Functionally Graded Materials Specimens Research Articles

Investigation of the mechanical and Thermal properties of functionally graded iron aluminide

Iron aluminide is used in many industrial applications such as valve of piston; In this work, the mechanical and thermal properties of samples made of functionally graded materials (FGMs) were studied. These specimens were manufactured by powder metallurgy, consisting of different chemical composition layers of (40–50) at% aluminum. The specimens consist of: single layers (B1, B2, B3) consisting of (40, 45, and 50) at% of aluminum and the rest of iron; FGMs (double-layer) (B4, B5, B6); and FGMs (three-layer) (B7). All results of FGM were compared with its constituent layers in all tests, including the x-ray diffraction examination, and they all showed the same phases with differences in intensity (Fe3Al, FeAl, Al13Fe4, FeAl2, Fe2Al5). From the mechanical compression test, the yield point, ultimate stress, and Young’s modulus results indicated that the FGMs have an average value compared with the layer that contained them. Thermal test: FGMs have the lowest values of thermal conductivity and thermal diffusivity compared with single-layer specimens. The specific heat of FGMs has the highest value. Thermal conductivity was recorded to range from 8.08 to 6.376 W mK−1 for single and FGM specimens, respectively; thermal diffusivity from 4.6 to 0.72 mm2 S−1; and specific heat from 1.77 to 8.84 MJ/m3K.

Microstructure and Mechanical Properties of P21-STS316L Functionally Graded Material Manufactured by Direct Energy Deposition 3D Print

Functionally graded materials (FGMs) have a characteristic whereby the composition and structure are gradually changed according to the location, and the mechanical properties or chemical properties are gradually changed accordingly. In this study, using a multi-hopper direct energy deposition 3D printer, an FGM material whose composition changes gradually from P21 ferritic steel to stainless steel 316L austenitic steel was fabricated. From optical microscope, scanning electron microscope, and X-ray diffraction analysis, columnar, cell, and point type solidified micro-structure and precipitations were observed depending on the deposited compositions. Electron probe microanalysis and electron backscatter diffraction analysis confirmed the component segregation, ferrite austenite volume fraction and phase distribution behavior according to compositions. In the FGM specimen test, the ultimate tensile strength of STS316L, which was the most fragile, was measured, and the toughness was measured for the notch area, which did not represent the FGM characteristics. Hardness showed changes according to FGM position and was suitable for FGM analysis. The maximum hardness was measured in the FGM duplex area, which was caused by grain refinement, precipitate strengthening, and solid solution strengthening. In nuclear power plant welds high strength can cause adverse effects on stress corrosion cracking, and caution is needed in applying FGM.

Investigation of the microstructure and thermo-mechanical properties of functionally graded materials fabricated by the vibrating centrifugal solid particle method

In this research, SiC/Al A413.1 functionally graded materials (FGMs) were fabricated by the vibrating centrifugal solid particle method (VCSPM), and the effects of the SiC particles on the microstructure and thermo-mechanical properties of an A413.1 aluminium alloy were investigated. The benefits of a vibration during centrifugal casting of FGMs are illustrated. After designing and fabricating the centrifugal casting machine, cylindrical FGM specimens were produced using the centrifugal solid particle method (CSPM) and VCSPM. This study used SiC particles with an average particle size from 50 to 62 μm as reinforcements to fabricate A413.1-10 wt% SiC functionally gradient composites at three annular mould speeds (900–1500 and 2100 rpm) and with or without a vibration of the mould. The Brinell hardness was measured; the yield strength (YS), ultimate tensile strength (UTS) and Young’s modulus (E) were determined by tensile testing; the density was determined by the Archimedes method; and the thermal expansion coefficients were measured with a dilatometer. A comparison of the samples produced by the conventional method and VCSPM shows a significant reduction in the porosity and an increase in the distribution gradient of the reinforcing particles for the VCSPM case. It can be concluded that in both processes, the mechanical and thermal properties improved in most cases by moving from the inner radius to the outer radius because of the movement of particles towards the outer radius from the centrifugal force. The results also show that the use of a vibration dramatically increased the rate and speed of migration of gas bubbles towards the inner radius, and the mechanical properties (hardness, YS, UTS and E) improved by moving from the inner to outer radius due to an increase in the percentage of silicon carbide particles. Upon increasing the velocity and using the VCSPM, the slope of these changes becomes steeper than those for the vibration-free mode and at low rotation speeds.

