Distance Learning in
Vibration and Shock Testing
Course Outline (33 Lessons)
Click on the links below to find out what you will learn on each lesson:
- Lesson 1- What are Vibration and Shock? Overview of the course.
- Lesson 2 – Introduction to Classical Sinusoidal Vibration. SDoF systems
- Lesson 3- Resonance Effects
- Lesson 4 – Torsional Vibration
- Lesson 5 – Control (Reduction) of Dynamic Motion
- Lesson 6 – Displacement and Velocity Measurements
- Lesson 7 – Acceleration and Force Sensors
- Lesson 8 – Acceleration and Force Signals
- Lesson 9 – Calibration
- Lesson 10 – Continuous Systems
- Lesson 11 – Analysis of Complex Motion
- Lesson 12 – Types of Tests
- Lesson 13 – Electrohydraulic Shakers
- Lesson 14 – Multiple Electrohydraulic Shakers
- Lesson 15 – Electrodynamic Shakers
- Lesson 16 – Multiple Electrodynamic Shakers
- Lesson 17 – Power Amplifiers for Electrodynamic Shakers
- Lesson 18 – Standards for Sine Testing
- Lesson 19 – Controlling Sinusoidal Vibration Testing
- Lesson 20 – Introduction to Random Vibration
- Lesson 21 – Measurement and Analysis of Random Vibration
- Lesson 22 – Random Vibration Testing Standards
- Lesson 23 – Controlling Random Vibration Tests and Screens
- Lesson 24 – Environmental Stress Screening (ESS)
- Lesson 25 – Accelerated Testing and Screening (HALT & HASS)
- Lesson 26 – Attaching Test Articles to Shakers – Test Fixtures
- Lesson 27 – Accommodating Oversized Loads
- Lesson 28 – Measuring and Quantifying Mechanical Shock
- Lesson 29 – SRS – The Shock Response Spectrum
- Lesson 30 – Mechanical Shock Testing
- Lesson 31 – Introduction to Modal Testing
- Lesson 32 – Buzz, Squeak and Rattle Testing
- Lesson 33 – Think, then test
Lesson 1- What are Vibration and Shock? Preview of the course.
Definitions, preliminary discussion, mention railroading, mention aircraft, modal analysis & testing, helicopters, convertiplane, ship vibration, shock, aircraft vibration, automotive electronics, shock, mention climatic testing, mention random vibration on high-performance aircraft, rocket liftoff, testing a satellite, vibration diagnostics (MHM), engine test cell, wind-induced vibrations, seismic event, connectors, fatigue failure & testing, electronics failures, sources of vibration, roadway vibration, automobile engine, machinery, buildings and offices, deciBels, acoustic measurements.
Lesson 2 – Introduction to Classical Sinusoidal Vibration
Why study it? Unidirectional motion, sine vibration, sinusoidal tones, sound propagation, wavelength & velocity, a little math, sine equations, what is a “g”?, cardboard vibration calculator, on-the-Web vibration calculator, early-day test spec.
Lesson 3- Resonance Effects
Concentrate on resonances, SDoF, SDOF animation, natural frequency, why important, useful model, electromechanical analogies, a little more math, calculating natural frequency, hand-held experiment, vary displacement D over big range, SDoF on shaker, magnification ortransmissibility, isolation, bandwidth, critical damping, massvs. weight.
Lesson 4 – Torsional Vibration
SdoF systems, what is torsional vibration?, math shows similarity to uniaxial vibration, animation of pendulum, electromechanical analogies, transmissibility, torque, torsional displacement, velocity, acceleration, measurements, strain gages, unbalance leads to vibration, engine simulator, rotational irregularities, torsional vibration and shock testing.
Lesson 5 – Control (Reduction) of Dynamic Motion
Vibration control strategies; best to quiet at source, energy absorption, problem of quieting a submarine, special gloves, isolators, transmissibility, review problem, avoid too-soft isolators, isolating shakers, elastomeric and metallic isolators, hydraulic dampers, vibrationvs. shock isolators, isolating levelers, locating the isolators, air bags, active isolation, passive absorbers.
