Search Results (197)

This article comprehensively reviews the tribological behavior of a Ti-6Al-4V alloy manufactured via electron beam powder bed fusion (EB-PBF), an additive manufacturing process for aerospace and biomedical applications. EB-PBF Ti-6Al-4V demonstrates wear resistance that is superior or comparable to conventional Ti-6Al-4V. The reported average friction coefficient ranges between ~0.22 and ~0.75 during sliding wear in dry and lubricated conditions against metallic and ceramic counterparts when loading 1–50 N under varied surface and heat treatment conditions, and between 1.29 and 2.2 during fretting wear against EB-PBF Ti-6Al-4V itself. The corresponding average specific wear rates show a broad range between ~8.20 × 10⁻⁵ mm³/Nm and ~1.30 × 10⁻³ mm³/Nm during sliding wear. Lubrication reduces the wear rates and/or the friction coefficient. Wear resistance can be improved via machining and heat treatment. Wear anisotropy is reported and primarily attributed to microhardness variations, which can be mitigated through lubrication and post-processing. The effects of applied load and frequency on EB-PBF Ti-6Al-4V are also discussed. The wear resistance at elevated temperatures shows a mixed trend that depends on the counterpart material and the testing methods. Wear mechanisms involve oxide tribo-layer formation, abrasive wear, and adhesive wear. Current limitations, future research directions, and a standardization framework are also discussed. Full article

This paper investigates the influence of initial porosity and its evolution on the mechanical behavior of metallic materials manufactured by additive manufacturing (AM), using the Gurson model to predict the initiation and propagation of damage in specimens produced via Laser Powder Bed Fusion (LPBF). The methodology combines experimental uniaxial tensile tests, numerical simulations based on the Gurson model, and the parametric identification method (PIP) to calibrate constitutive parameters (${\sigma }_{y0}$, ${\sigma }_{\infty }$, $\delta$, $\xi$). The specimens, made of AlSi10Mg with different printing directions (horizontal and vertical) and porosity levels, were evaluated to determine the relationship between density, anisotropy, and mechanical properties. The experimental results revealed that vertical printing accelerates fracture due to the concentration of stresses at the interfaces between layers, while the numerical simulations, compared with the von Mises model, showed greater accuracy of the Gurson model in predicting damage in porous materials. The analysis of porosity evolution highlighted the impact of void size and spacing on coalescence and ductility. The proposed methodology was validated, establishing a useful approach for evaluating the mechanical behavior of materials manufactured by AM. This work contributes to the advancement of the design of lightweight and resistant components, with applications in sectors such as aerospace and automotive, and suggests directions for future studies, including the investigation of other alloys and dynamic loading conditions. Full article

This study addresses the critical need to enhance productivity in industrial automatic systems by optimizing the mass of moving components. The primary challenge is determining the complex, dynamic loads on structural elements, a prerequisite for effective redesign, without access to physical prototypes for experimental measurement. This paper presents a solution through a case study of a load-bearing pylon in a fine blanking plant, which is subject to inertial loads and shocks from pneumatic actuators and shock absorbers. To overcome this challenge, a high-fidelity multibody simulation model is developed to accurately estimate the dynamic loads on the pylon. This data is given as input to the topology optimization (TO) process, following the Design for Additive Manufacturing (DfAM) framework, to redesign the pylon for mass reduction using a Powder Bed Fusion-Laser Beam (PBF-LB). Two materials, EOS Aluminum Al2139 AM and EOS Maraging Steel MS1, are evaluated. The findings demonstrate that the integrated simulation and redesign approach is highly effective. The redesigned pylon’s performance is verified within the same simulation environment, confirming the productivity gains before manufacturing. A cost analysis revealed that the additively manufactured solution is more expensive than traditional methods, and the final choice depends on the overall productivity increase. This research validates a powerful methodology that integrates dynamic multibody analysis with topology optimization for AM. This approach is recommended in the design phase of complex industrial machinery to evaluate and quantify performance improvements and make informed decisions on the cost-effectiveness of introducing AM components without the need for physical prototyping. Full article

The formation of metal–polymer composites by 3D printing PLA and PETG onto EN AW-5182 H111 aluminum substrates without the use of adhesives was investigated. Four surface treatments were evaluated on the metal substrate (fine sanding, coarse sanding, abrasive blasting, and acid etching), over which a polymer primer—prepared from PLA and PETG solutions—was applied. Subsequently, test specimens were fabricated using the same polymer through material extrusion (MEX) with filaments. Adhesion strength between the printed polymer and the metal substrate was assessed through perpendicular tensile, lap shear, and three-point bending tests. The 16-condition experimental matrix combined surface treatment, primer thickness, and bed temperature and was replicated for each test. Peak tensile and shear strengths confirmed the effectiveness of the proposed strategy, with PETG consistently showing a higher interfacial performance than PLA. ANOVA analysis identifies primer layer thickness (p = 0.023) and loading type (p = 0.031) as statistically significant variables. The results suggest that either abrasive or acid pretreatment, combined with a primer thickness ≥ 80 µm and moderate bed temperatures (65 °C for PLA and 90 °C for PETG), enables the fabrication of robust metal–polymer joints, which are particularly resistant to shear stress and suitable for industrial applications. Full article

