Browsing by Author "Gangadharan, K. V."

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Characterization of CNT Reinforced Al Functionally Graded Composite Laminates
(National Institute of Technology Karnataka, Surathkal, 2017) Udupa, Gururaja; Rao, Shrikantha S.; Gangadharan, K. V.
Functionally graded composite laminate materials(FGCL) are special kind of new generation materials aimed at meeting new requirements of engineering applications. It contains, two or multi-phase particulate composites in which material composition and microstructure are characterized by continuous, smooth variations on macroscopic scale designed to meet desired functional performance. The absence of sharp interfaces in FGCL reduce chances of material property mismatch and thus leading to significant improvement in damage resistance and mechanical durability. Therefore, FGCL’s are of great interest in disciplines as diverse as civil, electrical, mechanical, nuclear and nano engineering applications. However, the extent to which an FGCL can be tailored to meet the required performance –i.e., the design of FGCL strongly depends on the resultant effective properties and more importantly, on how these properties relate to its functional requirements. Hence, predicting mechanical, thermal or other relevant properties for given microstructure and its spatial distribution plays a significant role in the design of FGCL. Objective and scope of the present work includes planning, preparation of CNT reinforced Al Functionally graded composite laminates by mechanical Powder Metallurgy technique and experimental testing for its characteristic properties. FG samples are prepared by varying the content of CNT (0.1,0.2,0.3,0.4 and 0.5 wt.%)in weight percentage and tested. Such prepared FGCL samples are tested for physical and mechanical properties. Before the FGCL samples are prepared, simple composite samples are prepared for same weight fraction of CNT reinforcement to characterize the microstructure and tested for the hardness. These composites are tested as per the ASTM guidelines. Once the results are confirmed, FGCL samples are designed for same weight fraction of reinforcement in layered fashion. The weight fraction is proportionally increased from 0.1 to 0.5wt.% from one end to the other end of the sample. The density, hardness and tensile behavior of FGCL samples are experimentally evaluated. These properties are found to be increasing with addition of CNT reinforcement. The damping ratio of composite and FGCL is estimated from impact hammer test, which demonstrated the significance of FGCL on the damping characteristics compared to a conventional composite material.At present work, more focus on developing high wear resistance, light weight, good damping material with moderate good thermal conductivity material for brake rotor applications. Experimental investigation on FGCL proved good tensile stress properties with 0.5wt.% CNT reinforcement and these results are proven good agreement with characterization of microstructure. Microhardness for the cross-section of FG samples linearly varies with the increment in CNT reinforcement, which results in the variation of microstructure. Reduction in grain size found for 0.1 to 0.5wt.% CNT reinforcement, observed staggered layer of microstructure. The hardness of the developed material become high on the 0.5wt.% CNT reinforced side. Wear properties are investigated with proper Design of Experiments by using Taguchi techniques for three parameters(Load, Abrasive grit size, Weight percent of CNT). It revealed that reinforcement of CNT affected reduction in the friction between the matting surface due to the formation of lubrication layers. Good wear resistance is observed for 0.25 to 0.4 wt.% CNT reinforcement. This result is in good agreement with the observation of SEM images for same weight fraction of CNT reinforcement. ANOVA results proved load, wear surface(Abrasive grit size) are the prominent factors for wear and CNT reinforcements improved the wear resistance in the materials. Finally, the improvement in thermal conductivity has been observed on CNT reinforcement. Furthermore, FGCL’s are associated with particulate composites where the weight fraction of particles varies in one or several directions. One of the advantages of a monotonous variation of weight fraction of constituent phases is the elimination of stress discontinuity that is often encountered in laminated composites and accordingly, avoiding delaminating-related problems. Investigation on developed FGCL samples found good agreement with the continuity in microstructure without step deviation as well as the hardness variation. Good damping behavior and wear resistance ability with improved thermal conductivity features could be a promising proposition for brake rotor materials. Insertion of developed light weight CNT reinforced FGCL between the cast iron plate on brake rotor make a huge impact on weight reduction and cost economics.
