Design and Comparative Analysis of Viscoelastic Materials for Specially Designed Vibration Test Rig

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Design and Comparative Analysis of Viscoelastic Materials for Specially Designed Vibration Test Rig

Mahesh Vishwanath Gupta

Department of Mechanical Engineering MIT ADT Universitys School Of Engineering

Loni Kalbhor, Pune, India

Prof. Dr. Sudarshan Sanap

Department of Mechanical Engineering MIT ADT Universitys School Of Engineering

Loni Kalbhor, Pune, India

Abstract Rotating machines often have problems of instability when working at high rotations, which can result in sudden failures of the whole system or parts of it. This problem can be solved by including damping in the bearings. In general, with this type of control, not only can the vibration levels be reduced but also the area of stability can be enlarged. Viscoelastic materials are widely employed in vibration and noise control devices due to their high capacity of vibratory energy dissipation. In day today life in most of the companies balancing and noise reduction problems are absolute due to better designing techniques of manufacturing. Vibration isolators are used for the reduction of machine vibration in every industry, so we are implementing isolation method. The Viscoelastic material is having a wide application area and having desirable properties to minimize the effect of vibrations by absorbing the significant amount of vibration magnitudes. In this work it is proposed to estimate and evaluate different viscoelastic materials (Silicon Rubber, Flexible PVC) on specially designed vibration test rig of vibration analysis.

Keywords Viscoelastic Material, Vibration, Silicon Rubber, Flexible PVC.

  1. INTRODUCTION

    In day today life in most of the companies, balancing and noise reduction problems are absolute due to better designing techniques of manufacturing. Vibration dampers are used for the reduction of machine vibration in every industry, so we are implementing vibration dampers.

    When motorized equipment, such as electric motors, fans or pumps, is mounted to a solid structure, energy can be transferred from the equipment to the structure in the form of vibration. This vibration often radiates from the structure as audible noise and potentially reduces performance or damages equipment. Isolation mounts reduce the transmission of energy from one body to another by providing a resilient connection between them. Selecting an improper mount for an application, however, can actually make the problem worse. The incorrect mount may reduce the high frequency vibration, but resonant conditions at lower frequencies can actually amplify the induced vibration.

    Controlling the natural frequency provides one means to control vibration. Damping is the dissipation of energy, usually by releasing it in the form of low-grade heat. For example, dry friction, the most common damping mechanism, is the reason an object sliding on a surface will

    slow down and stop. Some mechanical devices use viscous damping as a means of energy dissipation. In these systems, fluid losses caused by a liquid being forced through a small opening provide the necessary energy loss. The shock absorbers on an automobile are an example of viscous dampers. Here in our present study I am going to reduce vibration by using viscoelastic material and then I am going to take the acceleration readings from FFT analyzer and compare the acceleration reading obtained from the FEM vibration analysis and find if vibration has reduced or not. The test rig is specially designed for the study.

  2. VISCOELASTIC MATERIALS

    Viscoelasticity is the property of materials that consists of both type, viscous and elastic characteristics when an external load is applied. viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Some phenomena in viscoelastic materials are:

    1. If the stress is held constant, the strain increases with time (creep).

    2. If the strain is held constant, the stress decreases with time (relaxation).

    3. If cyclic loading is applied, hysteresis (a phase lag) occurs, leading to a dissipation of mechanical energy.

    Properties of viscoelastic materials: Creep and Recovery, Stress Relaxation and Energy Absorption.

    Table No.1: Viscoelastic Materials used for Experiment

    Sr. No

    Name

    Image

    1.

    Natural Rubber

    2.

    Silicon Rubber

    3.

    Flexible PVC

  3. INTRODUCTION TO FINITE ELEMENT METHOD

    FEM allows detailed visualization of where structures bend or twist, and indicates the distribution of stresses and displacements. FEM software provides a wide range of simulation options for controlling the complexity of both modeling and analysis of a system. Similarly, the desired level of accuracy required and associated computational time requirements can be managed simultaneously to address most engineering applications. In our case we are going to perform the vibration analysis for a rotating unbalance shaft for all the case of isolation and compare the results for validation.

