Search Results (11,731)

This study focuses on the design and control system of a rotating nozzle for 3D construction printers. The development of a rotating nozzle is motivated by the need to enhance control over extrusion direction and material alignment, thereby improving the mechanical performance of printed structures by the use of non-circular nozzles. The typical 3D construction printer is equipped only with a stationary circular nozzle, which prevents the use of a non-circular nozzle due to the printer’s lack of a rotational mechanical system. This, in turn, limits the opportunity to enhance mechanical properties such as tensile and compressive strengths effectively. The proposed design is developed through computer-aided design (CAD) software, and the printer’s configuration is adjusted for integration of the rotational mechanism’s control system. This design includes a full description of the rotational mechanism and integration steps for the 3D printer. Besides the main motor of the 3D printer, an additional motor is installed next to the nozzle and controlled by a new axis (parameter), which is added into the G-code. A new axis, called “U”, is responsible for the rotation of the nozzle itself. For the development of this axis design, the cosine law is applied. The calculation is based on the three consecutive points in the G-code to obtain an accurate degree of rotation for the nozzle. The effectiveness of the system was confirmed by evaluating the compressive strength depending on printhead type. Based on testing results, one trowel printhead had the highest flexural strength of 5 MPa, and a trapezoidal printhead with teeth had the highest compressive strength of 8 MPa, compared to a circular default nozzle head with 6 MPa and 2 MPa for compressive and flexural strengths, respectively. The new optimized nozzle design is implemented in existing 3D printers, which allows it not only to develop its capability in the printing process but also to make sustainable contributions in the 3D construction industry. Full article

As a solid-state joining technology, friction stir welding (FSW) exhibits significant advantages for joining aluminium alloys, including low heat input and minimal formation of intermetallic compounds, thereby enhancing joint quality and mitigating deformation. This study investigates the single-sided and double-sided FSW processes of 3 mm thick 7075-T6 aluminium alloy sheets, focusing on characterising the microstructure and mechanical properties of the joints. Experimental results show that at a rotational speed of 1500 rpm and a welding speed of 80 mm/min, the double-sided co-directional FSW joint achieves a tensile strength of 388 MPa and an elongation of 7.09%, significantly outperforming those of the other two welding paths. In the weld nugget zone (WNZ), continuous dynamic recrystallization (CDRX) occurs, generating uniformly refined equiaxed grains (average size: 1.10 μm) and facilitating the transformation of low-angle grain boundaries (LAGBs) to high-angle grain boundaries (HAGBs). Meanwhile, the strong rotated cube texture is remarkably weakened and replaced by random recrystallized brass textures with the lowest kernel average misorientation (KAM) value in the WNZ. In contrast, the thermo-mechanically affected zone (TMAZ) accumulates a high density of LAGBs due to welding-induced plastic deformation. Microhardness testing reveals a typical “W”-shaped distribution: WNZ hardness is relatively high but slightly lower than that of the base metal (BM), and the minimum hardness of the advancing side (AS) of the heat-affected zone (HAZ) is higher than that of the retreating side (RS). This study confirms that double-sided co-directional FSW crucially regulates microstructural evolution and improves the mechanical properties of 7075-T6 aluminium alloy joints, providing a viable process optimisation strategy for high-quality welding of thin-gauge sheets. Full article

In order to clarify the road performance and load response behavior of polyurethane mixtures, a low-temperature bending test, dynamic modulus test, rutting test, Hamburg rutting test, and four-point bending fatigue test were conducted on multi-crushed stone polyurethane concrete (SPC-16) and polyurethane concrete (PC-20) as the test objects, and the results were compared with the road performance of an asphalt mastic crushed stone mixture (SMA-13). The differences in the load response between two typical polyurethane mixture pavement structures and a typical asphalt pavement structure were analyzed under four working conditions: a normal-temperature standard load, normal-temperature heavy load, high-temperature standard load, and high-temperature heavy load. The results showed that the low-temperature flexural tensile strength of the polyurethane mixture was 1.3–1.7-times that of SMA-13, the maximum flexural tensile strain was 1.1–1.8-times that of SMA-13, the dynamic stability of the polyurethane mixture was more than 15-times that of SMA-13, and the fatigue life of the polyurethane mixture was 8–12-times that of SMA-13. The surface deflection, base stress, and surface strain of the typical asphalt pavement structures and two typical polyurethane mixture pavement structures at the same temperature all increased with an increase in the load. The load response of the polyurethane mixture pavement structures under high-temperature conditions was relatively stable. Full article