Spark plasma sintering of SiC/graphite functionally graded materials

Previous studies have used various methods for sintering of SiC, carbon, and SiC/carbon functionally graded materials (FGM). However, no experimental studies on SiC/graphite FGM manufacturing using the spark plasma sintering (SPS) method have been reported. In this study, a SiC/graphite FGM specimen has been fabricated using SPS. The interface between the adjacent layers of the sintered specimen exhibits no apparent defects such as gaps or delaminations. The SiC and graphite phases in the specimen show no substantial change before and after sintering.

Development of step-wise functionally graded materials nano (3YPSZ/Al2O3) with improved fracture toughness and low thermal degradation for hip joint replacements

In this work high order (10 layers) step – wise functionally graded materials (FGM) of nano 3Y- tetragonal zirconia poly crystals (3YPSZ) and nano alumina (Al2O3) successfully prepared by powder technology technique. “Fracture toughness and hardness were measured by using indentation methods”. Low thermal degradation (LTD) was done at 134 ºC and 0.2 bar in autoclave, the amount of monoclinic phase of ZrO2 (m – phase) on the exposed surface was calculated by X-ray’s diffraction (XRD). Results showed prevent of m – t transformation after 40 hr in all FGM specimens, high fracture toughness along cross – section of specimens due to increase of zirconia content, which tetragonal phase is toughening agent. SEM observations and EDS analytic a long cross – section of specimen showed good distributed of 3YPSZ from EDS analytic and there were no agglomerates, some pores appear due to binder material that was used in pressing process.

Mechanical characterization of functionally graded materials produced by the fused filament fabrication process

Abstract In this research study, the design and fabrication workflow of functionally graded materials (FGMs) were introduced using fused filament fabrication (FFF) process. Rigid polymers were mechanically characterized in three printing directions. Tensile strength and modulus of elasticity values for YZ and XY printing orientation specimens indicated similar results. Printing in the XZ direction showed poor strength values in comparison with other printing directions. Interface analysis with different transition patterns was accomplished and the advantage of gradient transition was achieved. Micrography of specimens was analyzed to investigate the internal structure and was used to validate the test results. Statistical methods were applied to investigate the relationship between microstructural descriptors (volume fractions) and process-related parameters (printing temperatures). The results of the analysis of variance (ANOVA) have confirmed that printing temperature and concentration have a significant impact on tensile test results. The data-driven approach was employed to construct a linear regression models in order to formulate input data for finite element analysis (FEA). As a result of FEA simulation, effective Young’s modulus was calculated using a MATLAB code. FEA-predicted Young’s moduli were validated through experimental test results. The comparison of the numerical method and experimental values showed less than 5% error for FGM specimens printed in 250, 260 and 270 °C temperatures. FFF process with FGM could have potential applications in medical, structural, and automotive industries by locally varying material properties. This study presents a unique method of fabricating FGM structures with low-cost manufacturing process.

Experimental study on mechanical properties of Ni/TiO2 FGM processed by pressureless sintering technique

In the present work, an experimental investigation and characterization of Functionally Graded Materials (FGMs) is carried out. The Nickel (Ni) and Titanium dioxide (TiO2) materials are taken as principal materials and the powder metallurgy technique is used for the preparation of specimens. The Nickel powder has a particle size of 20 μm with more than 99% purity and Titanium dioxide powder having 35 μm particle size with more than 99% purity is used for this study. The FGM specimens are prepared with five layers, with pure Nickel on one side and pure Titanium dioxide on opposite side of the specimen; and the three intermediate layers comprising of mixture of Nickel and Titanium dioxide. The five layered FGM samples are prepared with one inch diameter round die and the compacted samples are heated up to 1200°C in an inert gas (argon) atmosphere. The microscopic result shows that the microstructure of Ni/TiO2 FGM has varied layer-by-layer and the interface between the layers are observed. As a part of mechanical characterization, both green and sintered FGM sample densities are measured for each layer of the sample. The Rockwell hardness test method is used to find the hardness of the each layer in the samples. Linear shrinkage of the specimen is calculated with the help of green sample dimensions. The Compression test is conducted on the sintered specimens by using universal testing machine; stress-strain behaviour and maximum stress reported.

