Materialwissenschaft und Werkstofftechnik最新文献

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.

After magnetization, the magnetic loss of FeSiAl/SrFe₁₂O₁₉ (SrM) soft magnetic composite is greatly reduced compared with that before magnetization, which has similar effect with FeSiAl magnetic powder core with applied external transverse magnetic field. The experimental results show that the internal bias field provided by SrM ferrite after magnetization increases the average domain size, reduces the number of domain walls and the displacement of domain walls, thereby effectively reducing the hysteresis loss. When the content of SrM ferrite is 8.1 wt.-%, the magnetic loss is reduced by about 50 %, and the overall performance is the best.

The hot compression experiments were performed at a deformation temperature of 720 °C to 870 °C and a strain rate of 0.0005 s⁻¹ to 5 s⁻¹. The strain-compensated Arrhenius constitutive equation and the hot processing map at a strain of 0.6 were established, and the dynamic recrystallization behaviors of the alloy in different power dissipation (η) regions were studied. The results show that the correlation coefficient (R) and average relative errors (AARE) of the established constitutive equations are 0.999 % and 2.523 % in the β phase region, and 0.988 % and 7.709 % in the α+β phase region, respectively. The hot processing map shows that the deformation parameters in the high power dissipation regions range from 810 °C to 870 °C/0.0005 s⁻¹ to 0.005 s⁻¹, accompanied by a power dissipation factor of 0.41 to 0.55. These regions result from a combination of continuous and discontinuous recrystallization mechanisms. With the decrease in the power dissipation value, the appearance of deformation bands (DBs) and localized flow (FL) in the microstructure increased.

Glass dust particles, generated in glass cutting industries as a process waste possess health risk and serious environmental issues. This paper essentially reports on exploring the possibility of using this waste glass dust as particulate filler in two different natural fibers (hemp/flax) reinforced polymer composites. Such composites are prepared by hand lay-up route, varying weight percentages of waste glass dust from 0 to 20. The physical and mechanical characterizations are evaluated experimentally. X-ray diffractogram analysis reveals the degree of crystallinity of the composites and the phases present in the raw filler. With the incorporation of waste glass dust, the flexural strength, inter-laminar shear stress and micro-hardness of the composites are improved up to about 52 %, 44 % and 20 % respectively. On the contrary, tensile and impact strengths tend to decrease about 32 % and 17 % with filler content. Using scanning electron microscopy, the possible mechanisms such as fiber-matrix de-bonding, fiber-pullout, matrix crack and rupture etc. are identified for failures of the composites under tensile, flexural and impact loadings. With low crystallinity and fairly good mechanical properties, these hybrid composites can have potential use in thermal insulations and low-load engineering applications.

For years, coated metal sheets have been used in cookware manufacturing. This paper focuses on employing experimental and numerical analyses to determine the quality and formability of commercially available polytetrafluoroethylene (PTFE)-coated aluminium sheets. For this purpose, examinations of the coating‘s microstructure, hardness, and friction coefficient through nano-indentation and scratch tests, were investigated. Tensile test was performed to obtain some mechanical characteristics of the coated aluminium sheets. Moreover, the forming limit curve for the studied material was established by conducting Nakazima test, covering both negative and positive domains of minor strain. The influence of sheet thickness on formability was investigated since using 2 mm and 1 mm thick sheets in this work. Finally, the limits of deep drawing process using the finite element method with Abaqus software was studied.