This study presents an experimental and numerical investigation of reinforced concrete beams incorporating micro polypropylene, macro polypropylene, and steel fibers. Three concrete series of equal strength classes were prepared and tested to evaluate compressive strength, splitting tensile strength, flexural performance, and deformation behavior under short-term loading. Strain development in both concrete and reinforcement was measured using strain gauges and mechanical deformometers. In parallel with the experimental program, a nonlinear finite element model was developed using the DIANA FEAsoftware 10.5 to simulate the deformation behavior and strain development of the tested beams. The concrete material was represented using a total strain-based smeared crack model with rotating crack orientation, while the contribution of fiber reinforcement was incorporated through a CMOD-based post-cracking tensile constitutive law. The numerical results showed good agreement with the experimental load–deflection and strain measurements, confirming the suitability of the adopted modeling approach. These findings demonstrate that the combined experimental–numerical framework provides a reliable tool for assessing the deformation and cracking behavior of fiber-reinforced concrete beams. The experimental results indicate that fiber type and combination strongly influence the deformation behavior and mechanical performance of reinforced concrete beams, with hybrid systems incorporating steel fibers exhibiting enhanced flexural response, improved strain compatibility, and more ductile behavior compared to polypropylene-only reinforcement. The inclusion of steel fibers led to distributed cracking, delayed stiffness degradation, increases of up to approximately 6.3% in concrete strains and 10.3% in reinforcement strains, and a substantial improvement in compressive strength (up to approximately 28.8%), confirming the synergistic effect of hybrid fiber reinforcement. Full article

This study examines the mechanical response of medium-manganese TRIP steels under different stress states, focusing on deformation-induced austenite-to-martensite transformation and ageing phenomena. Two steels with distinctly different ferrite–austenite morphologies and retained austenite (RA) fractions were analysed: a globular microstructure with 18% RA and a lamellar microstructure with 14% RA, produced by single (SA) and double annealing (DA), respectively. Continuous and interrupted tests were performed under in-plane shear, uniaxial tension, and plane strain stress states. Strain fields were analysed using high-resolution digital image correlation, while RA fractions were quantified as a function of strain by ex situ X-ray diffraction. The results demonstrate a pronounced stress-state dependence. SA samples exhibit discontinuous yielding, with uniaxial tests showing clear Lüders band formation. Both steels exhibit dynamic strain ageing manifested by Portevin–Le Chatelier (PLC) serrations and associated strain bands, which are most pronounced under uniaxial tension, weaker in plane strain, and barely detectable in in-plane shear. Static strain ageing is also evidenced by a strengthened yield response upon unloading–reloading in all samples. The SA globular microstructure exhibits higher PLC band inclination angles than the lamellar DA microstructure, consistent with its more pronounced anisotropy. The propagation velocity in uniaxial tensile samples decreases with increasing strain following the work-hardening response. For both steels, the austenite-to-martensite transformation rate is highest in uniaxial tension, slightly reduced in plane strain, and strongly suppressed under in-plane shear. A Beese–Mohr/Johnson–Mehl–Avrami–Kolmogorov formulation incorporating stress triaxiality and Lode angle captures these trends for both steels. For the stress states considered, the DA condition exhibits a consistently higher transformation rate than the SA condition, accompanied by a higher work-hardening rate. These findings highlight the coupled role of stress state and microstructural morphology in governing localisation behaviour and strain-induced transformation in medium-manganese steels. Full article

