When you develop a product or build a new structure, you need to make sure it meets the end user’s expectations. It should withstand the everyday pressures of its normal intended function and meet important quality standards. You also need to be able to monitor its condition continuously to ensure a long useful life.
Vibration testing is one of the most effective ways to understand the health and endurance of objects as small as individual machine components and as large as satellites and vehicle assemblies. Through vibration tests, you can identify and locate defects in these components, learn how different materials respond to environmental stresses, and ensure products are designed and built for their operational environment.
This post explains everything you need to know about vibration and how to test it, including the tools you may need.
What Is Vibration?
Vibration is a physical phenomenon that naturally occurs in all objects, including rotating machinery and stable structures. For example, buildings vibrate due to external forces such as earthquakes and wind. Vibration also occurs in living things when they contact external forces.
Types of Vibration
There are three types of vibrational force:
- Free vibration: Free vibration happens in response to an inertial force, which causes a spike in energy in the object. This vibration continues to slow until the excess energy dissipates and the object returns to equilibrium.
- Forced vibration: A forced vibration occurs when an alternating force disrupts a mechanical or structural system. An excellent example of forced vibration is a building’s vibration during an earthquake — the building’s frequency remains stable until the earthquake strikes and its energy undergoes a forced change.
- Damped vibration: Damped vibration occurs when gravitational or friction forces slow and eliminate forced vibrations. Many mechanical components and products come with built-in vibration dampers to minimize the effect of vibrations. For example, shock absorbers in cars work to dissipate vibrations from rough driving conditions. Testing for damped vibration helps to ensure those products are meeting their requirements.
Measurable Parameters of Vibration
Vibration testing analyzes the following parameters, typically in the frequency domain, to understand the condition of the test object:
- Velocity is the speed at which an object moves in a given direction during the test period. It’s directly related to the destructive force of vibration, making it a critical parameter to measure. It emphasizes both low and high frequencies equally.
- Acceleration measures how quickly movement picks up speed in a given period. This measurement is most effectively studied in high-frequency vibration testing because it emphasizes high frequencies. It can also be converted to velocity or displacement for additional insight.
- Displacement is the distance the measuring point has moved during the testing period. In contrast to acceleration, displacement emphasizes low frequencies and is mostly useful for broader evaluations.
Other important vibration characteristics to measure include:
- Intensity measures how far an object moves from its stationary position during vibration. Intensity is determined by analyzing a vibration’s amplitude.
- Periodicity measures the number of times a wave’s amplitude pattern repeats during a specified amount of time. Periodicity is determined by analyzing wave frequency.
- Resonance is when the force applied to the test object vibrates at the same frequency as the object’s natural frequency. Resonance results in the external force transferring the maximum amount of energy to the test object, which may reveal the limit of the test object.
What Is Vibration Testing?
Vibration testing analyzes vibration patterns within mechanical systems or individual components and structures to identify defects and evaluate the test object’s overall condition.
Vibration analysis allows manufacturers and engineers to:
- Detect and diagnose structural or system defects
- Determine a product’s limits and tolerances
- Ensure products are qualified for their intended purposes
- Confirm compliance with quality standards
- Improve product quality and durability
How Does Vibration Testing Work?
There are two ways to conduct vibration analyses — in the time domain or the frequency domain. The analysis you choose to run depends on what information you wish to gain.
Time Domain Analysis
Vibration waveforms occur in the time domain, which is graphed as amplitude against time. Analyzing this waveform can reveal general information about when and how a system is experiencing abnormalities.
Engineers conduct time domain analyses by extracting and studying the wavelength using the following parameters:
- Root-mean-square (RMS)
- Peak amplitude
- Standard deviation
- Crest factor
Ultimately, time domain analyses are best for diagnosing the overall condition of a system or component — a spectrum analysis is usually more effective in finding specific issues.
Frequency Domain Analysis
Transforming a wavelength to a spectrum using the Fast Fourier Transform (FFT) algorithm puts it in the frequency domain, which decomposes the wavelength into all its frequencies.
This methodology provides a more in-depth analysis than examining the wavelength in the time domain. Two ways to conduct frequency domain analyses include:
- Joint analysis: Vibration signals vary over time, so analyzing multiple spectrums simultaneously using the Gabor-Wigner-Wavelet technique is useful for getting a more detailed look into potential system issues.
- Modal analysis: Modal analysis studies the dynamic properties of a system or component within the frequency domain. This methodology utilizes computer software to visualize the different modes of vibration that the test object is experiencing. By adjusting variables such as stiffness or mass, you can understand how the test object will respond to different stimuli.
Vibration Testing Methods
There are three primary methodologies for vibration tests — sinusoidal, random, and composite. Each one reveals something different about the test object, so it’s important to carefully define which test you need to conduct before getting started.
Sinusoidal Vibration Testing
Sinusoidal or sine vibration testing is the oldest and simplest vibration testing method. The name comes from the plot produced by a sinusoidal vibration, which resembles a sine wave.
This method works by applying predictable, linear vibrations to the test object. It can be done in one of two ways:
- Applying a single focused tone to find the test object’s natural frequencies
- Sweeping the applied vibration across the frequency range to identify resonance frequencies and evaluate the object’s endurance over successive sweep cycles
Sinusoidal testing allows you to study how products behave under sustained extreme conditions, but it cannot accurately examine how a product will tolerate real-world conditions. For this reason, sine testing is best for low-risk products intended for light- and medium-duty applications, such as small household products.
Random Vibration Testing
Random vibration testing is an advanced testing method that introduces random variables into the test environment to replicate the unpredictable environments outside the lab.