Comparison of the dielectric properties of functionally graded material dielectrics and layered dielectrics used for electric stress control

Layered dielectric materials are currently in use for electric field stress control, but are limited by charge accumulation at the dielectric–dielectric interfaces. The current work uses micrometric particles to modify the effective permittivity of epoxy resin samples. Two broad kinds of samples are considered: discrete layered material (DLM) samples and functionally graded material (FGM) samples. DLM samples are obtained by bonding layers of epoxy resin with different filler loadings such that abrupt variation in permittivity might occur along the sample thickness. FGM specimens are prepared by hot pressing a comparatively large number of very thin layers of micro-filled epoxy resin with very small differences in permittivity one over the other, thus creating a gradual spatial permittivity gradation. Dielectric properties of FGM and DLM specimens are compared in this study. Space charge accumulation is studied using the pulsed electroacoustic method; the accumulated charge density is seen to be lower in FGM. The uniformity of electric field distribution under applied electric stress is computed, and the field utilisation factor in FGM is seen to have a higher value. Also, the dissipation factor is lower and the short-term breakdown strength is higher in FGM than in DLM samples, providing reason to prefer FGM for insulation to control electric stress.

Mechanics of bioinspired functionally graded soft-hard composites made by multi-material 3D printing

Functional gradients are material transitions that are found in nature and are known to result in materials with superior properties and multiple functionalities. The emerging multi-material 3D printing (=additive manufacturing, AM) techniques provide a powerful tool for the design and fabrication of bioinspired functionally graded materials (FGMs). In particular, the spatial distribution of materials can be controlled at the level of individual volumetric pixels (voxels i.e., cubes with side lengths of 20–40 μm), thereby ensuring accuracy, reliability, and reproducibility of the obtained properties and allowing for systematic studies of how various design variables affect the deformation and fracture behaviors of FGMs. Here, we designed, 3D printed, and mechanically tested tensile and notched FGMs specimens with step-wise (i.e., 5-, 10-, and 15-steps) and continuous (sigmoid and linear) gradients. The deformation and fracture mechanisms of these FGM composites were studied using digital image correlation, digital microscopy, and scanning electron microscopy. We further characterized the chemical composition and local mechanical properties of FGM composites using XPS and nanoindentation measurements, respectively. Tensile test specimens with a continuous gradient (i.e., linear) exhibited much higher Young’s moduli (≈3-folds) and ultimate strengths (≈2-folds) but lower elongations (≈2-folds drop) as compared to those with stepwise gradients (i.e., 5-steps). Similarly, notched specimens with linear gradients exhibited 2-folds higher values of the stiffness and fracture stress, but 1.5-folds lower fracture strains as compared to those with 5-steps gradients. Although we found non-uniform highly concentrated strain distributions in all specimens, FGMs with linear gradients showed a smoother strain distribution and smaller crack blunting zones as compared to those with stepwise gradients. Our results imply that for stiffness and strength linear-gradient perform better than abrupt hard-soft-hard specimens.

A comparative investigation of hardness and compression strength of Nickel coated B4C reinforced 601AC/201AC selective layered functionally graded materials