Lesson 6 – Displacement and Velocity Measurements
Why do we need instrumentation? How do we describe an event’s severity? Linearity, probability, distributions, metrology terms, displacement sensors, Vee scope, dial indicator, string pot, eddy current probe, LVDT, lasers, velocity sensors, integration.
Lesson 7 – Acceleration and Force Sensors
Accelerometers, wire strain gage type, need for high natural frequency, piezoresistive accelerometers, micromachined accelerometers, piezoelectric (crystal) accelerometers, compression, shear, bender, capacitive, triaxial accelerometers, handheld accelerometers, servo accelerometers, signal conditioning, connectors, mechanical errors, resonance, don’t drop, sensitivity, calibration, damaged base, bracket resonance, attachment devices, base bending, temperature sensitivity, mounting block, lateral sensitivity, how many accelerometers? accelerometer mass effect, seat cushion accelerometer, torsional accelerometer, double integration, force sensors, impedance head, microphones, sound intensity.
Lesson 8 – Acceleration and Force Signals
Data acquisition – avoiding errors, readout instruments , meters, microphones, mechanical spectrum analyzer, octave band analyzers, need for detailed spectrum analysis, faster recorders, frequencyvs. time, virtual instruments, resolution, electrical measurement errors, signal/noise ratio, dynamic range, signal conditioning, time constant, ground loops, attachment devices, triboelectricity in cables, low-noise cables, securing cables, keep high-Z wiring short, amplification inside case, distinguish good from bad data.
Lesson 9 – Calibration
Define calibration, why calibrate? traceability, national metrology institutes, ANSI, NIST etc. static calibration, crude checks – vee scope, absolute calibration, a visit to NIST, handheld calibrators, specialized shakers, comparison calibration, ratio method, group calibration, portable calibrators, low frequency calibration difficulties, high frequency calibration difficulties, random vibration calibration, calibrate at extreme temperatures, “chatter ball” calibration at 1g, gravity calibration, hammer calibration, microphone calibration, transverse sensitivity, calibrate how often?
Lesson 10 – Continuous Systems
“Diving board” mode of cantilever beam, calculating first bending natural frequency, effect of damping, laminated beam, video clips, summarizing chart, how many resonances? seeming lack of order, cable resonances, piano, guitar, superpositioning of modes, classical beams and plates, turbine rotor, orchestral cymbal, plates, force measurements, impedance head, modal hammer, six ratios, effect of damping, brake damping, additional ratio terms – semantic fog, active shape control, units of force, conversion factors – force, fatigue failures, axial resonances – toy telephone concept.
Lesson 11 – Analysis of Complex Motion
Review of sine vibration, complex vibration, adding sine waves, synthesize a square wave, Baron Fourier, spectral displays, isometric view, effect of band-pass filter, machinery vibration, rotor unbalance, dynamic balancing, bearings, misalignment, gear mesh, machinery health monitoring (MHM), costs, gear failure, meter has little value, data collectors, wireless data collection, multi-reed mechanical analyzer, electronic spectrum analyzer, four analyses, four more analyses, sampling, digital spectrum analysis, using a PC, data acquisition, sine and square wave video clips, digital analysis problems, aliasing, optical aliasing, leakage, windowing, waterfall display, newer displays, variety of readout instruments, automobile vibrations, inside engine video clip, helicopter, time synchronous averaging, industrial vibration measurements, centralized computer. Look ahead at random vibration.
Lesson 12 – Types of Tests
Climatic environmental tests, developmental testing, preproduction testing, production sample testing, reliability demonstration testing, choosing a shaker, mechanical shakers, package testers, an early test spec, need for multiple axes, need for controllable correlation and multiple shakers, bumpy dynamometer.
Lesson 13 – Electrohydraulic Shakers
Hydraulic actuators – basic uniaxial EH shaker construction, shaker limitations, fatigue testing, tables, shaker system, multiaxis shakers, accelerated testing, package and transportation testing, accelerated testing, axial & torsional analogies.
Lesson 14 – Multiple Electrohydraulic Shakers
Review of single axis EH shaker, tilted shaker, earthquakes are multi-axis, seismic shaker, common carrier, shaking RR gondola car, automotive transport, automotive BSR (buz, squeak and rattle), vibrating platforms, shaking helicopter pilot, automotive NVH tests, remote parameter control, BSR testing, “cube” shakers.