  4. EXPERIMENTAL SETUP

    Fig No.1 Vibration Test Rig

    Fig No.2 FFT Experiment Setup

    The Experiment Setup consists of the following components:

    1. Prime Mover (1 HP Motor-1500rpm)

    2. Bearings: P-206.

    3. Tachometer (rpm measurement)

    4. Shaft with Disc of 100gm unbalance

    5. Speed Controller

    6. Dewesoft FFT Analyzer

    7. 12mm thick Isolator (provided between motor and base plate and bearings and IC block connected to base plate).

    1. Parameters and Case of Experiments

      We measured the vibration acceleration values by using FFT analyzer at four different speeds or frequencies for five different cases of Isolation on the above shown test rig., in our setup the distance between the supports of the shaft remain the same and we are going to measure the acceleration by using accelerometer at two similar points (i.e. at the Bearing 2 Location 1 and Location 2) of the set up. We are going to run our setup at four different speeds or frequencies

      which are 300 rpm (5Hz), 600 rpm (10Hz), 900 rpm (15Hz), 1200 (20Hz). As there is only one unbalance in our system we can convert the rpm value to Hz by diving rpm with 60sec.

      The followings are the different cases of Isolation:

      CASE 1: No Isolation provided at the foundation of Motor, Bearing 1 and Bearing 2.

      CASE 2: Natural Rubber used as Isolator provide at the foundation of Motor, Bearing 1 and Bearing 2.

      CASE 3: Silicon Rubber used as isolator provide at the foundation of Motor, Bearing 1 and Bearing 2.

      CASE 4: Flexible PVC used as isolator provide at the foundation of Motor, Bearing 1 and Bearing 2.

      CASE 5: Composite of Natural Rubber, Flexible PVC and Silicon Rubber used as isolator provide at the foundation of Motor, Bearing 1 and Bearing 2.

      Table No.2 Arrangements of isolators at different position

      1. Location 1 (b) Location 2

      Fig No.3 Bearing 2 reading point

    2. EXPERIMENT PROCEDURE

      1. Procedure

        Step 1: Connect the setup with the FFT analyzer along with the accelerometer and unbalance mass to the disc.

        Step 2: Place the accelerometer on any one point of the Bearing 2 and set the window for FFT on Dewesoft X3 software.

        Step 3: Switch ON the main power supply and run the setup at a constant speed 300 rpm with the help of speed controller and tachometer.

        Step 4: Start the measure on the software for 3 to 5 sec and store the data for post processing open the FFT window and note the acceleration value.

        Step 5: Now increase the speed for 600, 900 and 1200 rpm note the values for all the speed and repeat the process for all the different cases of isolation.

        Step 6: Tabulate the data and plot the graphs and by interpretation suggest the suitable material giving more isolation.

        The tabulated data for Experiment for different cases is shown below.

      2. Experiment Readings

    3. Sr. No.

      Description

      Image

      1.

      Composite material between motor and foundation plate

      2.

      Natural rubber between Bearing 1 and IC block

      3.

      Flexible PVC between Bearing 2 and IC block

      4.

      Natural rubber between motor and foundation plate

      Frequency (Hz)

      5

      0.00279

      0.00205

      10

      0.00525

      0.00619

      15

      0.0145

      0.0153

      20

      0.0585

      0.0456

      Frequency (Hz)

      5

      0.00279

      0.00205

      10

      0.00525

      0.00619

      15

      0.0145

      0.0153

      20

      0.0585

      0.0456

      Table No.3: Case 1-No Isolation

    4. Graphical Representation

      1. Bearing 2-Location 1

        Fig No 4: Exp-Acceleration at Bearing 2 Location 1 Vs Speed

      2. Bearing 2-Location 2

    Location 1

    Bearing 2

    Location 2

    Frequency (Hz)

    5

    0.00203

    0.00198

    10

    0.00332

    0.00387

    15

    0.0148

    0.0132

    20

    0.0344

    0.0427

    Frequency (Hz)

    5

    0.00203

    0.00198

    10

    0.00332

    0.00387

    15

    0.0148

    0.0132

    20

    0.0344

    0.0427

    Table No.4: Case 2-Natural Rubber as Isolation

    Location 1

    Bearing 2

    Location 2

    Frequency (Hz)

