Vibration Testing

The Definitive Guide

This is a complete guide to Vibration Testing in 2020.​

So if you want to understand everything about Vibration Testing you’ll enjoy this guide

Let’s dive right in.

Chapter 1

Vibration Testing Fundamentals

In this chapter, I’ll answer the question: “What Is Vibration Testing?”.

I’ll also explain to you why vibration testing is so important.

Let’s get started.

What is Vibration Testing?

Vibration testing is the process of simulating or mimicking real-life conditions a device, product, component, or a structure will or could experience during its lifetime.  The thing being vibration tested is typically referred to as, the Unit Under Test (UUT) or Test Article.

A vibration testing is a vital step and time tested methods to both prove a product will survive the rigors of its intended use and improve product quality.  For example, vibration testing of aircraft components and structures has resulted in a high level of commercial aircraft safety.

Why is Vibration Testing So Important?

Most vibration experienced in life is random vibration. Which, is vibration comprised on many different frequencies at different amplitudes.

For example, an automobile traveling on the open street or highway, will have vibration input from the tires rolling on the road surfaces irregularities. An aircraft experiences random vibration from aerodynamic turbulence on the fuselage and wings and both random and sine vibration from the engines.

During the ascent, a rocket experiences significant random vibration from aerodynamic loads and from the rocket engine.

When you watched the Space Shuttle or SpaceX launch, you would here the annunciation for max-Q, this is the altitude and speed when aerodynamic loads are the greatest. Throughout its flight time from launch to orbit and then through re-entry.

All launch vehicles go through some level of vibration testing, from the component and device level up to the major assembly and entire vehicle level.

In general, a vibration test is used to demonstrate a device, product, component or a structure ability to withstand random and sine vibration from anything such as travel to earthquakes without losing any functionality or structural integrity under the specified loads.

Vibration testing can also identify mechanical weaknesses and or performance flaws by simulating air, sea, rail, ground transportation, and life-cycle aging.

It is vital for any vibration test to correctly reproduce any and all of the forces that could be encountered by-product or structure throughout the course of its lifespan.

Random vibration testing over time can help identify any weaknesses and design flaws, allowing you to further improve upon your product design.

Some items normally tested with random vibration included but are not limited to components and devices on aircraft, missiles, automobiles, construction and industrial equipment, consumer electronics, etc.

The type of vibration test depends on the use, for transportation there are ISTA and ASTM vibration test procedures, for aircraft there are RTCA DO-160 test procedures, for military equipment, there are MIL-STD test procedures, and for railroad equipment, there are special standards for vibration and shock.

Chapter 2

Types of Vibration Testing

In this chapter, I’ll talk about: “What Different Types of Vibration Testing Are There?”.

The type of vibration test depends on where the UUT or Test Article will be used; that is what vibration environment the UUT will see over its lifetime.

Random vibration may be acceptable for components on a passenger jet airplane, while sine on random is more appropriate for helicopter components.

Let’s get started.

What Are The Different Types of Vibration Testing?

When it comes to testing vibrations, there are several types of testing that can be done depending on your application. Below are the most common types of testing.

Graph

Random Test

A random vibration test is comprised of vibration energy at all frequencies over a specific frequency range. With the amplitude of each frequency of vibration defined in the appropriate test specification.

The vibration control system creates an output signal to the shaker at various frequencies, amplitudes and phases. The test spectrum or waveform will appear as a squiggly line on an oscilloscope trace.

Sine Vibration Test

The control system creates an output sine wave at a single frequency at a single time. The frequency of the sine wave is increased or decreased, swept, through a range of frequencies at a specific ramp rate, corresponding to the test specification.

Sine on Random

In this test the control system superimposes a sine wave on top of a random vibration signal, so the test article is subjected to simultaneous sine vibration and random vibration. Think, random vibration from a helicopter turbine engine with the sine input from the helicopter blades.

Random on Random

RoR vibration testing is known as using narrow-band with random peaks that are shown on top of each other by using a low-level broadband vibration.

Road Simulation Testing

Is, a specific type of random vibration used to simulate vibration the vehicle components or materials being shipped will be exposed to. ISTA and ASTM test procedures are used to determine if the flat screen TV will survive shipping from the factory to your house.

Sine Dwell Testing

A sine dwell test is performed when the UUT will see a constant sinusoidal input over a long time; months, years, etc. This occurs when the UUT is mounted on something that vibrates at a constant frequency or over a narrow range of frequencies. Think a wind turbine or a fuel pump on a back-up electrical generator.

Shock Testing

In addition to the types of vibration test procedures, there is testing that determines if the UUT will survive bumps and shocks. Think about a package or a rail car and the shock it receives when the rail cars couple into one another, or a semi-truck going over a bump, or the cooler in the back of your car/truck on a bumpy dirt road.

Shock exposure is very different from continuous random or sine vibration exposure, in that the transient input, usually called a waveform, starts and builds up to a maximum level very quickly and then dies down or diminishes very quickly. Think about an earthquake.

The various terms used in shock testing apply to how the shock test data is analyzed, such as Shock Response Spectrum (SRS), Classical Shock, or Transient Time History.

Chapter 3

3 Things to Prepare For

In this chapter, I’ll talk about, how to prepare for a vibration test.

I’ll also explain the 3 steps to a successful test.

Let’s get started.

Here are 3 steps to prepare for and succeed on your next project:

1. Understand your product’s application and environment

The first thing to think about is how and where the product you are working with will be used in order to better determine the scope and type of vibration testing.

Products mounted in vehicles experience a completely different vibratory environment than something like an aircraft product. For products that are exterior-mounted and that are exposed to outside elements, humidity, temperature cycling coupled with vibration may be appropriate.

If you’re trying to meet federal compliance requirements, a simulation test will measure your products ability to withstand different test environments and still operate normally.​

2. Choose the best vibration profile and levels for your product

For any product, a real-world vibration test will always be the best option. This ensures an accurate simulation of the product.

If real-world data is not readily available, Engineering Dynamics is equipped to collect and analyze just about any field vibration known to man by using multiple accelerometers, GPS tracking, video recording, and precisely replicate it within our vibration test systems.

3. Design the appropriate mounting fixtures

Mounting fixtures are what’s used to fasten items to the shaker machine and must be created to accurately transmit the vibration energy to the product without dampening or amplifying any of the vibration levels.

This should be taken into account early on in your planning stage since it most likely will require a lead time for design and fabrication.

Depending on the shape of the UUT and the test specification, design and fabrication of a test fixture can require significant time and cost to design and fabricate. For some testing and test articles, a bar-and-clamp basic style fixture is adequate.

The fixture should be aligned on the center of the vibration table, especially for larger testing items, in order to prevent over-testing and to minimize stress on the shaker.

Planning