Papers by Keyword: Functionally Graded Materials

Abstract: This study numerically investigates functionally graded (FG) interpenetrating phase composites (IPCs) comprising nitinol (NiTi) shape memory alloy (SMA) microstructure as smart architected reinforcement phase. This architected SMA phase is modeled with FG Schwarz-Primitive (P) triply periodic minimal surface (TPMS that is embedded with Pure magnesium (Mg) as a second-phase elastoplastic material. This unique material combination can provide the superelastic and phase transformation capabilities of NiTi alongside the lightweight and damping properties of Mg material. The functional response and phase transformation characteristics of NiTi SMA are embedded by using an in-house developed material subroutine constitutive model in finite element software Abaqus. The effective properties of the Mg-NiTi FG IPCs are evaluated using a three-unit-cell-based Representative Volume Element (RVE) approach subjected to periodic boundary conditions. The effective functional response includes the elastic stiffness and yield strength, as well as the phase transformation characteristics and martensitic phase evolution of the FG P-TPMS lattices within the IPCs. Additionally, the influence of the concentration of NiTi SMA and functional grading of TPMS structures on stress distribution and phase transformation is thoroughly analyzed. These results are evaluated based on the concentration and grading of NiTi TPMS phase on the FG TPMS IPCs. Results show that increasing NiTi content enhances both the elastic stiffness and strength of the Mg-NiTi composite, with phase transformation initiating at stress-concentrated neck regions of the P TPMS lattice. Whereas the functional grading causes localized stress near regions with minimal cross-sectional area, particularly at the necks between adjacent unit cells, making these zones identified as critical to early transformation and potential failure. This novel FG Mg-NiTi TPMS IPC offers a promising pathway toward lightweight, high-performance multifunctional materials.

Abstract: In this study, the microstructure and wear behavior of multilayer 316L stainless steel/TiC composite fabricated using selective laser melting (SLM) additive manufacturing were investigated. The produced samples consisted of three layers: 316L, 316L-5TiC, and 316L-10TiC (wt%). Microstructural evaluations revealed a homogeneous distribution of TiC particles in the matrix of the composite layers, with no cracks observed at the interfaces between layers, indicating a robust bond between the layers. Wear tests showed that the incorporation of TiC particles enhanced wear resistance, with the composite layer with 10 wt% TiC exhibiting the best wear resistance due to the hardness and reinforcing nature of TiC. Wear mechanisms included abrasive wear and fatigue wear due to fragmentation of TiC particles. The results suggest that SLM manufacturing can potentially be used to produce functionally graded composites for applications requiring high strength and wear resistance.

Abstract: This paper presented an experimental and numerical study of functionally graded materials made by the permanent casting method and in three models with different mixing ratios between aluminum and zinc alloys (FGM1, FGM2, and FGM3) as in figure 1. In the permanent casting process, three models of the functionally graded material were produced and mechanical tests were conducted on them such as tensile and hardness tests, and the behavior of tensile strength, yield strength, elastic modulus, and fatigue was analyzed on them. The fatigue test was conducted at six levels of load and at room temperature. Simulations were carried out for the three models and a simulated fatigue test for the functionally graded material into the Ansys program. The results of the fatigue test showed an apparent effect of the different mixing ratios of the functional-grade material. As well as the numerical results were, close to the experimental results. There was an improvement in the fatigue life compared to FGM3, by 23% to FGM2. In addition, the fatigue life of the FGM3 of 11% higher than from the FGM1 model. In addition to that, which is important, the improvement in the fatigue life characteristics of the third type was 36% compared to the alloys from which the functionally graded materials were made.

Abstract: Carbon nanotube (CNT) has received broad scientific and industrial attention due to their excellent mechanical and functional properties. However, CNT has not been effectively used for high performance composites because of degradation of mechanical properties due to insufficient dispersibility of CNT in the matrix. In this study, CNT/ aluminum (Al) matrix functionally graded materials (FGMs) have been focused on. The processes of dispersion of CNT have been carried out with the solvent of dimethylacetamide, and the dispersing agent of potassium carbonate, which is an inorganic salt, under ultrasonic sonication conditions. Centrifugal slurry methods have been applied to obtain gradient of content of CNT in CNT/ Al matrix FGMs. Tribological characteristics on CNT/ Al matrix FGMs have been investigated using a ball-on-disk tribometer. It has been demonstrated that CNT contributes to enhance wear resistances.

Abstract: This paper applies the stochastic finite element method (SFEM) to perform the natural frequency analysis of functionally graded material (FGM). It is assumed that the elastic modulus and width of the FGM beam vary along the thickness and width directions following exponential functions. The stochastic eigenvalue problem is solved independently by first-order perturbation and Monte Carlo simulation (MCS) method through changing elastic modulus as spatial randomness. The results show that the first-order perturbation method based SFEM produces a very close value to MCS method.

