers could reduce testing complexity and cost while accelerating the development process. The current literature reveals a gap in the design and analysis of thin-walled AM specimens, especially monolayers, under compressive loads. Specifically, the design of monolayer or thin-walled AM compression specimens without infill has not been thoroughly explored. This article addresses this gap by investigating the design and testing of AM monolayer compression specimens produced using FFF of PLA. Three distinct specimen geometries are considered—circular, helicoidal, and S-shaped—to evaluate their potential for understanding and predicting the compressive behavior of AM monolayer structures. Full article

The process of creating ceramic items using fused deposition modelling (FDM) enables the creation of intricate shapes for a variety of purposes, including tooling and prototyping. However, due to the numerous variables involved in the process, it is challenging to discern the impact of each parameter on the final characteristics of FDM components, which impedes the advancement of this technology. This paper deals with the application of statistical analysis in the study of the dependence of the flexural strength of sintered zirconia disks on the printing parameters (nozzle diameter, layer thickness, and infill pattern) of the fused deposition method printing of a ceramic–polymer filament containing 80 wt.% zirconia and 20 wt.% polylactide. X-ray-computed tomography and diffraction systems, scanning electron microscopy combined with energy-dispersive spectroscopy, were used for a microstructural analysis of the sintered samples. It was found that the nozzle diameter and infill pattern have no significant influence on the flexural strength values. It was assumed that this is due to the heterogeneous distribution of the ceramic phase in the manufactured filament during extrusion. On the other hand, correlation analysis and analysis of correlation diagrams have shown that the thickness of the filling layer has the greatest effect on flexural strength. The maximum (684 MPa) strength value was found in a sample printed with a layer thickness of 0.2 mm. The minimum layer thickness ensures a more uniform distribution of ceramic particles and minimizes defects in samples that occur during FDM printing. The results obtained make it possible to optimize the considered process of manufacturing ceramic products from ZrO₂ printed using FDM technology from extruded composite filaments. Full article

Urban growth, a pivotal characteristic of economic development, brings many environmental and ecological challenges. Modeling urban growth is essential for understanding its spatial dynamics and projecting future trends, providing insights for effective urban planning and sustainable development. This study aims to assess the spatiotemporal patterns of urban growth and morphological evolution in mainland Shanghai from 2016 to 2060 using the SLEUTH model under multiple growth scenarios based on the Shanghai Urban Master Plan (2017–2035). A comprehensive set of urban growth metrics and quadrant analysis were employed to quantify the magnitude, rate, intensity, and direction of urban growth, as well as morphological evolution, over time. We found that (1) significant urban growth was observed across most scenarios, with the exception of stringent land protection. The most substantial growth occurred prior to 2045 with an obvious north–south disparity, where southern regions demonstrated more pronounced increases in urban land area and urbanization rates. (2) The spatiotemporal patterns of the rate and intensity of urban growth exhibited similar characteristics. The spatial pattern followed a “concave shape” pattern and displayed anisotropic behavior, with the high values for these indicators primarily observed before 2025. (3) The urban form followed a diffusion–coalescence process, with patch areas dominated by the infilling mode and patch numbers dominated by the edge-expansion mode. This resulted in significant alternating urban growth models in the infilling, edge-expansion, and leapfrog modes over time, influenced by varying protection intensities. These findings provide valuable insights for forward-looking urban planning, land use optimization, and the support of sustainable urban development. Full article

Additive manufacturing (AM) has greatly revolutionized manufacturing due to its ability to manufacture complex shapes without the need for additional tooling. Most AM applications are based on geometries comprising curved shapes subjected to impact loads. The main focus of this study was on investigating the influence of infill density and the radius of curvature on the impact strength of parts manufactured via an FDM process. Standard geometrical specimens with varying part infill densities and radii of curvature were produced and subjected to Charpy impact tests to evaluate their impact strength. The results suggest that the impact strength increases with the increased density caused by higher amounts of material as well as by the changing cross-sectional areas of the beads. Also, the radius of curvature of the parts shows a clear inverse relationship with the impact energy absorbed by the specimens (i.e., increasing the radius decreased the impact energy of the parts) produced via an FDM process, which can be explained using the beam theory of structural mechanics. The maximum value of impact strength obtained was 287 KJ/m², and this was achieved at the highest infill density (i.e., solid) and for the smallest radius of curvature. Full article

