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A discrete element model of citrus fruit stalk with a diameter of 3 mm was established using the discrete element method (DEM). The intrinsic parameters and contact parameters of citrus fruit stalk were obtained through measurement. The bonding parameters of the discrete element model of citrus fruit stalk were calibrated through a three-point bending test and shear tests. Based on these parameters, the optimal bonding parameter combination was determined. This included: normal stiffness per unit area 4.6362 × 10 11 N m−3, shear resistance 1.2549 × 10 11 N m−3, bonded disc radius 0.222 mm, critical normal stress 9.5742 × 10 7 Pa and maximum shear stress 7.4007 × 10 7 Pa. These optimal parameters were applied to simulate the bending and shearing of a citrus fruit stalk using the established citrus fruit stalk model. Compared to experimental results, the deviation of bending strength and shear peak force were 1.25% and 1.78%, respectively. The results show that a DEM of citrus fruit stalk established can be used to properly simulate the bending and shearing of citrus fruit stalks and that the method of calibrating the parameters for accuracy is reasonable. The results are significant for the study of the mechanical properties of citrus fruit stalks and the optimisation of end-effectors of harvesting robots. Image 1 • A citrus fruit stalk model with a diameter of 3 mm established by DEM. • Parameters of the simulation model obtained by tests and parameter calibration. • Rationality of the parameters verified by simulation and measurement. [ABSTRACT FROM AUTHOR]

In this study, Al 84 Ni 8.4 Y 4.8 La 1.8 Co 1 particles reinforced Al-based composites were prepared by hot pressing sintering and subsequent hot extrusion. The glassy powders were produced by gas atomization and then employed to mechanical milling. After hot pressing sintering, the nano-scale intermetallic compounds precipitated from metallic glass matrix due to higher temperature than super-cooled liquid region. The mechanical properties of 2024 alloy were improved by addition of glassy particles. The ultimate compressive stress increased from 482 MPa for 2024 alloy to 545 MPa, 627 MPa and 735 MPa for composites with 20 w.t.% 40 w.t.% and 60 w.t.% glassy powders addition, respectively, together with considerable fracture strain ranging between 2.9% and 13.6%. And the mechanical properties could be predicted by using the Rule of Mixture, which predicts the mechanical properties of the bulks from the volume weighed average of the constituent properties. [ABSTRACT FROM AUTHOR]

In this work, we report bulk nanostructured equiatomic FeCoNiCu high-entropy alloy (HEA) with superior thermal stability and decent mechanical properties. High pressure torsion (HPT) was employed to refine the grains in the HEA into nanoscale (80 nm), and then Cu-rich particles were in-situ introduced at grain boundaries by subsequent annealing (≥700 °C), forming a multi-phase nanostructure. The Cu-rich particles are highly stable at high temperatures and impose a pinning effect on the grain boundaries, which significantly restricts grain growth (grain size <500 nm up to 900 °C), thus leading to outstanding thermal stability. On the other hand, the nanostructures also possess high yield strengths of 643∼1165 MPa, mainly attributing to grain boundary hardening. Meanwhile, the in-situ formed Cu-rich particles can concurrently deform with the matrix during straining, resulting in large total elongation (15∼20%). This work provides a novel strategy for designing bulk nanostructured HEA with good thermal stability and mechanical properties. [ABSTRACT FROM AUTHOR]

In the present study, bulk multiscale structured 5083 Al alloy with controlled microstructure was successfully fabricated by mechanical milling and spark plasma sintering. Microstructure observation revealed that due to the self-assemble of near-spherical powders (prepared by low-energy ball milling) and flaky powders (prepared by high-energy ball milling), near-harmonic structures were realized, i.e., the coarse grains (CGs) with retained dislocations were surrounded by fully recrystallized ultrafine grains (UFGs). Moreover, the volume fraction of the CGs and the UFGs can be easily manipulated by changing the composition of powders. Room temperature tensile tests suggested that the multiscale structured bulk samples exhibited significantly enhanced mechanical properties. For example, an ultimate tensile strength up to 460 MPa was realized in the sample consolidated from 20% near-spherical powders and 80% flaky powders. The strengthening and deformation mechanisms of the bulk samples and the strategies for further optimizing the mechanical properties of multiscale structured materials were discussed. • Bulk 5083 Al alloys with unique multiscale structure were fabricated by powder metallurgy. • The multiscale structure was tailorable depending on the ratio of the powder used. • The multiscale structure was composed of coarse grains and equiaxed ultrafine-grains. • The multiscale structured sample exhibited significantly enhanced tensile strength. [ABSTRACT FROM AUTHOR]

