Showing papers by "S. Sankaran published in 2020"

Effect of the structure and morphology of carbon nanotubes on the vibration damping characteristics of polymer-based composites

Abstract: The structure and morphology of the reinforcing material play an important role in the vibration damping characteristics of polymer composites. In this work, multiwalled carbon nanotubes (MWCNTs) with different structures and morphologies are incorporated into a polymer matrix. The vibration damping characteristics of the nanocomposites, in Oberst beam configuration, are studied using a free vibration test in cantilever mode. Inner tube oscillation is established as the vibration damping mechanism by correlating the extent of the loss factor obtained from the two nanocomposites with the dissimilarities in the structure and morphology of the two varieties of MWCNTs. Inner tube oscillation is simulated using molecular dynamics (MD). Since the open-ended double walled CNT (DWCNT) models used in earlier studies over predict the damping, we propose a capped DWCNT model. This can simulate the atomic interactions at the end caps of the tube. This study indicates that the contributions to the observed damping have their origins in the interaction between atoms that constitute the inner and outer tubes rather than the inter-tube frictional energy loss.

Microstructure and Mechanical Properties of Carbon Nanohorns Reinforced Aluminum Composites Prepared by Ball Milling and Spark Plasma Sintering

Abstract: Commercial purity aluminum was reinforced with different percentages of carbon nanohorns (CNH) using ball milling (1 h) followed by spark plasma sintering (SPS) at 550 °C for 5 min under 50 MPa pressure with heating rate 100 °C/min. The microstructure, hardness and compression properties of the spark-plasma-sintered carbon-nanohorns-reinforced aluminum (Al-CNH) composites were evaluated. Transmission electron microscopy revealed a uniform distribution of 0.3% CNH in Al, but above 0.3% CNH, agglomeration occurred. The compression strength of Al-0.3%CNH composites increased by 44% compared to the milled Al sample without CNH.

Grindability studies of thermomechanically processed advanced high strength steel using sol-gel and fused alumina grain-based grinding wheels:

Abstract: Advanced high strength steels have excellent strength-to-weight ratio and are widely used for automotive and structural applications Grinding is commonly used as a final machining process for thes

Subsurface Pore-Induced Quilting During Machining of Metal Foams

Abstract: Metal foams made by the melt route naturally have an interface region between the porous and nonporous structures. We investigate here the possible use of monolithic foam structures with such interfaces wherein the porous structure provides needed light-weighting while the nonporous region provides a functional surface such as the one needed for optics. Face turning is carried out in the nonporous region very near the interface to the porous areas. Using micro-computed tomography scans, pore positions are determined and the proximal effect of pores on the machined surface quilting effects are studied. Studies show that pore as near as 400 μm to the machined surface can cause significant quilting. Progress in developing finite element models to enable such predictions is also shown. This study could pave the way for the use of such structures for telescopic mirrors.

The Effects of Solutionizing Temperature on the Microstructure of Allvac 718Plus

Abstract: A study of the microstructural evolution of a Ni-based superalloy, Allvac 718Plus, in the forged condition, was performed by varying the solutionizing temperature. Different solutionizing temperatures were chosen to obtain different fractions of the gamma prime (Ni3(Al,Ti,Nb), γ′) and delta (Ni3Nb, δ) precipitates. The solutionizing temperatures ranged between 954 to 1100 °C based on the solvus temperature of the γ′ phase. The 954 °C solutionizing treatment resulted in incomplete dissolution of the γ′ phase and a relatively high-volume fraction of the δ phase, which formed preferentially at grain boundaries. The γ′ phase was completely dissolved during each of the other three solutionizing treatments (1000, 1050, and 1100 °C), while the fraction of the δ phase decreased with increasing solutionizing temperature. The 1100 °C solutionizing treatment led to significant grain growth of the matrix γ phase. After solutionizing, the samples were subjected to a standard two-step aging treatment (788 °C for 8 h followed by 704 °C for 8 h) to see the relative effect of the solutionizing on the precipitation during aging.