    5

    0.00185

    0.0019

    10

    0.00315

    0.00324

    15

    0.0119

    0.0135

    20

    0.0343

    0.0396

    Frequency (Hz)

    5

    0.00185

    0.0019

    10

    0.00315

    0.00324

    15

    0.0119

    0.0135

    20

    0.0343

    0.0396

    Table No.5: Case 3-Silicon Rubber as Isolation

    Location 1

    Bearing 2

    Location 2

    Fig No 5: Exp-Acceleration at Bearing 2 Location 2 Vs Speed

  5. FINITE ELEMENT ANALYSIS

    Ansys 15 FEM software is used to do the vibration analysis for the vibration setup. In this set up and identical CAD setup

    Table No.6: Case 4-Flexible PVC as Isolation

    Frequency (Hz)

    Bearing 2

    Location 1

    Location 2

    5

    0.00117

    0.00173

    10

    0.00247

    0.00202

    15

    0.0102

    0.0158

    20

    0.0282

    0.0278

    Frequency (Hz)

    5

    0.00188

    0.00192

    10

    0.00294

    0.00291

    15

    0.0128

    0.0134

    20

    0.0357

    0.0298

    Frequency (Hz)

    5

    0.00188

    0.00192

    10

    0.00294

    0.00291

    15

    0.0128

    0.0134

    20

    0.0357

    0.0298

    Table No.7 Case 5-Composite as Isolation

    is imported in the Workbench GUI of Ansys 14.5 and similar boundary conditions are applied on the geometry as in real practice to obtain the result of Acceleration values at the Bearing Location (1 and 2). These numerical results is compared with experiment values to find the agreement.

    Location 1

    Bearing 2

    Location 2

    1. CAD and Geometry Modification C. Meshing and Material Properties

      Fig No.6 Point mass geometry of motor and unbalance mass

      In real practice only rotation unbalance mass on shaft is responsible for creating unbalance in the system, motor is

      Meshing Details:

      Fig No.8 Meshing

      only used as a prime mover and is not involve in vibration generation. So to obtain the similar boundary conditions in GUI of Ansys we replace the motor geometry and unbalance mass by point mass of 25 kg and 0.1 kg connected at the foundation base plate of the setup and disc respectively.

    2. Boundary Conditions

      1. Fixed support at base

      2. Rotation of unbalance shaft at different frequencies Fig No.7 Boundary Conditions

    In boundary condition we have kept a fixed support at the stands of base plate. As fig (b) shows that the shaft is made to rotate between the two supporting bearings at different frequency (i.e. 5Hz, 10Hz, 15Hz and 20Hz) about y-axis of the GUI. Such Boundary condition gives nearly an identical working environment as that in real practical approach.

    1. No of Nodes: 88369

    2. No of Elements: 32854

    3. Elements Type: Mixed (Tri and Brick) Table No.8: Material Properties

    Material Name

    Youngs Modulus (GPa)

    Poisons ratio

    Density (kg/m3)

    MS

    210

    0.3

    7850

    Natural rubber

    4.5

    0.48

    930

    Flexible PVC

    1.4

    0.39

    915

    Silicon Rubber

    0.05

    0.49

    930

    1. FEM Results

      Fig No.9 Sample FEA Result for Bearings Location 1 and 2

      After the Ansys solver has completed the analysis part we can plot the result for the Ansys in the form of contour plot as shown in the Fig No.9.

      Use the probe pointer to indicate the values of acceleration obtained a bearings Location 1 and 2. Tabulated values of acceleration at Bearing 2 are shown in the below given tables for different cases as mentioned above.

