An Experimental Evaluation of the Application of Smart Damping Materials for Reducing Structural Noise and Vibrations Kristina M. Jeric Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science In Mechanical Engineering Mehdi Ahmadian, Chair Harley H. Cudney, Daniel J. Inman April 23, 1999 Blacksburg, Virginia Keywords: Structural Vibration, Piezoceramic, Piezoelectric, Passive Damping, Shunt Circuits, Vehicle Noise, Structural Noise Copyright 1999, Kristina M. Jeric
An Experimental Evaluation of the Application of Smart Damping Materials for Reducing Structural Noise and Vibrations Kristina M. Jeric (ABSTRACT) This study evaluates the application of smart damping materials for reducing structural noise and vibrations. The primary purposes of this study are to: 1. Explore the feasibility of smart damping materials, such as piezoelectric materials, for augmenting and improving the noise and vibration benefits of passive damping materials and 2. Provide a preliminary evaluation of the noise and vibration benefits, and weight savings of smart damping material as compared to conventional damping treatments. To achieve the objectives of the study, a special test rig, designed to measure both vibrations and structure-borne noise of a test plate, was constructed and validated in the early stages of the study. Upon validating the test rig and the instrumentation that was set up for data collection and processing, a series of tests were performed. The tests were intended to establish a baseline for the test rig and compare the performance of smart damping materials with a number of passive interior automotive treatments. Further, in order to evaluate the effect of smart damping materials on the sound transmission loss, a series of tests were conducted according to the SAE J1400 test specifications. The tests evaluate the transmission loss for smart damping materials for an undamped and a damped plate. The passive damping technique used for this study involved attaching piezoelectric patches with resonant electrical shunts. The vibration modes of the plate were determined both analytically and experimentally, using laser measurement techniques, in order to determine effective placement of the piezoceramic materials. Three piezoceramic patches were applied to control four structural resonance frequencies of the plate. The tests show that smart damping materials have substantial performance benefits in terms of providing effective noise and vibration reduction at a frequency range that is often outside the effective range of passive damping materials. Further, judging by the acceleration and noise reduction per added weight, the test results indicate that smart damping materials can decrease the vibration peak of a steel plate at 151 Hz by up to 16.24 db with an additional weight of only 0.11 lb. The addition of constrained-layer damping (CLD) can decrease that same peak by 18.65 db, but it weighs 10 times more. This feature of smart damping materials is particularly useful for solving particular noise or vibration problems at specified frequencies, without adding any weight to the vehicle or changing the vehicle structure.
Acknowledgements The successes of this project have been the result of tireless efforts on the part of many at Virginia Tech and Lear Corporation. First, I would like to thank my advisor and mentor, Dr. Mehdi Ahmadian, for all his time, effort, encouragement, and enthusiasm throughout my graduate studies in the Mechanical Engineering Department. I would also like to thank Drs. Daniel J. Inman and Harley C. Cudney for serving on my graduate committee. The financial and technical support provided by Lear Corporation is greatly acknowledged. In particular, I am indebted to Dr. Barry Wyerman who provided much of the materials that we needed for the tests, as well as practical insight and many useful suggestions for conducting the tests. I am grateful for all the help provided by Messrs Mark ZumMallen, John Gores, and Kevin Stone during the transmission loss tests at Lear Corporation. Additionally, the generous donations by 80/20 and PCB Piezoelectronics Inc. made the successful completion of this research possible. I would also like to greatly acknowledge the technical and design support of Dr. Robert West, Dr. Chul Hue Park, Dr. David Coe, Mr. Mark McEver, Mr. Chris Hobbs, and the Machine Shop Personnel at the Department of Mechanical Engineering. The support provided by the Advance Vehicle Dynamics Laboratory (AVDL) and the Center for Intelligent Material Systems and Structures (CIMMS) at Virginia Tech throughout the course of this study is also greatly acknowledged. Finally, I would like to express my appreciation to my parents, Anthony and Rosemarie Jeric, and my brother, Steve, for their endless love and support during my years at Virginia Tech. Their love, as well as the camaraderie of many good friends, made this journey absolutely wonderful.
