Mechanics of Advanced Materials and Modern Processes最新文献

Giant magnetostrictive materials are increasingly proposed for smart material applications such as in sensors, actuators, and energy harvesting applications. However, reviewing the literature on this topic, the reader observes a large amount of variability in the reported properties that are typically generated from overall strain or point-value strain measurements obtained with strain gages using the far field estimate to project the internal magnetic field in the specimen.

A full-field phase-sensitive thermography method is proposed to correlate the full-field infrared measurements to changes in the microstructure induced by a cyclic magnetic field in a giant magnetostrictive alloy material.

The results show the potential of the proposed method in rapidly uncovering the effects of geometry and defects on the magnetostrictive response. The results show responses at the microstructure level from both magnetocaloric and magnetostrictive effects.

The effects of the magnetostrictive material’s microstructural spatial variability and the specimen geometry on the localized magnetostrictive response warrant serious considerations but so far have not received significant attention. The method proposed is capable of highlighting magneto-elastic coupling in the composite specimens using the cycle magnetic field.

Now-a-days, newer hardened steel materials are coming rapidly into the market due to its wide applications in various fields of engineering. So the machinability investigation of these steel materials is one of the prime concern for practicing engineers, prior to actual machining.

The present study addresses surface roughness, flank wear and chip morphology during dry hard turning of AISI 4340 steel (49 HRC) using CVD (TiN/TiCN/Al₂O₃/TiN) multilayer coated carbide tool. Three factors (cutting speed, feed and depth of cut) and three-level factorial experiment designs with Taguchi’s L₉ Orthogonal array (OA) and statistical analysis of variance (ANOVA) were performed to investigate the consequent effect of these cutting parameters on the tool and workpiece in terms of flank wear and surface roughness. For better understanding of the cutting process, surface topography of machined workpieces, wear mechanisms of worn coated carbide tool and chip morphology of generated chips were observed by scanning electron microscope (SEM). Consequently, multiple regression analysis was adopted to develop mathematical model for each response, along with various diagnostic tests were performed to check the validity and efficacy of the proposed model. Finally, to justify the economical feasibility of coated carbide tool in hard turning application, a cost analysis was performed based on Gilbert’s approach by evaluating the tool life under optimized cutting condition (suggested by response optimization technique).

The results shows that surface roughness and flank wear are statistically significant influenced by feed and cutting speed. In fact, increase in cutting speed resulted in better surface finish as well as increase in flank wear. Tool wear describes the gradual failure of cutting tool, caused grooves by abrasion due to rubbing effect of flank land with hard particles in the machined surface and high cutting temperature. Chip morphology confirms the formation of saw-tooth type of chip with severity of chip serration due to cyclic crack propagation caused by plastic deformation. The total machining cost per part is found to be $0.13 (i.e. in Indian rupees Rs. 8.21) for machining of hardened AISI 4340 steel with coated carbide tool.

From the study, the effectiveness and potential of multilayer TiN/TiCN/Al₂O₃/TiN coated carbide tool for hard turning process during dry cutting condition possesses high yielding and cost-effective benefit to substitute the traditional cylindrical grinding operation. Apart, it also contributes reasonable option to costlier CBN and ceramic tools.

The theory of microstretch elastic bodies was first developed by Eringen (1971, 1990, 1999, 2004). This theory was developed by extending the theory of micropolar elastcity. Each material point in this theory has three deformable directors.

The governing equations of a transversely isotropic microstretch material are specialized in x-z plane. Plane wave solutions of these governing equations results into a bi-quadratic velocity equation. The four roots of the velocity equation correspond to four coupled plane waves which are named as Coupled Longitudinal Displacement (CLD) wave, Coupled Longitudinal Microstretch (CLM) wave, Coupled Transverse Displacement (CTD) wave and Coupled Transverse Microrotational (CTM) wave. The reflection of Coupled Longitudinal Displacement (CLD) wave is considered at a stress-free surface of half-space of material. The appropriate displacement components, microrotation component and microstretch potential for incident and four reflected waves in half-space are formulated. These solutions for incident and reflected waves satisfy the boundary conditions at a stress free surface of half-space and we obtain a non-homogeneous system of four equations in four reflection coefficients (or amplitude ratios) along with Snell’s law for the present model.

The speeds of plane waves are computed by Fortran program of bi-quadratic velocity equation for relevant physical constants of the material. The reflection coefficients of various reflected waves are also computed by Fortran program of Gauss elimination method. The speeds of plane waves are plotted against angle of propagation direction with vertical axis. The reflection coefficients of various reflected waves are plotted against the angle of incidence. These variations of speeds and reflection coefficients are also compared with those in absence of microstretch parameters.