Development and Evaluation of Damping characteristics and Shear properties of Magnetorheological elastomers
(National Institute of Technology Karnataka, Surathkal, 2017) Hegde, Sriharsha; Gangadharan, K. V.
Elastomers are widely used to reduce vibrations and noise in structures, machines, and instruments. The passive nature of elastomers inhibits its use over a wider range of frequencies. Incorporating ferromagnetic ingredients in the non-magnetic elastomer matrix makes these structures smart when exposed to a magnetic field. These elastomers are better than conventional elastomers and can be applied in a wide frequency range. They belong to a class of smart material called Magnetorheological materials whose rheological properties can be reversibly controlled by a magnetic field. This research is focused on preparation and damping characterization isotropic magnetorheological elastomers using different matrices by varying the volume percentage of carbonyl iron powder. Natural rubber, Nitrile rubber, RTV and HTV silicone and a new type of MRE by mixing RTV silicone and polyurethane was prepared and tested at various magnetic fields and input conditions. Experimental studies were conducted to understand the influence of matrix material, percentage concentration of carbonyl iron powder and magnetic field on the mechanical properties of the MREs i.e. shear modulus (G) and dynamic damping (loss factor η). Force vibration tests were performed to understand the enhancement of damping property of MRE samples. Experimentally it was proved that nitrile rubber and silicone-polyurethane hybrid MREs showed better damping performance than other matrix materials. The performance was also dependent upon the input strain rate and weakly on the operating frequency. The influence of size of the particle ingredient was investigated on a small scale. The inherent damping property of the matrix plays a major role in the respective MRE sample. Magnetic field and percentage particle content was found to be the dominating parameters influencing the damping properties. The dimension of the test sample, input strain and frequency also influence the damping on a lesser scale. Linear viscoelastic model was fitted to the experimental data using the MATLAB optimization tools which closely matched with the experimental values. The application of MRE as damping material was investigated by following ASTM E756-05 standard in sandwich beam configuration. The loss factor and shear modulus modifications were investigated under non-homogeneous magnetic field by subjecting it to impulse excitation.
Dynamic Analysis of Magnetorheological (Mr) Fluid Based Semiactive Suspension System for Vehicular Application Using Nonparametric Approach
(National Institute of Technology Karnataka, Surathkal, 2016) K, Hemanth; Kumar, Hemantha; Gangadharan, K. V.
The magnetorheological (MR) fluid dampers belong to a category of semi-active devices, in which damping force can be varied within a few milliseconds through the application of a magnetic field. The main aim of this project is to investigate the performance of MR damper used as a semi-active suspension system in vehicle models to improve the ride comfort and road holding quality of the vehicle, when subjected to average random road profile and road bump as inputs. Research work starts with design and development of MR damper, which includes optimization of MR damper to study the variation of magnetic flux density with variation of electromagnetic circuit parameters such as current magnitude, number of turns in the coil, coil core length, fluid flow gap and flange length. The optimization study shows that, the magnetic flux density induced in the fluid flow gap increases with increase of applied current, number of turns in the coil and coil core length. The magnetic flux density is seen to decrease with increase of fluid flow gap and flange length. The optimum fluid flow gap, which is obtained from the optimization technique has been considered for fabrication of MR damper. Experimental studies on a developed MR damper with different proportion of MR fluid have been conducted by using dynamic testing facilities at 1.5Hz and 2Hz operating frequencies. Based on the experimental results, the optimum level of parameters such as proportion of MR fluid and operating frequency are evaluated by using Taguchi design of experiments. Then, dynamic behaviour of MR damper with optimum level of parameters has been investigated. Developed damper shows the capability of improving both stiffness and damping properties with variation of electric current. Magnetostatic analysis of MR damper has been carried out, in order to find total magnetic flux density induced in the fluid flow gap. Total magnetic flux density induced in the fluid flow gap is divided into five categories by using statistical categorization technique. The average total magnetic flux density obtained