Search Results (88)

The hard bottom layer in paddy fields significantly impacts the driving stability, operational quality, and efficiency of agricultural machinery. Continuously improving the precision and efficiency of unmanned, precision operations for paddy field machinery is essential for realizing unmanned smart rice farms. Addressing the unclear influence patterns of hard bottom contours on typical scenarios of agricultural machinery motion and posture changes, this paper employs a rice transplanter chassis equipped with GNSS and AHRS. It proposes methods for acquiring motion state information and hard bottom contour data during agricultural operations, establishing motion state expression models for key points on the machinery antenna, bottom of the wheel, and rear axle center. A correlation analysis method between motion state and hard bottom contour parameters was established, revealing the influence mechanisms of typical hard bottom contours on machinery trajectory deviation, attitude response, and wheel trapping. Results indicate that hard bottom contour height and local roughness exert extremely significant effects on agricultural machinery heading deviation and lateral movement. Heading variation positively correlates with ridge height and negatively with wheel diameter. The constructed mathematical model for heading variation based on hard bottom contour height difference and wheel diameter achieves a coefficient of determination R² of 0.92. The roll attitude variation in agricultural machinery is primarily influenced by the terrain characteristics encountered by rear wheels. A theoretical model was developed for the offset displacement of the antenna position relative to the horizontal plane during roll motion. The accuracy of lateral deviation detection using the posture-corrected rear axle center and bottom of the wheel center improved by 40.7% and 39.0%, respectively, compared to direct measurement using the positioning antenna. During typical vehicle-trapping events, a segmented discrimination function for trapping states is developed when the terrain profile steeply declines within 5 s and roughness increases from 0.008 to 0.012. This method for analyzing how hard bottom terrain contours affect the position and attitude changes in agricultural machinery provides theoretical foundations and technical support for designing wheeled agricultural robots, path-tracking control for unmanned precision operations, and vehicle-trapping early warning systems. It holds significant importance for enhancing the intelligence and operational efficiency of paddy field machinery. Full article

Background: The study investigates newly developed composite materials with advanced filler technology and modified resin matrices, designed to enhance esthetic quality, clinical efficiency, and mechanical properties. This study evaluated the effect of two light-curing protocols—a conventional low-voltage (LV) protocol (10 s at 1200 mW/cm²) and a high-voltage (HV) protocol (3 s at 3000 mW/cm²)—on the microhardness (MH), bottom/top MH ratio, and the correlation between filler content (wt%, vol%) and MH of bulk-fill resin-based composites (RBCs). Four RBCs were tested: Tetric PlusFill (TPF), Tetric Plus Flow(TPFW), Tetric PowerFill (PFL), and Tetric PowerFlow (PFW). Materials and Methods: Samples were fabricated in the laboratory using specially designed cylindrical molds (diameter = 8 mm, height = 4 mm). Initial MH was measured on the top and bottom surfaces of composite specimens 24 h after light curing using a digital microhardness tester (QNESS 60 M EVO, ATM Qness GmbH, Mammelzen, Germany). The correlation between the filler content (wt%, vol%) and the MH of the RBCs was tested. For the calculation of depth-dependent curing effectiveness, the bottom/top ratio for initial MH was used. Conclusions: The MH of bulk-fill RBCs was found to be influenced by both material composition and the applied light-curing protocol. An increase in filler content resulted in higher MH values under both protocols, with the filler volume fraction exhibiting a stronger correlation than the weight fraction. While both flowable and sculptable Tetric Plus composites exhibited higher MH values under the HV protocol, Tetric Power composites demonstrated greater initial hardness under LV protocol. The flowable composite PFW showed the most pronounced reduction in MH under HV curing. The bottom/top MH ratio exceeded 80% in all tested materials, confirming adequate polymerization throughout the composite layers. Full article

