IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

The surface microstructures that contribute to the lotus leaf's superhydrophobicity are replicated onto a polymer surface using a two-stage (negative–positive) direct casting method and the replicates' <a href="https://www.sciencedirect.com/topics/materials-science/surface-morphology">surface morphology</a> is investigated in this study. Vinyl <a href="https://www.sciencedirect.com/topics/materials-science/polysiloxane">polysiloxane</a> (VPS), polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) are used for the replication and the replicates obtained are investigated using <a href="https://www.sciencedirect.com/topics/materials-science/confocal-microscopy">confocal microscopy</a>, <a href="https://www.sciencedirect.com/topics/materials-science/scanning-electron-microscopy">scanning electron microscopy</a> (SEM), and contact angle measurements. Geometric texture parameters such as peak height, peak/valley base width and inter-spacing between adjacent peak/valleys are measured for the lotus leaf and its replicates. Of the six combinations of positive and negative replicates attempted, VPS–PMMA and PDMS–PMMA replicates display shorter peak heights and larger base widths. These replicates have contact angles of 132.1° and 129.2° respectively, which are closest to the contact angle of the lotus leaf, 152.9°. Statistical two sample t-test revealed that VPS–PMMA's surface morphological parameters are closest to that of the lotus leaf. Also, theoretical calculations, based on two different methods from literature, using the measured geometric texture parameters show that polymer replicates satisfy criteria for a stable Cassie–Baxter wetting regime.

World University root node

Department of Mechanical Engineering

Surface and Coatings Technology

A morphological study on direct polymer cast micro-textured hydrophobic surfaces

Coated abrasive tools are popularly used in the industry for surface finishing. An important characteristic of these tools is their compliance (a grinding wheel is rigid in comparison) which permits smaller amounts of material removal, conformance to curved surface shapes, and assistance in blending the finished surfaces with the unfinished surfaces. This important characteristic is modeled using the finite element method by capturing suitable properties of the coated abrasive tool and its backing pad. Surface finishing experiments are conducted on a flat work surface in a machining center under position control (as opposed to force control) and the area of polished contact is measured along with the normal forces (using a dynamometer). The finite element model results of contact area and forces are compared with that of the experiment. The usefulness of this modeling approach is demonstrated by extracting force per grain and application to curved surfaces. © (2011) Trans Tech Publications, Switzerland.

Department of Metallurgical and Materials Engineering

Advanced Materials Research

Modeling effects of compliance in coated abrasive tools

In the conventional use of vibration-assisted machining the vibratory motion is applied to the tool either linearly along the direction of the cutting velocity or elliptically in the plane containing the cutting velocity and surface normal. In contrast to this, this study investigates vibrations that are applied along the cutting edge and perpendicular to the cutting velocity. Such a vibratory motion is expected to provide a small sawing action that will enhance the ductile fracture occurring ahead of the cutting tool as the chip separates from the bulk work material. This enhancement in fracture will then contribute to reducing the chip thickness and cutting forces. Also, the sawing action reduces the imprint left behind by the cutting tool leading to a better surface finish. To confirm these predictions orthogonal cutting with the assistance of transverse vibrations applied to the cutting tool are performed on Al-2024 tubes using a carbide cutting tool. Experiments are performed at different conditions of cutting speeds, feeds and amplitudes of vibration at a fixed vibration frequency of 40&nbsp;kHz. Cutting forces, chip thickness, and surface finishes are measured and compared with similar cutting conditions without application of vibration. In general, a reduction in cutting forces and feed forces is observed when transverse vibrations are applied. Chip thickness is also reduced and surface finish is improved upon application of vibration. Some explanations are offered to support these results.

International Journal of Machine Tools and Manufacture

Experimental investigation of transverse vibration-assisted orthogonal cutting of AL-2024

Drilling holes in CFRF' composite laminates induces damage near the hole surface. In this paper, we report investigations in drilling holes in unidirectional carbon-fiber reinforced laminated composite sheets of three thicknesses using a router; holes are also drilled with a dagger drill to compare results. Routers are commonly used for trimming the edges of composite sheets and not for drilling holes. The thrust force experienced by the tool during drilling is measured and the delamination and fiber pullout damage quantified using a surface profiler and optical microscope respectively. The router produces smaller delamination damage and fiber pullout than the dagger drill even though the router's plunging action applies a significantly higher thrust force. The flat end-mill type end of the router and its several intermittent cutting points give rise to these observations.

