Materialwissenschaft und Werkstofftechnik最新文献

Three-dimensional finite element models were built to describe the distribution of electromagnetic fields and fluid fields under a low frequency low voltage time-dependent pulsed magnetic field. The simulation results showed that eddy current circling around the axis of the melt can be induced by pulsed magnetic field. Periodic positive-negative Lorentz force in the melt was induced from the interaction between the current and magnetic field. The effects generated by the pulsed magnetic field included vibration, fluid flow and Joule heat. The melt flowed in the form of a multi-circle and the fluid velocity was composed of a base component and a pulse component. The temperature in the melt was homogeneous because of the fluid flow. Melt temperatures were measured and compared with the simulated results during solidification process of aluminum alloy A356 (Al−Si alloy), which qualitatively confirmed the decrease of temperature gradient. Moreover, the effects of material resistivity and electromagnetic parameters of the pulsed magnetic field were investigated. Materials with smaller resistivity took larger electromagnetic force. The fluid flowed much faster under larger excitation current density and frequency. Finally, the grain refinement mechanisms under the pulsed magnetic field were analyzed.

Aluminum oxide hollow microbeads/epoxy resin composite is a kind of epoxy resin-based multi-porous energy-absorbing material. This study improved the brittleness and toughness of epoxy resin. Adding hollow aluminum oxide microbeads with different mass fractions increased the energy absorption capacity. Quasi-static compression tests were carried out at room temperature to test the compression properties of epoxy resin/hollow microbead composites. The composites′ energy absorption properties and energy absorption efficiency were analyzed and calculated using the obtained compression curves. The fracture characteristics and microscopic morphology of the composite specimens were observed by scanning electron microscopy. It was found that aluminum oxide hollow microbeads, as reinforcement material, can effectively improve the brittleness and yield strength of epoxy resin materials and enhance the energy absorption performance and energy absorption efficiency of composite materials. With the increase in the mass fraction of hollow microbeads, the energy absorption performance of the composite material first increases and then decreases. Its performance is the most significant when the mass fraction of aluminum oxide hollow microbeads is 10 %.

This study explores the synergistic influence of hybridizing titanium oxide (TiO₂) filler on the mechanical properties and sliding wear behavior of epoxy composites reinforced with hairy cotton grass (HCG) fibres. The experimental results reveals that the combination with 9 wt-% HCG/4 wt-% titanium oxide observed better mechanical results (tensile-51.03 MPa, flexural-28.66 MPa, and impact energy-3.1 J) whereas higher hardness (40.77 HV) achieved at 9 wt-% hairy cotton grass/6 wt-% titanium oxide composites. There is deterioration in mechanical results at higher titanium oxide (6 wt-%) loading due to uneven distribution and particle agglomeration in hairy cotton grass-epoxy composites. The design of expert was generated by using control parameters, sliding velocity (1 m ⋅ s⁻¹–4 m ⋅ s⁻¹), TiO₂ content (0 wt-%–6 wt-%), and normal load (15 N–30 N) respectively. The optimization of the sliding wear rate was analysed by the Taguchi approach followed by an analysis of variance used for evaluating the significant of control parameters. The results showed a combination with significance sliding velocity of 1 ms⁻¹ (78.15 %)>titanium oxide content of 6 wt-% (20.28 %) >normal load of 30 N (1.57 %) exhibited an optimum value of specific wear rate.

