2. Thesis and Dissertations
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Item Performance Evaluation of Flexible Jute-Natural Rubber Composites for Impact Behaviour(National Institute of Technology Karnataka, Surathkal, 2020) M, Vishwas.; Joladarashi, Sharnappa.; Kulkarni, S M.A composite material is made from two or more constituent materials with significantly different physical or chemical properties which are combined to produce a material with characteristics different from the individual components. ‗Flexible composites‘ is a term coined to identify the composites making use of elastomeric polymers as matrix. These flexible composites exhibit usable range of deformations which are much larger than conventional stiff composites. The ability of flexible composites to undergo larger deformation and still provide high load carrying ability makes them suitable for many engineering applications. Flexible composites are better energy absorbers compared to conventional stiff composites subjected to impact loading. The objectives and scope of the present study includes proposing, developing and characterizing the flexible ‗green‘ composite for impact applications. An extensive literature review was carried out to explore the potential constituent materials for impact applications and accordingly the present study is carried out to explore the possible use of jute and rubber for impact applications. Initially, the feasibility of using natural rubber (NR) as a constituent material in composite is studied using commercially available finite element (FE) package. Further different stacking sequences of the flexible green sandwich composite are optimized and the three stacking sequences are selected for experimental study. These three optimized stacking sequences of the proposed flexible green sandwich composite are prepared using compression moulding technique and are characterized for their physical and mechanical properties. Further, the proposed flexible green composites are studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment. Finally, the impact behaviour of the proposed flexible composites is studied under low velocity impact (LVI) and lower ballistic impact. The mechanical characterization of the proposed flexible composites revealed that the composite with jute/rubber/jute (JRJ) exhibits better tensile and tear strength compared to jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ) with JRJ exhibiting 57.7% and 64.47% higher tensile strength compared to JRRJ and JRJRJ respectively. Also, the tear strength of JRJ is found to be 0.4% and 2.38%higher than JRRJ and JRJRJ respectively. The interlaminar shear strength (ILSS) studies shows that short beam strength of JRJRJ is better compared to JRRJ and JRJ with JRJRJ exhibiting nearly 2.1 times and 2.75 times better ILSS compared to JRRJ and JRJ respectively. The proposed flexible green composites are further studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment, the outcome of which reveals that JRJ provides better results compared to its counterpart JRRJ and JRJRJ. Various factors affecting the wear behaviour of the flexible composites are also studied from which it is clear that abrading distance and sand concentration affects the weight loss of the proposed flexible green composite in case of two body wear and slurry erosion respectively. Flexible ‗green‘ composites of different stacking sequences are further subjected to impact tests at low velocity and lower ballistic velocity at different impact energies. The results of low velocity impact reveals that flexible green composite with JRJ stacking sequence exhibit better energy absorption and the stacking sequences JRJRJ exhibit better resistance to damage with no appreciable variation in specific energy absorption of the composites. The lower ballistic impact study reveals that the flexible composites are better energy absorbers with JRJRJ exhibiting better lower ballistic response compared to JRJ and JRRJ. The ballistic limit of JRJRJ is enhanced by 39.7% and 6% compared to JRJ and JRRJ respectively. The energy absorption at ballistic limit of JRJRJ is more compared to JRJ and JRRJ by 97.7% and 12.7% respectively. The energy absorption of JRRJ is enhanced by 75.5% compared to JRJ. The specific energy absorption (SEA) of JRJRJ is enhanced by 52% and 2.7% compared to JRJ and JRRJ respectively. The proposed flexible green composite can be a potential material for sacrificial structures in order to protect the primary structural components.Item Machinability Characteristics in Drilling of Glass Microballoon /Epoxy Syntactic Foam(National Institute of Technology Karnataka, Surathkal, 2019) Ashrith, H. S.; Doddamani, MrityunjayPolymer composites are steadily substituting the conventional materials in aerospace, marine, automobile and many other engineering applications owing to their unique properties such as lightweight feature combined with high specific strength and superior corrosion resistance. Weight reduction of composite materials is of great interest in aerospace, marine and automobile applications to meet the stringent guidelines of fuel consumption and emissions in the coming years. Structural weight reduction without compromising the desired properties can be achieved by using a unique class of composite called syntactic foams, wherein the matrix is filled with hollow particles called microballoons. Even though the composites are produced to near-net shape, drilling is unavoidable during final stage of production process for the assembly of various structural components using fasteners. Many problems arise during drilling of composites due to non-homogeneous and anisotropic nature of the material. Nearly 60% of the composite parts are rejected during aircraft assembly due to drilling induced damages. The focus of the present study is to achive good quality holes in drilling of glass microballoon/epoxy syntactic foams by selecting appropriate process parameters. In the present investigation, epoxy resin (LAPOX L-12) is used as the matrix resin and borosilicate glass microballoon (GMB) is used as hollow filler without any surface treatment. Syntactic foams are fabricated by dispersing 20, 40 and 60 vol.