Transactions of the North American Manufacturing Research Institution of SME

Drilling holes in CFRP composite laminates using a router tool

This paper reports investigations in machining of thin substrates with thickness less than 100μm. The machining process induces severe plastic deformation through the thickness of the machined thin workpiece due to the high ratio of the depth of cut to workpiece thickness. The diamond face turning is used to machine thin workpieces down to a thickness less than 100μm. The microstructure of the machined sample is studied and x-ray diffraction used to observe the crystallographic orientation / texture. The microstructures of the thin machined workpieces are seen to become more random, denser, and finer with the shape of the grains less elongated as compare to the bulk and thick machined sample. The x-ray diffraction analyses indicate that machining of thin substrates changes the texture or orientation. Different deformation mechanisms may occur when machining thin workpiece especially at thicknesses below 100μm. © (2010) Trans Tech Publications.

Key Engineering Materials

Microstructural changes during precision machining of thin substrates

This study investigates how the infusion of a self-directed learning approach impacts on learning, teaching and curriculum content. Segments of a traditional mechanical engineering module, Net Shape Engineering were redesigned to promote self-directed learning. Instructional strategies were selected to promote SDL processes such a self-management, self-monitoring and self-modification. Two of 3 lessons reported here were restructured using structured problem solving and compared with the traditional approach. Data was collected using SDLRS, questionnaires and MCQ scores. It was found that the instructional strategy promoted self-management, self-monitoring and self-modification. In addition, the approach promoted active learning through greater engagement and interaction. There was however a difference in student preferences for the two approaches. The Low SDLRS scorers liked the approach because they could be more involved in the learning and they felt it improved their understanding. On the other hand, Average SDLRS scorers preferred the traditional method because it saved time, was more structured, provided them with hardcopy notes and opportunities for copying notes. They also felt they did not have to go through the time consuming process of discovering answers for themselves or bring laptops to class. © 2010 Santhakumari Thanasingam & Sathyan Subbiah.

ASCILITE 2010 - The Australasian Society for Computers in Learning in Tertiary Education

A case study on redesigning a mechanical engineering curriculum to promote self-directed learning

Effect of cold work on the mechanical response of drawn gold wire is studied using finite element (FE) simulations. The drawing simulations were conducted in a single stage as well as multi-stage, i.e. two steps for the equivalent area reduction on a micrometer size gold wire. The effect of wire drawing process parameters such as die angle, coefficient of friction and area reduction were considered for the simulations. A clear variation in residual stresses from tensile to compressive is seen across the wire cross-section. Mechanical properties are assessed via residual stress state and the hardness variation across the drawn wire cross-section; the hardness is determined using simulated micro-indentation tests. The effect of this stress is also observed in the indentation response. In the area of tensile residual stresses increasing pile-up was seen at the indenter edges, while in the area of compressive stresses the opposite was observed. The results clearly show the dominating role played by the residual compressive and tensile stresses across the wire section in its mechanical response. © 2010 Elsevier B.V. All rights reserved.

Computational Materials Science

Effect of cold work on the mechanical response of drawn ultra-fine gold wire

Evidence of ductile fracture leading to material separation has been reported recently in ductile metal cutting [S. Subbiah, S.N. Melkote, ASME J. Manuf. Sci. Eng. 28(3) (2006)]. This paper investigates the effect of finite edge radius on such ductile fracture. The basic question of whether such ductile fracture occurs in the presence of a finite edge radius is explored by performing a series of experiments with inserts of different edge radii at various uncut chip thickness values ranging from 15 to 105 μm. Chip-roots are obtained in these experiments using a quick-stop device and examined in a scanning electron microscope. Clear evidence of material separation is seen at the interface zone between the chip and machined surface even when the edge radius is large compared to the uncut chip thickness. Failure is seen to occur at the upper, middle, and/or the lower edges of the interface zone. Based on these observations, a hypothesis is presented for the events leading to the occurrence of this failure when cutting with an edge radius tool. Finite element simulations are performed to study the nature of stress state ahead of the tool edge with and without edge radius. Hydrostatic stress is seen to be tensile in front of the tool and hence favors the occurrence of ductile fracture leading to material separation. The stress components are, however lower than those seen with a sharp tool. © 2007 Elsevier B.V. All rights reserved.