The discharge behavior of agricultural materials from silos is significantly influenced by external driving forces. Pressurized discharge from silos is an effective method for analyzing localized stress distribution and controlling flow rates. In this study, a combined approach of experiments and Discrete Element Method (DEM) simulations was employed to investigate the forced flow behavior of rice particle beds. Detailed analyses were conducted on flow patterns, velocity distributions, mass flow rates, dynamic arch formation, bottom stress distribution, and load propagation. Furthermore, the dissipative power during discharge was calculated based on the local shear at the silo wall, and a master curve for the dissipative power was presented. This curve facilitates the prediction of energy dissipation during silo discharge under various conditions. The findings provide a foundation and data support for the structural optimization of silos. Full article

Red sandstones of the Cambrian age are globally distributed and represent an important sedimentation phase during this critical time interval. Their sedimentology and geochemistry can provide key information about the sedimentation style, paleoclimatic conditions, and weathering trends during the Cambrian. In the Salt Range of Pakistan, the Khewra Sandstone constitutes the Lower Cambrian strata and consists of red–maroon sandstones with minor siltstone and shale in the basal part. Cross-bedding, graded bedding, ripple marks, parallel laminations, load casts, ball and pillows, desiccation cracks, and bioturbation are the common sedimentary features of the formation. The sandstones are fine to medium to coarse-grained with subangular to subrounded morphology and display an overall coarsening upward trend. Petrographic analysis indicates that the sandstones are sub-arkose and sub-lithic arenites, and dolomite and calcite are common cementing materials. X-ray Diffraction (XRD) analysis indicates that the main minerals in the formation are quartz, feldspars, kaolinite, illite, mica, hematite, dolomite, and calcite. Geochemical analysis indicates that SiO₂ is the major component at a range of 53.3 to 88% (averaging 70.4%), Al₂O₃ ranges from 3.1 to 19.2% (averaging 9.2%), CaO ranges from 0.4 to 25.3% (averaging 7.4%), K₂O ranges from 1.2 to 7.4% (averaging 4.8%), MgO ranges from 0.2 to 7.4% (averaging 3.5%), and Na₂O ranges from 0.1 to 0.9% (averaging 0.4%), respectively. The results of the combined proxies indicate that the sedimentation occurred in fluvial–deltaic settings under overall arid to semi-arid paleoclimatic conditions with poor to moderate chemical weathering. The Khewra Sandstone represents the red Cambrian sandstones on the NW Indian Plate margin of Gondwana and can be correlated with contemporaneous red sandstones in the USA, Europe, Africa, Iran, and Turkey (Türkiye). Full article

Discontinuous fibers are commonly added to matrix materials in additive manufacturing to enhance properties, but such benefits may be constrained by print and fiber orientation. The additive processes of forming rasters and layers in powder bed fusion inherently cause anisotropy in printed parts. Many print parameters, such as laser, temperature, and hatch pattern, influence the anisotropy of tensile properties. This study characterizes fiber orientation attributed to recoating non-encapsulated fibers and the resulting anisotropic tensile properties. Tensile and fracture properties of polyamide 12 reinforced with 0%, 2.5%, 5%, and 10% discontinuous carbon fibers by volume were characterized in two primary print/tensile loading orientations: tensile loading parallel to the recoater (“horizontal specimens”) and tensile load along the build axis (“vertical specimens”). Density and fractographic analysis indicate a homogeneous mixture with low porosity and primary fiber orientation along the recoating direction for both print orientations. Neat specimens (zero fiber) loaded in either direction have similar tensile properties. However, fiber-reinforced vertical specimens have significantly reduced consistency and tensile strength as fiber content increased, while the opposite is true for horizontal specimens. These datasets and results provide a mechanism to tune material properties and improve the functionality of selectively laser-sintered fiber-reinforced parts through print orientation selection. These datasets could be used to customize functionally graded parts with multi-material selective laser-sintering manufacturing. Full article

