Mechanical shock testing applies a short, controlled acceleration pulse to a product to prove it survives the impacts, drops and pyrotechnic events it will see in service. Most specifications define that pulse either as a classical waveform, such as an 11 ms half-sine, or as a shock response spectrum derived from measured field data. The standard you’re working to, the size of the test article and the required velocity change determine whether you need a free-fall machine, a pneumatic machine or a shaker.
What is mechanical shock testing?
Mechanical shock testing is a laboratory method for reproducing transient mechanical loads on hardware in a repeatable way. Shock events last from fractions of a millisecond to tens of milliseconds and excite the resonances of structures, circuit boards, connectors and mounts.
Engineers run shock tests to:
- Qualify equipment to a contractual specification.
- Find fragility limits during development.
- Screen production parts for workmanship defects.
- Validate packaging for handling and transportation.
What are classical shock pulses?
Classical shock pulses are simple waveforms defined by peak acceleration (g) and duration (ms). The area under the pulse is the velocity change (ΔV), which is the parameter that drives machine selection.
| Pulse | Shape | Ideal velocity change | Typical generation | Notes |
|---|---|---|---|---|
| Half-sine | Smooth rise and fall | 2 × A × T ÷ π | Elastomer programmers on drop or pneumatic machines | The most widely specified classical pulse |
| Terminal-peak sawtooth | Linear rise, rapid decay | A × T ÷ 2 | Crushable (for example, lead) programmers | Produces a more uniform response across frequency than a half-sine |
| Trapezoidal (square wave) | Fast rise, flat top, fast fall | Approximately A × T | Gas (pneumatic) programmers | Delivers a large velocity change at a controlled g level |
As a worked example, a 50 g, 11 ms half-sine (A = 490 m/s², T = 0.011 s) has an ideal velocity change of about 3.4 m/s, or 11.3 ft/s. Rebound off the programmer adds to that, which is why required drop height differs from simple free-fall math.
Free-fall vs. pneumatic shock machines: what’s the difference?
A free-fall shock machine raises a table and drops it onto a programmer, so velocity change comes from gravity and drop height. A pneumatic shock machine uses compressed gas to accelerate the table, reaching higher impact velocities and higher g levels in a compact frame.
| Free-fall shock machine | Pneumatic shock machine | |
|---|---|---|
| Energy source | Gravity (drop height) | Stored gas pressure plus gravity |
| Velocity change | Limited by practical drop height | Higher for a given machine size |
| Peak g and duration | Moderate g, longer pulses | Very high g, short pulses |
| Typical use | Equipment and component shock, package testing | Microelectronics and high-g component qualification |
| Emerson Apparatus models | FSM series, 5–5,000 lb payloads, tables from 4×4 in to 60×60 in | PSM100–PSM2500, 100–2,500 lb payloads |
Emerson Apparatus, which incorporated VST (Vibration & Shock Technologies) in 2019, lists its pneumatic machines for half-sine, square-wave, trapezoidal and terminal-peak sawtooth pulses, with closed-loop control, horizontal capability and ratings up to 30,000 g for MIL-STD-883 work. Achievable levels depend on payload and pulse. Shock amplifier options on both machine types extend peak g for very short pulses, and Emerson’s ShockTool software handles shock control and pulse analysis.
Electrodynamic shakers can also run shock tests. They excel at synthesizing SRS-based waveforms but are limited by stroke, velocity and force.
What is a shock response spectrum (SRS)?
A shock response spectrum shows the peak response that a series of single-degree-of-freedom oscillators, each tuned to a different natural frequency, would experience when their common base sees a given shock. It describes a shock by its damage potential across frequency rather than by the shape of the time history.
Key points for test engineers:
- Q = 10 (5% damping) is the common analysis default.
- The maximax absolute acceleration spectrum is the usual presentation.
- Different time histories can share a similar SRS, so an SRS can’t be converted back to a unique waveform.