Coastal profile models are frequently used for the computation of storm-induced erosion at (nourished) beaches. Attention is focused on new developments and new validation exercises for the detailed process-based CROSMOR-model for the computation of storm-induced morphological changes in sand and gravel coasts. The following new model improvements are studied: (1) improved runup equations based on the available field data; (2) the inclusion of the uniformity coefficient (C_u = d₆₀/d₁₀) of the bed material affecting the settling velocity of the suspended sediment and thus the suspended sediment transport; (3) the inclusion of hard bottom layers, so that the effect of a submerged breakwater on the beach–dune morphology can be assessed; and (4) the determination of adequate model settings for the accretive and erosive conditions of coarse gravel–shingle types of coasts (sediment range of 2 to 40 mm). The improved model has been extensively validated for sand and gravel coasts using the available field data sets. Furthermore, a series of sensitivity computations have been made to study the numerical parameters (time step, grid size and bed-smoothing) and key physical parameters (sediment size, wave height, wave incidence angle, wave asymmetry and wave-induced undertow), conditions affecting the beach morphodynamic processes. Finally, the model has been used to study various alternative methods of reducing beach erosion. Full article

Background/Objectives: Enteric coating protects active pharmaceutical ingredients from gastric degradation, but conventional tablets may present swallowing difficulties in geriatric and pediatric patients. Hence, this study intended to develop pH-responsive multiparticulates, formulated into orally disintegrating tablets (ODTs), for targeted intestinal drug delivery in individuals with dysphagia. Methods: Multiparticulates were developed via sequential seal coating, drug layering, sub-coating, and enteric coating on inert cores using a fluidized bed coater (Pam Glatt, India; bottom spray). Selected enteric-coated batches were directly compressed into ODTs using microcrystalline cellulose (Avicel PH102) and mannitol (Pearlitol SD 160) as fillers, with Explotab^®, Ac-Di-Sol^®, or crospovidone M^® as superdisintegrants. Results: Multiparticulates exhibited mean diameters of 197.671–529.511 μm and span values of 0.603–0.838. Span value < 1, indicating a narrow size distribution. Electron microscopy confirmed the spherical morphology of Batches 7a and b. Enteric-coated batches (5b, 6, 7a, 7b) released ≤10% of the drug in 0.1 N HCl at 2 h. Optimized formulation ODT 7b released 7.904% of the drug under gastric conditions and 79.749% in phosphate buffer (pH 6.8) within 2.5 h, following first-order drug release kinetics. ODT 7b demonstrated hardness (2.538 ± 0.144 kg/cm²), wetting time (11.17 ± 1.051 s), friability (0.712%), and drug content (99.81 ± 1.01%) within acceptable limits. Conclusions: The pH-dependent multiparticulates provided sustained intestinal drug release and, when incorporated into ODTs, yielded a dosage form with a rapid wetting time and acceptable mechanical properties. This dosage form can offer a promising approach for improving compliance and therapeutic efficacy in patients with swallowing difficulties (dysphagia). Full article

Laser cladding with ultrafast cooling rates enables effective fabrication of metallic glass matrix composite (MGMC) coatings, significantly enhancing the hardness, corrosion resistance, and mechanical properties of metallic substrates. In this study, a multi-layer Zr₆₅Al_7.5Ni₁₀Cu_17.5 (at. %) MGMC coating was successfully fabricated by laser cladding technology. The effects of the region-dependent microstructural evolution on micro-mechanical properties and corrosion resistance were systematically investigated. The results indicated that the high impurity content of the powder feedstock promoted the crystallization of the coating during laser cladding. Moreover, coarse columnar crystals in the bottom region of the coating nucleated epitaxially at the coating/substrate interface and propagated along the thermal gradient parallel to the building direction, while dendritic crystals dominated the middle region under moderate thermal gradients. In the top region, fine dendritic and equiaxed crystals deposited in the amorphous matrix, due to the lowest thermal gradient and the highest cooling rate. Correspondingly, nanoindentation results revealed that the top region exhibited peak hardness (H), maximum elastic modulus (E), and optimal H/E ratio, exceeding values in both the bottom region and substrate. Simultaneously, the metallic glass matrix composite coating demonstrated significantly better corrosion resistance than the substrate due to its amorphous phase and protective passive film formation. This work advances amorphous solidification theory while expanding applications of metallic glasses in surface engineering. Full article

