What’s up with Bump Testing ?

By: Jack D. PetersConnection Technology Center, Inc

590 Fishers Station DriveVictor, New York 14564

(585) 924-5900 x834

www.ctconline.com

Jack D. Peters

Bump Testing

2

What is a bump test ?

A bump test is the measured response of an impact to an object.The force of the impact is not controlled or measured.The response of the object is not controlled, BUT IS MEASURED.A single channel response measurement.

Jack D. Peters

Bump Testing

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Why do a bump test ?

To excite and measure the natural frequency(s) of an object.

To identify a resonanceTo understand a change in massTo understand a change in stiffnessTo understand a change in damping

Jack D. Peters

Bump Testing

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How does it work ?

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1

8V

-8

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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Sine Waves ?

EmptyEmptyEmptyEmptyEmptyEmptyEmptyEmptyEmpty

0.1V

-0.1

Real

s1.999023 0 s

Fundamental 1

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Bump Testing

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Bumps from Sine Waves ?

0.1V

-0.1

Real

s1.999023 0 s

Time Record 1

8V

-8

Real

s1.999023 0 s

Time Record 1

Jack D. Peters

Bump Testing

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100th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1

8V

-8

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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50th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1Bump 1

4V

-4

Real

s1.999023 0 s

Fundamental 1

Jack D. Peters

Bump Testing

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20th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 1

EmptyEmpty

2V

-2

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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10th Harmonic

5th Harmonic 110th Harmonic 1

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1

EmptyEmptyEmpty

1V

-1

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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5th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 1

EmptyEmptyEmptyEmpty

0.5V

-0.5

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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4th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1

EmptyEmptyEmptyEmptyEmpty

0.4V

-0.4

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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3rd Harmonic

Fundametal 12nd Harmonic 13rd harmonic 1

EmptyEmptyEmptyEmptyEmptyEmpty

0.3V

-0.3

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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2nd Harmonic

Fundamental 12nd Harmonic 1

EmptyEmptyEmptyEmptyEmptyEmptyEmpty

0.2V

-0.2

Real

s1.999023 0 s

Bump 1

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Bump Testing

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Fundamental

EmptyEmptyEmptyEmptyEmptyEmptyEmptyEmptyEmpty

0.1V

-0.1

Real

s1.999023 0 s

Fundamental 1

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Bump Testing

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2nd Harmonic

Fundamental 12nd Harmonic 1

EmptyEmptyEmptyEmptyEmptyEmptyEmpty

0.2V

-0.2

Real

s1.999023 0 s

Bump 1

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Bump Testing

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3rd Harmonic

Fundametal 12nd Harmonic 13rd harmonic 1

EmptyEmptyEmptyEmptyEmptyEmpty

0.3V

-0.3

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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4th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1

EmptyEmptyEmptyEmptyEmpty

0.4V

-0.4

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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5th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 1

EmptyEmptyEmptyEmpty

0.5V

-0.5

Real

s1.999023 0 s

Bump 1

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Bump Testing

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10th Harmonic

5th Harmonic 110th Harmonic 1

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 1

EmptyEmptyEmpty

1V

-1

Real

s1.999023 0 s

Bump 1

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Bump Testing

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20th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 1

EmptyEmpty

2V

-2

Real

s1.999023 0 s

Bump 1

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Bump Testing

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50th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1Bump 1

4V

-4

Real

s1.999023 0 s

Fundamental 1

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Bump Testing

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100th Harmonic

Fundamental 12nd Harmonic 13rd Harmonic 14th Harmonic 15th Harmonic 110th Harmonic 120th Harmonic 150th Harmonic 1100th Harmonic 1

8V

-8

Real

s1.999023 0 s

Bump 1

Jack D. Peters

Bump Testing

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How does it work ?

Bump testing or impact testing works because the bump or impact contains all of the individual frequencies or sign waves.When you bump or impact the object under test, you will excite all of the natural frequencies of that object.

Jack D. Peters

Bump Testing

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What do you impact with ?