This paper presents a comparative study focused on a modal parameters estimation of specimens manufactured by the FDM technique using a fixed embedded vibrometer based on the laser Doppler principle and roving hammer-impact method. Part of this paper is devoted to testing a fixed circular plate with a honeycomb infill pattern while varying the number of excitation points (DOFs), the number of analysis lines of fast Fourier transformation (FFT), and the locations or numbers of reference degrees of freedom (REFs). Although these parameters did not significantly affect the values found for the natural frequencies of the structure, there were changes in the estimates of the mode shapes (affected by the low number of DOFs), in the height and sharpness of the peaks of the CMIF functions (caused by the increased number of FFT lines), and in the number of identified modes (influenced by the chosen location(s) of REFs), respectively. Subsequently, the authors compared the results of experimental modal analyses carried out under the same conditions on three circular plates with honeycomb, star, and concentric infill patterns made of PLA. The results confirm that specimens with honeycomb or star infill patterns have a higher stiffness than those with concentric infill patterns. The low values of the damping ratios obtained for each structure indicate a strong response to excitation at or near their natural frequencies. Full article

Urbanization is a multifaceted process characterized by changes in urban areas through various means, such as sprawl, ribbon development, or infill and compact growth. This phenomenon changes the pattern of the local climate zone (LCZ) and significantly affects the climate, vegetation dynamics, energy consumption, water resources, and public health. This study aims to discern the impacts of changes in urban growth on the LCZ and land surface temperature (LST) over a two-decade period. A comprehensive methodology that integrates statistical analysis, data visualization, machine learning, and advanced techniques, such as remote sensing technology and geospatial analysis systems, is employed. ENVI, GEE, and GIS tools are utilized to collect, process, and monitor satellite data and imagery of temporal and spatial variations in intensive or diffuse urbanization processes from 2003 to 2023 to analyze and simulate land use and land cover (LULC) changes, urbanization index (UI), LCZ patterns, and LST changes over the years and to make overlapping maps of changes to recognize the relation between LULC, LCZ, and LST. This study focuses on Seville’s urban area, which has experienced rapid urbanization and a significant increase in average temperature during the last few decades. The findings of this study will provide actionable recommendations into the interplay between urban growth and climate and highlight the pivotal role of urban growth in shaping resilience and vulnerable areas based on microclimate changes. Urban planners can leverage these insights to predict alternatives for the future development of urban areas and define practical climate mitigation strategies. Full article

Thermoplastic polyimides (TPIs) are promising lightweight materials for replacing metal components in aerospace, rocketry, and automotive industries. Key TPI attributes include low density, thermal stability, mechanical strength, inherent flame retardancy, and intrinsic fluorescence under UV light. The application of advanced manufacturing techniques, especially 3D printing, could significantly broaden the use of TPIs; however, challenges in melt-processing this class of polymer represent a barrier. This study explored the processability, 3D-printing and hence mechanical, and fluorescence properties of TPI coupons, demonstrating their suitability for advanced 3D-printing applications. Moreover, the study successfully 3D-printed a functional impeller for an overhead stirrer, effectively replacing its metallic counterpart. Defects were shown to be readily detectable under UV light. A thorough analysis of TPI processing examining its rheological, morphological, and thermal properties is presented. Extruded TPI filaments were 3D-printed into test coupons with different infill geometries to examine the effect of tool path on mechanical performance. The fluorescence properties of the 3D-printed TPI coupons were evaluated to highlight their potential to produce intricately shaped thermally stable, fluorescence-based sensors. Full article

This study evaluates the storm surge inundation risk in three anthropogenically infilled estuaries—Xichong, Renshan, and Kaozhouyang—located in the Guangdong–Macao–Hong Kong Great Bay Area, China. By integrating GIS spatial analysis with storm surge modeling, we conducted 204 numerical experiments to simulate storm surge inundation under varying typhoon intensities and astronomical tide conditions. Results revealed that coastal terrain plays a crucial role in influencing storm surge levels and inundation extents. Specifically, the pocket-shaped terrain in the Renshan and Kaozhouyang estuaries amplified storm surges, resulting in higher inundation levels compared to the relatively open terrain of Xichong. Furthermore, anthropogenically reclaimed land in these estuaries appear to be particularly vulnerable to storm-induced inundation. Overall, this study underscores the importance of considering coastline morphology and the anthropogenic modifications of coastal terrain in storm surge risk assessments, offering valuable insights for disaster prevention and mitigation strategies. The use of ArcGIS spatial analysis coupled with storm surge modeling, facilitated by high-resolution DEMs, provides a statistical risk assessment of inundation. However, more complex flooding dynamics models need to be developed, particularly when terrestrial bottom friction information, which is heavily modified by human activities, can be accurately incorporated. Full article