High hardness and compression strength are the essential properties in many engineering applications. Requirement of light weight materials with high mechanical properties as a function of direction leads to the development of Aluminium based Functionally Graded Materials (FGM). Two different matrix metal blends 601AC and 201 AC are used for the comparison. Mechanical Alloying technique (MA) is used to blend the metal powders. The FGM specimens with 2 layers, 3 layers and 5 layers are fabricated using Powder Metallurgy (P/M) technique. B4C with Nickel coating and without Nickel coating is used as particulate. Two different average particle size of B4C (20 μm and 50 μm) was selected. The configurations used for the FGMs are 0%/5% for 2 layered specimen, 0%/5%/10% for 3 layered specimen and 0%/5%/10%/15%/20% for five layered specimen. Specimens are prepared according to ASTM B925-3 standard for micro-hardness test and compressive strength test. Graphs are plotted in terms of number of layers, particle size, sintering temperature, and coating condition. From the experiments it is observed that, number of layers influences the hardness and compressive strength. The average specimen hardness is enhanced from 55 HV for two layered FGM to 73 HV for three layered FGM. The compressive strength is increase from 613 MPa for three layered specimen without Nickel coated B4C to 732 Mpa for three layered specimen with Nickel coating. Best possible combination of all parameters is observed from the experiment is particle size of 20 μm, sintering temperature of 570 °C, and B4C particulate with Nickel coating. Compared to the hardness values for two different matrix materials 601AC/201AC, closure values are observed for the best possible combination of other variables. Where-as for the compressive strength 201AC matrix shows superior values compared to 601AC for the best possible combination of all the other variables.

Characterisation of four-layered Al-Al2O3 functionally graded material prepared through powder metallurgy and pressureless sintering

In this research study, four-layered aluminium-aluminium oxide (Al-Al2O3) functionally graded material (FGM) was prepared through powder metallurgy (PM) route considering 0%, 10%, 20% and 30% weight percentage of ceramic concentration. The sintering temperature and time used are 620°C and 120 min following two-step sintering cycle. The prepared FGM samples were characterised by densification and shrinkage. Microstructural and elemental analyses were carried out by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Mechanical characterisation was carried out using Vickers microhardness tests. It was observed that cylindrical FGM specimens (green compact) were successfully prepared and diameter of cylindrical structure was decreased after sintering process. It was also observed that there was no existence of macro-crack or micro-crack within the individual layer or at the interface and smooth transition occurred from one layer to next layer. Elemental analyses confirmed the gradient distribution of material composition layer by layer.

Hot-pressed sintering of W/Cu functionally graded materials prepared from copper-coated tungsten powders

The three-layered (W–60 vol%Cu/W–40 vol%Cu/W–20 vol%Cu) W/Cu functionally graded material (FGM) containing a Cu network structure was fabricated at different temperatures by hot-pressed sintering produced from copper-coated tungsten powders. The effects of various sintering temperatures on relative density, microstructure, thermal conductivity, hardness and flexural strength were investigated. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis show that a Cu network extends throughout the W/Cu FGM specimens sintered at 1065 °C and the graded structure can be retained perfectly, and W particles are distributed homogeneously. The low-temperature sintering densification of W/Cu FGM arises because the sintering mode of the copper-coated tungsten particles includes just sintering Cu to Cu, rather than Cu to W, Cu to Cu and W to W, as required for conventional powder particles. The relative density of W/Cu FGM sintered at 1065 °C for 3 h under a load of 25 MPa is 96.1%. The thermal conductivity is up to 204 W·m−1·K−1 at normal temperature and 150 W·m−1·K−1 at 800 °C. And the Vickers hardness varies with the gradient of different layers from 3.34 to 4.05 GPa.

Effect of varied alumina/zirconia content on ballistic performance of a functionally graded material

Functionally graded materials (FGMs) are characterized by continuous variation in their composition and structure with thickness or volume. Hence, the corresponding changes in the properties and functions of the FGMs can be investigated to create new materials. In this study, four-layered FGM specimens with three different compositions, i.e., Al2O3/(0, 5, 10, 15%) ZrO2, Al2O3/(0, 10, 20, 30%) ZrO2 and Al2O3/(0, 15, 30, 45%) ZrO2, were designed. The ceramic specimens were hexagons whose sides were 11mm long. Accordingly, 6061-T6 Al was used as a back plate. A ballistic test was conducted using 0.3″ armor-piercing bullets with an initial speed of 868±15m/s. Numerical simulation software, i.e., LS-DYNA, was employed to analyze stress transfer and the fracture of the FGM specimens under impact. The ballistic test showed that the Al2O3/(0, 5, 10, 15%) ZrO2 FGM exhibited the best impact resistance performance. The investigation of microstructures through observation using a SEM did not show delamination in the FGM interlayer after impact. Furthermore, the abrasion between the ceramic and projectile increased. XRD analysis verified the phase transformation of ZrO2 from the tetragonal phase to the monoclinic phase. This transition delayed crack growth and increased material toughness, thereby promoting the impact resistance performance of the FGMs.