Typically, random testing uses shakers that allow the operator to apply vibrations to the test object at random intervals. This process provides insight into the product’s ability to withstand the stresses of everyday operation — for example, if a product gets damaged quickly during random testing, the manufacturer will know to go back and examine how to improve its durability.
Random vibration testing applies to all types of objects, but it’s especially critical for high-risk products intended for heavy-duty applications, such as military equipment or airplane components.
Composite Vibration Testing
Some applications require more specific testing than is possible using sine or random vibration testing alone.
Popular composite methods include sine-on-random and random-on-random testing, but the combination possibilities are virtually endless.
Combined Environmental Testing
Environmental factors such as temperature, humidity, and altitude significantly affect an object’s vibration. By controlling for and altering environmental variables during vibration testing, you can create a test environment that accurately reflects real-world conditions.
Benefits of Vibration Testing
Here’s why vibration testing is such an essential part of the research and development process for products of all kinds:
- Increases reliability and longevity
- Reduces cost to manufacture parts by eliminating over-designed parts/components (packaging, shipping, phones, etc.)
- Designed and built for their operational environment
- Regular vibration testing streamlines predictive maintenance procedures
- It helps your company remain compliant with important quality standards
Tools for Vibration Testing
Choosing the right testing instrumentation for your application is key to collecting accurate, high-quality data.
Most vibration test systems involve one of the following sensors:
- Load cell
- Torque cell
- Strain gauge
These sensors attach to the test object or the surface the test object rests on, such as a shaker table.
A shaker system tests an object by subjecting it to swept-sine, random and transient shocks.
Typical shaker systems consist of several different parts that work together to collect data:
- The vibration control system (VCS) initiates and controls the shaker’s movement based on the type of test the operator wishes to conduct.
- The power amplifier or hydraulic power supply provides sufficient power to move the shaker throughout the specified test duration.
- The accelerometer measures the acceleration of the test object and sends control signals to the VCS.
You can use three different types of shakers:
- Mechanical vibration shakers: Mechanical shakers are the most common shaker type across most industries. Their simple design makes them easy to operate and reliable, but they’re limited in oscillation adjustment and vibration speed.
- Servo-hydraulic (SH) shakers: An SH shaker works by electrically activating a hydraulic vibration table, which applies the vibration to the test subject. Because they have more adjustment capability than mechanical shakers, these instruments are best for mid-range applications.
- Electrodynamic (ED) shakers: ED shakers are well-suited for advanced applications, such as aviation and aerospace manufacturing, due to their fine-tuning capabilities and ability to reach high vibration rates.
How to Know Which Tool to Use
Using the right tools is critical to obtaining accurate and complete data. You want to choose the tool that can safely accommodate the items you wish to test and create an appropriate test environment.
Considering the following factors can help you determine which instrument is best for the test you wish to run:
- Type of test
- Sampling rate
- Vibration levels
- Dynamic frequency range
- Maximum velocity
- Maximum frequency
- Typical operating environment
- Testing duration
If you’re having trouble finding a suitable off-the-shelf tool for the tests you need to run, look into a custom solution. Working with a trustworthy manufacturer like Team Corporation helps you create a vibration testing solution to meet your unique requirements, so you can expect reliable results every time.
Applications for Vibration Analysis
Vibration analysis is essential for products across all industries. Some examples of real industrial applications include:
- Aerospace: Rockets and probes experience extreme vibrational forces from takeoff to touchdown. For example, NASA’s Space Launch System (SLS) must undergo extensive modal testing to determine the rocket’s natural frequency before it can launch. This analysis helps controllers distinguish the rocket’s natural frequency from external vibrations, which is crucial information for effective operation while in orbit.
- Automotive: Testing vehicle parts before installation helps manufacturers reduce or even eliminate the risk of defective systems.
- Aviation: Extensive vibration testing helps aircraft manufacturers detect flaws in parts, preventing potential system failures from turning into accidents during operation.
- Civil engineering: Civil engineers use vibration testing to identify potential structural flaws in bridges, buildings, and pipelines.
- Consumer goods: Household products need to withstand the demands of everyday use. Vibration testing helps establish the limits of these products and ensure their safety for end users.
- Defense: By utilizing vibration testing, defense manufacturers can ensure that equipment and weapons systems are safe to transport and effective in combat situations.
- Electronics manufacturing: Electronics manufacturers conduct vibration tests on prototypes to identify potential breakage and defects.
- Equipment maintenance: Vibration testing allows you to monitor the condition of industrial machinery and all its parts, including complex components like meshing gear teeth, combustion equipment, and rotating shafts.
- Medical equipment manufacturing: Hospital equipment failure is literally a matter of life and death. By testing products before release, manufacturers can prevent failures in critical life-saving equipment.
Important Standards for Vibration Testing
Various industries and standards organizations have documented vibration testing regulations and standards to define acceptable results. Some noteworthy standards include:
- MIL-STD-810: Method 514 of this military standard — last updated in 2019 — defines acceptable vibration test methodology for rugged equipment.
- ISTA Testing Programs: Programs from the International Safe Transit Association (ISTA) are designed to ensure that products can withstand the random high-frequency stresses of transport.
- ISO 10816: This directive from the International Organization for Standardization (ISO) defines standards specific to vibration testing applications across all industries.
Choose Team Corporation for Your Vibration Testing Needs
At Team Corporation, we provide various solutions to address all your vibration testing needs. Our precision vibration testing systems deliver accurate, high-quality results you can trust to provide valuable insight into your products.
We’re committed to delivering on our promises. When you choose our vibration test solutions, you’ll get a reliable warranty and ongoing support throughout your equipment’s useful life. Contact us today for more information about our vibration testing products, or get in touch with one of our global representatives to discuss how our products can address your unique testing requirements.