Department of Mechanical engineering
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Item Reverberation time improvement of lecture auditorium: A case study(Sage, 2018-01) Sharma, GauravIn this study, reverberation time of a lecture auditorium has been analyzed experimentally and analytically. It is well-known fact that reverberation time affects the speech intelligibility and hence should be within the range of possible optimum values. Experiments were performed to calculate the reverberation time of a lecture auditorium constructed at Indian Institute of Technology Mandi (IIT Mandi), for different internal conditions such as furniture and curtains. Experimental results were compared with the theoretically calculated values of reverberation time. It is found that acoustic performance of the lecture auditorium has significantly improved using curtains on the windows and furniture. For further improvement, it has also been suggested to use the carpet on the floor of the auditorium. The theoretical value of reverberation time is also calculated to show the improvement which can be achieved using carpet. The effect of audience on reverberation time has also been studied theoretically.Item Random excitation technique for measurement of acoustic properties(Springer Nature, 2017-08) Sharma, GauravThis chapter presents a case study approach for Modelling and Simulation of Random Excitation Technique for Measurement of Acoustic Properties like acoustic impedance and reflection coefficient. The basic theory, experimental formulation and set-up required are discussed in detail. Adequate options are suggested, if there is a variation of requirements from the given scenario.Item Design for manufacturability in additive manufacturing using a graph based approach(ASME, 2015-09) Ranjan, RajitAdditive Manufacturing (AM) processes are used to fabricate complex parts using a layer by layer approach. This enables designers to be more creative with their designs and build parts which may be difficult to manufacture using conventional processes. However, as AM is in its infancy, relevant literature with respect to design guidelines for AM is not readily available. This research proposes a novel approach to implement design guidelines in AM using a systematic graph based approach. These design rules will assist designers to come up with efficient part designs that can be manufactured with minimum part errors. The design rules are formulated by studying the relationship between input part geometry and AM process parameters. A feature graph based design analysis method is proposed along with a Producibility Index (PI) which is used to compare the designs. Modifications in part design based on these rules and their comparison is presented in the form of three case studies.Item Integration of design for manufacturing methods with topology optimization in additive manufacturing(ASME, 2017) Ranjan, RajitAdditive manufacturing (AM) processes are used to fabricate complex geometries using a layer-by-layer material deposition technique. These processes are recognized for creating complex shapes which are difficult to manufacture otherwise and enable designers to be more creative with their designs. However, as AM is still in its developing stages, relevant literature with respect to design guidelines for AM is not readily available. This paper proposes a novel design methodology which can assist designers in creating parts that are friendly to additive manufacturing. The research includes formulation of design guidelines by studying the relationship between input part geometry and AM process parameters. Two cases are considered for application of the developed design guidelines. The first case presents a feature graph-based design improvement method in which a producibility index (PI) concept is introduced to compare AM friendly designs. This method is useful for performing manufacturing validation of pre-existing designs and modifying it for better manufacturability through AM processes. The second approach presents a topology optimization-based design methodology which can help designers in creating entirely new lightweight designs which can be manufactured using AM processes with ease. Application of both these methods is presented in the form of case studies depicting design evolution for increasing manufacItem Octree data structure for support accessibility and removal analysis in additive manufacturing(Elsevier, 2018-08) Ranjan, RajitMetal Additive Manufacturing (AM) processes have made it possible to build parts with complex geometric features by adopting a layer-by-layer approach. However, additional support structures are needed to support overhanging surfaces and reduce distortion that may occur in these parts. This increases the overall build time of the part and leads to additional post processing efforts for removal of support structures. Often, removal of these supports becomes difficult due to complex part features that may interfere with support removal. Further, support structures have a detrimental effect on the surface finish on the areas of the part that come in contact with the supports. Thus, minimizing the need for support structures and ensuring its maximum removal is essential for an efficient part build in AM. Part build orientation is the main parameter that influences the need for support structures to build a part. This paper presents an approach to identify the best build orientation for a part such that the overall part build time is minimized while ensuring maximum removal of supports and minimizing the contact area between the part surface and supports. A hierarchical octree data structure has been used to analyze support accessibility and the area of support in contact with part. In addition, this paper also focuses on identification of optimal number/direction of part set-ups required