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September 14, 2016
Mike Wells
Sales Engineer, Intertek TT
31 Flavors of Vibration
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Mike Wells
Sales Engineer
Intertek Plymouth
Meet Your Presenter
Our Founding Father Thomas Edison founded ETL Testing Laboratories in 1896. Today, nearly 120 years later, Intertek is the trusted Industry Partner for safety, performance and product testing.
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Our Global Network and Capabilities
Global ATIC Business with over 40,000 Employees
100+ countries
1,000+ laboratories and offices
Global Market Leader in
Assurance
Global Market Leader in TIC
3,000 auditors
90,000 audits
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What We Do
What We Do Everyday Which Economic Sectors Where
Assurance
Testing
Inspection
Certification
Products
Trade
Resources 100+ countries
1,000+ laboratories 40,000+ people
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31 “Flavors” of Vibration
31 principles of vibration testing to be discussed
• Trivia
• Application
• Value
• Limitations
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What is Vibration?
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point.
Simply put, Vibration is the physical repetitive motion of some object either about or in relation to another point of reference.
Vibration can occur in six different directions (Degrees of Freedom)
• Three Orthogonal axes, ( X, Y, Z)
• Three Rotational directions about those axes • Yaw, Pitch, Roll
Understanding Vibration
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Trivia:
− Every product has many resonances or natural frequencies
− Often the most damage occurs to a product at the first natural frequency
Application:
− Identify resonance/model study
− Durability
− BSR
Value:
− Identifying the mode shapes (or lack of mode shapes) in a frequency range can help ensure a product will not experience excessive fatigue
Limitations:
− Real world is more than the first mode shape
− 2000-3000 Hz upper limit
− Multi-axis mode shapes can interact to cause more damage
1) Single Axis-Sine Sweep
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Trivia: − Every product has many resonances or
natural frequencies − Often the most damage occurs to a
product at the first natural frequency Application:
− Durability Value:
− Determines the minimum life or time to failure of a product subjected to the worst possible vibration frequency range for its geometry
Limitations: − Real world is more than the first mode
shape − 2000-3000 Hz upper limit − Multi-axis mode shapes can interact to
cause more damage
2) Single Axis- Sweep/Dwell
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3) Single Axis –Random
Trivia: − One of the most common forms of vibration − Often combined with Temperature and Humidity
Application: − Durability − Resonance search − BSR
Value: − Quickest and most readily available vibration testing − Many standards − Relatively simple setup
Limitations: − Real world is more than single axis – will miss
things − 2000-3000 Hz upper limit
G 2̂/hz
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0 500 1000 1500 2000
G 2̂/hz
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Random Vibration
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Trivia: −Many single axis machines can
be used in three directions. • Vertical • Horizontal • Lateral
Application: −Durability
Value: − Ensures that a product can
survive vibration from multiple directions
Limitations: −Can not find failures and fatigue
associated with simultaneous multi-axis vibration
− 2000-3000 Hz upper limit
4) Three Axis - Sequential, One Axis at a Time
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Trivia:
− Vibration and Temperature stress often concentrate at the same location on a product
− Other environmental stresses like sun load, power cycling, pressure cycling are easily added
Application:
− Durability
− Performance
Value:
− Determine the durability and performance of a product in a range of thermal and humidity conditions while vibrating
Limitations:
− Typically -60 to 155°C
− 2000-3000 Hz upper limit
− Multi-axis mode shapes can interact to cause more damage
− Adding some environmental stress are difficult:
• Altitude
• Toxic gasses
5) Single Axis with Temperature and Humidity
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Trivia:
− Velocity is the rate of change of position; acceleration is the rate of change of velocity; jerk is the rate of change of acceleration
Application:
− Simulate damage from dropping, shipping, or extreme environments such as military and aerospace applications
− The magnitude of the shock is only half the story, the shape of the shock is also important; sawtooth, trapezoid and many other shapes can define the impulse
Value:
− The impulse of a shock table can induce the natural frequencies in a product and cause dynamic pulses to pass through the product uncovering weaknesses in the design or the packaging that cannot be found any other way
Limitations:
− The smaller the payload the better; very large pay loads cannot reach very large impulses even though they are more likely to see large impulses in real life
6) Vertical Mechanical Shock
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7) Horizontal Mechanical Shock
Trivia: − Most shock comes from dropping or exploding but some times the shock comes
from a side impact or launch. In these cases the downward pull of gravity relative to the side impulse can change the way a product reacts.