This paper presents a systematic review of research investigating the effects of elevated temperatures on sedimentary rocks. The literature was selected using keyword-based searches of titles, abstracts, and keywords in the Scopus and Web of Science databases. In total, 107 relevant articles published between 2010 and 2024 were critically examined to address research questions on temperature-treated sedimentary rocks. Furthermore, both bibliometric analysis and systematic synthesis of experimental data were performed. The review identifies sandstone as the most-studied rock type, followed by limestone. It reveals that standard experimental methods include unconfined compressive strength (UCS), Brazilian tensile strength (BTS), and P-wave velocity tests. The study’s findings indicate that a temperature threshold of 400–600 °C governs deterioration in engineering properties, driven by the quartz α–β transition in sandstones and calcite decomposition in limestones. Normalized data show that UCS, BTS, and elastic modulus decline significantly beyond this threshold, while porosity increases. The study highlights the influence of fabric anisotropy, mineralogy, and heating conditions on rock behaviour, and identifies research gaps related to confined testing, real-fire scenarios, and anisotropic rocks. Based on a comprehensive analysis of the literature, the principal factors and processes occurring at different temperature ranges were identified and discussed. Full article

This study investigates the processability and performance limits of high-density polyethylene (HDPE) recovered from mixed polyolefin waste under realistic mechanical recycling conditions. The waste stream was processed by extrusion and injection molding, with parameters actively adapted. ATR-FTIR and DSC analysis confirmed HDPE as the matrix, contaminated with minor fractions of polypropylene (PP), PET, and polyurethane (PU). The reprocessed material exhibited a single melting peak at 132 °C and a melt flow rate (MFR) of 9.9 ± 0.6 g 10 min⁻¹, indicative of moderate degradation. Mechanical testing revealed reduced tensile strength and elongation at break compared to virgin HDPE, indicating compositional heterogeneity and poor interfacial adhesion. Field emission scanning electron microscopy (FESEM) revealed dispersed inclusions and microvoids acting as stress concentrators, consistent with reduced ductility. Crucially, progressive reduction of back pressure during processing optimization was essential for stabilizing melt flow and minimizing shear-induced degradation. This adjustment enabled consistent mold filling despite the material’s variability. The results demonstrate that mixed HDPE waste can be successfully valorized for non-structural applications such as plastic lumber or pallets, providing a sustainable pathway for recycling heterogeneous streams without costly pre-treatment or compatibilization. Full article

Designing armor units that can withstand harsh marine environments while remaining cost-effective is a central challenge in modern breakwater engineering. This study introduces a newly designed artificial armor unit and evaluates its performance in comparison with established alternatives such as the accropode, core-loc, and conventional rock armor. The findings reveal that the new unit achieves a lower packing density, reducing the number of units required and thereby improving overall cost-effectiveness. Armor layers formed from the newly designed unit exhibited higher porosity than accropode but lower than core-loc, effectively avoiding the slender geometries that compromise durability. Structural analysis using STAAD.Pro confirmed that the new unit developed lower tensile stresses, with reductions of 15% compared to accropode and 35% compared to core-loc under flexure, torsion, and combined loading, demonstrating superior integrity. Hydraulic stability tests showed that the randomly placed newly designed units resisted failure at a stability number (N_s) of 1.4, lowering run-up by 50% and overtopping by 59%, while the uniformly placed newly designed units reached 1.5 without failure, with run-up and overtopping reductions of 30% and 37%, respectively. Collectively, these outcomes highlight the clear hydraulic and structural advantages of the new design over conventional systems, establishing it as a stronger and more resilient solution for breakwater protection. Full article

To enhance the anti-ultraviolet aging capacity of high-density polyethylene (HDPE) monofilaments for fishery applications, this study prepared pure HDPE and a blend of HDPE/UHMWPE (80/20 wt%) monofilaments via a melt spinning process. Systematic ultraviolet accelerated-aging experiments were conducted on these monofilaments for durations ranging from 0 to 600 h. The evolution of material properties was assessed using various quantitative characterization methods, including scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and mechanical tensile testing. The results indicate that after 600 h of aging, the density and size of surface cracks in the blended monofilament are significantly lower than those observed in pure HDPE. The carbonyl index (CI) and unsaturated index (UI) of the blend are approximately 55% and 40% of those of pure HDPE, respectively. Additionally, the initial thermal decomposition temperature (T_5%), as determined by TGA, decreases by only 13 °C, which is a considerably lower reduction than the 28 °C observed for pure HDPE. Furthermore, the attenuation rates of breaking strength and elongation at break for the blended monofilament are 43.7% and 54.0%, respectively, which are markedly lower than the corresponding rates of 54.5% and 66.0% for pure HDPE. Research indicates that the observed performance improvement is closely linked to the synergistic mechanism of the “physical hindration–structural skeleton” formed by the UHMWPE phase. Furthermore, this mechanism may interact synergistically with the antioxidants present in the system, thereby altering the material’s failure mode from “rapid brittle failure” to “progressive slow deterioration.” This study offers novel modification strategies and experimental references for developing high-performance, UV-resistant polyolefin materials suitable for fishery applications. Full article