Materials Science and Engineering A

Effect of finite edge radius on ductile fracture ahead of the cutting tool edge in micro-cutting of Al2024-T3

This paper provides data along with experimental evidence of ductile material separation that supports the Atkins’ model of machining, which includes the energy needed for material separation along with shear and frictional dissipation. This model proposed earlier explicitly includes the energy needed for material separation in addition to that needed for shear and friction. However, no experimental evidence for material separation via ductile tearing or fracture was provided. In this work, orthogonal cutting is performed on oxygen-free high conductivity (OFHC) copper, a highly ductile metal, at very low speeds and low uncut chip thickness where size-effect is observed. The chip–workpiece interface is observed under a scanning electron microscope to find evidence of material separation via ductile fracture. For values of fracture toughness and shear yield stress, that are of the same order of magnitude as that reported in literature for OFHC copper, the Atkins model captures the trend and the predictions are seen to be comparable to experimental data.

Journal of Materials Processing Technology

Evaluation of Atkins’ model of ductile machining including the material separation component

A semi-empirical procedure is developed to determine the presence of white layer formation in AISI 1045 annealed steel. The procedure tries to capture both thermal and mechanical effects on white layer formation. Machining tests are conducted over a wide range of cutting speeds and flank wear. Microstructure and cutting force data are obtained from the tests and analyzed. Analysis of the data indicates a possible correlation between white layer depth, the maximum workpiece surface temperature and the unit thrust force increase due to flank wear. In particular, the onset of white layer formation is found to be dependent on a critical combination of the maximum workpiece surface temperature and the unit thrust force increase. The semi-empirical procedure based on this critical combination of parameters is experimentally verified.

Prediction of white layer in turning of 1045 annealed steel including thermo-mechanical effects

Orthogonal micro-cutting experiments using quick-stop device are performed on Al2024-T3 and OFHC Copper to study the chip-workpiece interface in a SEM. Evidence of ductile tearing ahead of the tool at cutting speeds of 150 m/min has been found. A numerical finite element model is then developed to study the energy consumed in material separation in micro-cutting. The ductile fracture of Al2024-T3 in a complex stress state ahead of the tool is captured using a damage model. Chip formation is simulated via use of a sacrificial layer and sequential elemental deletion in this layer. Element deletion is enforced when the accumulated damage exceeds a predetermined value. A Johnson-Cook damage model that is load history dependent and with strain-to-fracture dependent on stress, strain-rate, and temperature is used to model the damage. The finite element model is validated using the cutting forces obtained from orthogonal micro-cutting experiments. Simulations are performed over a range of uncut chip thickness values. It is found that at lower uncut chip thickness values, the percentage of energy expended in material separation is higher than at higher uncut chip thicknesses. This work highlights the importance of the energy associated with material separation in the non-linear scaling effect of specific cutting energy in micro-cutting.

MSEC

Evidence of Ductile Tearing Ahead of the Cutting Tool and Modeling the Energy Consumed in Material Separation in Micro-Cutting

A recent development in cutting tool materials for turning hard steels is very high purity cubic Boron Nitride (cBN) without any binder. The performance of this material in interrupted hard turning is studied experimentally in this work. Two new parameters, interruption ratio (IR) and interruptions per unit length (IL) have been defined to characterize cutting interruptions. Turning experiments on 52100 bearing steel (58 HRC), are conducted to study the effect of interruptions on tool life and surface integrity (white layer formation). IL is seen to affect the flank wear in both binderless cBN and in the high cBN tool material. The binderless cBN performed better than the high-cBN tool only for the case where IR is low and IL is high. The flank wear in both tool materials is characterized by groove formation indicating likelihood of three-body type abrasive wear mechanism. While offering no noticeable advantage at low cutting speeds, the binderless cBN's performance at higher speeds does not seem to deteriorate as much as the high cBN tool. Also, the binderless cBN tool is seen to produce thinner white layer than the high cBN tool.