Application: − Simulate damage from side impacts, explosion, or extreme environments such
as military and aerospace applications − The magnitude of the shock is only half the story, the shape of the shock is also
important, sawtooth, trapezoid and many other shapes can define the impulse Value:
− The impulse of a shock table can induce the natural frequencies in a product and cause dynamic pulses to pass through the product uncovering weaknesses in the design or the packaging that can not be found any other way
Limitations: − The smaller the payload the better; very large pay loads can not reach very
large impulses even though they are more likely to see large impulses in real life − With Horizontal shock, this limitation is even greater because gravity cannot
assist
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8) Single Axis – Sine on Random
Trivia:
− The same total energy applied in a sine vibration will do more damage, at one frequency, then the same energy applied randomly
Application:
− Simulating reciprocating engine environments
Value:
− Provides the specific sine vibration of a engine at a specific frequency while still providing energy at a range of other frequencies where other mode shapes may exist
Limitations:
−May require special controls
−Need to know the frequency of the source of the vibration
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9) Single Axis – Low Frequency Displacement
Trivia: − At low frequency, the displacement becomes more important than the vibration
energy − The physical displacement needed at 1Hz is exponentially greater than what is
needed at 10Hz for the same acceleration − May require long stock cylinders, push pull cables and other cyclic setups
instead of a vibration machine Application:
− Wire harnesses, tubing, connectors, doors, hinges, latches and other components with lots of potential motion
− Tall, High Center-of-Gravity item tip-over testing Value:
− Many low frequency failures are only reproduced with sufficient displacement − High energy at a high frequency will not produce the results needed
Limitations: − Difficult to combine with high frequency − Can require unique and custom setups
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Trivia: − Real world vibration is always six axis
(three linear directions, and three rotations) − There are failure modes the can only be
reproduced with multiple degrees of freedom
Application: − Simulating real world vibration profiles − Key Life Testing/ Full System Life Testing
Value: − Closest vibration environment to simulating
the real world − Can reproduce real world events accurately
in the laboratory Limitations:
− Most six axis systems are limited to 5Hz – 70 Hz. A few will go to 350 Hz. Real world goes out to thousands of Hz.
− Can require RLDA
10) Six Axis-Time Wave Form Replication
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11) Six Axis-Random (Controlled)
Trivia: − A PSD (Power Spectrum Density) works well on single axis but does not
contain “phase” information for multi axis −Uniform random vibration in six axis is sometimes called White noise or
Pink noise Application:
− Simulating real world vibration profiles − Key Life Testing / Full System Life Testing
Value: −When real world time histories are not available a reverse Fourier transform
can be performed on a spectrum to produce a simulated time history Limitations:
−Real world six axis time histories have specific event phase relationships that may be missed or deemphasized in a six axis random vibration
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Trivia: − Air hammer machines were first developed
from air hammers used on the sides of grain cars from railroads
Application: − Typically applied to solid state electronics to
activate modes shapes such as surface mount chips on electronics
− HALT and HASS testing Value:
− The only type of vibration machine able to achieve very high frequencies over 3000 Hz
Limitations: − Difficult to achieve low frequencies − No Control – Random only − May not be repeatable from one machine to
another − Failures in wire harnesses are often missed
by air hammer testing
12) Six Axis-Air Hammer
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13) Combined Six Axis – Air Hammer & Single Axis
Trivia: −A single axis machine is just like a giant speaker, you can even play
music through it
Application: −When controlled lower frequency vibration is needed along with very
high frequency (Solid state electronics with wire harnesses)
Value: −Broader frequency range brings two tests into one
Limitations: −The air hammer has to be custom setup and the vibration spectrum
custom designed into the fixture
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14) Combined Six Axis – Air Hammer & Servo Hydraulic
Trivia: − Servo hydraulics are limited in frequency by the speed of the servo valve.
