Characterization of CNT Reinforced Al Functionally Graded Composite Laminates

Abstract

Functionally graded composite laminate materials(FGCL) are special kind of new generation materials aimed at meeting new requirements of engineering applications. It contains, two or multi-phase particulate composites in which material composition and microstructure are characterized by continuous, smooth variations on macroscopic scale designed to meet desired functional performance. The absence of sharp interfaces in FGCL reduce chances of material property mismatch and thus leading to significant improvement in damage resistance and mechanical durability. Therefore, FGCL’s are of great interest in disciplines as diverse as civil, electrical, mechanical, nuclear and nano engineering applications. However, the extent to which an FGCL can be tailored to meet the required performance –i.e., the design of FGCL strongly depends on the resultant effective properties and more importantly, on how these properties relate to its functional requirements. Hence, predicting mechanical, thermal or other relevant properties for given microstructure and its spatial distribution plays a significant role in the design of FGCL. Objective and scope of the present work includes planning, preparation of CNT reinforced Al Functionally graded composite laminates by mechanical Powder Metallurgy technique and experimental testing for its characteristic properties. FG samples are prepared by varying the content of CNT (0.1,0.2,0.3,0.4 and 0.5 wt.%)in weight percentage and tested. Such prepared FGCL samples are tested for physical and mechanical properties. Before the FGCL samples are prepared, simple composite samples are prepared for same weight fraction of CNT reinforcement to characterize the microstructure and tested for the hardness. These composites are tested as per the ASTM guidelines. Once the results are confirmed, FGCL samples are designed for same weight fraction of reinforcement in layered fashion. The weight fraction is proportionally increased from 0.1 to 0.5wt.% from one end to the other end of the sample. The density, hardness and tensile behavior of FGCL samples are experimentally evaluated. These properties are found to be increasing with addition of CNT reinforcement. The damping ratio of composite and FGCL is estimated from impact hammer test, which demonstrated the significance of FGCL on the damping characteristics compared to a conventional composite material.At present work, more focus on developing high wear resistance, light weight, good damping material with moderate good thermal conductivity material for brake rotor applications. Experimental investigation on FGCL proved good tensile stress properties with 0.5wt.% CNT reinforcement and these results are proven good agreement with characterization of microstructure. Microhardness for the cross-section of FG samples linearly varies with the increment in CNT reinforcement, which results in the variation of microstructure. Reduction in grain size found for 0.1 to 0.5wt.% CNT reinforcement, observed staggered layer of microstructure. The hardness of the developed material become high on the 0.5wt.% CNT reinforced side. Wear properties are investigated with proper Design of Experiments by using Taguchi techniques for three parameters(Load, Abrasive grit size, Weight percent of CNT). It revealed that reinforcement of CNT affected reduction in the friction between the matting surface due to the formation of lubrication layers. Good wear resistance is observed for 0.25 to 0.4 wt.% CNT reinforcement. This result is in good agreement with the observation of SEM images for same weight fraction of CNT reinforcement. ANOVA results proved load, wear surface(Abrasive grit size) are the prominent factors for wear and CNT reinforcements improved the wear resistance in the materials. Finally, the improvement in thermal conductivity has been observed on CNT reinforcement. Furthermore, FGCL’s are associated with particulate composites where the weight fraction of particles varies in one or several directions. One of the advantages of a monotonous variation of weight fraction of constituent phases is the elimination of stress discontinuity that is often encountered in laminated composites and accordingly, avoiding delaminating-related problems. Investigation on developed FGCL samples found good agreement with the continuity in microstructure without step deviation as well as the hardness variation. Good damping behavior and wear resistance ability with improved thermal conductivity features could be a promising proposition for brake rotor materials. Insertion of developed light weight CNT reinforced FGCL between the cast iron plate on brake rotor make a huge impact on weight reduction and cost economics.