Lesson 15 – Electrodynamic Shakers
Theory, construction, degaussing, armature guidance, shaker assembly, wanted and unwanted shaker motions, isolating the shaker, long-stroke shakers, single-turn driver coil, cooling, inverted shaker, system, limitations, narrowband random derating, combined environment testing, piezoelectric shaker.
Lesson 17 – Power Amplifiers for Electrodynamic Shakers
System block diagram, exciting the field winding, what does the power amplifier do? history, MG sets preceded power amplifiers, demand for current & voltage, narrowband ratings, noise and distortion, effect of distortion, need for amplifier maintenance.
Lesson 18 – Standards for Sine Testing
Military test standards, US railway gage, MIL-E-005272, more complex programs, what is an octave? logvs. linear sweeping, shipboard vibration testing, allied countries’ test standards, tailoring of MIL test standards, commercial test standards, International organizations, testing COTS equipment, nuclear power plant tests, telecom seismic tests, “cookbook” standards, detecting resonant magnification, redesign for lesser resonant magnification, modification without redesign for COTS.
Lesson 19 – Control of Sinusoidal Vibration Testing
Why perform sine vibration tests? System block diagram. Where locate control accelerometer? Resonance search tests, “smart” strobe light, resonant dwell tests, manual control, sine testing automated, analog controls, tracking filter, digital control, remote control of shaker, shortcomings of motion control, passive vibration absorber, crankshaft dampers, constant motion not found in real world, force control, controlling response vibration, intense noise (acoustic) testing, multiple control accelerometers, response control strategy.
Lesson 20 – Introduction to Random Vibration
Sources of random vibration, aircraft, flow in pipes, random means what? rocket flight, automotive, robot driver, musical instruments, difficult concept, automotive, video demo, simulation, g2/Hz, PSD or ASD, shaker force needed, tustin unit, m2/s3.
Lesson 21 – Measurement and Analysis of Random Vibration
Review sine vibration & Fourier transform pair, review complex vibration, random vibration in the time domain, frequency domain – several video clips, time domain – Gaussian distribution, meaning of RMS, TRMS meter, probability density, time domain shows random to be gentle, is your field vibration Gaussian? is your test vibration Gaussian? mixture of sinusoids? spectral slice, bandpass filter, mechanical example, earthquakes, don’t stack your resonances, random vibration calibration of accelerometers.
Lesson 22 – Random Vibration Ttesting Standards
Why are standards not effective? MIL-STD-810, IEC standards, IEEE seismic tests, Bellcore NEBS standard, interpreting standards, focus on frequency domain, real world spectra not simple, deciBel tolerances, lin-lin graph better representation, sufficient force? “Willoughby” spectrum, area under graph, US CAR spec, multi sine on random, narrowband random on random, analyzing narrow bandwidth peaks, spectral graphs misleading, don’t forget the time domain, clipping, detecting resonant magnification, design for lesser resonant magnification.
Lesson 23 – Controlling Random Vibration Tests and Screens
Random vibration test practice. What are the control tasks? Manual, then automatic analog control, computer or digital control, DOS-based control, Windows control, modifying a PC computer for shaker control, how computer controls tests, consider not specifying g2/Hz, data acquisition, test spectrum based upon field data, averaging, real world not stationary, much realism is lost, realistic vibration testing, shaker compensation, forget about PSD sounds & feels more natural, what if I must test to a spectrum? , U-D story “Vibration Time History Testing”, time history replication, sine on random tests, narrow band random on random tests, unwanted high frequency vibration, vibration test mishap at JPL, shaker system protection, intense noise testing, combined environment reliability testing, progressive wave acoustic test.
Lesson 24 – Environmental Stress Screening
What is ESS? hardware vs. software reliability, MIL services pioneered ESS, costs of electronics failure, why is ESS needed? Treadmill analog – latent defects precipitated, relates how to electronics? automotive electronics ESS, focus on random vibration, ESS concepts, EST 2-axis shaker, Shinken pioneer 3-axis shaker, NAVMAT P9492, Willoughby spectrum and area beneath, don’t worry about overall RMS, shaded area much less than total area, Gaussian distribution, sine distribution, not a test, stimulation, not simulation, most effective stimuli, how severe? Experiment, need thermal ramping and random vibration, is ESS helping us? uses up useful life? apply power and monitor outputs, extensions to HASS and HALT, are uniformity and repeatability necessary?