The fastest servo valve operates at 2000 Hz providing a maximum controlled frequency of less then 1000 Hz.
−Most six axis machines are further limited by the natural frequency of the table and actuators
Application: −When controlled, lower frequency six axis vibration is needed along with
very high frequency (electronic controlled appliances or devices) Value:
− Broader frequency range brings two tests into one Limitations:
− The air hammer has to be custom setup and the vibration spectrum custom designed into the fixture
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Trivia: − There is an Failure Mode Verification
Testing (FMVT ) method and an FMVT machine − FMVT Machine is a 3 dimensional fractal
equation Application:
− Smaller components and products that require large displacement and some higher frequency
Value: − Low frequency (up to 4” peak to peak)
combined with a broader spectrum out to 2,500 Hz and beyond
− Up to 60 g’s peak vibration and impulses Limitations:
− 100 lbs maximum limit, random only
15) Six Axis – FMVT®
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What Kind of Vibration Do You Use?
Single axis only? Six axis only? Both six axis and single axis?
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16) Bearing Fretting – Multi-axis Motion and Vibration Hybrid
Trivia: −Sometimes low frequency, low displacement is more damaging than the
higher displacement − In fact, sometimes no vibration is more damaging
Application: −Bearings, especially roller and ball bearings −Simulates small displacement oscillations that can damage bearings
designed to turn continuously Value:
−Only successful method for reproducing certain types of chronic bearing failures
Limitations: −Requires a custom setup
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Trivia: −Most BSR testing is conducted on
regular electro-dynamic (ED) vibration machines
Application: − Subjective measurement of
buzzing, squeaking and rattling of components and systems
Value: − Testing is done using existing ED
single axis shakers on the same fixtures used for vibration testing
Limitations: −Difficult to get the noise level from
a regular shaker lower enough for good quantitative measures
17) Subjective BSR – Buzz Squeak and Rattle on Loud ED
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Trivia: − The low DB vibration machine at
Intertek Plymouth is quieter than the middle of the night in a deep forest after a new fallen snow
Application: − Quantified measures of buzzes,
squeaks and rattles
− Measuring amplitude direction and troubleshooting sources of noises
Value: − No other technique can identify true
sounds and sources as quickly
Limitations: − Modest weight limit and dedicated
equipment
18) Quantitative BSR – BSR on Low DB Room
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19) Modal Hammer
Trivia: −A perfect triangle wave contains all frequencies from the period of the
wave up to infinity −A real triangle wave will have an upper end frequency limit determined
by how “sharp” the wave is Application:
−Determine mode shapes of products quickly and easily Value:
−Simpler to use than a vibration fixture and a sine sweep on a single axis machine
Limitations: −Can only measure mode shapes, does not do any damage or durability
testing
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Trivia: − In the 1980s, the F-18 was
instrumented with so many flow sensors that a mini computer on board preprocessed the data because the telemetry stream did not have enough bandwidth
Application: − Collect real world data to be used to
simulate the real world in the laboratory
Value: − No amount of computer modeling can
beat the real world Limitations:
− Requires a fully functional product or surrogate to collect data. Often can not be done until later in development.