% GMBs in epoxy matrix using manual stirring method. Nine different types of syntactic foams specimens with 20, 40 and 60 vol.% of GMBs are fabricated using three different densities (varying wall thickness) of GMBs (SID-200Z: 200 kg/m3, SID-270Z: 270 kg/m3 and SID-350Z: 350 kg/m3). All the prepared samples are coded as per EYYY-R convention. Epoxy resin is denoted by ‘E’ and ‘YYY’ represents density of GMBs. Neat epoxy specimens are also fabricated under similar processing conditions for comparison. Extensive micrography of fabricated foams confirms the uniform distribution of GMBs in the epoxy matrix without forming the clusters. Experimental density of all the fabricated syntactic foams is lower than neat epoxy resin. Density of foams decreases with decreasing GMB wall thickness and increasing volume fraction of GMBs. Density reduction in the range of 18-53% is noted as compared to neat epoxy indicating significant weight saving potential of the proposed syntactic foams.Experiments are conducted using vertical computer numerical control machine and TiAlN coated tungsten carbide twist drills of varying diameter based on full factorial design (FFD). Cutting speed (v), feed (f), GMB content (R), GMB wall thickness (w) and drill diameter (D) are taken as input parameters, while thrust force, surface roughness, specific cutting coefficient, cylindricity, exit side circularity error and exit side damage factor are considered as responses for evaluating the quality of drilled hole. Three levels for each input process parameters (v: 25, 75 and 125 m/min; f: 0.04, 0.08 and 0.12 mm/rev; R: 20, 40 and 60 vol.%; w: 0.716, 0.925 and 1.080 µm; D: 8, 12 and 16 mm) are selected to consider the nonlinear effects among the parameters. Experiments are repeated for three times and the average values are used for analysis. Mathematical models based on response surface methodology (RSM) are developed using Minitab 14 software for analyzing the influence of the input parameters on the measured responses. Adequacy of the developed mathematical models is confirmed using analysis of variance. Higher R-squared values indicate that the developed mathematical models can be effectively used as a tool in industrial practices to predict the machinability characteristics of GMB reinforced epoxy foams during drilling. Individual and interaction effect of process parameters on the responses are analyzed using RSM based mathematical models. Individual effects are studied by varying one parameter at a time in the mathematical models while keeping all the remaining process parameters at the intermediate levels. Two parameters are varied at the same time while keeping the other parameters at the intermediate level in the mathematical models to study the interaction effect of process parameters on the chosen responses. Thrust force is found to be increasing with increasing feed and drill diameter, while it decreases with increasing GMB content. Thrust force of all the foams is found to be lower as compared to neat epoxy resin. Thrust force is observed to be decreased by 40-55% as compared to neat epoxy due to the incorporation of GMBs. Drill diameter, feed and GMB content have a significant effect on the thrust force while the effect of cutting speed is found to be insignificant. v125f0.04R60D8 is the optimum condition for minimizing thrust force of E200 and E270 foams while performing machining at v25f0.04R60D8 minimizes the thrust force of E350 syntactic foam. Extensive microscopy is conducted on the drilledspecimens to understand crack initiation and propagation mechanisms. Surface roughness of the drilled hole is measured using Mitutoyo surftest with a cut-off length of 0.8 mm. As compared to neat epoxy, the surface roughness of syntactic foams increases by 14-20 times. However, surface roughness in foams decreases with increasing GMB volume fraction. Surface roughness is strongly governed by drill diameter and cutting speed. Minimum surface roughness for E200 and E270 foams is obtained at v25f0.12R60D16, while v25f0.12R60D12 is found to be optimum for E350 foam. Specific cutting coefficient increases with increasing drill diameter and decreasing feed. Increasing GMB content significantly decreases specific cutting coefficient by 40-55% as compared to neat epoxy specimens. v25f0.12R60D8 is the optimum condition for E350 foam, while machining at v125f0.12R60D8 is found to be beneficial for E200 and E270 foams for minimizing specific cutting coefficient. Coordinate measuring machine is used to measure the cylindricity, exit side circularity and maximum diameter of drilled hole for damage estimations. Cylindricity of the foams increases with