This study investigates the microstructure evolution and mechanical properties of DSS2209 duplex stainless steel fabricated via cold metal transfer wire arc additive manufacturing (CMT-WAAM). The as-deposited thin-wall components exhibit significant microstructural heterogeneity along the build height due to thermal history variations. Optical microscopy, SEM-EDS, and EBSD analyses reveal distinct phase distributions: the bottom region features elongated blocky austenite with Widmanstätten austenite (WA) due to rapid substrate-induced cooling; the middle region shows equiaxed blocky austenite with reduced grain boundary austenite (GBA) and WA, attributed to interlayer thermal cycling promoting recrystallization and grain refinement (average austenite grain size: 4.16 μm); and the top region displays coarse blocky austenite from slower cooling. Secondary austenite (γ₂) forms in interlayer remelted zones with Cr depletion, impacting pitting resistance. Mechanical testing demonstrates anisotropy; horizontal specimens exhibit higher strength (UTS: 610 MPa, YS: 408 MPa) due to layer-uniform microstructures, while vertical specimens show greater ductility (elongation) facilitated by columnar grains aligned with the build direction. Hardness ranges uniformly between 225–239 HV. The study correlates process-induced thermal gradients (e.g., cooling rates, interlayer cycling) with microstructural features (recrystallization fraction, grain size, phase morphology) and performance, providing insights for optimizing WAAM of large-scale duplex stainless steel components like marine propellers. Full article

This study investigates the influence of varying layer thickness through interlayer machining in Wire Arc Additive Manufacturing (WAAM) and its impact on microstructural evolution, mechanical properties, and residual stress distribution. It compares four types of WAAM samples: As-built with uneven layer thickness without interlayer machining and uniform layer thicknesses of 2 mm, 1.5 mm, and 1 mm achieved through interlayer machining. As-built components exhibited coarse columnar grains and uneven deposition, adversely affecting hardness and strength. Interlayer machining at reduced layer thickness refined grains, restricted growth, and induced plastic deformation, leading to enhanced mechanical properties. Grain refinement achieved reductions of 62.7% (top), 77.6% (middle), and 64.3% (bottom), significantly improving microstructural uniformity. Microhardness increased from 150 to 180 HV (as-built) to 210 to 230 HV (machined to maintain 1 mm layer thickness), marking a 40–43% improvement. Tensile strength was enhanced, with UTS increasing from 494.72 MPa to 582.11 MPa (17.6%) and YS from 371 MPa to 471 MPa (26.9%), although elongation decreased from 59% to 46% (22% reduction). Residual stress was reduced by 55–60%, improving structural integrity. These findings highlight interlayer machining as a key strategy for optimizing WAAM-fabricated components while balancing mechanical performance and manufacturing efficiency. Full article

