Why Hardware Sees Vibration: One Life, Start to Finish

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Why Hardware Sees Vibration: One Life, Start to Finish

Trace a piece of hardware from the factory to the end of its life
Name every vibration environment it meets along the way
Say what each one does to it

A Test Is a Question About One Moment

A vibration test asks about one moment in the hardware's life
To ask it well, see the whole life first
The Stockpile-to-Target Sequence (STS): every step from the day it is built to the day it is used or retired, with the environment at each
The same idea elsewhere: life cycle environmental profile, mission profile, use profile

Vibration Is Two Columns in a Wide Table

The STS covers every environment: heat, humidity, altitude, salt fog, sand and dust, electromagnetic interference, radiation, accidents
Vibration and shock are two columns of it
The vibration test is usually one of a set, and the set has to agree: same article, same steps, same requirement document

Walk One Article Through Its Life

Manufacture and assembly: carts, forklifts, hoists, floor vibration from the next bay
Shipment: truck, rail, cargo aircraft, ship, each with its own character and duration
Storage: quiet for years, then handled again at every inspection
Maintenance and surveillance: disassembly, bench handling, transport both ways
Mating to the platform, then carriage: engine tones and buffet for hours
Delivery: launch, staging, separation and pyrotechnic events, reentry

Normal and Abnormal

Normal: the design must survive it and keep working through it
Abnormal: the accidents; survive safely, not expected to work afterward
Vibration testing lives almost entirely in the normal column
The lab's profiles descend from the normal steps through measurement, enveloping and the standards

Character Decides the Test Type

Broadband and stationary (road, rail, boost): a random test
Tonal and mixed (aircraft carriage, machinery): a sine test, or sine on random
Transient (separation, pyrotechnic, drop, gunfire): a shock test
Real environments combine these, and real tests have to cover the combinations

The Sequence as a Timeline

Figure 1.2. The sequence as a timeline, factory to target, with the character and duration of the environment at each step.

What Vibration Does to Hardware

Fatigue at resonances
Fretting and wear at joints and contacts
Connector and solder failures
Relative motion between parts meant to stay put
Joints that loosen
Most failures: at a resonance, near a stress concentration, and cumulative

The Steps as a Table

Step	Environment	Character	Duration scale	Test type it points to	Sets up
Manufacture, assembly	handling, floor vibration	transient, low broadband	minutes	shock; low-level random	loosening and contact damage, mostly at joints
Transport	road, rail, aircraft, ship	broadband; tonal on aircraft	hours to days	random; sine or sine on random	fatigue at resonances, fretting
Storage	quiet, then handling at inspection	transient	years, then minutes	shock	material set, creep, then loosening
Maintenance, surveillance	bench handling, transport	transient, broadband	hours	shock, random	connector and joint wear, handling errors
Mating	hoists, carts, bolt-up	transient	minutes	shock	bolts under- or over-torqued
Carriage	engine tones on broadband buffet	tonal and mixed	hours	sine or sine on random	fatigue at resonances, especially at stress concentrations
Launch, boost	broadband, high level	broadband, stationary	minutes	random	fatigue, more relative motion between components
Separation, terminal	pyrotechnic, aerodynamic	transient	milliseconds to seconds	shock	brittle failure, latch and contact chatter, electronic failure

Figure 1.3. The same steps as a table: environment, character, duration scale, the test type it points to, and the failure mode each tends to set up. These are the vibration and shock columns of a wider table.

Decide

Before anything else, place the test on the article's sequence
Which step, what character, how long
If nobody can say which step the test represents, the test is not ready to run

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