Contents 1 Introduction.... 1 1.1 Introduction... 1 1.2 Research Objectives... 2 1.3 Approach... 3 1.4 Outline.... 3 2 Background.... 4 2.1 Piezoelectric Theory... 4 2.2 Applications for Piezoceramics... 5 2.3 Literature Search... 6 2.3.1 Control of Structural Noise and Vibration with Smart Materials.. 7 2.3.2 Vehicle Vibration and Noise Control Using Smart Materials... 8 2.3.3 Increasing Transmission Loss with Piezoceramics... 8 2.3.4 Passive Damping Using Shunted Piezoceramics... 9 2.4 Shunt Circuit Design... 12 2.4.1 Shunt Tuning... 14 2.5 Summary... 17 3 Experimental Setup... 18 3.1 Test Stand Design... 18 3.1.1 Bottom Box Enclosure... 19 3.1.2 Top Box Enclosure... 22 3.1.3 Excitation Frame... 22 3.1.4 Electromagnetic Shaker... 25 3.1.5 Total Test Stand Assembly... 25 3.2 Test Setup... 26 3.2.1 Test Plate Setup... 26 3.2.2 Transducer Arrangement... 28 3.2.3 Data Acquisition System... 28 3.3 Validation Tests... 30 3.3.1 Vibration Response Validation... 30 iv
3.3.2 Acoustic Response Validation... 33 3.3.3 Repeatability and Linearity... 34 3.4 Summary... 36 4 Baseline Tests and Smart Plate Development... 37 4.1 Baseline Tests... 37 4.2 Test Plate Vibration Characteristics... 37 4.2.1 Test Plate Resonance Frequencies... 38 4.2.2 Test Plate Mode Shapes... 38 4.2.2.1 Analytical Mode Shapes... 38 4.2.2.2 Experimental Mode Shapes... 40 4.3 Test Plate Acoustic Characteristics... 43 4.4 Smart Plate Development... 46 4.4.1 PZT Placement and Application... 46 4.4.2 Attaching PZTs to Structures... 47 4.4.3 Smart Damping Plate Test Setup... 49 4.5 Summary... 50 5 Smart Damping Test Results and Benefits... 51 5.1 Vibration Benefits of Smart Damping for Undamped Plates... 52 5.1.1 Third-Octave Analysis... 50 5.2 Acoustic Benefits of Smart Damping for Undamped Plates... 55 5.2.1 Third-Octave Analysis... 57 5.3 Benefits of Smart Damping for Damped Structures... 61 5.3.1 Vibration Benefits of Adding Smart Damping to Damped Structures... 62 5.3.2 Acoustic Benefits of Adding Smart Damping to Damped Structures... 65 5.4 Weight Saving Benefits of Smart Damping Materials... 68 5.5 Summary... 73 6 Transmission Loss Tests... 74 6.1 Test Setup... 74 v
6.2 Transmission Loss Calibration Tests... 75 6.3 Transmission Loss Testing and Results... 77 6.3.1 Tuning the PZT Shunts... 77 6.3.2 Transmission Loss Test Results... 79 6.4 Summary... 83 7 Conclusions.... 85 7.1 Summary... 85 7.2 Recommendations for Future Research... 85 References... 87 Appendix A... A1 Appendix B...B1 Appendix C...C1 Appendix D.... D1 Vita... vi
List of Figures 2.1 Basics Symbols and Terminology in Piezoelectricity... 5 2.2 Literature Search Flowchart... 7 2.3 Shunt Circuit Design Concepts Used by Hagood and Wu... 10 2.4 Shunting of Piezoelectric Materials (Single Shunt)... 12 2.5 Operational Amplifier Circuit Emulating a Variable Inductance... 13 2.6 Experimental Shunt Circuit Board... 14 2.7 Single Shunt Circuit and Power Supply Configuration... 14 3.1 Vibration and Acoustics Test Stand Schematics... 19 3.2 Frame for Bottom Box Enclosure... 20 3.3 Section View of Bottom Box Enclosure Side... 21 3.4 Front Side of Bottom Box Enclosure with Door... 21 3.5 Inside of Reception Chamber... 22 3.6 Excitation Frame... 23 3.7 Excitation Frame Mount to Bottom Box... 24 3.8 Clamping Frame on Excitation Frame... 24 3.9 Electromagnetic Shaker and Stinger Rod Assembly... 25 3.10 Total Test Stand Assembly... 26 3.11 Standard Test Plate in Testing Position... 27 3.12 Acoustic Barrier Arrangement... 27 3.13 Microphone Placement in the Reception Chamber... 28 3.14 Shaker Table Test Stand and Data Acquisition Schematic... 29 3.15 Periodic Chirp Signal Generated by HP Analyzer... 30 3.16 Frame Acceleration Response without Test Plate Installed... 31 3.17 Effect of Test Plate on Frame Acceleration Response... 32 3.18 Sample Frequency Response Function Data for Standard Test Plate... 32 3.19 Sample Sound Pressure Levels with and without Plate... 33 3.20 Sample Frequency Response Function Data for Standard Test Plate... 34 3.21 Linearity Tests Results for Two Levels of Frame Acceleration... 35 3.22 Repeatability Test Results for Standard Test Plate... 36 vii