As a hard and brittle material, the processing of C_f/SiC ceramic matrix composites (CMCs) faces significant challenges, especially in the processing of small-sized shapes. To address this challenge, laser processing with gas-assisted nanosecond laser (GNL) and waterjet-guided nanosecond laser (WNL) modes were applied to fabricate thin kerfs in the C_f/SiC composite. The surface morphology, microstructure, and chemical composition of the processed C_f/SiC composite were investigated comparatively. The results revealed that the coupling of helium in the GNL mode laser processing could make full use of the laser energy, but resulted in spattering in the kerf margin and a recast layer in the kerf surface, accompanied by obvious oxidation, while the coupling of the waterjet in the WNL mode laser processing decreased the oxidation significantly and removed the remelting debris, which produced a clear and flat kerf surface. Due to the taper caused by laser energy dissipation, the single-path laser processing in the C_f/SiC composite had a limited depth. The maximum depth of the kerf prepared by single-path laser processing with the GNL mode was about 328 μm, while that with the WNL mode was about 302 μm. The multi-path laser processing with the GNL and WNL modes could fabricate a through kerf in the C_f/SiC composite, but the coupling medium obviously influenced the surface morphology and microstructure of the underlying region. The kerf surface prepared by the GNL mode had a varied surface morphology, which transited from the top layer, covered with oxide particles and some cracks, to the bottom layer, featured with micro-grooves and small oxides. The kerf surface prepared by the WNL mode had a consistently smooth and clean morphology featured with broken carbon fiber and residual SiC matrix. The slow laser energy dissipation and open environment in the GNL mode resulted in a bigger HAZ and relatively serious oxidation, which caused local phase transformation and microstructure degradation. The isolation condition and rapid cooling in the WNL mode decreased the HAZ and restrained the oxidation, almost keeping the original microstructure. The thicknesses of the HAZ in the GNL- and WNL-processed C_f/SiC composite were about 200 μm and 100 μm, respectively. The WNL-processed C_f/SiC composite had a lower oxidation and thermal damage surface, which is instructive for the processing of the C_f/SiC composite. Full article

To address the failure issue of local wear in QT400-18 transition shafts used in high-speed trains, laser cladding remanufacturing of a ductile cast iron surface was carried out using 45 wt.%Fe + 55 wt.% Inconel625 powder. The phase composition, microhardness, interfacial bonding strength, and wear resistance of the cladding layer were analyzed. The results show that the cladding layer is primarily composed of a γ (Ni, Fe) solid solution and a small amount of eutectic carbides. The microstructure of the cladding layer forms columnar dendrites, cellular dendrites, and equiaxed crystals from bottom to top. The microstructure of the single-layer, single-pass interface consists of ferrite, acicular martensite, and ledeburite, while the multi-layer, multi-pass interface consists of ferrite, granular pearlite, and discontinuous ledeburite. The average microhardness of the single-layer, single-pass cladding layer is approximately 350 HV_0.5, and the hardness of the fine-grained and coarse-grained regions of the multi-layer, multi-pass cladding layer is approximately 330 HV_0.5 and 250 HV_0.5, respectively. The interfacial bonding strength reaches 96.5% of the base material strength. The wear mechanism of the cladding layer is mainly mild abrasive wear, with significantly better wear resistance than the base material. Full article

To ensure lateral roadway retention in composite hard rock mining roofs, selecting a proper cutting height is crucial. If the cutting height is too low, the residual hard roof may experience secondary fractures under additional stress, which threatens roadway stability and safe mining production. Conversely, if the cutting height is too high, the overlying rock layers may bear uneven stress, increasing the risk of collapse. To conduct a detailed cutting height analysis for composite hard rock roof retention, the 12 1103 working face at the Qiuji Coal Mine was chosen as the research subject. Using the collapse characteristics of a goaf roof and the theory of composite beams, a lateral mechanical model of a goaf roof was constructed. By integrating the ultimate tensile stress theory and the Maxwell model, the optimal cutting height for a composite hard roof was derived. Using UDEC numerical simulation software, a model for lateral roadway retention was established to compare and analyze the roof collapse effects, vertical displacement, and vertical stress at different cutting heights. The results indicated that a cutting height of 7.8 m (with the bottom of the hole 0.48 m from the four gray layers) achieved the best cutting effect. Field engineering tests further validated the rationality of the calculated results. Using field surveys, the cutting height was adjusted from the original 9.35 m to 7.8 m for the 12 1103 working face. With a working face length of 946 m, this adjustment could save approximately 212,900 yuan in drilling construction costs and improve construction efficiency by 15%. This study provides a theoretical basis and practical reference for selecting cutting heights under similar geological conditions. Full article