Precast rectangular reinforced concrete (PRRC) beams are joined on construction sites using concrete in situ to achieve the desired length. Limited research exists on the effect of intermediate connection shapes and the types of infilled concrete on the flexural performance of PRRC beams. This paper presents a comprehensive experimental and numerical investigation into the performance of PRRC beams with various intermediate connection geometries and infilled materials under flexural loading. The study examines rectangular, triangular, and semi-circular intermediate connections, along with the performance of beams infilled with normal concrete (NC), engineered cementitious composites (ECC), ultra-high-performance ECC (UHPECC), and rubberized ECC (RECC). The experimental results indicate that the rectangular intermediate connection exhibits superior performance in terms of strength and energy absorption compared to the triangular and semi-circular shapes. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC for any shape of intermediate connection. Moreover, beams with rectangular connections and UHPECC infill exhibited the most significant increase in energy absorption and ultimate load compared to the beams with ECC and RECC. The ultimate load of the beams with UHPECC and tensile reinforcement bar diameters of 10 mm and 12 mm increased by 13% and 29%, respectively, compared to the control beam. The energy absorption of the beams with tensile reinforcement bar diameters of 10 and 12 mm was found to be 75% and 184% higher, respectively, than the control beam. In addition, an increase in tensile bar diameter was found to enhance both the energy absorption and the ultimate load capacity of the beams, regardless of the type of infill concrete. Beams incorporating UHPECC demonstrated the most significant improvements in strength and energy absorption, outperforming those with ECC and RECC. In particular, beams with rectangular connections and UHPECC infill exhibited an increase in energy absorption and ultimate load of up to 184% and 29%, respectively. UHPC was calculated to be as high as 184%, and 29%, respectively, compared to the control beams. In addition, an increase in tensile bar diameter was found to enhance both energy absorption and ultimate load capacity. Finite element modeling (FEM) was developed and validated against the experimental results to ensure accuracy. A parametric study was conducted to study the effects of various concrete types in triangular and semi-circular connections, as well as the influence of intermediate connection length on semi-circular connections under flexural loads. The findings reveal that increasing the length of intermediate connections increases the ultimate load of the beams. Full article

Traditional prosthetic liners are often limited in customization due to constraints in manufacturing processes and materials. Typically made from non-compressible elastomers, these liners can cause discomfort through uneven contact pressures and inadequate adaptation to the complex shape of the residual limb. This study explores the development of bioinspired cellular metamaterial prosthetic liners, designed using additive manufacturing techniques to improve comfort by reducing contact pressure and redistributing deformation at the limb–prosthesis interface. The gyroid unit cell was selected due to its favorable isotropic properties, ease of manufacturing, and ability to distribute loads efficiently. Following the initial unit cell identification analysis, the results from the uniaxial compression test on the metamaterial cellular samples were used to develop a multilinear material model, approximating the response of the metamaterial structure. Finite Element Analysis (FEA) using a previously developed generic limb–liner–socket model was employed to simulate and compare the biomechanical behavior of these novel liners against conventional silicone liners, focusing on key parameters such as peak contact pressure and liner deformation during donning, heel strike, and the push-off phase of the gait cycle. The results showed that while silicone liners provide good overall contact pressure reduction, cellular liners offer superior customization and performance optimization. The soft cellular liner significantly reduced peak contact pressure during donning compared to silicone liners but exhibited higher deformation, making it more suitable for sedentary individuals. In contrast, medium and hard cellular liners outperformed silicone liners for active individuals by reducing both contact pressure and deformation during dynamic gait phases, thereby enhancing stability. Specifically, a medium-density liner (10% infill) balanced contact pressure reduction with low deformation, offering a balance of comfort and stability. The hard cellular liner, ideal for high-impact activities, provided superior shape retention and support with lower liner deformation and comparable contact pressures to silicone liners. The results show that customizable stiffness in cellular metamaterial liners enables personalized design to address individual needs, whether focusing on comfort, stability, or both. These findings suggest that 3D-printed metamaterial liners could be a promising alternative to traditional prosthetic materials, warranting further research and clinical validation. Full article