4.1 Vibration Baseline Test Results for Undamped Plate... 38 4.2 Finite Element Model Results for Test Plate... 39 4.3 Initial Mode Shape Identification... 40 4.4 Standard Test Plate Response with Five Resonant Peaks Identified... 41 4.5 Laser Scanner Test Setup... 41 4.6 Velocity Field for Peak 3 at 147 Hz from Laser Scanning Measurements... 42 4.7 Acoustic Baseline Test Results for Undamped Plate... 43 4.8 Baseline Test Results Illustrating Vibration and Noise Correlation... 44 4.9 Velocity Field for Peak 2 at 121 Hz from Laser Scanning Measurements... 45 4.10 PZT Placement on the Test Plate... 46 4.11 PZT Placement and Shunting Strategy... 47 4.12 Vacuum Procedure Setup... 48 4.13 Smart Damping Plate Testing... 49 5.1 Test Plate Configurations Used to Evaluate the Benefits of Smart Damping... 51 5.2 Unshunted and Shunted Plate Vibration Response... 52 5.3 Effect of Adding Smart Material to an Undamped Plate... 53 5.4 Third-Octave Band Analysis of Vibrations for Undamped and Shunted Plates... 54 5.5 Decrease in Undamped Plate Vibrations (Third-Octave Band)... 54 5.6 Effect of Smart Damping on Structure-Borne Noise of an Undamped Plate... 56 5.7 Noise Reductions Due to Smart Damping for an Undamped Plate... 56 5.8 Third-Octave Band Analysis of Structure-Borne Noise for an Undamped Plate. 58 5.9 Decrease in Structure-Borne Noise for an Undamped Plate... 58 5.10 Third-Octave Band Analysis for Undamped and Shunted Plates... 59 5.11 Decrease in Acoustic Levels Using Smart Damping... 60 5.12 Correlation of Plate Vibration Reductions to Structure-Borne Noise Reductions... 60 5.13 Passive Treatments Used with Smart Damping Materials... 61 5.14 Vibration Benefits of Smart Damping Materials for a Damped Plate... 63 5.15 Vibration Decrease Due to Smart Damping Materials Applied to a Damped Plate... 64 5.16 Acoustic Benefits of Smart Damping Materials for a Damped Plate... 66 viii
5.17 Decrease in NSPL Due to Smart Damping Materials Applied to a Damped Plate... 67 5.18 Damping Treatments Applied to Test Plates... 69 5.19 Different Foam Pads and Carpeting Damping Treatments... 69 5.20 Decrease in Accelerations with Respect to Added Weight... 71 5.21 Decrease in Normalized Sound Pressure Levels with Respect to Added Weight 72 6.1 Floor Plan of Transmission Loss Test Facility... 74 6.2 Modified Test Window, Reverberation Room Side... 75 6.3 Modified Test Window with Barrier Material for Calibration Test... 76 6.4 Undamped Plate with Smart Damping in Modified Test Window, Reception Chamber Side... 78 6.5 Plate Vibrations with Unshunted and Shunted PZTs... 79 6.6 Sound Pressure in Reception Chamber Before and After Turning on Shunt Circuits... 80 6.7 Transmission Loss for Test Plate with Unshunted and Shunted PZTs... 80 6.8 Transmission Loss for Test Plate with Unshunted and Shunted PZTs... 81 6.9 Transmission Loss Results of Shunted and Unshunted PZT Plate with Constrained Layer Damping... 82 6.10 Increased Transmission Loss Normalized with Respect to Added Weight... 83 ix
List of Tables 4.1 Experimentally-Determined Mode Shape Results... 43 5.1 Effect of Smart Damping on Peak Vibrations... 53 5.2 Normalized Noise Level Reductions Due to Applying Smart Damping to an Undamped Plate... 57 5.3 Different Treatments Tested with Smart Damping... 68 5.4 Weights of Different Treatments... 70 x