Lesson 25 – Accelerated Testing and Screening
Why worry about reliability? Marketing 2006, time for HALT, review of failures and reliability, distributions, HALT, ESS, HASS, thermal stress, how does vibration disclose defects? On-off cycling, need two simultaneous events, all failures are relevant, root cause failure analysis needed. Our own lab or go outside? Failure mechanisms, math models. Multi axis testing and screening, don’t use tilt fixture, pneumatic vibrators, IBM pneumatic hammer, pseudo- or quasi-random vibration, not uniform spectrum, table details, heat barrier, rear access, rollout table, poor low frequency input, air ducting, vibration units attached to table bottom, controls, view of vibrators, Entela’s FMVT machine, acoustical excitation, air ducting, accelerated testing, exaggeration factors, doubling & redoubling PSD, Hieber re accelerated testing, failure mechanisms.
Lesson 26 – Attaching Test Articles to Shakers
Function of fixture, understanding fixture behavior, where to locate the control accelerometer? fixture transmissibility, deliberately resonant fixtures, standard fixture configurations, special-purpose fixtures, fixture design, fixture fabrication, inserts, too many interfaces, welding, fixture materials, foam for damping, fixture mechanical impedance, force-controlled testing, bolting to DUT and to shaker, multiple control accelerometers, experimentally evaluating a new fixture, fixture criteria, Lissajous patterns, fixture care (maintenance) between tests, fixtures for BSR testing, fixtures for ESS, HALT, HASS.
Lesson 27 – Accommodating Oversized Loads
Table xpanders, shaker horizontal – use of auxiliary supports, support from above, support from beneath – slip table, long-stroke ED shaker, axial resonance, combined environment testing, why shaking horizontally? bolted connections in shear, increase fixture-to-slip plate friction, problems with high cg, hydrostatic bearings, hydrostatic bearing support from above, driving load’s cg.
Lesson 28 – Measuring and Quantifying Mechanical Shock
What is shock? How different from vibration? shock excites all resonances simultaneously, instrumentation: equipment limitations, velocity less dynamic range, fairing a shock pulse, choosing a shock accelerometer, high-frequency filter cutoff effects, low frequency filter cutoff effects, accelerometer limitations, ver-ranging, factory shock, laser measurement of shock displacement responses, pyroshock, accelerometer mounting and cabling, windowing, inexpensive shock recorders, factory shock, mechanical shock recorders, accelerometer-based recorders, concealable recorders, shock calibration, Hopkinson bar calibration.
Lesson 29 – SRS – The Shock Response Spectrum
Time domain review, why do we need SRS? designer and test lab use SRS, history of SRS, studying earth motion, early studies of shipboard shock, understanding the SRS, the maximax spectrum, SRS of half-sine pulse, Smith & Hollowell introduction to the SRS.
Lesson 30 – Mechanical Shock Testing
Shock test tandards, falling carriage machines, hard disk drive shock testing, packaging fragility tests, Damage Boundary Curve, resonant frequency search test, drop testing, drop package machines, hammer machines, barge tests, more recent Navy shock testers, explosive pyro tests, classical pulses on shaker, SRS tests on shakers, automotive crash tests, railroad crash tests.
Lesson 31 – Introduction to Modal Testing
Review of esson 10 (continuous systems), what is a mode? modal analysis, modal analysisvs. modal test, modal testing, predicting responses, coupling shaker to load, sources of error, exciting modes with one or more shakers, scanning laser metrology, automobile modal test example, many accelerometers, smart sensors, shaker exciting automobile, supporting automobile, supporting spacecraft, piezoelectric actuators, exciting modes with a hammer, windowing, validate finite element analysis, modal suppression.
Lesson 32 – Buzz, Squeak and Rattle Testing
Buzz, squeak & rattle (BSR), itch, sound quality measurements, loudness – sones and phons, buzz, squeak and rattle testing, sine sweeping, structural stiffness is important, sound limits, enclosures needed, remote control of shaker, BSR solutions.