The Instrumented Indentation Test: An Aiding Tool for Material Science and Industry

Engineering materials encompass a wide spectrum of structural-functional products that are commonly used in the transportation (automotive, aerospace, naval), construction, machinery, and tooling industries [...]

Integral Methodology for the Multiphysics Design of An Automotive Eddy Current Damper

The present work reports an integrated (experimental and numerical) methodology that combines the development of a finite element multiphysics model with an experimental strategy to optimally design an eddy current damper for automotive suspensions. The multiphysics model couples the whole set of time-dependent electromagnetic, thermal, mechanical, and fluid–wall interaction (CFD) partial differential equations. The developed FE model was validated against both literature model predictions and in-house experimental data. The electromagnetic model takes into account the magnetic material characteristics of the ferromagnetic material and iron poles. Loss sep-aration and the Jiles–Atherton hysteresis models were invoked to determine the heat generated in the soft iron parts. The computation of the fluid–wall interaction phenomena in the air gap allowed for the prediction of the temperature field across the solid materials, including the magnets. The design of the EC damper addresses the effects of the geometries of the stator and rotor, as they are the most critical geometries for maximizing the functions of an eddy current damper. The magneto-thermal simulations suggested that the heating of the permanent magnets remains within a safe region over the investigated operational frequency range of the eddy current damper

Mechanical Behaviour of TiAl Spherical Particles Including Friction Effect

Pubblicazione su CD-RO

Nano-indentation properties of tungsten carbide-cobalt composites as a function of tungsten carbide crystal orientation

Tungsten carbide-cobalt (WC-Co) composites are a class of advanced materials that have unique properties, such as wear resistance, hardness, strength, fracture-toughness and both high temperature and chemical stability. It is well known that the local indentation properties (i.e., nano- and micro-hardness) of the single crystal WC particles dispersed in such composite materials are highly anisotropic. In this paper, the nanoindentation response of the WC grains of a compact, full-density, sintered WC-10Co composite material has been investigated as a function of the crystal orientation. Our nanoindentation survey has shown that the nanohardness was distributed according to a bimodal function. This function was post-processed using the unique features of the finite mixture modelling theory. The combination of electron backscattered difiraction (EBSD) and statistical analysis has made it possible to identify the orientation of the WC crystal and the distinct association of the inherent nanoindentation properties, even for a small set (67) of nanoindentations. The proposed approach has proved to be faster than the already existing ones and just as reliable, and it has confirmed the previous findings concerning the relationship between crystal orientation and indentation properties, but with a significant reduction of the experimental data

Micro-macro relationship between microstructure, porosity, mechanical properties, and build mode parameters of a selective-electron-beam-melted Ti-6Al-4V alloy

The performance of two selective electron beam melting operation modes, namely the manual mode and the automatic ‘build theme mode’, have been investigated for the case of a Ti-6Al-4V alloy (45–105 μ;m average particle size of the powder) in terms of porosity, microstructure, and mechanical properties. The two operation modes produced notable differences in terms of build quality (porosity), microstructure, and properties over the sample thickness. The number and the average size of the pores were measured using a light microscope over the entire build height. A density measurement provided a quantitative index of the global porosity throughout the builds. The selective-electron-beam-melted microstructure was mainly composed of a columnar prior β-grain structure, delineated by α-phase boundaries, oriented along the build direction. A nearly equilibrium α + β mixture structure, formed from the original β-phase, arranged inside the prior β-grains as an α-colony or α-basket weave pattern, whereas the β-phase enveloped α-lamellae. The microstructure was finer with increasing distance from the build plate regardless of the selected build mode. Optical measurements of the α-plate width showed that it varied as the distance from the build plate varied. This microstructure parameter was correlated at the sample core with the mechanical properties measured by means of a macro-instrumented indentation test, thereby confirming Hall-Petch law behavior for strength at a local scale for the various process conditions. The tensile properties, while attesting to the mechanical performance of the builds over a macro scale, also validated the indentation property measurement at the core of the samples. Thus, a direct correlation between the process parameters, microstructure, porosity, and mechanical properties was established at the micro and macro scales. The macro-instrumented indentation test has emerged as a reliable, easy, quick, and yet non-destructive alternate means to the tensile test to measure tensile-like properties of selective-electron-beam-melted specimens. Furthermore, the macro-instrumented indentation test can be used effectively in additive manufacturing for a rapid setting up of the process, that is, by controlling the microscopic scale properties of the samples, or to quantitatively determine a product quality index of the final builds, by taking advantage of its intrinsic relationship with the tensile properties

Correlation between the indentation properties and microstructure of dissimilar capacitor discharge welded WC-Co/high-speed steel joints