In this study, thermoplastic polyurethane (TPU) parts were fabricated using fused filament fabrication (FFF) by varying key process parameters, namely extruder temperature (210–230 °C), layer thickness (200–400 µm), and printing speed (30–50 mm/s). A Box–Behnken experimental design was used to systematically evaluate the combined influence of these parameters on surface roughness (R_a), dimensional deviation (DD), and ultimate tensile strength (UTS). After fabrication, all specimens were subjected to a Tetrahydrofuran (THF)-based chemical smoothing process to modify surface characteristics. Surface roughness measurements showed a substantial reduction after chemical smoothing, with values decreasing from an initial range of 13.17 ± 0.21–15.87 ± 0.23 µm to 4.01 ± 0.18–7.35 ± 0.16 µm, corresponding to an average decrease of approximately 50–72%. Dimensional deviation improved moderately, from 260–420 µm in the as-printed condition to 160–310 µm after post-processing, representing a reduction of about 20–38%. Mechanical testing revealed a consistent increase in UTS following chemical smoothing, with values improving from 30.24–40.30 ± 0.52 MPa to 33.97–47.94 ± 0.36 MPa, yielding an average increase of approximately 10–24%. Then, the experimental data were used for multi-objective optimization of the FFF process parameters, using a non-dominated sorting genetic algorithm (NSGA-II) implemented in Python 3.11, to identify best parameter combinations that provide a balanced surface quality, dimensional accuracy, and mechanical performance. Full article

The growing volume of decommissioned wind turbine blades, primarily made of glass fibre-reinforced polymers (GFRP), poses major recycling challenges. This study explores a microwave (MW)-assisted thermochemical recycling to recover high-quality fibres from GFRP waste. Two routes were evaluated: (i) a dry route using direct MW heating, and (ii) a semi-wet route involving solvent pre-swelling followed by microwave pyrolysis. The dry route suffered from poor heating due to GFRP’s inherently low dielectric loss, whereas the semi-wet route enabled more effective resin degradation. Five swelling agents were tested: acetic acid (AcOH), hydrogen peroxide (H₂O₂), an AcOH/H₂O₂ mixture, dimethylformamide (DMF), and dimethyl sulfoxide (DMSO). Among these, DMSO achieved 92% resin removal in 9 min at 350 °C. Recycled fibres retained 1.48 ± 0.41 GPa strength (81% of virgin). Gas chromatography–mass spectrometry (GC–MS) analysis of pyrolysis oils revealed predominantly phenolic products with limited bisphenol A (BPA) retention. To demonstrate practical relevance, the semi-wet method was applied to real wind blade waste, where recovered fibres retained 72% of their tensile strength versus virgin fibres. These results indicate that the process remains effective for industrially aged GFRP. This study confirms the feasibility of MW-based semi-wet recycling and offers insights to support future process refinement, which will ultimately contribute to more sustainable end-of-life solutions for GFRP waste. Full article

The growing demand for sustainable alternatives to synthetic composites has increased the interest in natural-fibre-reinforced composites (NFRCs), due to their reduced environmental impact. This study presents a comparative investigation of the mechanical properties of mono-fibre and intraply sisal/flax hybrid composites as cost-effective bio-based solutions. Flax offers high tensile performance but is constrained by higher cost and geographical availability. Sisal, on the other hand, is widely available at lower cost, but exhibits a coarser morphology and reduced processing versatility. Mechanical testing demonstrated that intraply hybrids achieved well-balanced performance, with reduced flax content still delivering competitive tensile strength and stiffness when compared to the higher performing mono-fibre flax composites. However, sisal-rich and hybrid laminates outperformed mono-fibre flax composites in transverse and shear behaviour, with the 67% sisal/33% flax hybrid composite exhibiting the highest transverse properties and the 33% sisal/67% flax hybrid achieving the highest shear properties. Rule-of-mixtures models predicted longitudinal tensile behaviour effectively, while Halpin–Tsai models successfully estimated shear but not transverse and compressive properties. Compressive strength showed limited variation across configurations. Failure analysis identified intra-yarn fracture in flax, limited resin infiltration in sisal, and compressive failure modes such as brooming and microbuckling. Overall, intraply sisal/flax hybrid mats provide a structurally efficient, sustainable, and economically viable alternative to mono-fibre natural composites. Full article