- Tailored tests start with measured field data, reduce it to an SRS, then synthesize a lab waveform that envelops it within tolerance.
MIL-STD-810 vs. MIL-STD-883: how do they differ?
MIL-STD-810 is an environmental engineering standard for equipment of all sizes, built around tailoring tests to the life-cycle environment. MIL-STD-883 is a test method standard for microcircuits, where shock tests are fixed, very high-g screens.
| MIL-STD-810H, Method 516 (Shock) | MIL-STD-883, Method 2002 (Mechanical Shock) | |
|---|---|---|
| Scope | Equipment and subsystems across transport, handling and operation | Microelectronic devices |
| Philosophy | Tailor levels to measured or predicted environments | Standard test conditions called out by the procurement document |
| Pulse definition | SRS-based waveforms or classical pulses, as tailored | Half-sine pulses |
| Levels | Program-specific | Lettered conditions from A (500 g, 1.0 ms) to G (30,000 g, 0.12 ms) |
| Typical equipment | Shakers, drop and pneumatic shock machines, drop and pendulum rigs | High-g pneumatic shock machines with small fixtures |
Method 516 in MIL-STD-810H organizes testing into eight procedures: functional shock (I), transportation shock (II), fragility (III), transit drop (IV), crash hazard shock (V), bench handling (VI), pendulum impact (VII), and catapult launch and arrested landing (VIII). Pyroshock and gunfire shock are covered separately in Methods 517 and 519. Always work from the revision and procedure named in your contract or test plan.
Why do fixtures make or break a shock test?
A shock fixture must transmit the pulse to the test article without adding its own resonances. A flexible fixture rings, amplifying some frequencies and attenuating others, so the article sees a different shock than the control accelerometer reports.
Good fixture practice includes:
- Stiffness first. Push the fixture’s first resonance above the frequency range of interest.
- Light, stiff materials. Magnesium and aluminum are common; Emerson Apparatus builds cube, L and T fixtures in both, designed with FEA.
- Axis coverage. Cube fixtures let one setup cover three axes and both directions.
- Controlled mounting. Use specified bolt torque and mount the control accelerometer near the article’s attachment points.
- Survey before qualifying. Run a low-level pulse and review the response before committing flight or production hardware.
What instrumentation do shock tests need?
Accurate shock data depends on the right accelerometer, sample rate and filtering. Piezoresistive accelerometers with DC response capture long-duration pulses and velocity change well, while piezoelectric sensors suit many high-frequency measurements but can show zero shift under severe metal-to-metal impacts. A common guideline is to sample at least ten times the highest frequency of interest, with appropriate anti-aliasing filtering.
Field measurement closes the loop on tailoring. Instrumented Sensor Technology (IST) builds self-contained recorders that capture real transport and handling shock:
- EDR-5 series: built-in triaxial accelerometers from ±10 to ±200 g, up to 50,000 samples per second per channel, external IEPE inputs, and unattended deployments of hours to months.
- SnapShock-PLUS: peak g, duration, velocity change and time stamp for each event, with a drop-height mode for package studies.
- DynaMax Suite software: waveform, PSD and statistical analysis to turn field data into lab test profiles.
IST also rents recorders for one-off test programs.
Shock test support in Huntsville and across the Southeast
Huntsville’s concentration of missile, space and defense electronics programs makes shock qualification a daily concern for local test labs and contractors. From our Huntsville headquarters, Vaughn Associates helps engineers size shock machines, plan fixtures, upgrade controls on legacy machines and choose recorders for field measurement.
We represent Emerson Apparatus across all Vaughn territories and IST across our territories (Tennessee and Mississippi only in our Tennessee, Arkansas and North Mississippi territory; North Carolina only in our North Carolina, Virginia, Maryland and D.C. territory). Explore shock and vibration test equipment and shock and vibration data recorders, review the Emerson Apparatus and IST pages, or request application help.