increasing the cutting speed, feed and drill diameter. Increasing GMB content decreases the cylindricity by 46-69% as compared to neat epoxy. Drill diameter, feed and GMB content have a significant effect on cylindricity of drilled holes. v25f0.04R60D8 is noted to be the optimum conditions for E200 and E270 foams while v75f0.04R60D8 parametric setting is most suitable for thick-walled (E350) foams to minimize cylindricity. Circularity error increases with increasing cutting speed and drill diameter, while it decreases with increasing feed and GMB content. Increasing the microballoon volume fraction decreases the circularity error of foams by 18-67% as compared to neat epoxy. Circularity error of the holes is highly influenced by drill diameter followed by GMB volume fraction and wall thickness. v25f0.12R60D8 is the optimum condition for minimizing the circularity error of all the type of foams. The damage factor is dependent on the thrust force developed during drilling process. Drill diameter, feed and GMB content have a significant effect on damage factor of the drilled holes. Optimum conditions for minimizing damage factor is observed to same as that of thrust force. A reduction in the damage factor by 26-42% is noted in foams with increasing GMB content as compared to neat epoxy. Optimum conditions based on response surfacemethodology for minimizing all the responses are not same and the trade-off among various process parameters necessitates multi-response optimization. In the present work, grey relation analysis (GRA) is used for finding a specific combination of process parameters for minimizing all the response at the same time to obtain a good quality hole in drilling GMB/Epoxy syntactic foams. According to GRA, v125f0.08R60D8 is the optimal condition for producing a quality hole in E200 foams, whereas v25f0.12R60D8 is found to be optimal for E270 and E350 syntactic foams. Higher GMB content is preferred in the foams from drilling operations perspective, which is also beneficial for weight sensitive applications. Influence of GMB wall thickness on the responses is studied by keeping the GMB content at 60 vol.%, as higher filler content significantly improves the hole quality. Response surface plots for varying wall thickness of GMBs are plotted using the developed mathematical models to study the interaction effects among input process parameters. Increasing microballoon wall thickness from w0.716 to w1.080 increases thrust force, specific cutting coefficient and damage factor by 40%. Surface roughness, cylindricity and circularity error of drilled holes are significantly affected by GMB wall thickness and is found to be decreased by 30, 41 and 56% respectively. Combination of higher particle wall thickness and feed with lower cutting speed and drill diameter (v25f0.12w1.080D8) is the optimum condition for producing a sound hole quality as observed from GRA. Hole quality is highly influenced by drill diameter followed by the interaction between cutting speed and GMB wall thickness. Finally, microscopy is conducted to analyze the shape and size of chips produced during drilling. Cutting tools are inspected using a confocal microscope post drilling operation and micrographs show negligible tool wear due to the superior wear resistance of TiAlN coating. Observations and parameters settings explored in this work offers guidelines for the industrial practitioners to produce quality holes in drilling of GMB reinforced epoxy composites.Item Investigation on Mechanical and Wear Properties of Composites from Recycled Polymer for Gears with Optimized Compression Moulding(National Institute of Technology Karnataka, Surathkal, 2014) Prabhu, B Krishna.; Kulkarni, S. M.Cost of a product can be visualized as sum of the cost of materials and process cost. In a competitive world, producing quality products at low cost is need of the day. In reducing the process cost, the use of off line techniques like Design for manufacturing (DFM), design of experiments (DOE), Six Sigma optimization and process modeling could be adopted. Further, judicious development of low cost materials, will help in bringing down the total cost of the product. In view that polymer consumption is growing at a fast pace, reusing post consumer polymers could help reducing the material cost component of the product. Recycling engineering plastic such as post consumed Polyethylene Terephthalate (PET) provides not only a cheap and abundantly available source of material but also expands the sphere of application for recycled PET (r-PET). However, owing to reduction in the properties due to recycling procedures, the plastic need to be developed suitably, to meet the requirements of an application. Reinforcing r-PET with suitable material could address this issue. Fly ash cenospheres are low cost material that could be useful in improving the properties of recycled polymers. The cost of the product developed from low cost recycled materials could be further reduced by developing suitable low cost process. Compression moulding could be a low cost process. The process however needs to be optimized for moulding product with appreciable quality. Thus the present study is focused on developing r-PET based composites with FA cenospheres as reinforcement and compression moulding as a manufacturing process in order to cater the requirements of an industry to produce low cost engineering components such as gears. In the