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The fatigue behavior of thin electrical steel sheets under cyclic loading is investigated in dependence on the edge surface. Therefore, four different edge conditions are compared, whereas the edge is either laser cut, shear cut, wire cut, or polished. Strain- and stress-controlled fatigue tests are performed to determine S-N curves in the low cycle regime as well as in the high cycle regime. Microstructural data is collected by non-contacting (optical) Profilometry, Nanoindentation, X-Ray Diffraction, and Electron Backscatter Diffraction to understand the differences in fatigue life by considering surface roughness, residual stresses, hardness, and microstructure. Shear cut specimens achieve the lowest fatigue life, while the other edge conditions reach relatively similar values in the LCF regime. Crack initiation is mainly intergranular in the case of defect-free edges. This tendency has a considerable influence on the observed fatigue behavior.
Carbon Particle In-Situ Alloying of the Case-Hardening Steel 16MnCr5 in Laser Powder Bed Fusion
(2021)
The carbon content of steel affects many of its essential properties, e.g., hardness and mechanical strength. In the powder bed fusion process of metals using a laser beam (PBF-LB/M), usually, pre-alloyed metal powder is solidified layer-by-layer using a laser beam to create parts. A reduction of the carbon content in steels is observed during this process. This study examines adding carbon particles to the metal powder and in situ alloying in the PBF-LB/M process as a countermeasure. Suitable carbon particles are selected and their effect on the particle size distribution and homogeneity of the mixtures is analysed. The workability in PBF-LB is then shown. This is followed by an evaluation of the resulting mechanical properties (hardness and mechanical strength) and microstructure in the as-built state and the state after heat treatment. Furthermore, potential use cases like multi-material or functionally graded parts are discussed.
A high-power diode laser was used to generate single- and multi-bead coatings of Stellite™ 6 by coaxial laser cladding over flat grey cast iron (EN-GJLP-200) as a preliminary study to develop a wear and corrosion resistant coating for brake disks on a cost-effective substrate. In this article, we have focused on a detailed quantitative analysis of the effect of different laser powers (1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 kW) on the bead geometry, dilution, microstructure, and hardness. Coatings dilution or composition depends directly on the laser power as well as bead geometry. The typical microstructure of the coatings comprises a solid solution of α (hcp)- and β (fcc)-Co with a dendritic structure as a metal matrix and an interdendritic lamellar eutectic, which contains predominantly β-Co, chromium carbides Cr7C3 and Cr23C6 as well as blocky tungsten carbide W2C. Coating hardness depends on the chemical composition and microstructure that is modified by the deposition parameters. Low laser power results in high carbide fraction and most refined microstructures, accounting for harder coatings.
The shear cutting of electrical steel sheets has a significant influence on the magnetic and mechanical material properties. Due to plastic deformation and strain hardening in the area of the punched edge, the electrical steel sheets exhibit a characteristic hardness profile. This study deals with the modelling of the resulting hardness profile by means of finite-element simulations. Elastic-plastic material properties are obtained from spherical nanoindentation testing as a function of the local hardness. In particular, representative stress-strain values are determined by applying Tabor's concept of indentation stress-strain curves. The choice of the appropriate stress- and strain-constraint factors is discussed with respect to the nanoindentation test setup used. Following this, the representative stress-strain values are analytically described to determine true stress-strain curves for the local assignment of different material models depending on the hardness. The implementation of the modelling approach in a finite-element simulation is presented for a punched electrical steel sheet specimen under monotonic loading. The simulation results are basically in good agreement with experimental data and confirm the expected influence on the mechanical material behaviour due to the shear cutting process.
Fused filament fabrication allows for the additive manufacturing of complex geometries without requiring moulds. However, due to large air voids and poor layer adhesion, the mechanical properties of parts manufactured using fused filament fabrication lag behind those of parts manufactured using conventional techniques. A previous study found that the tensile strength and Young’s modulus of such parts could be increased by a heat-treatment process. However, large air voids were still present after annealing. This study, therefore, investigates the influence of a post-pressure-treatment process on the mechanical performance and the air void ratio of continuous glass fibre-reinforced polyamide 6 in the directions perpendicular to the fibres. Without the treatment, Young’s modulus on the plane parallel to the printing bed is eight times higher than Young’s modulus perpendicular to it. Annealing at 1 MPa homogenises the material and leads to a significant increase of both the tensile strength (55 MPa) and Young’s modulus (5 GPa). Increasing the pressure to 3 MPa only slightly increases the mechanical performance, whereas a further increase to 6 MPa causes no significant changes.