Background: Automated semi-solid extrusion (SSE) material deposition is a promising new technology for preparing personalized medicines for different patient groups and veterinary applications. The technology enables the preparation of custom-made oral elastic gel tablets of active pharmaceutical ingredient (API) by using a semi-solid polymeric printing ink. Methods: An automated SSE material deposition method was used for generating chewable gel tablets loaded with propranolol hydrochloride (-HCl) at three different API content levels (3.0 mg, 4.0 mg, 5.0 mg). The physical appearance, surface morphology, dimensions, mass and mass variation, process-derived solid-state changes, mechanical properties, and in-vitro drug release of the gel tablets were studied. Results: The inclusion of API (1% w/w) in the semi-solid CuraBlend^TM printing mixture decreased viscosity and increased fluidity, thus promoting the spreading of the mixture on the printed (material deposition) bed and the printing performance of the gel tablets. The printed gel tablets were elastic, soft, jelly-like, chewable preparations. The mechanical properties of the gel tablets were dependent on the printing ink composition (i.e., with or without propranolol HCl). The maximum load for the final deformation of the CuraBlend™-API (3.0 mg) gel tablets was very uniform, ranging from 73 N to 80 N. The in-vitro dissolution test showed that more than 85% of the drug load was released within 15–20 min, thus verifying the immediate-release behavior of these drug preparations. Conclusions: Automated SSE material deposition as a modified 3D printing method is a feasible technology for preparing customized oral chewable gel tablets of propranolol HCl. Full article

The use of porous concrete in various infrastructure applications such as pavements, infiltration beds, and low-volume load areas is increasingly encouraged due to its environmental benefits. The performance of porous concrete is strongly influenced by its pore structure and overall porosity. Researchers have employed multiple methodologies to characterise pore size and distribution, and to assess their effects on permeability, hydraulic conductivity, and compressive strength. This review investigates several pore measurement techniques aimed at improving both the hydraulic and mechanical performance of porous concrete. Among these, image analysis emerges as the most accurate method for assessing porosity distribution, offering higher resolution and fewer limitations compared to traditional techniques. Despite these advancements, a debate remains regarding the relative importance of effective porosity versus total porosity. This work comprehensively evaluates and synthesises existing methods for pore structure analysis, thereby enhancing our understanding of how porosity influences concrete behaviour. The findings indicate that effective porosity alone is insufficient to predict hydraulic conductivity, whereas total porosity has a considerable effect on compressive strength. This insight can be used to optimise the balance between strength and permeability in porous concrete, supporting its broader implementation as a sustainable construction material. Full article

With the rapid development of the livestock farming industry, the treatment of livestock farming wastewater has become increasingly important. The microbial-algal biofilm method has gained widespread attention for cattle wastewater treatment owing to its non-toxic nature, resistance to shock loading, and high treatment efficiency. In this study, three types of substrates—polyurethane sponge, ceramic material, and moving bed biofilm reactor media—were evaluated. The formation of biofilms was assessed through variations in chlorophyll content, microscopic observations, and measurements of biofilm dry weight and attachment rate. Biofilm characterization on the different substrates was conducted via Fourier transform infrared spectroscopy, confocal laser scanning microscopy, and scanning electron microscopy. The results demonstrated that polyurethane sponge was the most effective substrate. Furthermore, a single-factor experiment was conducted to optimize the cultivation conditions for the microbial-algal biofilms and identify the optimal parameters based on the ability of the biofilm to remove COD, TN, TP, and NH₄⁺-N. The optimal conditions were as follows: an illumination intensity of 8000 lux, red light, a temperature of 20 °C, a pH of 7, and an aeration intensity of 8 L/min. Under these conditions, the pollutant removal rates were exceptionally high: ~73.4% for COD, 51.8% for TP, 57.0% for TN, and 75.1% for NH₄⁺-N. Full article

Dredging of fine sediments and dumping of fines at disposal sites produce passive plumes behind the dredging equipment. Each type of dredging method has its own plume characteristics. All types of dredging operations create some form of turbidity (spillage of dredged materials) in the water column, depending on (i) the applied method (mechanical grab/backhoe, hydraulic suction dredging with/without overflow), (ii) the nature of the sediment bed, and (iii) the hydrodynamic conditions. A simple parameter to represent the spillage of dredged materials is the spill percentage (R_spill) of the initial load. In the case of cutter dredging and hopper dredging without overflow, sediment spillage is mostly low, with values in the range of 1% to 3%, The spill percentage is higher, in the range of 3% to 30%, for hopper dredging of mud with intensive overflow. Spilling of dredged materials also occurs at disposal sites. The spill percentage is generally low, with values in the range of 1% to 3%, if the load is dumped through bottom doors in deep water, creating a dynamic plume which descends rapidly to the bottom with cloud velocities of 1 m/s. The most accurate approach to study passive plume behavior is the application of a 3D model, which, however, is a major, time-consuming effort. A practical 1D plume dispersion model can help to identify the best parameter settings involved and to conduct fast scan studies. The proposed 1D model represents equations for dynamic plume behavior, as well as passive plume behavior including advection, diffusion and settling processes. Full article