The microstructure and tensile properties of Mg- x Al- y Zn-2Ca ( x + y = 8 wt%) alloys with various Al and Zn contents have been investigated. The results showed that all the alloys exhibited dendritic microstructure with α-Mg matrix and eutectic compounds distributed at dendritic boundaries. The category and amount of eutectic compounds were influenced obviously by Al and Zn contents. Two Laves phases, i.e. C36 and C15, Q phase and/or Ca 2 Mg 6 Zn 3 isomorphs phases were observed in as-cast alloys. The majority of second phase was C36 in high Al-containing alloys. By decreasing Al content, the C36 was transformed to C15 Laves phase and Ca 2 Mg 6 Zn 3 isomorphs phase. Both C36 and C15 Laves phases contained a certain amount of Zn. The tensile strength and ductility of Mg-Al-Zn-Ca alloys were greatly dependent on the category and the morphology of second phases. The C36 Laves phase exhibited better strengthening effect, while the Q phase easily led to the formation of cavities at high temperature, thus decreasing heat resistance of the alloy. The alloy containing the majority of networked C36 phase shows optimal mechanical properties at both room temperature (RT) and elevated temperature. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, hybrid structured B4C particles reinforced Al2024 matrix composites were prepared by the powder metallurgy method. The composites made from 100% mechanical milled composite powders have fracture strength of 670MPa. With the addition of un-milled Al2024 powder increased from 10vol% to 40vol%, the room temperature compression strength decreased from 1115MPa to 739MPa, without any visible plastic deformation. However, when the fraction of un-milled Al2024 powder increased to 50vol%, the compression strength was decreased to 580MPa, while retaining a remarkable fracture strain up to 10%. The microstructures of the composites with different composition were examined by a scanning electron microscope and a transmission electron microscope. The contribution from different strengthening mechanisms was discussed. The hybrid structures are proved to account for the dramatic change of the fracture mechanism of the composites. [Copyright &y& Elsevier]

The effects of cutting parameters on the peak force and success rate of cutting citrus fruit stems are investigated. Experiments were carried out in a system composed of electric horizontal cutting force test platform and a digital push–pull force meter. The cutting parameters included the diameters and moisture content of fruit stems, the weight of citrus fruit, the cutting speed and the gap between the two blades, deflection and inclination angles of citrus fruit stems. Regression analyses show that the peak force increases with the increase of diameters of fruit stems and the weight of fruits. Meanwhile, the peak force decreases when the moisture content of fruit stems and the cutting speeds increase. The regression results also show complex relationship of peak force with the gap between the two blades, the deflection angles of stems, and the inclination angles of stems. The effects of the gap between the two blades, the deflection angles of stems, and the inclination angles of stems on the success rate reveal that a high cutting success rate occurred when the gap between blades was smaller than the diameter of stem, or the deflection angle was smaller than 70° and the inclination angle was larger than 20°. Based on our results, the end-effector of harvesting citrus fruit can be designed using the structural parameters including a 1 × 10−3 m gap between the two blades, a declination angle in a range of [−70°,70°] and an inclination angle in a range of [25°, 90°]. Image 1 • Effects of several key parameters on citrus stem cutting were investigated. • Peak force increased when fruit weight, stem diameter or θ d e f increased. • Peak force decreased when cutting speed, MC of fruit stems increased. • 1 mm blade gap ensure the success rate of cutting at appropriate peak force. • Larger θ d e f and smaller θ i n c can cause failure of cutting. [ABSTRACT FROM AUTHOR]