from thestatistical categorization technique has been used to evaluate the damper force. Based on this, non-parametric model has been developed and polynomial function is used to relate the damper force as a function of current. Bouc-Wen model has been used to benchmark the developed non parametric model. The parameters of the Bouc-Wen model are evaluated by minimizing the error between the experimental and predicted force using non-dominated sorting genetic algorithm II (NSGA-II) optimization technique. The hysteresis behaviour of the MR damper is predicted by both models (non-parametric model and Bouc-Wen model) and validated with the experimental investigations. Both parametric and non-parametric models predict the behaviour, which is having good agreement with experimental results. Different mathematical models such as quarter car model (2 DOF), half car model (4 DOF) and full car model (7 DOF) of the vehicle with passive and semiactive suspension systems are formulated. Newly developed non-parametric model of MR damper is used in vehicle model as semi-active suspension system with suitable control strategy. Ride comfort and road holding performances of passive and semiactive suspension systems are found under average random road profile as input. In comparison, the vehicle with MR based suspension system provides better vibration isolation for a vehicle than passive suspension system.
Experimental and modeling of the translation stiffness of magnetorheological elastomer
(National Institute of Technology Karnataka, Surathkal, 2018) Poojary, Umanath R.; Gangadharan, K. V.
Magnetorheological elastomer is a potential resilient element to meet the vibration mitigation demands of a dynamic system over broad-band frequency. It comprises of ferromagnetic fillers dispersed in a non-magnetic elastomer matrix. Under the influence of an external magnetic field, these fillers readily interact and modify the properties of Magnetorheological elastomer. The response of magnetorheological elastomer under dynamic loading includes the contributions from the viscoelastic properties of matrix and the field sensitive characteristics of the filler. These properties are unique for a particular combination of matrix and the filler. The properties of Magnetorheological elastomer are sensitive to the changes in the operating parameters such as frequency and displacement amplitudes. This demands a large number of experiments to characterize the viscoelastic properties of Magnetorheological elastomer. On the contrary, the overall process of dynamic characterization is simplified by adopting a phenomenological modeling approaches based on the theory of linear viscoelasticity. It is important that the model should be able to represent viscoelastic behavior over wide frequency range in a simple form. The present study is focused on modeling the translation stiffness to realize the concept Magnetorheological elastomer as boundary support damping applications. The dynamic tests are performed on Magnetorheological elastomer under shear mode (volume preserving deformation state) according to the dynamic blocked transfer stiffness method. The viscoelastic properties are evaluated at different frequency, magnetic field and strain amplitudes. These properties are expressed in terms of dynamic stiffness, and the loss factor evaluated from the force-displacement hysteresis loops. The test results indicated that the properties of Magnetorheological elastomer enhanced with an increase in magnetic field and the frequency. The magnetic field dependency is more pronounced compared to frequency. At larger values of frequency and magnetic field, the viscoelastic properties are saturated. For the tested MRE samples, the saturation behavior is observed at 50 Hz and 0.3 T. With an increase in strain the viscoelastic behavior of Magnetorheological elastomer changes from linear to nonlinear. Under magnetized state, the nonlinear behavior occurs at lower strain levels as the matrix-filler frictional energy dissipation isiv intensified. In addition, Magnetorheological elastomer exhibits the Payne effect with the variation in input strain amplitude. The Payne effect is more pronounced under non-magnetized state and it diminished under magnetized state due to the contribution from the filler –filler interactions. The material behavior of Magnetorheological elastomer is modeled by adopting the phenomenological models based on the viscoelastic constitutive relations. In the present study, integer and fractional order derivative based viscoelastic constitutive relations are used. Integer order based model comprises of six parameters, and the fractional order model are represented by five parameters. The parameters of the model are identified by minimizing the error between the response of the model and dynamic compression (translation) test data. Performance of the model is evaluated with respect to the