    2. FEM Values

    Frequency (Hz)

    5

    0.00229

    0.00229

    10

    0.00427

    0.00427

    15

    0.01891

    0.01890

    20

    0.04829

    0.0482

    Frequency (Hz)

    5

    0.00229

    0.00229

    10

    0.00427

    0.00427

    15

    0.01891

    0.01890

    20

    0.04829

    0.0482

    Table No.9: Case 1-No Isolation

    2. Bearing 2-Location 2

    Location 1

    Bearing 2

    Location 2

    Frequency (Hz)

    5

    0.00167

    0.001675

    10

    0.00301

    0.00300

    15

    0.01499

    0.01499

    20

    0.04148

    0.04148

    Frequency (Hz)

    5

    0.00167

    0.001675

    10

    0.00301

    0.00300

    15

    0.01499

    0.01499

    20

    0.04148

    0.04148

    Table No.10: Case 2-Natural Rubber as Isolation

    Location 1

    Bearing 2

    Location 2

    Table No.11: Case 3-Silicon Rubber as Isolation

    Frequency (Hz)

    5

    0.00134

    0.001341

    10

    0.00213

    0.002137

    15

    0.01260

    0.012601

    20

    0.02681

    0.026798

    Frequency (Hz)

    5

    0.00134

    0.001341

    10

    0.00213

    0.002137

    15

    0.01260

    0.012601

    20

    0.02681

    0.026798

    Table No.12: Case 4-Flexible PVC as Isolation

    Fig No 11: FEM-Acceleration at Bearing 2 Location 2 Vs Frequency

    Frequency (Hz)

    Bearing 2

    Location 1

    Location 2

    5

    0.001502

    0.00150

    10

    0.002640

    0.002641

    15

    0.013135

    0.013124

    20

    0.041131

    0.041102

    Frequency (Hz)

    Bearing 2

    Location 1

    Location 2

    5

    0.001502

    0.00150

    10

    0.002640

    0.002641

    15

    0.013135

    0.013124

    20

    0.041131

    0.041102

    VIII. RESULTS COMPARISIONS

    We can compare the value of all the cases with respect to particular point and find the % error between the experiment results and FEM results with each other.

    The tabulated data for each Case is mentioned below in the form of table as given below.

    Location 1

    Bearing 2

    Location 2

    Case 1: No Isolation

    Table No 14: No Isolation- Exp. and FEM Error

    Bearing 2 Location 1

    Frequency (Hz)

    Experiment Value

    FEM Value

    % Error

    5

    0.00279

    0.00229181

    17.8561

    10

    0.00525

    0.00427332

    18.6033

    15

    0.0145

    0.01891268

    -30.4322

    20

    0.0585

    0.04829682

    17.44133

    Bearing 2 Location 2

    Frequency (Hz)

    Experiment Value

    FEM Value

    % Error

    5

    0.00205

    0.00229263

    -11.8355

    10

    0.00619

    0.00427332

    30.9640

    15

    0.0153

    0.01890554

    -23.5656

    20

    0.0456

    0.04829274

    -5.90513

    Bearing 2 Location 1

    Frequency (Hz)

    Experiment Value

    FEM Value

    % Error

    5

    0.00279

    0.00229181

    17.8561

    10

    0.00525

    0.00427332

    18.6033

    15

    0.0145

    0.01891268

    -30.4322

    20

    0.0585

    0.04829682

    17.44133

    Bearing 2 Location 2

    Frequency (Hz)

    Experiment Value

    FEM Value

    % Error

    5

    0.00205

    0.00229263

    -11.8355

    10

    0.00619

    0.00427332

    30.9640

    15

    0.0153

    0.01890554

    -23.5656

    20

    0.0456

    0.04829274

    -5.90513

    Table No.13: Case 5-Composite as Isolation

    Frequency (Hz)

    Bearing 2

    Location 1

    Location 2

    5

    0.001537

    0.001536

    10

    0.002681

    0.002681

    15

    0.013614

    0.013617

    20

    0.032559

    0.032515

    All the reading in the above table are for the magnitude of acceleration in g unit terms. All the values are measured at Bearing 2 Location 1 (at the top of the bearing housing surface) and Location 2 (at the surface of IC block and bearing housing mountings base) as shown in fig 3 (a) and (b)