Phase Contamination Characterization of Stepwise-Built Functionally Graded Hydroxyapatite/Titanium (HA/Ti) Sintered under Various Atmospheres

Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) test were utilized to detect the phase transformation of a HA/Ti Functionally Graded Material (FGM) prepared via Powder Metallurgy (PM) technique. The effects of oxygen (O2), nitrogen (N2), forming (N2+H2) and Argon (Ar) sintering atmospheres on the FGM specimens were examined by considering the gas flowing duration. It was found that the original metallurgical profile of pure Ti in HA/Ti FGM sintered under N2 atmosphere was almost preserved. However the carburization of the pure Ti was observed on the specimen. Medium alkyl halides (C-Br) and alkenes (-C=C-) stretches were detected, producing the dominant elements in the pure Ti layer of the specimen. The almost stable constituent element remains in the specimen sintered under flowing N2+H2 atmosphere as detected by XRD result. This proved the significance of controlling the sintering atmosphere during the entire sintering process. The results achieved reveal the high tendency of Ti and HA elements to react with the sintering environment, thus very precise furnace with controllable atmosphere is crucial for the fabrication of the HA/Ti FGM.

Compressive evaluation of homogeneous and graded epoxy-glass particulate composites.

The propagation of stress waves in epoxy-glass particulate composites and graded materials was studied experimentally. Materials tested in this study consisted of an epoxy matrix with various concentrations of spherical glass particles having a mean diameter of 42μm. Plate impact experiments were performed using a gas gun. Embedded within the specimens were manganin stress gauges used to record propagating compressive longitudinal stress waves through the material. High strain rate experiments using a Split Hopkinson Pressure Bar (SHPB) apparatus were also performed to evaluate the dynamic strength of the specimens, while quasi-static compression tests were undertaken to characterize their quasi-static behavior. Ultrasonic wave speed measurements were carried-out in order to obtain additional material properties and characterize the gradation in functionally graded materials (FGM). It was found that low volume fractions of particles are detrimental to the performance of the material under impact loading, while concentrations in the range of about 30 to 45% by volume exhibit characteristics of higher degrees of scattering. This suggests that materials in this latter range would be more effective in the thwarting of destructive shock waves than the homogeneous matrix material. Impact testing of FGM specimens suggests that impact loading on the stiff (high volume fraction) face results in much higher levels of scattering. Therefore, such materials would be effective for use in light weight armor or as shielding materials due to their effective attenuation of mechanical impulses.

Numerical modeling of wave propagation in functionally graded materials using time-domain spectral Chebyshev elements

Numerical modeling of the Lamb wave propagation in functionally graded materials (FGMs) by a two-dimensional time-domain spectral finite element method (SpFEM) is presented. The high-order Chebyshev polynomials as approximation functions are used in the present formulation, which provides the capability to take into account the through thickness variation of the material properties. The efficiency and accuracy of the present model with one and two layers of 5th order spectral elements in modeling wave propagation in FGM plates are analyzed. Different excitation frequencies in a wide range of 28–350 kHz are investigated, and the dispersion properties obtained by the present model are verified by reference results. The through thickness wave structure of two principal Lamb modes are extracted and analyzed by the symmetry and relative amplitude of the vertical and horizontal oscillations. The differences with respect to Lamb modes generated in homogeneous plates are explained. Zero-crossing and wavelet signal processing–spectrum decomposition procedures are implemented to obtain phase and group velocities and their dispersion properties. So it is attested how this approach can be practically employed for simulation, calibration and optimization of Lamb wave based nondestructive evaluation techniques for the FGMs. The capability of modeling stress wave propagation through the thickness of an FGM specimen subjected to impact load is also investigated, which shows that the present method is highly accurate as compared with other existing reference data.