Aeolian sand is abundant in arid deserts, but its high replacement in cement-stabilized bases can reduce strength and raise cracking risk. Strain localization and crack evolution are also poorly quantified. This study aimed to optimize the early age performance of cement-fly ash stabilized aeolian sand gravel (CFSAG) and clarify its failure mechanism. A Box–Behnken response surface methodology varied the cement content, cement-to-fly ash ratio, coarse aggregate gradation, and aeolian sand content. The 7-d unconfined compressive strength (UCS) and splitting tensile strength (STS) were tested. Digital image correlation (DIC) recorded full-field strains and crack metrics in compression and splitting. SEM–EDS was used to interpret microstructural changes. The aeolian sand content dominated UCS, whereas the cement content and cement-to-fly ash ratio mainly controlled STS. Factor interactions were non-negligible and supported the joint optimization of the two strength indices. DIC identified a crack propagation threshold near 0.9 P_max in splitting. Excess aeolian sand (>50%) caused earlier localization, more cracks, and wider openings. In the appropriate amount of aeolian sand mixtures, hydration products filled voids and improved paste continuity. SEM–EDS indicated that excessive fines increased porosity and weakened the interfacial transition zone. Overall, the combined RSM–DIC–SEM approach links mix design with deformation and microstructure evidence. It provides practical guidance to balance strength and cracking resistance at early ages for cement-stabilized bases in desert highway engineering. Full article

Granite residual soil (GRS) is highly susceptible to water-induced softening, posing significant risks of slope instability and collapse. Conventional impermeable grouting often exacerbates these hazards by blocking groundwater drainage. This study investigates the efficacy of a permeable water-reactive polyurethane (PWPU) in stabilizing GRS, aiming to resolve the conflict between mechanical reinforcement and hydraulic conductivity. Uniaxial compression tests were conducted on specimens with varying initial water contents (5%, 10%, and 15%) and PWPU contents (5%, 10%, and 15%). To reveal the multi-scale failure mechanism, synchronous acoustic emission (AE) monitoring and digital image correlation (DIC) were employed, complemented by scanning electron microscopy (SEM) for microstructural characterization. Results indicate that PWPU treatment significantly enhances soil ductility, shifting the failure mode from brittle fracturing to strain-hardening, particularly at higher moisture levels where failure strains exceeded 30%. This enhancement is attributed to the formation of a flexible polymer network that acts as a micro-reinforcement system to restrict particle sliding and dissipate strain energy. An optimal PWPU content of 10% yielded a maximum compressive strength of 4.5 MPa, while failure strain increased linearly with polymer dosage. SEM analysis confirmed the formation of a porous, reticulated polymer network that effectively bonds soil particles while preserving permeability. The synchronous monitoring quantitatively bridged the gap between internal micro-crack evolution and macroscopic strain localization, with AE analysis revealing that tensile cracking accounted for 79.17% to 96.35% of the total failure events. Full article

Samples of medium-carbon low alloyed steel (0.45 wt% C, 2.61 wt% Mn, 1.57 wt% Si) with bainite microstructure were welded using the cold metal transfer method. A series of single welding “dots” was made to produce welding joints using austenitic welding wires. The heat input was adjusted to the minimal possible level of 500–800 J per “dot”. Tensile tests of welded samples demonstrated that quality welds were obtained. All samples were broken via welded metal, showing tensile strength 530–670 MPa, which is inherent to the material of the welding wires. It was determined that the time required for phase transformations in the heat-affected zone during the thermal cycle is an order of magnitude greater than the time of temperature flash during producing a single welding “dot”. The results of extensive hardness measurements of material in the heat-affected zone, along with macro- and microstructure investigations, are presented. It has been demonstrated that cold metal transfer welding technology can be successfully used for welding steel with high carbon equivalent and bainite microstructure without preheating and with minimal deterioration of properties in the heat-affected zone. Full article