  6. GRAPHICAL REPRESENTATION

1. Bearing 2-Location 1

Fig No 10: FEM-Acceleration at Bearing 2 Location 1 Vs Frequency

Case 2: Natural Rubber as Isolator

Table No 15: Natural Rubber Isolation- Exp. and FEM Error

Bearing 2 Location 1

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00203

0.00167519

7.478

10

0.00332

0.00300551

9.472

15

0.0148

0.01499289

-1.303

20

0.0344

0.04148715

-20.602

Bearing 2 Location 2

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00198

0.00167539

15.384

10

0.00387

0.00300541

22.340

15

0.0132

0.01499187

-13.574

20

0.0427

0.04148715

2.840

Case 3: Silicon Rubber as Isolator

Table No 16: Silicon Rubber Isolation- Exp. and FEM Error

Bearing 2 Location 1

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00185

0.00150296

18.758

10

0.00315

0.00264066

16.169

15

0.0119

0.01313598

-10.386

20

0.0343

0.04113127

-19.916

Bearing 2 Location 2

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.0019

0.00150296

20.896

10

0.00324

0.00264076

18.495

15

0.0135

0.01312477

2.779

20

0.0396

0.04110272

-3.794

Case 4: Flexible PVC as Isolator

Table No 17: Flexible PVC Isolation- Exp. and FEM Error

Bearing 2 Location 1

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00117

0.00134154

-14.661

10

0.00247

0.00213794

13.443

15

0.0102

0.01260685

-23.596

20

0.0282

0.02681446

4.913

Bearing 2 Location 2

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00173

0.00134154

22.454

10

0.00202

0.00213733

-5.808

15

0.0158

0.01260165

20.242

20

0.0278

0.02679814

3.603

Case 5: Composite as Isolator

Table No 18: Composite Isolation- Exp. and FEM Error

Bearing 2 Location 1

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00188

0.00153712

18.238

10

0.00294

0.002681344

8.797

15

0.0128

0.013614231

-6.361

20

0.0357

0.032559539

8.796

Bearing 2 Location 2

Frequency (Hz)

Experiment Value

FEM Value

% Error

5

0.00192

0.001536916

19.952

10

0.00291

0.002681038

7.868

15

0.0134

0.01361729

-1.621

20

0.0298

0.032515691

-9.113

The results between experiment value and FEM value are mostly having the different of 5 to 15 % of error. This is because of small difference in the boundary conditions considered in FEM and Experiment situation. Some of the difference are consideration of point mass, consideration of joints and threaded volume, environmental disturbances sensed by accelerometer in during practical work.

But even if we consider the above differences in FEM or in experiment still there will some error due to some other random error present in the system which cannot be removed and hence we get the approximate value itself to conclude are work.

Fig No.12 No Isolation-Acceleration Vs Frequency at Bearing 2 Location 2

VII CONCLUSION

From the experimental and FEM results recorded in the result tables, variation in vibration acceleration magnitude, reduction in vibration acceleration magnitude & graphs of similar cases are plotted & observed in previous chapter. From these results following conclusions were made;

  • Undoubtedly the Viscoelastic material shows its utility as a vibration damping material and can be used as vibration isolators in variety of applications.

  • For all the cases flexible PVC and silicon rubber gives better results than natural rubber, when compared for vibration magnitude.

  • For all cases of natural rubber, variation in magnitude is more as compared to silicon rubber, flexible PVC and composite material i.e. Flexible PVC gives less variation.

  • At bearing 2 for all the cases considered operating speed flexible PVC gives better result when compared with natural rubber & Silicon rubber and composite material for vibration magnitude, % reduction & variation in magnitude.

  • During the case of mass unbalance where vibration amplitude increases substantially, and the force frequency decreases, when the isolators are provided and is least for PVC when all the cases are running at one constant speed.

  • From the FEM analysis also we get that the acceleration magnitude reduces more for viscoelastic material and is least for PVC.

REFERENCES

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  3. Panda, K.C.,Dutt J.K., Design of Optimum Support Parameters for Minimum Rotor Response and Maximum Stability Limit, Journal of Sound and Vibration, 223 (1), pp. 1-21, May 1999.

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  7. N. Venugopal, C.M. Chaudhari, Nitesh P. Yelve, An Investigation on Vibration of Visco-elastic materials by Using Taguchi Method & ANOVA, NCRTM 2006.

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  9. Severino P. C. Marques, Guillermo J. Creus, Computational Viscoelasticity, Springer Heidelberg Dordrecht London, New York, pp. 3, 2012.

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