The effect of polyphenylene sulfide binder content on the properties of injection molding polyphenylene sulfide/NdFeB magnets were investigated. The maximum filling amount of NdFeB magnetic powder was 87.6 wt.-%, and the mixing process and subsequent injection molding of the polyphenylene sulfide/NdFeB were in good condition. The melt mass-flow rate of the polyphenylene sulfide/NdFeB granular materials reached 121.7 g/10 min, the compressive strength of the polyphenylene sulfide/NdFeB magnet was 92.18 MPa, and its maximum magnetic energy product reached 5.59 MGOe. The structure and morphology characteristics of polyphenylene sulfide/NdFeB magnets were investigated using scanning electron microscopy and atomic force microscopy. The corrosion behavior of polyphenylene sulfide/NdFeB magnets was also studied using potentiodynamic polarization curves and electrochemical impedance spectroscopy. The results indicated that the injection molding process facilitated the uniform coating of polyphenylene sulfide particles on NdFeB powder, which directly enhanced the corrosion resistance of polyphenylene sulfide/NdFeB magnets. With an increase in polyphenylene sulfide content, the surface of polyphenylene sulfide/NdFeB magnets became more uniform. The corrosion current density of 13 wt.-% polyphenylene sulfide/NdFeB magnet was approximately one order of magnitude lower than that of 9 wt.-% polyphenylene sulfide/NdFeB magnet, indicating an improved corrosion resistance of polyphenylene sulfide/NdFeB magnet.

Bolted connections are a highly efficient joining method, especially for constructions with mixed materials or final coated parts as well as maintenance-friendly constructions, and significantly influence the design. The VDI 2230–1 forms the basis for the dimensioning of such joints in mechanical engineering. To meet tolerance requirements in the assembly of components and subassemblies and to enable a efficient production process, the holes for the connections are often designed as oversized round or slotted holes. However, the increased nominal hole clearance is not taken into account in the calculation steps R0 to R13 for the calculation of highly stressed bolted joints with one cylindrical bolt according to VDI Guideline 2230–1, which leads to overdimensioning or auxiliary constructions. The practical verification often can only be supported by cost-intensive individual case studies based on laboratory tests. The investigations shown in this paper aim on the determination of the pressure distribution in the interface, the bolt resilience as well as the influence of the hole geometry on the plate resilience to create a well founded data basis for the development of an analytical calculation model according to VDI 2230–1 for bolted connections with increased nominal hole clearance.

Elastic-porous metal rubber, commonly employed in dynamic environments, has received special attention nowadays. Utilization of equivalent metal rubber models in the finite element analysis becomes imperative because of the complexity of the spatial network structure and the extensive numerical calculations involved in it. In this work, the nonlinear characteristics of metal rubber are represented by hyperelastic constitutive models, and the Mullins effect is discussed. The relative deviations of the displacement-load curve among the test results and three dynamic models are analyzed: the hysteretic Bergström–Boyce model, the viscoelastic generalized Maxwell model, and the nonlinear spring-viscous damping element model. The results indicate that the damage value of the Mullins effect is positively correlated with the magnitude of the strain during unloading, and the performance degradation of metal rubber is weakened after multiple cycles. The time domain characteristics of the generalized Maxwell model demonstrate that the dynamic analysis of metal rubber at different frequencies have obvious deviations. The rate correlation of metal rubber affects the dynamic stiffness under different amplitudes This is reason that the nonlinear spring-viscous damping element model is deviated. Regardless of the frequency or amplitude, the Bergström–Boyce model has been found to exhibit a lower relative deviation and match well with the dynamic experiment.

The 3 K and 6 K (meaning that 3000 or 6000 carbon filaments are contained in one bundle) carbon fibers were embedded by pure aluminum sheets to have a sandwich composite structure under the accumulative roll bonding method. The tensile and cupping tests were carried out to reveal the strengthening mechanism of carbon fibers embedded in the aluminum+carbon fibers composite sheets. The improvements of ultimate tensile and cupping strengths of aluminum+carbon fibers composite sheets reached to be as high as 48 % and 38 %, compared with that of as-received sheets. With the detailed observation of the tensile and cupping fractures, the underlying strengthening mechanism comes from the bridging effect of carbon fibers during tensile and cupping tests. The accumulative roll bonding method was approved to be an effective way for aluminum+carbon fibers composite sheets preparation with higher tensile and cupping strength.