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Why do we do a Sine Sweep Vibration Test?

- Part Responses to a Sine Wave Input are important to characterize a part/assembly for several reasons:
- Characterize Model Response
- Endurance Limits of Part(s)
- Actual characterized response under test, instead of Calculated
- Characterize response of Test Equipment so it can be “backed out” of the performance data
- General Investigation. If we don’t understand how a part will perform, or life of the part (related to Endurance) we can characterize it. A more well Known Phrase would be “Destructive Testing”

What is Sine Sweep Vibration?

- Wikipedia describes vibration as a Oscillatory motion about an equilibrium point.
- For a Sine Sweep Vibration it is a movement back in forth usually in one DOF. The movement is in a controlled oscillatory motion that can be defined as a sinusoidal function.
- The Sine Wave Amplitude, and rate at which you wish to “Sweep” through the range of frequencies of interest are programmed inputs into the Vibration Table you’ll be using for testing.

A Sine Sweep Signal Input

Types of Sine Sweeps

Typical Sine Sweep is a linear input

The Sinusoidal Signal input can be customized:

Y(t)=Sin{2}}

Non-Linear Sine frequency Change inputs are used if you want to spend less time testing at a certain frequency or range of frequencies for pragmatic reasons

A Sine Sweep Signal Input

- For a test engineer the parameters for a Sine Sweep input are already provided to you by an Analyst or exists as an industry standard input profile. Some materials, Parts, and Environments have been already well characterized
- It is Relevant to have an understanding that Displacement, Velocity, and Acceleration are related due to first Order Harmonic Oscillation in a Single DOF

Sine Sweep Signal Input

- In a single DOF we can derive the relationships to find our test parameters for Displacement, Velocity and Acceleration at any given frequency input.

Sine Sweep Signal Input

Displacement, Velocity, Help define your input signal normally shown as Acceleration

Sine Sweep Signal Response from Force Input

- As we’ve investigated through SolidWorks in HW 8 for class we found that there is a complex motion response of a part in all Degrees of freedom with a directed input at a coordinate axes.

Sine Sweep Signal Response

Calculated Response (Transmissibility) Relative to Q factor

Sine Sweep Signal Response

Digging further we know that Part under test will have a response through a range of frequencies through the Transmissibility relationship

Sine Sweep Signal Input (Actual)

- Previously we showed the way the Ramping of acceleration is determined.
- The area of inspection for the expected response about resonance is found In the Dwell area

Dwell Area

Ramping of Acceleration

MAX G Allowed

Sine Sweep Signal Response

Test Response of Two metal bars at different Lengths

Knowing this we can set a pre-determined Sine Sweep signal Input to the part under test.

We “Plateau” the area of interest in order to better further investigate the response area, and to have a Factor of Safety for the Acceleration input.

Response at Resonance

LET US NOT BREAK OUR PART

Vibration Test Set-Slip Table

One Example of Vibration table offering a Single DOF vibration Axis

Vibration Test Set-Slip Table

Example of a Slip Table

Things to note in Table setup

Control accel should be on the farthest edge of the table and as close as possible to the product.

Multiple Control Accels can be used and Averaged.

Accel should be Tri-axial in configuration

Table should already be characterized with support fixture

Vibration Test Set-Control Accel

Software by Unholtz-Dickie Corporation VWIN IIVibration Control & Analysis System

VibrationTest Set-Measurement Accels

- Parameters for individual Accel performance

Additional Homework

- The audience should take note that this is the simplest of vibration tests. It is worth your energy to dig further in and understand how other tests are performed and why.
- One in particular is called Random Testing. This is more representative of what the product will see In the real environment.

References

- Kevin Napolitano, and Daniel Linehan[Multiple Sine Sweep Excitation for Ground Vibration Tests], Proceedingsofthe IMAC-XXVII Society for Experimental Mechanics Inc, February 9-12, (2009).
- Connection Technology Center “Learn Basic Vibration Monitoring with CTCs Vibration University,” <https://www.ctconline.com/__ctc_university.aspx?one=1 >(2012).
- Dr. Paul Ibanez ANCO Engineers, Inc., "An Introduction to Shake Tables for Seismic Testing of Equipment And Glossary of Vibration Terminology," ancoengineers.com, October 1st,(2008).
- http://shodhganga.inflibnet.ac.in/bitstream/10603/2274/11/11_chapter%203.pdf, ch.3 Page 54
- Unholtz-Dickie Corporation, Fixture Design Notes
- Unholtz-Dickie Corporation, VWIN II / VWIN XL / VWIN VIBRATION CONTROLLER OPERATING MANUAL
- Tom Irvine, http://www.vibrationdata.com/tutorials.htm

Auxiliary Plot Units/Slope

Simply an Octave is a doubling of the Frequency limits (think musical instruments).

Auxiliary Plot Response Example-Dislacement

http://nptel.iitm.ac.in/courses/105101004/downloads/04%20Chapter.pdf

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