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Damping Test Methodologies
Charles Moritz, Blachford Inc.
Tom Lewis, Damping Technologies, Inc.
Richard Fridrich, Fridrich Acoustical Consulting
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Damping Not Dampening
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Roof
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Roof
Doors
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Roof
DoorsBrakes
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Roof
DoorsBrakes
Aircraft
Fuselage
Damping Test Methodo logies
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Where is damping used?
Cars & Trucks Floor
Dash panel
Roof
DoorsBrakes
Aerospace
Fuselage
Engine Nacelle
Spacecraft
Damping Test Methodo logies
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Where is damping used?
Damping Test Methodo logies
Photo courtesy American Acoustical Products
Marine
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Where is damping used?
AppliancesSinks
Etc.
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Damping Test Methodologies
Damping Test Methodo logies
It is important to have techniques to:
Rank order the effectiveness of alternate dampingmaterials
Evaluate new materials
Characterize damping materials for modeling
Provide information for specifications
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Equations of Motion Spring mass damper system
tj
m Fesxdt
dx
Rtd
xd
m
2
2
Steady State Solution
)(
smjRj
Fex
m
tj
Rm
s
mx(t)
F(t)
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Steady State Solution
If you know the force input and response, youcan measure the damping but only atresonances
Measurement of the transfer function at resonance isthe basis for many damping measurementtechniques
Oberst Bar (SAE J1637, ASTM E-756)
Center Point (ISO 16940)
Modal Analysis
Damping Test Methodo logies
)(
smjRj
Fex
m
tj
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Transient Solution
)cos(2
tAex dt
mRm
A and depend on the initial conditions
Systems with low damping take a long time toreach steady-state
Damping can be determined from the transient
solution by exciting a system at resonance andmeasuring the decay time
Damping Test Methodo logies
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Geiger Plate SAE J671
Excite a 20 x 20 x 1/4 thick steel plate at its
resonance (100-200 Hz) and measure thedecay time
Photo courtesy Kolano and Saha Engineers
Damping Test Methodo logies
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Geiger Plate
Can examine how various application strategiesaffect damping
Substrate is thicker than in many applications so
the results may not compare wellDamping is determined at one frequency and
temperature based on the decay rate
Complex Modulus information is not obtained
Damping Test Methodo logies
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Temperature/Frequency Dependence
Damping Test Methodo logies
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
-35 -15 5 25 45
Temperature (C)
CompositeLossFactor
200 Hz 400 Hz 800 Hz
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Oberst Bar - SAE J1637/ASTM E-756
Clamp Beam Exciter
Damping Test Methodo logies
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Oberst Bar - SAE J1637/ASTM E-756
Sample FRF with Low-Level Damping
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Oberst Bar - SAE J1637/ASTM E-756
Sample FRF with Increased Damping
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Oberst Bar - SAE J1637/ASTM E-756
Calculations are more complex than Geiger Plate
Damping is determined at several frequencies
Test equipment can be placed in an environmental
chamber for damping measurement at varioustemperatures
ASTM E-756: measure dynamic mechanical propertiessuch as the material loss factor and complex
modulus by measuring both bare and damped bars.Results can be used for making predictions
Damping Test Methodo logies
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Center Point ISO 16940
Developed to measure the damping inlaminated glass
Technique is now utilized for many types of
materials
Photo courtesy Kolano and Saha Engineers
Damping Test Methodo logies
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Center Point ISO 16940
Using an impedancetransducer measure theforce and response of thebeam at resonance
Measure the damping basedon the transfer function
Can determine the compositeloss factor, bending,rigidity modulus, and
flexural rigidity ratio Photo courtesy Kolano and Saha Engineers
Damping Test Methodo logies
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Center Point ISO 16940
Can also be expanded to plates to measure thedamping from non-traditional materials suchas fibrous materials or floor systems
Damping Test Methodo logies
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Modal Analysis
Used to measure the response of a structure tovarious inputs
Figures courtesy of Dr. Dan Russell, Kettering University
Damping Test Methodo logies
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Modal Analysis
Animation courtesy of Dr. Dan Russell
Kettering University
Need to make sure the response isdue to a structural resonance
Measurement of the actualapplication
Analysis software may not beoptimized for damping and useradjustments may be needed
Difficult to measure the responseat different temperatures
Damping Test Methodo logies
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Summary
Damping is used in many applicationsCurrent test methods provide for rank ordering, new
material evaluation, material properties for modeling,etc.
Real-world damping materials add mass and stiffness aswell as damping making it difficult to evaluate in-situ
Damping Characteristics vary by temperature andfrequency
Trends due to difficulties in measuring actual applicationsindicate increased use of math modeling and greater
demand for damping material properties
Damping Test Methodo logies