For a specific material, numerical simulation in presence as well as in absence of microstretch shows that the coupled longitudinal displacement (CLD) wave is fastest wave and the coupled transverse microrotational (CTM) is observed slowest wave. The coupled longitudinal microstretch (CLM) wave is an additional wave due to the presence of microstretch in the medium. The presence of microstretch in transversely isotropic micropolar elastic solid affects the speeds of plane waves and the amplitude ratios of various reflected waves.

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Electrical Discharge Machining (EDM) is a well-established non-conventional machining process for the machining of electrically conductive and difficult-to-machine materials. But its applications are limited because of the slow machining rate and poor surface finish. Powder mixed EDM (PMEDM) is unitary of the recent progresses in the EDM process in which powder particles mixed in the dielectric fluid results in higher machining rate and better surface quality. In the past, limited work has been found on PMEDM of Inconel-800 material. ?Researchers have reported about machining with different powder particles like aluminum powder, silicon carbide, graphite etc. in the dielectric fluid of EDM, but the effect of powder particles, i.e. Tungsten carbide, cobalt and boron carbide along with tool material i.e. copper, copper-chromium and graphite on Inconel-800 material has not been explored. The purpose of the present work is to look into the issue of tool material (Cu, copper-chromium, and graphite) along with powder particles (tungsten carbide, cobalt and boron carbide) suspended in EDM oil on Inconel-800 material.

The present work includes optimization of Material Removal Rate (MRR) and Tool Wear Rate (TWR) for the machining of Inconel-800 material using Powder Mixed Elctric Discharge Machining (PMEDM). Different input parameters such as peak current, pulse on-time, pulse off-time, tool and powder materials along with effect of three micro powder particles, i.e. tungsten carbide, cobalt and boron carbide and three electrodes i.e. copper, copper-chromium, and graphite have been considered for the experimentation. The box-Behnken method of Response Surface Methodology (RSM) has been used for designing the experiments along with the Desirability Approach for multiple response parameters optimization. The adequacy of the proposed mathematical models have also been tested using analysis of variance (ANOVA). Microstructure analysis and transfer of different factors on the machined surface has also been investigated using Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS) and X - Ray Diffraction (XRD).

The results showed that peak current, pulse on-time, and tool material significantly affects the Material Removal Rate (MRR) while peak current, pulse on-time, tool material and powder materials affected the Tool Wear Rate (TWR). Pulse off-time has a trifling effect on both MRR and TWR, while powder particles on MRR. From desirability approach, the optimal combination of parameters found to be current 1 amp, pulse on-time 0.98 μs, pulse off-time 0.03 μs, tool material 0.31 and the powder (suspended particles) 0.64.

The analysis of the experimental observations highlights that the current, pulse on-time and tool material have found to be the most decisive factors for MRR, while current, pulse on-time, tool material and powder particles for TWR.

Copper is the primary metal used in integrated circuit manufacturing of today. Even though copper is face centered cubic it has significant mechanical anisotropy depending on the crystallographic orientations. Copper metal lines in integrated circuits are polycrystalline and typically have lognormal grain size distribution. The polycrystalline microstructure is known to impact the reliability and must be considered in modeling for better understanding of the failure mechanisms.

In this work, we used Voronoi tessellation to model the polycrystalline microstructure with lognormal grainsize distribution for the copper metal lines in test structures. Each of the grains is then assigned an orientation with distinct probabilistic texture and corresponding anisotropic elastic constants based on the assigned orientation. The test structure is then subjected to a thermal stress.

A significant variation in hydrostatic stresses at the grain boundaries is observed by subjecting the test structure to thermal stress due to the elastic anisotropy of copper. This introduces new weak points within the metal interconnects leading to failure.

Inclusion of microstructures and corresponding anisotropic properties for copper grains is crucial to conduct a realistic study of stress voiding, hillock formation, delamination, and electromigration phenomena, especially at smaller nodes where the anisotropic effects are significant.

Machining using vertical CNC end mill is popular in the modern material removal industries because of its ability to remove the material at a fast rate with a reasonably good surface quality.

In this work, the influence of important common machining process variables like feed, cutting speed and axial depth of cut on the output parameters such as surface roughness and amplitude of tool vibration levels in Al-6061 workpieces has been studied. With the use of experimental result analysis and mathematical modelling, correlations between the cutting process conditions and process outputs are studied in detail. The cutting experiments are planned with response surface methodology (RSM) using Box-Behnken design (BBD).

This work proposes a multi-objective optimization approach based on genetic algorithms using experimental data so as to simultaneously minimize the tool vibration amplitudes and work-piece surface roughness. The optimum combination of process variable is further verified by the radial basis neural network model.

Finally, based on the multi-objective optimization approach and neural network models an interactive platform is developed to obtain the correct combination of process parameters.