The combined isotropic-kinematic hardening model enables the description of the cyclic transient elastic-plastic material behaviour of steel. However, the determination of the material model parameters and understanding of their influence on the material response can be a challenging task. This study deals with the individual steps of the material model calibration for the simulation of thin electrical steel sheets under cyclic loading. Specific recommendations are made for the determination of kinematic and isotropic hardening material parameters. In particular, the isotropic hardening evolution is described by Voce's exponential law and a simple multilinear approach. Based on the multilinear approach, which allows for different slopes in the evolution of the yield surface size, an alternative calibration of the isotropic hardening component is proposed. As a result, the presence of the yield plateau in the first half cycle can be accurately captured, while convergence issues in the material model definition for numerical simulations can be avoided. The comparison of simulated load cycles with experimental cyclic tests shows a good agreement, which indicates the suitability of the proposed material model calibration for electrical steel.
The Laves phase reinforced CoCrMoSi alloy system has emerged as a candidate material to protect the surface of components to withstand harsh environments under wear and/or corrosion. However, previous reports have raised some concerns and restricted a wider selection of iron-based substrates to be coated, especially limiting the carbon content. This work aims to outline the Laves - Carbides phases in the microstructure and its effect on the properties of T400 alloy deposited on GGG40 ductile iron. Dilution of 26 % ensured Laves formation either as primary or secondary, due to high-silicon substrate selected. Departing from 41 % dilution, the alloy changed to a completely carbide strengthened system. Therefore, for the lowest dilution the coatings hardness is dictated by Laves phase whereas, for higher ones, carbides are the most influent phases.
In this study, the fatigue behavior of thin electrical steel sheets under cyclic loading is investigated. Results from strain-controlled and stress-controlled fatigue tests with different specimen geometries and different test setups are presented and compared with conventional testing methods. The results imply that conventional testing methods should be adjusted for testing thin electrical steel sheets because the fatigue life depends significantly on the test setup as well as the specimen geometry. Therefore, this study proposes an improved specimen geometry and test setup for stress- and strain-controlled fatigue tests of thin electrical steel sheets depending on the desired testing parameters.
Investigations of the third body using pin-on-disc and brake dynamometer on all-MMC brake rotors
(2018)
Fused Deposition Modeling (FDM) is a well-established manufacturing method for producing both prototype and functional components. This study investigates the mechanical properties of FDM components by material and process-related influencing variables. Tensile tests were conducted on seven different materials in their raw filament form, two of which were fiber-reinforced, to analyze their material-related influence. To cover a wide range from standard to advanced materials relevant for load-carrying components as well as their respective variations, polylactic acid (PLA), 30% wood-fiber-reinforced PLA, acrylonitrile butadiene styrene (ABS), polycarbonate (PC), a blend of ABS and PC, Nylon, and 30% glass-fiber-reinforced Nylon were selected. The process-related influencing variables were studied using the following process parameters: layer thickness, nozzle diameter, build orientation, nozzle temperature, infill density and pattern, and raster angle. The first test series revealed that the addition of wood fibers significantly worsened the mechanical behavior of PLA due to the lack of fiber bonding to the matrix and significant pore formation. The polymer blend of ABS and PC only showed improvements in stiffness. Significant strength and stiffness improvements were found by embedding glass fibers in Nylon, despite partially poor fiber–matrix bonding. The materials with the best properties were selected for the process parameter analysis. When examining the impact of layer thickness on part strength, a clear correlation was evident. Smaller layer thicknesses resulted in higher strength, while stiffness did not appear to be affected. Conversely, larger nozzle diameters and lower nozzle temperatures only positively impacted stiffness, with little effect on strength. The part orientation did alter the fracture behavior of the test specimens. Although an on-edge orientation resulted in higher stiffness, it failed at lower stresses. Higher infill densities and infill patterns aligned with the load direction led to the best mechanical results. The raster angle had a significant impact on the behavior of the printed bodies. An alternating raster angle resulted in lower strengths and stiffness compared to a unidirectional raster angle. However, it also caused significant stretching due to the rotation of the beads.