This study examines the microstructure and mechanical properties of 5356 aluminum alloy under low heat input conditions during arc additive manufacturing, focusing on the challenges posed by excessive heat input, which hinders specimen formation and affects dimensional accuracy. The study analyzes the characteristics of single-pass multilayer straight-walled specimens fabricated under varying low heat input conditions, along with evaluations of their mechanical properties, including their microstructure, microhardness, and tensile strength. This study demonstrates that as the heat input increases from 87.5 J/mm to 190.0 J/mm, the width of the vertical wall specimens increases significantly, whereas the change in single-layer height remains minimal. The specimen width increases from 5.22 mm to 8.87 mm, representing a change of 3.65 mm, while the single-layer height increases by only 0.16 mm. The microstructure primarily consists of the α(Al) matrix and the skeletal β(Al₃Mg₂) phase. As heat input increases, some of the β(Al₃Mg₂) phase dissolves, resulting in a decrease in its distribution density, a reduction in its quantity, and an increase in its size. The average hardness increases from 69.40 HV at 87.5 J/mm to 77.89 HV at 154.2 J/mm, before decreasing to 73.56 HV at 190.0 J/mm. As the heat input increases, the tensile strength and elongation of both horizontal and vertical specimens initially increase and then decrease. The tensile strength and elongation of the horizontal specimens are slightly greater than those of the vertical specimens. The microstructure and mechanical properties vary across different regions. In the upper region, the β(Al₃Mg₂) phase is uniformly distributed, with high density and small size. The fracture surface exhibits fine, uniform dimples, displaying the best microhardness and mechanical properties, with a tensile strength of 245.88 MPa. In the middle region, the distribution density of the β phase decreases, the size increases, and the dimples become slightly coarser. Consequently, the microhardness and mechanical properties decline. At the bottom, due to the higher cooling rates, the β phase does not dissolve significantly. The distribution density is high, the dimples are large and uneven, and the microhardness and mechanical properties are the lowest, with a tensile strength of 236.00 MPa. Full article

The microstructure of additively manufactured 316L stainless steel is hierarchical, and on a fine scale, it contains cell structures and dislocations. These microstructures define the mechanical properties, and it is thus of importance to quantify them and understand their thermal stability. This study investigates the heterogeneity of the microstructure in laser powder bed-fused 316L with a focus on variations in the cell and dislocation structures through the sample thickness along the build direction. While at the coarse scale the microstructure is rather homogeneous throughout its thickness, there are significant variations in the dislocation network, highlighting a higher dislocation density near the bottom layers than near the top. Furthermore, post-processing heat treatment at 500 °C and 800 °C reveals different stabilities of the cell structures, with significant cell dissolution at 800 °C, particularly at the top of the build. Microhardness measurements corroborate these findings, showing higher hardness in the bottom layers across all conditions, e.g., an increase in hardness from 225 HV to 236 HV is observed in the as-built condition. These results underpin the suggestion that significant microstructural heterogeneity may exist through the thickness in as-built parts, which affects the mechanical properties and subsequent heat treatments. Full article