process of optimization, Six Sigma based DMAIC/DMADV methodology along with Taguchi’s method and RSM are utilized where as development of r-PET/FAC composite is carried out using design of experiments (DOE). Entire work is envisaged in five stages. The first stage of the experimentation is carried out with an intention to establish a thermo-mechanical moulding process for r-PET. Six Sigma DMADV methodology is utilized along with Failure Modes and Effects Analysis (FMEA) for successive improvement in the moulding procedure. A reduction in risk priority number (RPN) from 900 to 315 and finally to 8 is achieved on successive improvement in the process using FMEA. At the end of its successful application, a good, repeatable sample quality is achieved. In the second stage, R-PET, reinforced with FAC is studied for a set of compression moulding process variables and material variables using DOE as statistical tool. Five factors, critical to quality (CTQs) viz. moulding pressure (5, 10, 15 MPa); moulding time (5, 10, 15 min.); mould cooling (water, air, water and air); moulding temperature (50, 100, 150 ˚C) and weight fraction of cenospheres (5, 10, 15%), are considered at three levels. The DOE methodology adapted for such investigations showed a down ward trend for FAC content. The cause investigated using fractographic analysis, concludes debonding of FAC from the matrix due to improper interfacial characteristics. Further, the composite underwent brittle fracture making it not much useful for gear applications. The remedy considered for developing r-PET composite that makes it suitable for the gear application is to blend the matrix with an appropriate recycled polymer and to improve interfacial interactions of FAC with matrix by suitably treating FAC with (3-Aminopropyl) trimethoxy silane (3APTMS). The wear property of the composite however, proves promising as FAC reduced Specific wear rate (SWR). The preliminary work in developing the matrix, in the third stage, involves blending rPET with five softer polymers from recycled regime. R-LLDPE, r-LDPE, r-HDPE, r-PP and r-Nylon are these five polymers. Experimentation of r-PET blends suitably selects rLDPE as better suited polymer owing to its flexural and wear properties. . Blending rPET with 10% r-LDPE improves the toughness by 100% and by 112% at 30%. This is followed by r-HDPE that shows 25% and 100% increase at respective composition. Flexural strength and SWR of r-PET/r-LDPE blends affected marginally whencompared to the plastics considered in this study. The next part of third stage involves developing the composite with matrix blended with r-LDPE (30% by wt.), reinforced with FAC (5, 10, 15% by wt). An improvement in the fracture strain, over 87 % is noted at 30% of r-LDPE and 15% FAC. An improvement in toughness by about 66 MPa at 5% FAC and 13 MPa at 30% of FAC is observed. Thus studies on matrix blending conclude that blending r-PET with r-LDPE helps in reducing the brittleness of r-PET. Further, 3APTMS (6, 8, 10% by wt.) is used for treating FAC and to improve the interface. Reinforcing r-PET with 3APTMS (10% by wt.) treated FAC (T-FAC) improved flexural strength of r-PET/T-FAC composite. An increase of 34% strength at 5% T-FAC, 57% increase at 10% and 120% improvement in strength at 15 % of T-FAC is observed owing to surface treatments given to FAC. Such an increase in the properties leads to improvement in the toughness of the composite. Toughness improves by 95% at 5% of T-FAC, 200% at 10% and an increase of 271% in toughness when r-PET is reinforced with 15% T-FAC is observed. Owing to blending and treating of reinforcement, flexural and wears properties improved significantly. Further M-r-PET/T-FAC composite is also tested for their properties. The results of M-r-PET/T-FAC composite conclude favorably for developing low cost material from recycled means. In the next stage, the process and material thus developed are optimised for flexural and wear properties. In the fourth stage the process and material parameters are optimized for improved properties of the composite. Six Sigma DMAIC optimisation tool, Analysis of variance (ANOVA), Response surface methodology (RSM) are used to determine the optimum values. The final optimum parameters for moulding r-PET reinforced with FAC are Moulding pressure – 11.2 MPa, 3APTMS -7.9 % by wt., r-LDPE - 29 % by wt., moulding Temperature - 52.6 ºC and FAC – 12.5%. Confirmation experiments for these optimum values are done to verify the validity of the process adopted. In the fifth and final stage the material developed in the previous stages is moulded into gears with optimized compression moulding and their performance is evaluated on an indigenously designed and fabricated gear test rig. The increase in the gear life by about275% w. r .t the starting composite (r-PET/FAC) seems good for the applications sought for them. The gear can handle a load of about 30.5 N and can take about 50,000 revolutions. With such an improvement shown by the composite material developed in this work, it could be considered as an alternative to the existing gears made from neat polymers for lower loading applications. Thus the objectives set for this research work that to develop a low cost composite material from environment hazardous waste materials with optimized compression moulding for gear applications are met with the systematic application of Six Sigma methodologies as explained in this work.