Transactions of the North American Manufacturing Research Institute of SME

Tool life and white layer formation in interrupted hard turning with binderless cBN tool

The contribution of material separation in cutting ductile metals to the constant force component, and, hence, to the size effect in specific cutting energy is explored in this paper. A force-decomposition-based framework is proposed to reconcile the varied reasons given in literature for the size effect. In this framework, the cutting force is broken down into three components: one that is decreasing, another that is increasing, and the third that remains constant, with decreasing uncut chip thickness. The last component is investigated by performing orthogonal cutting experiments on OFHC copper at high rake angles of up to 70 deg in an attempt to isolate it. As the rake angle is increased, the resulting experimental data show a trend toward a constant cutting-force component independent of the uncut chip thickness. Visual evidence of ductile tearing ahead of the tool associated with material separation leading to chip formation is shown. The measured constant force and the force needed for ductile crack exten sion are then compared. Copyright © 2006 by ASME.

Journal of Manufacturing Science and Engineering, Transactions of the ASME

The constant force component due to material separation and its contribution to the size effect in specific cutting energy

The specific cutting energy in machining is known to increase nonlinearly with decrease in uncut chip thickness. It has been reported in the literature that this phenomenon is dependent on several factors such as material strengthening, ploughing due to finite edge radius, and material separation effects. This paper examines the material strengthening effect where the material strength increases as the uncut chip thickness decreases down to a few microns. This increase in strength has been attributed to various factors such as strainrate, strain gradient and temperature effects. Given that the increase in material strength in the primary and secondary deformation zones can occur due to many factors, it is important to understand the contributions of each factor to the increase in specific cutting energy and the conditions under which they are dominant. This paper analyzes two material strengthening factors: (i) the contribution of the decrease in the secondary deformation zone cutting temperature, and (ii) strain gradient strengthening, and their relative contributions to the increase in specific cutting energy as the uncut chip thickness is reduced. Finite Element (FE) based orthogonal cutting simulations are performed using aluminum 5083-H116, a work material with a small strain-rate hardening exponent, thus minimizing strain-rate effect. Suitable cutting conditions are identified under which the temperature and strain gradient effects are dominant. Orthogonal cutting experiments are used to validate the model in terms of the cutting forces. The simulation results are then analyzed to identify the contributions of the material strengthening factors to the size effect in specific cutting energy. Copyright © 2005 by ASME.

American Society of Mechanical Engineers, Manufacturing Engineering Division, MED

Material strengthening mechanisms and their contribution to size effect in micro-cutting

Integrity of the surface is very important in hardened steel applications such as bearings. Rotary tool turning is currently being explored to process such parts. It is important to know the effect of this process on surface characteristics such as white layer formation. This paper compares the characteristics of hardened steel surfaces produced by rotary tools with surfaces created under identical conditions using a conventional fixed cutting tool. Improved surface integrity with respect to white layer formation has been observed with rotary tools. The paper also reports other related observations such as forces and tool wear. The amount of heat going into the workpiece in rotary tool cutting versus fixed tool cutting is compared using an approximate thermal analysis.

White layer formation in hardened steel turned with a rotary tool

A partial explanation of the size-effect in the specific cutting energy in micro-cutting is provided in this paper. For a simple orthogonal cutting condition, with constant width of cut, the specific cutting energy is viewed as a ratio of the cutting force and the uncut chip thickness. Size-effect, i.e., an unbounded increase in the specific cutting energy with decrease in uncut chip thickness, will occur under two conditions: one, if a component of the cutting force remains constant with uncut chip thickness and two, if some component of the cutting force increases with the uncut chip thickness. Experiments have been performed at high rake angles in an attempt to isolate and detect the presence of the constant component of the cutting force. The trend confirming the presence of this component is reported and explained. Copyright © 2004 by ASME.

On the size effect in micro-cutting at low and high rake angles

A ballistic trajectory in air of a powered projectile where the thrust always balances the drag is termed as a pseudovacuum trajectory. For a solid-fuel-ramjet (SFRJ)-powered gun-launched projectile this trajectory can be achieved by the control of engine mass-flow rate, either by a bypass control of inlet air or by a regression rate control of fuel. Based on one-dimensional considerations, the procedures for a preliminary design of the propulsion system for an SFRJ-assisted gun-launched projectile and the methods to calculate the control requirements are presented. Using these, typical configurations of SFRJ suitable for 155-mm gun-launched projectiles are analyzed for different launch angles. The results indicate that the control requirements by either method are minimal and thus, demonstrate the self-throttling characteristics of SFRJ.