optimized parameters estimated at different sets of regularly spaced arbitrary input frequencies. A linear and quadratic interpolation function is chosen to generalize the variation of parameters with respect to the magnetic field and frequency. The predicted response of the model revealed that the fractional order element model describes the properties of magnetorheological elastomer in a simpler form with reduced number of parameters. The fractional order based model has a greater control over the real and imaginary part of the complex stiffness, which facilitates in choosing a better interpolating function to improve the accuracy of the model. Furthermore, it is confirmed that the realistic assessment of the model performance is based on its ability to reproduce the results obtained from optimized parameters. The material models based on the viscoelastic constitutive relations are not adequate to describe the amplitude dependent characteristics. These attributes are incorporated in the model by adding a linearized Bouc-Wen element. The proposed model comprised of eight parameters, which are identified by minimizing the least square error between the model predicted and the experimental response. The variations of each parameter with respect to the operating conditions are represented by a generalized expression. The parameters estimated from the generalized expression are used to assess the ability of the model in describing the dynamic response of Magnetorheological elastomer. The proposed model effectively predicted the stiffness characteristics with an accuracy, more than 94.3% and the correspondingv accuracy in predicting the damping characteristic is above 90.1%. This model is capable of fitting the experimental value with a fitness value of more than 93.22%.
Studies on Vibration and Acoustic Response Characteristics of Sandwich Aerospace Structures
(National Institute of Technology Karnataka, Surathkal, 2018) Arunkumar, M. P.; Jeyaraj, P.; Gangadharan, K. V.
Numerical investigation carried out on vibration and acoustic response characteristics of structures used in aerospace application is presented. Sandwich panels are used as structural members in aircraft due to their high stiffness to weight ratio. Vibro acoustic characteristics of sandwich panels with honeycomb, truss and foam filled truss core are analysed in this work. Equivalent 2D finite element model is used to obtain the free and forced vibration response of sandwich panels using commercial finite element solver ANSYS. Further, vibration response of the sandwich panel is given as an input to the Rayleigh integral code built-in-house using MATLAB to obtain the acoustic response characteristics. Initially, influence of important geometrical parameters on vibration and acoustic response characteristics of sandwich panels which are typically used as aerospace structures are investigated. Different types of sandwich panels analysed are (a) Honeycomb core (b) Truss and Z core and (c) Foam core. It is found that for a honeycomb core sandwich panel in due consideration to space constraint, the better acoustic comfort can be achieved by reducing the core height and increasing the face sheet thickness. It is also observed that, triangular core gives better acoustic comfort for the truss core sandwich panel compared to other types of core. Further, a sandwich panel with fibre reinforced plastic (FRP) facing and aluminium honeycomb core is investigated to analyse the effect of inherent material damping associated with FRP facing on vibro-acoustic response characteristics. The result reveals that FRP panel has better vibro-acoustic and transmission loss characteristics due to high stiffness and inherent material damping associated with them. It is observed that resonant amplitude of the vibro-acoustic response is significantly controlled by modal damping factors which is calculated based on modal strain energy. It is also demonstrated that FRP facing can ivbe used to replace the aluminium panel without losing acoustic comfort with nearly 40 % weight reduction. Effect of foam filling in empty space of the truss core sandwich panel on sound radiation and transmission loss (STL) characteristic is also studied. Results revealed that polyurethane foam (PUF) filling in empty space of the truss core, significantly reduces resonant amplitudes of both vibration and acoustic responses. It is also observed that foam filling reduces the overall sound power level by about 12 dB. Similarly, sound transmission loss studies revealed that, at resonance frequencies nearly 20 dB is reduced. In order to validate the accuracy of results, free and forced vibration response of a honeycomb core sandwich panel made of aluminium is obtained experimentally. The experimental results are compared with the proposed numerical results. From the results, it is observed that numerical and experimental results are in good agreement.