to remove the maximum possible support structures from a part. A 2D setup map highlighting the feasible directions of setups for support removal has also been presented. The results of these analyses have been presented with the help of four sample parts.Item New support structures for reduced overheating on downfacing regions of direct metal printed parts(2019) Ranjan, RajitIn Laser Powder Bed Fusion (LPBF), the downfacing surfaces usually have increased surface roughness and reduced dimensional accuracy due to local overheating and warpage. To partially overcome this a new supporting structure is developed in this study, namely the contactless support. This is a thin blade parallel to the critical area which transfer the heat away from the melt pool via conduction through the powder bed instead of direct contact. The support is tested in different geometries and printing conditions to define the optimal distance from the part and its effectiveness is evaluated by measuring the surface roughness of the samples. Numerical modelling of heat transfer phenomenon is also employed to determine the thermal history of the printing process and understand which parameters define the optimal distance for the thermal supports. Finally topology optimization is used to create a support structure which minimize the wasted material while keeping the heat flow optimal.Item A mold insert case study on topology optimized design for additive manufacturing(2019) Ranjan, RajitThe Additive Manufacturing (AM) of injection molding inserts has gained popularity during recent years primarily due to the reduced design-to-production time and form freedom offered by AM. In this paper, Topology Optimization (TO) is performed on a metallic mold insert which is to be produced by the Laser Powder Bed Fusion (LPBF) technique. First, a commercially available TO software is used, to minimize the mass of the component while ensuring adequate mechanical response under a prescribed loading condition. The commercial TO tool adopts geometry-based AM constraints and achieves a mass reduction of ~50 %. Furthermore, an in-house TO method has been developed which integrates a simplified AM process model within the standard TO algorithm for addressing the issue of local overheating during manufacturing. The two topology optimized designs are briefly compared, and the advantages of implemeItem Improving the manufacturability of metal AM parts(Mikroniek, 2019) Ranjan, RajitNumerous challenges of additive manufacturing (AM) are tackled in the European Horizon 2020 project PAM^2 by studying and linking every step of the AM process cycle. For example, PAM^2 researchers from the design, processing and application side have collaborated in this work to optimise the manufacturability of metal AM parts using an improved Topology Optimisation (TO) approach, including a thermal constraint. Additionally, the project is focusing on modelling, post-processing, in- and post-process quality control and industrial assessment of AM parts, with the aim of moving beyond the state-of-the-art of precision metal AM.Item Role and effectiveness of plastic deformation and stress relief in zirconium: origin of residual stress(Indian Institute of Technology Bombay, 2014-05) Kumar, GulshanIndustrially produced Zircaloy-4 clads were subjected to pressurized water in standard closed end burst test and shown to possess different ductilities. The latter was not determined by microstructure and crystallographic texture: but was shown to have a clear scaling with hydrostatic component (Ph) of the measured tri-axial residual stress matrix. The study then tried to bring out the origin of residual stresses during plastic deformation and stress relief annealing. Zircaloy-4 sheets were cold rolled to different percentages of deformation 20%, 40% and 60% and were well electro polished before undergoing measurement in X-ray diffraction and electron backscattered diffraction (EBSD) for measuring residual stress and plastic strain. A clear gradient of elastic and plastic strains were predicted through finite clement simulation. Such predictions were verified against experimental data on microtexture and bulk crystallographic texture. Microfocused X-ray also provided clear distinction in residual stress developments between different features of the deformed microstructures. For example deformed Zirconium grains were classified as fragmenting and non-fragmenting. The latter, mostly basal, had strongest signatures of residual stresses. During recovery, microstructure dependent stress-relief was established. Initial recovery or stress relief was primarily through reductions in orientation gradients in non-fragmenting grains. Only during the latter stages, recrystallization and stronger orientation sensitive stress-relief was noted for the fragmenting grainsItem Orientation dependent mechanical properties of commercially pure (cp) titanium(2014-12) Kumar, GulshanThe present investigation is an attempt at correlating the crystallographic orientation and mechanical properties of hexagonal commercially pure titanium (cp-titanium). Annealed cp-titanium sheets are subjected to tensile deformation along the rolling direction, along 45° to the rolling direction and along 90° to the rolling direction respectively. Crystallographic textures and mechanical properties of these cp-titanium samples are investigated in the present study. The hardness of different grains/orientations is estimated through nanoindentation, grain average misorientation, orientation estimated elastic stiffness and Taylor factor measurements. It is observed that the hardness of the grains close to basal orientation is higher compared to non-basal orientations. It is further observed that the estimated bulk mechanical properties of cp-titanium have a direct relationship with the volume fraction of basal grains/orientations.