Over the last few years, many classifications have been proposed for functionally graded materials (FGMs). In this Paper, critical review of different available classifications for FGM based on their physical, structural and manufacturing characteristics are presented. Advantages and limitations of each fabrication method for use in a given application is correspondingly considered. In addition, new classifications based on gradation control and accuracy, residual stresses, specific energy consumption, environmental impact evaluated throughout the complete life cycle and manufacturing costs are proposed. These classifications mainly reflect the needs of both FGM designers and industrial manufacturers. Based upon the presented classifications and the recent advances in analysis and production techniques, new major directions for FGMs research are proposed.
Horizontal centrifugal casting machine was adopted to fabricate tubes of functionally graded materials (FGM) made of commercially pure aluminum reinforced with different weight fractions of SiC particles. Tubes with 2.5, 5 and 10%wt. SiCpwere produced in the speed range 800 to 1100 rpm. Wear experiments involving dry sliding under different loading conditions were conducted on samples taken from three consecutive layers across the wall of the FGM tubes. Analysis of variance (ANOVA) was used to determine the significant FGM production parameters and wear test parameters (normal load and test duration) affecting the wear resistance of the samples. Obtained wear test results have been used to build a regression model to predict the expected weight loss across the wall thickness of the tube depending on the production parameters and the loading conditions.
Composites made from food packaging waste are recently introduced to the industry as promising materials that aim to reduce the environmental waste and to develop cost effective products. They possess good physical properties, which makes them potential competitors to wood based composite structures such as commercial particleboard (PB), and medium density fiberboard (MDF). Despite the expected advantages, the mechanical and dynamic behaviour of this genuine structure still needs to be studied and tested to evaluate its suitability for light weight structure applications. Experimental modal analysis is conducted on specimens made of food packaging waste, sandwich structured packaging waste with woven glass-fiber skin, MDF and PB. The dynamic testing results show superior damping ratio for the food packaging waste composites compared to the wood-based specimens. Natural frequencies exhibit comparable dynamic stiffness with respect to MDF, and PB. Further investigation has been made to evaluate both the modulus of rapture and the static stiffness of the material by conducting flexural tests on all specimens. Sandwich structure produced from food packaging waste and veneered with woven glass-fiber fabric exhibit excellent magnitudes for the modulus of rupture in addition the highest damping ratio.
Limited natural resources increase the demand on highly efficient machinery and transportation means. New energy-saving mobility concepts call for design optimisation through downsizing of components and choice of corrosion resistant materials possessing high strength to density ratios. Component downsizing can be performed either by constructive structural optimisation or by substituting heavy materials with lighter high-strength ones. In this context, forging plays an important role in manufacturing load-optimised structural components. At the Institute of Metal Forming and Metal-Forming Machines (IFUM) various innovative forging technologies have been developed. With regard to structural optimisation, different strategies for localised reinforcement of components were investigated. Locally induced strain hardening by means of cold forging under a superimposed hydrostatic pressure could be realised. In addition, controlled martensitic zones could be created through forming induced phase conversion in metastable austenitic steels. Other research focused on the replacement of heavy steel parts with high-strength nonferrous alloys or hybrid material compounds. Several forging processes of magnesium, aluminium and titanium alloys for different aeronautical and automotive applications were developed. The whole process chain from material characterisation via simulation-based process design to the production of the parts has been considered. The feasibility of forging complex shaped geometries using these alloys was confirmed. In spite of the difficulties encountered due to machine noise and high temperature, acoustic emission (AE) technique has been successfully applied for online monitoring of forging defects. New AE analysis algorithm has been developed, so that different signal patterns due to various events such as product/die cracking or die wear could be detected and classified. Further, the feasibility of the mentioned forging technologies was proven by means of the finite element analysis (FEA). For example, the integrity of forging dies with respect to crack initiation due to thermo-mechanical fatigue as well as the ductile damage of forgings was investigated with the help of cumulative damage models. In this paper some of the mentioned approaches are described.
Metal foams are interesting materials; not only for their metallic constituents, but also for the characteristics gained by the voids distribution. Metal foams find increasingly more applications in several industrial applications due to their novel physical, mechanical, thermal, electrical and acoustic properties. The high specific strength or stiffness in conjunction with distinct functional properties make them potential material for lightweight construction, energy and sound absorption applications. This investigation focuses on the parameters affecting the foaming process of aluminum based on CaCO3 as an economical foaming agent. The foaming parameters (e.g. percentage of the foaming agent, stirring speed and time, pre-foaming temperature) are decisive in controlling the resulting foam structure. The physical and mechanical properties of the resultant foam could be correlated to the different foaming parameters. The addition of aluminum and Al2O3 powder to the melt showed a remarkable improvement in the characteristics of the produced foam.
Tailor-welded blanks (TWBs) are primarily used in the automotive industry. Popular applications include: side frames, doors, pillars and rails. The TWB concept has several disadvantages. The most important disadvantage is the effect of the weld line on the formability of the TWB. This paper investigates the weldment quality by evaluating the localized stresses, strains and distortions that develop during welding. For the purpose of investigation, TWBs made of 304 stainless steel and A619 low carbon steel have been numerically simulated using a finite volume formulation. Blanks with different configurations (blank sizes, thicknesses and weldment type) have been simulated, so that the optimal processing parameters for each configuration can be determined. Conclusion about the scaling effect and the residual stresses in the welded blanks could be drawn based upon the evaluation of the different configurations.
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