Papers by Keyword: Graded Material

Abstract: Professional paper shows the general characteristics of graded materials, their previous industrial use and potential use of graded materials in the future. In any case, today the use of graded materials is increasing and moving from the laboratory environment into everyday use. However, the subsequent processing of the graded material remains the big unknown, and represents a major challenge for researchers and industry around the world. It could be said that the study of machinability of these materials is in its infancy and in this area are many unanswered questions. Machinability problem of graded materials was undertaken at the Faculty of Mechanical Engineering in Maribor. After a radical study of the literature and potential machining processes of graded materials, we started with the implementation of cutting processes on the workpiece. This professional paper presents the first results of the analysis, which will be used for further research and machinability study of graded materials.

Abstract: A Continously Embedded Force Doublet over the Particular Region can be Regardedas the Distributing Eigen Strain. this Fact Implies that many Sorts of Inelastic Strain can Bereplaced by the Force Doublet. in the Present Paper, the Force Doublet is Used to Alter the Localconstitutive Relationship. as a Result, a Method for Analyzing the General Inclusion Problem Inwhich the Material Properties of the Inclusion are Not only Different from those of the Matrixmaterial but also can be even a Function of Spacial Coordinate Variables is Proposed. Thetheoretical Background of the Present Analysis is Explained Followed by some Representativenumerical Results.

Abstract: The sliding frictional contact problem for a laterally graded half-plane has been considered. Two finite element (FE) models, in macro and micro scales have been developed to investigate the effective parameters in contact mechanics of laterally graded materials loaded by flat and triangular rigid stamps. In macro scale model, the laterally graded half-plane is discretized by piecewise homogeneous layers for which the material properties are specified at the centroids by Mori-Tanaka method. In micro scale model, functionally graded material (FGM) structure has been modeled as ideal solid quadrant particles which are spatially distributed in a homogeneous matrix. Boundary conditions and loading is the same in both models. The microstructure has modeled as rearrangement and sizes changing of particles are possible to provide the possibility of crack nucleation investigation in non-singular regions. Analyses and comparison of the results showed that micro and macro scale results are in very good agreement. Also, increasing the grains aspect ratio and using optimum distribution of grains decrease stress distribution roughness on the surface. Therefore, the possibility of surface cracking far from stamp’s edges decreased.

Abstract: Five-layered Al/Al-Cu functionally graded material (FGM) was fabricated by powder metallurgy technology. The microstructure and composition of the prepared specimen were studied. Vickers hardness, flexural strength and fracture surface morphology were also measured. The results showed that Al/Al-Cu graded material with dense structure and compositional continuous change was obtained by solution-precipitation method. The graded materials presented a compositional continuous change along the graded direction because of the diffusion effect, and the Vickers hardness was liner proportional to the distribution of Cu content. Compared with pure sintered Al, remarkable improvement on hardness and fracture strength was achieved due to the CuAl2 phase dispersively distributed in the matrix. With the increase of Cu content, the fracture mode changed from tough fracture to the tendency of brittle fracture.

Abstract: Bamboo is a typical natural graded material, from the inner layer to the middle layer, and then to the outer layer. The elastic modulus is increasing gradually. The cracks grown on the inner layer and outer layer have different effects on the intensity. In this paper, the influence of the gradient distribution on the fracture behavior of the mixed-mode I and П cracks located in different layers is studied. The displacement measurement of bamboo specimens on asymmetric loading using digital speckle correlation method (DSCM) is performed and the crack tip opening displacement (COD), the stress intensity factor can be obtained. The results show that the COD of the crack in the outer layer is less than that of the crack in the inner layer, the stress intensity factor in the outer layer is greater than that of the crack in the inner layer, that means the property of the gradient distribution of bamboo has the protecting function for the static crack in the inner layer.

Abstract: The microstructure of cuttlebone is investigated using Scanning Electron Microscopy (SEM). A graded aspect ratio of the base cells between layers is evident in some samples. A method for designing graded biomaterials mimicking this cuttlebone microstructure is developed. Simplified 3D biomaterial samples are created using CAD software. These biomaterials are fabricated using a stereolithographic apparatus (SLA). The homogenisation technique is used to evaluate the mechanical properties of the original cuttlebone sample and the fabricated biomaterial sample. Good agreement is found between the Young’s moduli of corresponding layers. However, it is inconclusive whether the Young’s moduli have a proportional relationship to the aspect ratio of the base cell at this stage of the study.

Abstract: TiN/Al2O3 functionally graded composite was fabricated by in-situ aluminothermic reduction of TiO2 in coke bed from mixtures of TiO2 powder and metal Al powder. The reaction process, phase composition, and microstructure of sample treated at 1500°C for 3h were analyzed by XRD, SEM and EPMA. The results indicated that the thermite reduction of TiO2 involves several transitional stages and its initial reaction temperature is lowered by prior reaction between Al and TiO2. EPMA analysis showed that the TiN/Al2O3 ratio in TiN/Al2O3 functionally graded material products changes gradually across the samples without distinct interface between the different layers. The microstructure of the composite changes gradually, and the size of TiN grains increases from the verge region of samples to the centre of samples. These results above were in agreement with thermodynamic analysis.

Abstract: Ti-Ni based functionally graded alloy is a kind of the promising material, which has potential to be used in aero engines. Using laser rapid forming, a Ti-Ni graded alloy with a continuous compositional gradient from pure Ti to Ti-50wt.%Ni were fabricated. On comparison with the graded alloy, a series of homogenous deposits with the typical composition between pure Ti to Ti-50wt.%Ni were also laser rapid formed. The phase evolution along the compositional gradient direction in the graded alloy is: α+β→β+Ti2Ni →(TiNi +Ti2Ni)+ TiNi; and the phase evolution in the corresponding compositional homogeneous deposit is: α+β→ β+(β+Ti2Ni)→ β+Ti2Ni+(β+Ti2Ni)→ (TiNi+Ti2Ni)+TiNi. The phase transformation and microstructural evolution along the compositional gradient were analyzed by using the microstructure selection map.

Abstract: In this study, 2 mol% Y2O3 (2Y), 1 mol% Y2O3+6 mol% CeO2 (1Y6Ce) and 12 mol% CeO2 (12Ce)-doped tetragonal ZrO2 ceramics were made by spark plasma sintering (SPS) for 2 min at 1450°C under a pressure of 60 MPa. The influence of stabilizers on microstructure, phase and mechanical properties of the ZrO2 ceramics was investigated. After sintering, the 2Y and 1Y6Ce were intact, containing full tetragonal ZrO2 phase on the polished cross-sectioned surface, whereas the 12Ce exhibited macro-cracks, corresponding to a large amount of monoclinic ZrO2 phase. Graded microstructure and mechanical properties were observed in the 1Y6Ce, showing a gradually decreased fracture toughness from sample edge towards centre, together with the slight decreased hardness. The 2Y had a uniform microstructure and mechanical properties. The formation of the graded structure and toughness profile was explained in terms of the gradual CeO2 reduction to Ce2O3 in the Y2O3+CeO2 doped ZrO2 ceramics.