The geometrically non-linear formulation based on Von-Karman’s hypothesis is used to study the free vibration isosceles triangular plates by using four types of mixtures of functionally graded materials (FGMs - AL/AL₂O₃, SUS304/Si₃N₄, Ti- AL-4V/Aluminum oxide, AL/ZrO₂). Material properties are assumed to be temperature dependent and graded in the thickness direction according to power law distribution.

A hierarchical finite element based on triangular p-element is employed to define the model, taking into account the hypotheses of first-order shear deformation theory. The equations of non-linear free motion are derived from Lagrange's equation in combination with the harmonic balance method and solved iteratively using the linearized updated mode method.

Results for the linear and nonlinear frequencies parameters of clamped isosceles triangular plates are obtained. The accuracy of the present results are established through convergence studies and comparison with results of literature for metallic plates. The results of the linear vibration of clamped FGMs isosceles triangular plates are also presented in this study.

The effects of apex angle, thickness ratio, volume fraction exponent and mixtures of FGMs on the backbone curves and mode shape of clamped isosceles triangular plates are studied. The results obtained in this work reveal that the physical and geometrical parameters have a important effect on the non-linear vibration of FGMs triangular plates.

Wire Electrical discharge machining (WEDM) has higher capability for cutting complex shapes with high precision for very hard materials without using high cost of cutting tools. During the WEDM process, the wire behaves like a metal string, straightened by two axial pulling forces and deformed laterally by a sum of forces from the discharge process. Major forces acting on the wire can be classified into three categories. The first is a tensile force, pulling the wire from both sides in axial direction and keeping it straight. The second is the dielectric flushing force that comes from circulation of the dielectric fluid in the machining area. The third category consists of forces of different kinds resulting from sparking and discharging. Large amplitude of wire vibration leads to large kerf widths, low shape accuracies, rough machined surfaces, low cutting speeds and high risk of wire breakage. Such tendencies for poor machining performance due to wire instability behavior appear with thinner wires.

The present work investigates a mathematical modeling solution for correlating the interactive and higher order influences of various parameters affecting wire vibration during the WEDM process through response surface methodology (RSM). The adequacy of the above proposed model has been tested using analysis of variance (ANOVA).

Optimal combination of machining parameters such as wire tension, wire running speed, flow rate and servo voltage parameters has been obtained to minimize wire vibration.

The analysis of the experimental observations highlights that the wire tension, wire running speed, flow rate and servo voltage in WEDM greatly affect average wire vibration and kerf width.

Drilling is one of the most widely used process in orthopaedic surgical operation and the same drill bit is used a number of times in hospitals. Using the same drill bit a several times may be the cause of osteosynthesis and osteonecrosis.

In the present work, the effect of repeated orthopaedic surgical twist drill bit on the tool wear, force, torque, temperature and chip morphology during porcine cortical bone drilling is studied. Results were compared with rotary ultrasonic drilling (RUD) on the same bone using a hollow drill tool coated with diamond grains. A sequence of 200 experiments (100 with each process, RUD and CD) were performed with constant process parameters.

Wear area on the drill bit is significantly increased as the drill bit is used repeatedly in CD, whereas no attritious wear was found on the diamond coated grains in RUD.

Comparative results showed that cutting force, torque and temperature increased as a function of tool wear in CD as the same drill bit was used a number of times. No significant variation in the cutting force and torque was observed in RUD as the number of drilled holes increased.

The commonly used flow models for Fiber Reinforced Polymers (FRPs) often neglect the flow-induced anisotropy of the suspension, but with increasing fiber volume fraction, this plays an important role. There exist already some models which count on this effect. They are, however, phenomenological and need a fitted model parameter. In this paper, a micromechanically-based constitutive law is proposed which considers the flow-induced anisotropic viscosity of the fiber suspension.

The introduced viscosity tensor can handle arbitrary anisotropy of the fluid-fiber suspension which depends on the actual fiber orientation distribution. Assuming incompressible material behaviour, a homogenization method for unidirectional structures in contribution with orientation averaging is used to determine the effective viscosity tensor. The motion of rigid ellipsoidal fibers induced by the flow of the matrix material is described based on Jeffery’s equation. The reorientation of the fibers is modeled in two ways: by describing them with fiber orientation vectors, and by fiber orientation tensors. A numerical implementation of the introduced model is applied to representative flow modes.

The predicted effective stress values depending on the actual fiber orientation distribution through the anisotropic viscosity are analyzed in transient and stationary flow cases. In the case of the assumed incompressibility, they show similar effective viscous material behaviour as the results obtained by the use of the Dinh-Armstrong constitutive law.

The introduced model is a possible way to describe the flow-induced anisotropic viscosity of a fluid-fiber suspension based on the mean field theory.