The welding of cemented carbide to tool steel is a challenging task, of scientific and industrial relevance, as it combines the high level of hardness of cemented carbide with the high level of fracture toughness of steel, while reducing the shaping cost and extending the application versatility, as its tribological, toughness, thermal and chemical properties can be optimally harmonised. The already existing joining technologies often impart either insufficient toughness or poor high-temperature strength to a joint to withstand the ever-increasing severe service condition demands. In this paper, a novel capacitor discharge welding (CDW) process is investigated for the case of a butt-joint between a tungsten carbide-cobalt (WC-Co) composite rod and an AISI M35 high-speed steel (HSS) rod. The latter was shaped with a conical-ended projection to promote a high current concentration and heat at the welding zone. CDW functions by combining a direct current (DC) electric current pulse and external uniaxial pressure after a preloading step, in which only uniaxial pressure is applied. The relatively high heating and cooling rates promote a thin layer of a characteristic ultrafine microstructure that combines high strength and toughness. Morphological analysis showed that the CDW process: (a) forms a sound and net shaped joint, (b) preserves the sub-micrometric grain structure of the original WC-Co composite base materials, via a transitional layer, (c) refines the microstructure of the original martensite of the HSS base material, and (d) results in an improved corrosion resistance across a 1-mm thick layer near the weld interface on the steel side. A nano-indentation test survey determined: (e) no hardness deterioration on the HSS side of the weld zone, although (f) a slight decrease in hardness was observed across the transitional layer on the composite side. Furthermore, (g) an indication of toughness of the joint was perceived as the size of the crack induced by processing the residual stress after sample preparation was unaltered

Particle In Cell Simulation of Combustion Synthesis of TiC Nanoparticles

A coupled continuum-discrete numerical model is presented to study the synthesis of TiC nanosized aggregates during a self-propagating combustion synthesis (SHS) process. The overall model describes the transient of the basic mechanisms governing the SHS process in a two-dimensional micrometer size geometry system. At each time step, the continuum (micrometer scale) model computes the current temperature field according to the prescribed boundary conditions. The overall system domain is discretized with a desired number of uniform computational cells. Each cell contains a convenient number of computation particles which represent the actual particles mixture. The particle-in-cell (discrete) model maps the temperature field from the (continuum) cells to the respective internal particles. Depending on the temperature reached by the cell, the titanium particles may undergo a solid-liquid transformation. If the distance between the carbon particle and the liquid titanium particles is within a certain tolerance they will react and a TiC particle will be formed in the cell. Accordingly, the molecular dynamic method will update the location of all particles in the cell and the amount of transformation heat accounted by the cell will be entered into the source term of the (continuum) heat conduction equation. The new temperature distribution will progress depending on the cells which will time-by-time undergo the chemical reaction. As a demonstration of the effectiveness of the overall model some paradigmatic examples are shown.Comment: submitted to Computer Physics Communication

Indentation modulus at the macro-scale level measured by Brinell and Vickers indenters by using the primary hardness standard machine at INRiM

In this paper, the experimental procedure and calculation model for the measurement of the indentation modulus by using the primary hardness standard machine at INRiM in the macro-scale range at room temperature is described. The indentation modulus is calculated based on the Doerner-Nix linear model and from accurate measurements of indentation load, displacement, contact stiffness, and hardness indentation imaging. Measurements are performed with both pyramidal (Vickers test) and spherical indenters (Brinell test). Test force is provided by a dead-weight machine, and the occurring displacement is measured by a laser-interferometric system. The geometrical dimensions of both the Vickers and Brinell indentations are measured by means of a micro-mechanical system and optical microscopy imaging techniques. Applied force and indentation depth are measured simultaneously, at a 16 Hz sampling rate, and the resultant loading-unloading indentation curve is obtained. Preliminary tests are performed on metal and alloy samples. Considerations and comments on the accuracy of the proposed method and analysis are discussed

Determination of the yield radius and yield stress in 2198-T3 aluminum alloy by means of the dual-scale instrumented indentation test

A new dual-scale instrumented indentation test (DualS-IIT) methodology is here proposed to determine the yield stress (in a tensile-like sense). The methodology involves measuring the bulk yield radius, as defined by the expansion cavity model (ECM), induced by a Vickers macro-indentation in a medium plane cross-section. The bulk yield radius is measured by means of a subsurface nano-hardness survey along the load direction in correspondence to the transition interface between the hemispherical strain hardened region and the surrounding elastic region. The methodology has been applied to an Al–Li (A2198-T3) alloy and a yield stress of 297 MPa has been measured (in agreement with a tensile test); moreover, anomalous plastic deformation behaviour has appeared under indentation. The combination of macro- and nano-indentation tests in one single experiment, as in the proposed methodology, offers a unique experimental basis to directly correlate the mechanical properties of a material at two different scales, which at present is an open issue in the research on indentation

Correlation between the bath composition and nanoporosity of DC-electrodeposited Ni-Fe alloy

The outstanding mechanical strength of as-deposited DC-electrodeposited nanocrystalline (nc) Ni-Fe alloys has been the subject of numerous researches in view of their scientific and practical interest. However, recent studies have reported a dramatic drop in ductility upon annealing above 350°C, associated with a concomitant abnormal rapid grain growth. The inherent cause has been ascribed to the presence of a detrimental product or by product in the bath, which affects either the microstructure or causes defects in the concentration and/or distribution of the as-deposited films. The present work has been inspired by the observed abnormal behaviour of annealed electrodeposited nc Ni-Fe alloy, which has here been addressed by considering the relationship between the composition of the bath (iron-chloride, nickel-sulphate solution, saccharin and ascorbic acid) and deposition defects (e.g. grain boundary pores) in the case of an nc Ni-Fe (Fe 48 wt%) alloy. The current investigations have included X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) in both as-deposited and post-annealed conditions (300°C–400°C). XPS depth profiling with Ar ion sputtering showed a significant amount of C and O impurities entrapped in the foils during deposition. As such impurities are often overlooked in common analytical techniques, new scenarios may need to be rationalised to explain the observed drop in tensile ductility of the as-deposited Ni-Fe alloys