charles t moritz

8/12/2019 Charles t Moritz

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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



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Cars & Trucks Floor

Dash panel

Roof



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Cars & Trucks Floor

Dash panel

Roof

Doors



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Cars & Trucks Floor

Dash panel

Roof

DoorsBrakes



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Cars & Trucks Floor

Dash panel

Roof

DoorsBrakes

Aircraft

Fuselage



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Cars & Trucks Floor

Dash panel

Roof

DoorsBrakes

Aerospace

Fuselage

Engine Nacelle

Spacecraft



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Photo courtesy American Acoustical Products

Marine


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AppliancesSinks

Etc.



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Damping Test Methodologies


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


)(

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



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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



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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



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Temperature/Frequency Dependence


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



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Sample FRF with Low-Level Damping



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Sample FRF with Increased Damping



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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



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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



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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



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Can also be expanded to plates to measure thedamping from non-traditional materials suchas fibrous materials or floor systems



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Modal Analysis

Used to measure the response of a structure tovarious inputs

Figures courtesy of Dr. Dan Russell, Kettering University



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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



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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


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