Pin Drops !High frequency contentLow energy value

Cow Plops !Low frequency contentHigh energy value

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Bump Testing

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Energy Value vs. Frequency

The item used to deliver the impact to the object under test will determine the energy that is delivered to the object.

Large objects with considerable mass should be impacted with rubber or wood. This will generate high energy low frequency responses. (cow plops)Small objects with considerable stiffness should be impacted with metal or hard plastics. This will generate low energy high frequency responses. (pin drops)

Jack D. Peters

Bump Testing

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Set-up

UNIFORM WINDOWTake your time – Bump aroundDo not over range or clip the input signal800 – 1600 lines of resolutionTry some different frequency spansOnly 1 bump for each time recordAbout 4 averages (depends on noise)

Jack D. Peters

Bump Testing

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Why the Uniform Window ?

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Bump Testing

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What to Bump ?

1” diameter steel round stock

36” length

Clamped in “V” blocks at each end

CTC AC140 accelerometer stud mounted on center (100 mV/g)

Jack D. Peters

Bump Testing

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Bump It ! Two Responses !

2G

-2

Real

s1 0 s

Time Record 1 TIME4.63

0.015G

rms

0

Real

Hz100 0 Hz

Auto Pwr Spec 1 HZ4.63

dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G

X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG

Time Waveform

Frequency Spectrum

Jack D. Peters

Bump Testing

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Mental Health Check !

2G

-2

Real

s1 0 s

Time Record 1 TIME4.63

0.015G

rms

0

Real

Hz100 0 Hz

Auto Pwr Spec 1 HZ4.63

dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G

X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG

Time Waveform

Frequency Spectrum

76.17 msec/5 = 15.23 msec

F = 1/0.01523 sec = 65.64 Hz

65.5 Hz

Jack D. Peters

Case History

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CASE HISTORY

Bumps in the Road !

Jack D. Peters

Case History

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So Easy !!!!!!

0.6G

rms

0

Real

Hz200 0 Hz

Auto Pwr Spec 1 HZ3.63

4.5G

-4.5

Real

s3.998047 0 s

Time Record 1 TIME3.63

X:109 Hz Y:539.6552 mG

Time Waveform

Frequency Spectrum

109 Hz

Jack D. Peters

Case History

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Zoom

0.3G

rms

0

Real

Hz150 50.00001 Hz

Auto Pwr Spec 1 HZ1.63

2G

-2

Real

s8 0 s

Time Record 1 TIME1.63

X:109.125 Hz Y:214.7374 mG

dX:554.6875 ms dY:-729.2974 mGX:164.0625 ms Y:1.379613 G

Time Waveform

Frequency Spectrum

109.125 Hz

Jack D. Peters

Case History

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Zoom & Mental Health Check

0.3G

rms

0

Real

Hz150 50.00001 Hz

Auto Pwr Spec 1 HZ1.63

2G

-2

Real

s8 0 s

Time Record 1 TIME1.63

X:109.125 Hz Y:214.7374 mG

dX:554.6875 ms dY:-729.2974 mGX:164.0625 ms Y:1.379613 G

Time Waveform

Frequency Spectrum

109.125 Hz

554 msec/5 = 110.8 msec

F = 1/0.1108 sec = 9.02 Hz What

the

He_ _ !

Jack D. Peters

Case History

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So Easy ??????

0.6G

rms

0

Real

Hz200 0 Hz

Auto Pwr Spec 1 HZ3.63

4.5G

-4.5

Real

s3.998047 0 s

Time Record 1 TIME3.63

X:109 Hz Y:539.6552 mG

Time Waveform

Frequency Spectrum

109 Hz

Jack D. Peters

Case History

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What’s This ?

0.6G

rms

0

Real

Hz200 0 Hz

Auto Pwr Spec 1 HZ3.63

4.5G

-4.5

Real

s3.998047 0 s

Time Record 1 TIME3.63

X:109 Hz Y:539.6552 mG

Time Waveform

Frequency Spectrum

109 Hz????

Jack D. Peters

Case History

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Log – Can’t Live With It, Can’t Live Without It !