Composite coatings reinforced with varying mass fractions of SiC particles were successfully fabricated on 316 stainless steel substrates via laser cladding. The phase compositions, elemental distribution, microstructural characteristics, hardness, wear resistance and corrosion resistance of the composite coatings were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Vickers hardness testing, friction-wear testing and electrochemical methods. The coatings have no obvious pores, cracks or other defects. The phase compositions of the Hastelloy C276 coating includes γ-(Ni, Fe), Ni₂C, M₆C, M₂(C, N) and M₂₃C₆. SiC addition resulted in the formation of high-hardness phases, such as Cr₃Si and S₅C₃, with their peak intensity increasing with SiC content. The dendrites extend from the bonding zone towards the top of the coatings, and the crystal direction diffuses from the bottom to each area. Compared with the dendritic crystals formed at the bottom, the microstructure at the top is mostly equiaxed crystals and cellular crystals with smaller volume. When SiC powder particles are present around the crystals, the microstructure of the cladding layer grows acicular crystals containing Si and C. These acicular crystals tend to extend away from the residual SiC powder particles, and the grain size in this region is smaller and more densely distributed. This indicates that both melted and unmelted SiC powder particles can contribute to refining the grain structure of the cladding layer. The optimal SiC addition was determined to be 9 wt%, yielding an average microhardness of 670.1 HV_0.5, which is 3.05 times that of the substrate and 1.19 times that of the 0 wt% SiC coating. The wear resistance was significantly enhanced, reflected by a friction coefficient of 0.17 (43.59% of the substrate, 68% of 0 wt%) and a wear rate of 14.32 × 10⁻⁶ mm³N⁻¹·m⁻¹ (27.35% of the substrate, 40.74% of 0 wt%). The self-corrosion potential measured at 315 mV, with a self-corrosion current density of 6.884 × 10⁻⁶ A/cm², and the electrochemical charge-transfer resistance was approximately 25 times that of the substrate and 1.26 times that of the 0 wt%. In this work, SiC-reinforced Hastelloy-SiC composite coating was studied, which provides a new solution to improve the hardness, wear resistance and corrosion resistance of 316L stainless steel. Full article

Background/Objectives: Two fibre optic probes were custom designed to perform Raman and near-infrared spectroscopic measurements. Our long-term objective is to develop a non-destructive tool able to collect data in hard-to-access locations for real-time analysis or diagnostic purposes. This study evaluated the quantitative performances of Probe A and Probe B using model pharmaceutical tablets. Methods: Measurements were performed using pharmaceutical tablets containing hydroxyl propylcellulose, titanium dioxide (anatase), lactose monohydrate, and indomethacin (γ form). Material content and thickness of bilayer samples (samples consisting of a top layer and a bottom layer of differing materials) were also assessed using Probe A to evaluate its capabilities to collect sub-surface information. Principal component analysis and partial least squares regression models were using individual and fused data to evaluate the performances of the different probe configurations. Results: Hydroxymethyl cellulose ($R_P^2=0.98$, RMSEP = 2.27% w/w) and lactose monohydrate ($R_P^2=0.97$, RMSEP = 2.96% w/w) content were most effectively estimated by near-infrared spectroscopy data collected using Probe A. Titanium dioxide ($R_P^2=0.99$, RMSEP = 0.21% w/w) content was most effectively estimated using a combination of 785 nm Raman spectroscopy and near-infrared spectroscopy using Probe B. Indomethacin ($R_P^2=0.97$, RMSEP = 1.01% w/w) was best estimated using a low-level fused dataset collected using 0 mm, 2.5 mm, and 5.0 mm lateral offsets of 785 nm spatially offset Raman spectroscopy using Probe A. Conclusions: The different probe configurations were able to reliably collect data and demonstrated robust quantitative performances. These results highlight the advantage of using multiple techniques for analysing different structures. Full article

The fabrication of multi-layer alloys by additive friction stir deposition (AFSD) results in a complicated microstructure and mechanical property evolution due to the repeated thermal inputs impacting the existing deposited layers. This work systematically studied the microstructure and mechanical properties of several areas (last layers, intermediate layers, and first layers) of a 16-layer 2195 alloy component fabricated by AFSD to ascertain the effect of repeated thermal cycling. The periodic heat input resulted in the minimal quantities of T₁-phase only appearing in the last layers of the sample, while the θ′-phase developed a complex precipitate with the δ′ and β′ phases. The mechanical properties of the 2195 sample exhibit a gradient development related to the microstructure, with a decrease in strength and hardness from top to bottom. The samples located in the last layers show the highest microhardness of 117.0 Hv, yield strength of 296.6 MPa, ultimate tensile strength of 440.6 MPa, and elongation of 27.1%, respectively. Full article