Abstract: In this paper, the metal/ceramic functionally graded composites are prepared. The thermal stress of TiC/Ti functionally graded composites are simulated by Abaqus finite element analysis software to study the influence of the number of layers, the gradient layer thickness and the gradient of distribution index.The optimal structural parameters of the TiC/Ti functional gradient composites are obtained as the number of layers of 6 and the gradient distribution index 0.8. According to the optimized structural parameters, Ti and C powders are mixed by high-energy ball milling, then the TiC/Ti functional gradient composites are prepared by spark plasma sintering. The gradient distribution of composition and microstructure in TiC/Ti functionally graded composites are achieved, which can solve the problem of mismatch for the physical properties between the metal and the ceramic in the composite material.

Abstract: The finite block method (FBM) is developed to determine stress intensity factors with orthotropic functionally graded materials under static and dynamic loads in this paper. The higher order derivative matrix for two and three dimensional problems can be constructed directly. For linear elastic fracture mechanics, the COD and J-integral techniques to determine the stress intensity factors are applied. Several examples are given and comparisons have been made with both analytical solutions and the finite element method in order to demonstrate the accuracy and convergence of the finite block method.

Abstract: For axially functionally graded beams with elastic modulus varying through the longitudinal directions, a measurement model for Young's modulus is presented based on the classic Euler-Bernoulli beam theory. When the force and deflection of cantilever beams are measured by the experiment method, the Young's modulus of axially functionally graded beams can be obtained by the measurement model. By the derivation rule of compound functions, the validity of the measurement model is proved. For the axially functionally graded beams with elastic modulus varying according to the power law and the exponential law respectively, the deflection is simulated by the finite element method. The simulated elastic modulus by the model is in accord with the theoretical value well.

Abstract: In the jet engine the temperature of exhaust gases should be as high as possible, from the point of view of its efficiency. The value of this temperature is limited by toughness of the turbine blades material. Superalloy Inconel 625, which is commonly used in aerospace industry, indicates 13% less yield point in 800^OC than in 25^OC. The temperature of exhaust gases can reach 1500^OC. The blade material has to be protected due to this fact. The one possibility of turbine blade protection is using of thermal barriers coatings (TBC). The coating has a very low thermal conductivity and therefore it protects against the thermal shock failure of the substrate material. The TBC can be manufactured as: 1) monocrystalline, 2) layered structures (e.g. [1-3]) or 3) as a functionally graded material (e.g. [4-7]). The differences between the properties of blade material and TBC can lead to significant increase of the high shear stresses in the substrate-TBC interface.In this paper numerical analyses of cooled turbine blade with various kinds of functionally graded thermal coatings were performed. The main aim was to find the optimal material properties distribution of the functionally graded TBC to avoid damage initiation and growth between TBC and substrate. In the calculations the effect of temperature on material properties both mechanical and thermal was taken into consideration.

Abstract: The manufacture of graded materials has gained an enormous interest during the last decade due to the diversity of industrial and biological materials systems that require or are actually designed to implement that criterion; those natural or artificial materials offer multiple possibilities of applications. In this work, a novel uniaxial and sequential compaction device has been successfully designed and fabricated, in order to obtain samples with three different layers; this new device is suitable for both conventional and non-conventional powder metallurgy (PM) techniques. In addition, this device allowed us to use different combinations of powders and space-holder particles, irrespective of their nature, sizes, morphologies and proportions. It has no restriction about applying different compaction pressures for every layer, which may result in increasing or decreasing porosity. This compaction device is especially powerful if the aim is obtaining samples with radial graded porosity for biomedical applications (replacement of cortical bone involved in different joints and dental restorations) and nuclear applications (mimicking burnt used nuclear fuel). Specifically in this work, different samples with radial graded porosity were fabricated and then microstructurally and mechanically characterized: i) Commercially pure titanium (CP Ti) samples, starting from blends CP Ti with 20 vol.%, 40 vol.% and 60 vol.% of Sodium Chloride (NaCl) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 800 MPa of compaction pressure and 1250 °C for 2h in high vacuum of sintering; and ii) CeO₂ samples, starting from blends CeO₂ with 0.5 vol.%, 3.0 vol.% and 7.5 vol.% of Ethylene Bis Stearamide (EBS) as space holder, which were placed in core, intermediate and external layers, respectively; processing conditions were 460 MPa in external layer and 700 MPa in core and intermediate layers of compaction pressure, and 1700 °C during 4h in static air of sintering. This new device has proved to have unique advantages for solving problems of structural integrity in conventional PM manufacturing in a simple, economic and reproducible way.