4.5G

-4.5

Real

s3.998047 0 s

Time Record 1 TIME3.63

1G

rms

1E-05

Mag (Log)

Hz200 0 Hz

Auto Pwr Spec 1 HZ3.63X:109 Hz Y:539.6552 mGX:11 Hz Y:12.05162 mG

Time Waveform

Frequency Spectrum

Log "Y" Scale

109 Hz11 Hz

Jack D. Peters

Case History

39

0 – 50 Hz Span

0.008G

rms

0

Magnitude

Hz50 0 Hz

Auto Pwr Spec 1 HZ2.63

0.4G

-0.4

Real

s15.99219 0 s

Time Record 1 TIME2.63

X:10.8125 Hz Y:2.774957 mG

Time Waveform

Frequency Spectrum

10.81 Hz

Jack D. Peters

Case History

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0 - 50 Hz (expanded “x” scale)

0.008G

rms

0

Magnitude

Hz50 0 Hz

Auto Pwr Spec 1 HZ2.63

0.4G

-0.4

Real

s4 0 s

Time Record 1 TIME2.63

X:10.8125 Hz Y:2.774957 mG

dX:460.9375 ms dY:-131.8069 mGX:148.4375 ms Y:152.3216 mG Time Waveform

Frequency Spectrum

10.81 Hz

460.9 msec/5 = 92.18 msec

F = 1/0.09218 sec = 10.84 Hz

Jack D. Peters

Bump Testing

41

Back to Bump Testing

2G

-2

Real

s1 0 s

Time Record 1 TIME4.63

0.015G

rms

0

Real

Hz100 0 Hz

Auto Pwr Spec 1 HZ4.63

dX:76.17188 ms dY:-1.36474 GX:23.4375 ms Y:1.63297 G

X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG

Time Waveform

Frequency Spectrum

76.17 msec/5 = 15.23 msec

F = 1/0.01523 sec = 65.64 Hz

65.5 Hz

Jack D. Peters

Amplification Factor

42

Using the Time Waveform

Log decrement = [1/n[LN(A0/An)]] = [1/5[LN(1.633/0.268)]] = 0.36

Damping ratio = Log dec/2Pi = 0.36/2Pi = 0.36/6.28 = 0.057

Amplification factor = 1/(2*Damping) = 1/(2*0.057) = 8.68

2G

-2

Real

s1 0 s

Time Record 1 TIME4.63X:99.60938 ms Y:268.2297 mGX:23.4375 ms Y:1.63297 G Time Waveform

A0 = 1.633 GAn = 0.268 G

n = 5 cyclesLN = natural log

F = 1/0.01523 sec = 65.64 Hz

Jack D. Peters

Amplification Factor

43

Using the Spectrum

0.015G

rms

0

Real

Hz100 0 Hz

Auto Pwr Spec 1 HZ4.63X:70.75 Hz Y:8.475402 mGX:65.5 Hz Y:12.23725 mGX:58.75 Hz Y:8.550765 mG Frequency Spectrum

F = 65.5 Hzf2 = 70.75 Hzf1 = 58.75 Hz

-3dB

Find the –3dB points = AF * .707 = 12.24 mG * .707 = 8.65 mG

Find the frequencies at the –3dB points (f1 and f2)

Amplification factor = F/ (f2 - f1) = 65.5/(70.75 – 58.75) = 5.46

Jack D. Peters

Mass & Stiffness

44

Fn = 1/2Pi k/m

INCREASE the stiffness ( k )

INCREASE the frequency (F)

INCREASE the mass ( m )

DECREASE the frequency ( F )

Jack D. Peters

Damping

45

Control the Response

Un-Damped

Damped

Jack D. Peters

Bump Testing

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Summary

Take your timeChoose your weaponBump aroundUniform WindowLook at the time waveformLook at the frequency spectrum

Do a mental health checkCalculate the amplification factorChange the massChange the stiffnessAdd dampingBump around

Jack D. Peters

Thank You !

47

Thank You !

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