Estimating bed load in rivers is a critical aspect of river engineering. Numerous methods have been developed to quantify bed load transport, often yielding varying results depending on the bed surface texture and grain size. This study aims to investigate how vegetation on channel banks and bed material particle size influence bed load transport, bed shear stress, velocity distribution, and the Shields parameter. It also examines the impact of geometric changes in the channel cross-section on bed load transport capacity. To address these objectives, a novel simulation method was developed to analyze the effects of vegetated banks, bed material size, and channel geometry. Field investigations were carried out in two reaches of the Taleghan River in Iran—one with vegetated banks and one without. Complementary flume experiments were conducted at two scales, incorporating vegetation on the sidewalls. Results showed that Shields parameter distribution corresponded with bed load distribution across cross-sections. Increase in flow rate and the Shields parameter led to higher bedload transport rates. Near vegetated banks, flow velocity, shear stress, and bedload transport were significantly reduced, with velocity profiles showing distinct variations compared to non-vegetated sections. Full article

Background/Objectives: Guided bone regeneration (GBR) is a regenerative technique used to treat maxillary osseous defects to enable implant placement for prosthetic rehabilitation. It is generally performed with the use of barrier membranes and bone substitute materials of human or animal origin. Here, we report the clinical and histological outcomes of a horizontal GBR, treated using only synthetic biomaterials. Methods: A graft of nanocrystalline hydroxyapatite (NH) embedded in a silica gel matrix was used to fill a horizontal bone defect. The graft was covered with a titanium-reinforced dense polytetrafluoroethylene (TR-dPTFE) membrane, and primary closure was completed and maintained for 10 months. Then, the site was re-opened for membrane removal and implant insertion. During implant bed preparation, a bone biopsy was obtained for histological evaluation. A metal–ceramic crown was fitted, and the 5-year follow-up after prosthetic loading showed clinical and radiographically healthy tissues. Results: Histological examination revealed good integration of the biomaterial into the surrounding tissues, which were composed of lamellar bone trabeculae and connective tissue. New bone formation occurred not only around the NH granules but even inside the porous amorphous particles. Conclusions: The combination of NH and the TR-dPTFE membrane produced good clinical and histological results, which remained stable for 5 years. Full article

The water adsorption property was shown to be the critical process limiting the thermal output in the adsorption heat storage driven by the air humidity process, which was different for the physical adsorbent and the physical/chemical adsorbent. In this study, coconut shell-based activated carbon (CAC), a hierarchically porous material that is both low-cost and mass-producible, was utilized as a physical adsorbent and as a matrix for loading calcium chloride (CAC/Ca). The incorporation of calcium chloride in CAC, with a 24% content, resulted in a 4~102% increase in water uptake capacity. The water uptake dynamics of high-thickness adsorbents are inhibited, especially for CAC/Ca. In the context of the adsorption test conducted within a fixed-bed reactor, an increase in air velocity was observed to facilitate water vapor supply, thereby culminating in higher output temperatures for both CAC and CAC/Ca, indicating a higher hydration conversion. The maximum discharge powers of CAC/Ca increased from 2 kW/m³ to 20 kW/m³, with the air velocity increasing from 0.5 m/s to 2.5 m/s. The heat-release densities of CAC and CAC/Ca at the air velocity of 2.5 m/s were 156 kJ/kg and 547 kJ/kg, respectively. Full article

The limited build space of additive manufacturing (AM) machines constrains the maximum size of AM components, while manufacturing costs rise with geometric complexity. To enhance value and overcome size limitations, it can be more efficient to join non-AM and AM components to meet the requirements by means of a hybrid structure. Adhesive bonding is particularly suitable for such joints, as it imposes no constraints on the joining surface’s geometry or the adherend’s material. To ensure structural integrity, it is conceivable to exploit the design freedom underlying AM processes by optimizing the topology of the AM component to stress the adhesive layer homogeneously. This study explores the feasibility of this concept using the example of an axially loaded single-lap tubular joint between a carbon fiber-reinforced composite tube and an additively manufactured laser-based powder-bed-fusion aluminum alloy sleeve. The sleeve topology was optimized using the finite element method, achieving a $75 \%\mathrm{P}$ reduction in adhesive stress increase compared to a non-optimized sleeve. Due to the pronounced ductility of the two-component epoxy-based adhesive, the static bond strength remained unaffected, whereas fatigue life significantly improved. The findings demonstrate the feasibility of leveraging AM design freedom to enhance adhesive joint performance, providing a promising approach for hybrid structures in lightweight applications. Full article