Stochastic multiscale fracture analysis of three-dimensional functionally graded composites

A new moment-modified polynomial dimensional decomposition (PDD) method is presented for stochastic multiscale fracture analysis of three-dimensional, particle-matrix, functionally graded materials (FGMs) subject to arbitrary boundary conditions. The method involves Fourier-polynomial expansions of component functions by orthonormal polynomial bases, an additive control variate in conjunction with Monte Carlo simulation for calculating the expansion coefficients, and a moment-modified random output to account for the effects of particle locations and geometry. A numerical verification conducted on a two-dimensional FGM reveals that the new method, notably the univariate PDD method, produces the same crude Monte Carlo results with a five-fold reduction in the computational effort. The numerical results from a three-dimensional, edge-cracked, FGM specimen under a mixed-mode deformation demonstrate that the statistical moments or probability distributions of crack-driving forces and the conditional probability of fracture initiation can be efficiently generated by the univariate PDD method. There exist significant variations in the probabilistic characteristics of the stress-intensity factors and fracture-initiation probability along the crack front. Furthermore, the results are insensitive to the subdomain size from concurrent multiscale analysis, which, if selected judiciously, leads to computationally efficient estimates of the probabilistic solutions.

Numerical Simulation of Mixed-Mode Crack Propagation in Functionally Graded Materials

This paper addresses the numerical simulation of mixed-mode crack propagation in Functionally Graded Materials (FGMs) by means of eXtended Finite Element Method (XFEM), endowed with elastic and toughness properties which gradually vary in space. The method allows to follow crack paths independently of the finite element mesh, this feature is especially important for FGMs, since the gradation of the mechanical properties may lead to complex propagation paths also in simple symmetric tests. Each step of crack growth simulation consists of the calculation of the mixed-mode stress intensity factor by means of a non-equilibrium formulation of the interaction integral method, determination of the crack growth direction based on a specific fracture criterion. A specific fracture criterion is tailored for FGMs based on the assumption of local homogenization of asymptotic crack-tip fields in FGMs. The present approach uses a user-defined crack increment at the beginning of the simulation. Crack trajectories obtained by the present numerical simulation agree well with available experimental results for FGMs. The computational scheme developed here serve as a guideline for fracture experiments on FGM specimens (e.g. initiation toughness and R-curve behavior).

Fabrication of Net‐Shape Functionally Graded Composites by Electrophoretic Deposition and Sintering: Modeling and Experimentation

It is shown that electrophoretic deposition (EPD) sintering is a technological sequence that is capable of producing net‐shape bulk functionally graded materials (FGM). By controlling the shape of the deposition electrode, components of complex shapes can be obtained. To enable sintering net‐shape capabilities, a novel optimization algorithm and procedure for the fabrication of net‐shape functionally graded composites by EPD and sintering has been developed. The initial shape of the green specimen produced by EPD is designed in such a way that the required final shape is achieved after sintering‐imposed distortions. The optimization is based on a special innovative iteration procedure that is derived from the solution of the inverse sintering problem: the sintering process is modeled in the “backward movie” regime using the continuum theory of sintering incorporated into a finite‐element code. The experiments verifying the modeling approach include the synthesis by EPD of Al2O3/ZrO2 3‐D (FGM) structures. In order to consolidate green parts shaped by EPD, post‐EPD sintering is used. The fabricated deposits are characterized by optical and scanning electron microscopy. The experimentally observed shape change of the FGM specimen obtained by EPD and sintering is compared with theoretical predictions.

Experimental Investigations on Deformation and Fracture Behavior of Glass Sphere Filled Epoxy Functionally Graded Materials

In this paper, deformation and fracture behavior of glass sphere filled epoxy functionally graded materials (FGM) are numerically evaluated and experimentally studied. The fabrication of the FGM is described in detail, and the spatial gradation of elastic modulus and the microscopic structure in FGM are measured and analyzed. The deformation and fracture characterization of the FGM specimen with a crack oriented along the direction of the elastic gradient under three point bend are studied by the experimental and the finite element method. The influences of crack location at both the stiff and the compliant sides of the FGM specimen on crack initiation, deformation field and stress intensity factor are analyzed. The results are: (a) The neutral-axis in the FGM specimen under three-point-bending will shift toward the stiffer side; (b) The initial fracture load increases with the increase of elastic modulus at the crack tip; (c) The elastic gradients shield a crack on the compliant side and lower the stress intensity factor when compared to the one with crack on the stiff side. These results will be useful for better design and reliable evaluation of FGM.