Materialwissenschaft und Werkstofftechnik最新文献

The necessity to adapt sustainable development, green chemistry and industrial ecology leads to the creation of newer materials and the utilization of waste. In this context, this work aims at exploring the feasibility of the fabrication of hybrid composites comprised of a polymeric resin reinforced with a natural fiber (hemp) and an industry waste filler (dolomite dust). While the hemp fiber content is kept constant, epoxy-based hybrid composites are fabricated with different weight percentages of dolomite dust using the conventional hand lay-up route. The microstructural features of the constituent materials are studied using stereo and scanning electron microscopes which show the shape and size of dolomite particles and the arrangement of fibers. An x-ray diffraction analysis revealed the presence of hematite, graphite, lime and manganite. The presence of functional groups like hydroxyl, carboxyl and azide is ascertained from the transmittance spectra of Fourier transform infrared spectroscopy. The density and void fractions are increasing with the amount of filler particles in the composite. It is observed that the tensile and flexural strengths of the composites marginally drop with increase in dolomite dust content, but there is a reasonable improvement in their inter-laminar shear strength, micro-hardness and impact strength values.

This study investigated the effect of magnetic particle size and volume fraction on the shear yield stress and dynamic viscosity of magnetorheological fluids. Magnetorheological fluids with varying volume fractions of micro- and nanoscale magnetic particles were prepared. A plate-on-plate shear test bench was constructed to evaluate the fluids under a constant shear rate, with the applied current ranging from 0 A to 1.2 A. Results indicated that the shear yield stress initially increased and then decreased as the volume fraction of magnetic nanoparticles increased, reaching a maximum of 47 kPa at a volume fraction of 7 %. However, the excessive addition of magnetic particles or large-diameter particles led to settling and reduced stability of the fluids. The findings suggest that optimizing the size and volume fraction of magnetic particles is crucial for maximizing the shear yield stress of magnetorheological fluids.

The content of peroxide in acrylonitrile is critical for the production of polyacrylonitrile-based carbon fibers. Peroxide-free acrylonitrile is used as a blank solution for testing the peroxide content of acrylonitrile, which storage conditions are important to the test. Of course, for the change of peroxide content in acrylonitrile stored for a period of time has an effect on the production of carbon fiber. In order to study the effect of storage conditions on peroxide in peroxide-free acrylonitrile and acrylonitrile, the changes at refrigerator and room temperature were studied, respectively. Studies have shown that storage at temperatures below 20 °C for 3 months hardly affect the use of either peroxide-free acrylonitrile or acrylonitrile. The experimental results obtained are useful for practical production and testing, which can improve the accuracy of testing and stability of production.

Machine hammer peening is a surface treatment technique employed to enhance the surface properties of the treated samples. In this present work, the theoretical analysis, finite element simulation and experiment of single peening are carried out to investigate the relationship between the machine hammer peening force and geometric dimensions of the single peening indentation deformation, including diameter and depth. The single peening experimental results are in accordance with theoretical and simulation analysis. The machine hammer peening experiment with grate tool path are done and the results including surface topography, surface roughness, surface hardness, x-ray diffraction analysis and wear resistance are discussed. This work seeks to explore the effects of process parameters like machine hammer peening force, indentation and pitch spacing on surface roughness and hardness. The results reveal that the surface hardness and roughness are positively associated with machine hammer peening force and small indentation and pitch spacing lead to high hardness. The x-ray diffraction analysis validate machine hammer peening is a mechanical treatment without new compound generated. The friction test results in an enhancement in wear resistance of treated samples.

Additive manufacturing, notably laser powder bed fusion (LPBF), excels in producing complex geometries and is widely used in the automotive, aerospace, and naval industries. Laser powder bed fusion enables the creation of components with the required stiffness and strength at a lighter weight than traditional manufacturing methods. Aluminium alloys are particularly promising for laser powder bed fusion in the automotive and aerospace sectors. To enhance the effectiveness of laser powder bed fusion-produced components, optimized process parameters must be designed for specific materials. This study investigates the influence of processing parameters, scan speed, scan strategy, and hatch space, on the relative density, surface roughness, and microhardness of AlSi12 samples fabricated by laser powder bed fusion. A Taguchi L27 orthogonal array was used to systematically analyze the effects of these parameters. A regression model was developed and evaluated through analysis of variance using signal-to-noise (S/N) ratios to identify optimal parameter values. Results indicated that the scan pattern significantly affects relative density, while hatch space impacts surface roughness and microhardness. Optimal solutions were obtained through multi-objective optimization using the non-dominated sorting genetic algorithm (NSGA-II) and Pareto search algorithms. Experimental validation showed average errors of 0.483 % and 0.461 % for NSGA-II and Pareto search algorithms, respectively.

GH4169 is a precipitation-strengthened nickel-based high-temperature alloy, and its mechanical behavior at different temperatures is of significant importance for practical applications. Here, an in situ study on the mechanical properties and microstructural evolution of the GH4169 alloy at different temperatures was conducted using scanning electron microscopy in combination with digital image correlation. The results demonstrate the existence of a linear relationship between the local average strain and the macroscopic strain. At temperatures of 20 °C, 100 °C, 180 °C, and 260 °C, the local average strain is 1.96, 2.13, 2.26, and 2.30 times the macroscopic strain, respectively, which shows a clear trend. This indicates that the temperature has a significant influence on the plasticity of the alloy. Additionally, the strain is concentrated below the notch, whereby at a macroscopic strain of 1.7 % at 20 °C and 260 °C, the local maximum strain at the notch is 52 % and 83 %, respectively. Furthermore, when the macroscopic strain reaches 2.12 %, the local maximum strain at the notch is 72 % and 103 %, respectively. At this point, cracks start to initiate and gradually propagate. In situ observations show that at the beginning of the tensile plasticity stage, the plastic strain rate in the grains is twice the rate at the grain boundaries; subsequently, both rates tend to stabilize, and a high-strain zone appears inside the grains and is coordinately transferred to the surrounding grains through the grain boundaries. The final stage of damage of the alloy consists of perforation fracture, and the presence of a large number of cracked carbides at the fracture results in specimen cracking.