20) RLDA – FDR Road Load Data Acquisition Field Data Replication
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Trivia: − The highest stress on a tuning
fork is at its base Application:
− Fatigue of small parts or joints that can be fixtured into the “base” of a resonance arm (tuning fork)
Value: −When very high cycle fatigue
bending is needed, using a “tuning fork” setup to induce the fatigue allows for very high cycle rates
Limitations: −Requires custom fixturing
21) Resonance Induced Fatigue-Bending
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22) Resonance Induced Fatigue-Torque
Trivia: −Torsional fatigue is just regular fatigue out on a limb
Application: −Fatigue on small parts or joints that can be fixtured orthogonal to the
base of a resonance arm (tuning fork)
Value: −When very high cycle fatigue torsion is needed, using a “tuning fork”
setup to induce the fatigue allows for very high cycle rates
Limitations: −Requires custom fixturing
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Trivia: − When the space shuttle first
launched, a strut in the nose cone was bent from shock waves bouncing off of the concrete launch pad below
Application: − Missiles and other aerospace
vehicles that experience transition through the speed of sound
Value: − Transonic Acoustic vibration can only
be reproduced with sonic nozzles that create the sonic boom (a phenomena only a few air molecules thick, but represents an extreme change in air pressure across the wave)
Limitations: − Big custom setup
23) Transonic Acoustic Vibration
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Trivia: − At a live rock concert, you can feel
the air moving in front of the speaker systems
Application: − Experimental alternative to air
hammer machines for high frequency testing
Value: − Using Acoustic vibration provides for
mid to high frequency with more control than air hammer machines
Limitations: − Not in full production yet
− Very loud
24) Six-Axis Acoustic Vibration
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Trivia: − Engineers are just bigger kids with
bigger toys Application:
− BSR fixtures need to hold a product firmly and without producing noise
− They do not have to endure durability − They need to be light − They can be made out of “erector set”
type construction Value:
− A well-made set of modular BSR fixture pieces can hold any number of components with minimal custom fixturing
Limitations: − Cannot be used for durability testing
25) BSR Fixture Design
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Trivia: −Doubling the natural frequency of
a fixture requires the fixture to be four times stiffer without adding any mass
Application: − Single-axis durability vibration
Value: − A well-made vibration fixture will
not induce any natural frequencies of its own into the part, providing an accurate test
Limitations: −Height: The higher you go, the
harder it is to be “resonance free” to a target frequency
26) Single-Axis Fixture Design
𝐹𝐹𝑛𝑛 = 12𝜋𝜋
𝑘𝑘𝑚𝑚
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27) Single Axis Fixture with Motion Design
Trivia: −Push-pull cables, like the cables on a 10 speed bicycle, are used on
tractor-trailers and can be purchased from a big-rig supply company
Application: −Often products have buttons, levers or doors that must be pushed,
pulled, twisted or actuated during vibration
Value: −Any device with mechanical linkages will vibrate differently when in
each position. Moving the product while under vibration provides a more thorough test.
Limitations: −Many actuators do not work well under vibration
−Fixtures become more complicated
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Trivia: − Designing a six-axis fixture to hold
and actuate the full interior of a automobile can take as much engineering as designing the interior itself
Application: − Six-axis vibration is usually
conducted with full actuation of mechanical and electrical systems
− The fixture must hold the part as well as provide for all of the actuation and access
− Don’t forget to provide for inspection and instrumentation of all systems during the test
28) Six-Axis Fixture Design
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29) HALT and FMVT Fixture Design
Trivia: −When the vibration spectrum is broad enough, it is impossible to
construct a fixture with no resonance in the test range
Application: −A vibration fixture for HALT or FMVT does not have to be resonant free
−They must provide for all stress sources used
−They must provide for all instrumentation and inspection
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Trivia: −Accelerometers and there
cables are the number one source of troubles during a vibration test
Application: −Cables must not be allowed to
kink, be crushed, pinched or twisted
−Accelerometers should not be dropped, crushed, or torqued
−A cable will likely fail intermittently at first, making diagnoses difficult
30) Accelerometer Care and Feeding
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31) Other Instrumentation – Strain Gauges, Pressure Sensors, Load Cells, etc.
Trivia: −A thermocouple does not measure temperature, it measures the
electrical effects of temperature on a junction
Application: −All instrumentation measures a phenomena that may be affected by
more than one source
− Load cells are affected by temperature and vibration
−Thermocouples and accelerometers can pick up EMI
−Strain gauges can measure strain, temperature and EMI
−Pressure sensors may be susceptible to EMI, grounding and even vibration, depending on the design
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Time for the Q&A Session
Additional questions can be emailed to:
[email protected] after the webinar
QUESTIONS?
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Thank You For Attending
For more information, visit us on the web at www.intertek.com
© Intertek, 2016 These materials may not be reproduced and distributed in whole or part to third parties without the express permission of Intertek.
