Random Vibration & Shock Testing - Fundamentals

This three-day course will commence by reviewing basic vibrations, sources and causes.  Then we’ll explore vibration measurements, analysis and calibration. Our discussion is supported by projected visuals and video clips. We’ll compare sinusoidal vs. random vibration with emphasis on testing systems, specifications, standards and procedures. 

We’ll discuss ESS, HALT and HASS.  We’ll emphasize vibration and shock test fixture design, fabrication, experimental evaluation and usage. Also shock measurement, shock response spectrum (SRS) and classical shock testing. Modal testing will be reviewed 

Throughout, we emphasize topics you will use immediately.

We will have a virtual visit to the laboratory, where we will view and hear sine and random vibration on shakers. We will perform a resonance demonstration, using first sine and then random vibration. 

We will demonstrate shock testing, using both a shaker and a shock test machine. 

Many participants protectively install commercial-off-the-shelf (COTS) equipment in flight, land vehicles and shipboard locations subject to severe vibration and shock.  Many participants laboratory test that protected equipment (1) to assure maximum equipment survival and possible combat, also (2) to meet commercial test standards, IEC documents, DO-160, military standards such as STANAG, MIL-STD-810, etc. Few if any engineering schools teach about such protection or such testing. Thus we offer this specialized course. 

Steve Brenner has been working in the field of environmental simulation and reliability testing for over 30 years. Beginning in the late sixties with reliability and design verification testing on the Lunar Module, the Space Shuttle in the eighties, to semiconductor manufacturing equipment in the nineties, Mr. Brenner has always been involved with the latest techniques for verifying equipment integrity through testing. Mr. Brenner began his career as an Environmental test engineer with Grumman Aerospace Corporation in New York, worked as design verification and reliability engineer for the Air Force, an Environmental Test Engineer for Lockheed Missiles and Space company, and spent 18 years with Kaiser Electronics in San Jose, where he managed the Environmental Test Lab and was involved with the design of hardware intended for severe environments. Mr. Brenner has been working as a consultant in the reliability testing field since 1996.

Anyone with the following needs or interests:

I need practical knowledge about mechanical vibration and mechanical shock test, measurement, analysis, designing for dynamics also calibration and/or control because:

• I instrument land, sea and air vehicles as well as fixed-based equipment, in order to measure mechanical vibration and/or shock in service and during transport.
• I analyze dynamic responses to mechanical vibration and shock inputs during normal and abnormal transport.
• My title may be mechanical engineer, mechanical designer or packaging engineer. I design (ruggedize) products that must withstand factory handling + transport + normal and abnormal usage. I design products to dynamic requirements, which I don’t fully understand. Then I send a prototype to our lab for testing. I really don’t understand what our lab does. I’d better find out.
• I write contracts for procuring high-reliability equipment. I need to understand HALT, ESS and HASS. When do these acronyms apply? How do I insure that potential contractors will appropriately implement the random vibration requirements of these acronyms? What is g2/Hz?
• I work in an environmental test lab. We perform vibration and shock tests on prototype hardware. These tests may be part of developing a new product, of determining vibration levels for future production ESS (environmental stress screening) or production tests, or of investigating in-service or transport failures.
• I calibrate various vibration and shock sensors (including accelerometers) and analyze vibration and/or shock.
• I design to control (reduce, protect) the intensity of vibration and/or shock, which otherwise may damage delicate equipment.
• I maintain machinery whose vibration signature can warn of approaching failure. 

If you thought, “aha – that’s what I’m supposed to do” to any of the job descriptions listed above, then this course is intended for you. It will help you move up your own “learning curve.” A smaller group, for whom the instructor also intends this course: supervisors of any of the above listed activities. Perhaps you were thrust into this responsibility without adequate training. Maybe your predecessor had no opportunity to alert you to potential difficulties. You certainly need to know what your people are talking about. Possibly you had no formal training for your present responsibilities. You need to explain your department’s activities to your superiors in the technically correct language. Perhaps you need to decide between “in house” and “outside” testing.

After this short course, you will be able to

• measure vibration and shock,
• calibrate vibration and shock measurement systems,
• convert field measured data into a test program,
• interpret vibration and shock test requirements,
• supervise vibration and shock tests,
• specify and successfully purchase test equipment to perform vibration and shock tests,
• specify, design, and experimentally evaluate vibration and shock test fixtures,
• specify and perform ESS, HALT and HASS. 

When you visit a lab or review a test program, you will have a good understanding of the requirements and execution of dynamics tests and will be able to ask meaningful questions and understand lab peoples’ responses.

Introduction for management and participants

• Purpose of environmental testing, particularly vibration and shock
• Purpose of environmental stress screening (ESS), nowadays HALT & HASS
• Types of vibration tests: resonance search/dwell, fatigue, specification

Discussion of attendees’ prior knowledge – Classical sinusoidal vibration never observed in service; useful concept

• Introduction: terminology, structural resonant behavior, passive and active isolation
• Sinusoidal vibration measurements: units, sensors, readouts, errors
• Calibration of sensors and systems; traceability to NIST

 Introduction to spectrum analysis Sinusoidal vibration testing

• Electrohydraulic and electrodynamic shakers; theory, tradeoffs, limits
• Power amplifier theory, operation, limitations, distortion effects
• Controls for sinusoidal vibration testing
• Sinusoidal vibration test practice
• Interpretation of standards; e.g. MIL-STD-810, DO-160, etc.
• Controversial test methodology: tracking filters, switching and averaging among sensors

 Introduction to random vibration

• Sources of random vibration in service and transportation
• No possible equivalence to sinusoidal vibration
• Terminology and definitions
• Spectral density measurement and analysis – the frequency domain. What is g²/Hz?
• Probability density – the time domain

 Random vibration test practice

• Interpreting and implementing standards, e.g. MIL-STD-810
• Equalization before testing; methods and limits
• Controls
• Electronic protection for test items and shaker system
• Simultaneous multaxis vibration testing fixed spelling
• Intense acoustic noise testing

 Combined environment (CERT) testing; reliability tests, e.g.MIL-STD-781 Environmental stress screening (ESS) of electronics hardware production

• Development of ESS techniques into the 21st century

 Highly accelerated life testing (HALT), environmental stress screening (ESS) and highly accelerated stress screening (HASS) of electronics hardware production.

• Single vs. multi-axis vibration.
• Pneumatic repetitive-shock (RS) machines.
• Acoustic excitation of printed wiring boards (PWB).

 Vibration and shock test fixtures; fixtures for stress screening

• Recommended designs, materials, fabrication methods
• Experimental evaluation before use
• Practical limits: transverse motion; specimen size and weight
• Where to put the control accelerometer, and why

Accommodating oversized loads

• Table expanders
• Slip plates and alternatives

 Instrumentation for measuring shock in service and during tests

• Sensors, readouts, errors
• Calibration

 Shock spectrum analysis; shock response spectrum

 Shock testing standards and methods

 Modal testing

 Witnessing of tests

 Course summary; optional final examination; award of certificates