Vibration Testing for military compliance is a crucial aspect for products aiming to serve in military applications. To ensure that these products can endure a severe military environment, they must undergo rigorous testing at a state-of-the-art vibration testing lab. This process involves defining the environmental life cycle that the product will encounter and then developing and executing a qualification test plan based on specific military standards. Completing these tests and documenting them in a detailed report is integral to achieving military compliance.

Why Perform Military Compliance Vibration Testing?

Military compliance vibration testing is especially crucial for military products integrated into complex and costly systems, where failure can lead to significant consequences. The principle reasons for executing this testing include the following:

1. Ruggedizing Your Product:  Testing your product to a military standard vibration profile will ensure that it can withstand harsh vibration exposures that it would experience throughout its life cycle.
2. Evaluating Performance: Military compliance vibration testing ensures that items will perform properly under harsh vibration conditions.  If your component does not function properly, it could cause a failure of a complicated system. 
3. Reducing Maintenance and Preventing Field Failures:  A robust product will have less or no field failures, reduce downtime and maintenance which is critical for military applications. 

Focusing specifically on vibration testing for military compliance, this article delves into various military standards that are vital in evaluating a product’s durability and ruggedness. These include MIL-STD-167, MIL-STD-202, MIL-STD-750, MIL-STD-810, and MIL-STD-883, each with their specific testing methods for a range of environmental conditions including sinusoidal and random vibration testing.

• MIL-STD-167 Department of Defense Test Method Standard – Mechanical Vibrations of Shipboard Equipment
• MIL-STD-202 Department of Defense Test Method Standard for Electronic and Electrical Component Parts
• MIL-STD-750 Test Methods for Semiconductor Devices
• MIL-STD-810 Department of Defense Test Method Standard for Environmental Engineering Considerations and Laboratory Tests
• MIL-STD-883 Department of Defense Test Method Standard for Microcircuits

MIL-STD-167 applies to equipment installed on Navy ships with conventionally shafted propulsion.  MIL-STD-167-1 covers mechanical vibrations caused by unbalanced rotating components of Naval shipboard equipment.  MIL-STD-167-2 is for mechanical vibrations from reciprocating machinery and lateral, longitudinal vibrations of propulsion systems and shafting. 

MIL-STD-202 establishes uniform methods for testing electronic and electrical component parts.  MIL-STD-202 defines component parts to include capacitors, resistors, switches, relays, transformers, inductors, etc.  This standard is intended to apply only to small component parts, weighing less than 300 pounds or having a root mean square test voltage up to 50,000 volts. 

MIL-STD-750 is intended to apply only to testing semiconductor devices.  Semiconductor devices include such items as transistors, diodes, voltage regulators, rectifiers, tunnel diodes, and other related parts.

Contact DES, where precision meets passion for excellence.

MIL Standard 810 Testing: The DES Commitment

MIL-STD-810, known for its stringent requirements, is crucial for products intended for military use, and at DES, we ensure that these products meet and exceed these rigorous standards.

Our approach to MIL Standard 810 testing is comprehensive and meticulous. We understand that each product has its unique set of challenges and requirements. Therefore, our testing process is not just about meeting the basic compliance standards; it’s about thoroughly understanding the product’s lifecycle and the environmental stresses it will endure.

Our state-of-the-art facilities are equipped to conduct the methods under MIL-STD-810H, ensuring that we cover a wide range of environmental conditions. From high and low temperatures to shock and vibration, our tests are designed to mimic the harsh conditions that products will face in real-world military environments. This thorough testing not only ensures compliance but also aids in enhancing the product’s design and durability.

Choosing DES for MIL Standard 810 testing and all other military compliance testing means partnering with a team that values precision, quality, and customer satisfaction above all else. Our experience and expertise in this field make us a trusted partner for numerous manufacturers, from small component producers to large-scale military equipment manufacturers.

Contact Delserro Engineering Solutions today to learn more about our MIL Standard 810 testing services and how we can assist in bringing your products to the highest standards of military readiness and reliability.

MIL Standard 883: Advanced Testing for Microelectronics

As mentioned in the previous list, MIL-STD-883 is critical for the testing of microelectronics used in military applications. This Department of Defense Test Method Standard for Microcircuits is essential for ensuring that microelectronic devices can withstand the demanding conditions of military use. MIL-STD-883 encompasses a comprehensive suite of test procedures tailored to assess the robustness and reliability of various microelectronic devices, including monolithic, multichip, film, and hybrid microcircuits, as well as microcircuit arrays and their constituent elements.

The standard plays a pivotal role in validating the endurance of microelectronics in extreme environmental conditions. This includes evaluating their performance under conditions of extreme temperature, vibration, and other stress factors that are commonly encountered in military environments.

For manufacturers and designers of microelectronic devices, adhering to MIL-STD-883 is not just about compliance; it’s about guaranteeing the highest levels of performance and reliability of their products in some of the most challenging conditions. This is especially crucial given the increasing complexity and miniaturization of electronic components in military hardware.

Delserro Engineering Solutions (DES) provides comprehensive testing services to ensure compliance with MIL-STD-883. Our advanced testing capabilities help manufacturers navigate the complexities of MIL-STD-883, offering the assurance that their microelectronics meet all necessary military specifications. With our state-of-the-art facilities and technical expertise, we are equipped to handle the rigorous testing requirements of MIL-STD-883, delivering results that manufacturers can trust for their high-performance microelectronic products.

Vibration Testing Lab: Cutting-Edge Solutions by DES

At Delserro Engineering Solutions (DES), our state-of-the-art vibration testing lab is equipped to provide comprehensive solutions for military compliance. Understanding the criticality of these tests for military applications, we offer advanced testing procedures that replicate the exact conditions products will face in the field.

Moreover, DES recognizes the importance of customizing vibration testing to meet the specific requirements of each product and its intended use. Whether it’s testing for land and sea vehicles, aircraft, helicopters, or ground transport, we tailor our vibration testing procedures to ensure the most relevant and rigorous evaluation.

Our expertise extends beyond just executing standard tests. We work closely with our clients to develop comprehensive test plans that not only meet the required standards but also provide valuable insights into product performance and potential areas for enhancement. This approach helps in identifying and rectifying deficiencies early in the design process, saving time and costs, and ultimately leading to a more robust and reliable product.

With DES’s vibration testing lab, clients can expect not just testing, but a partnership that focuses on enhancing the quality and durability of their products. Reach out to us to discuss how we can assist in fulfilling your military vibration testing requirements with our cutting-edge solutions and expert guidance.

Contact DES today to discuss your vibration testing lab requirements.

If you want to learn more about vibration testing, please read these related blog articles:

MIL-STD-810 Vibration Testing Overview

MIL-STD-810: Vibration Testing Category 4 – Truck/Trailer – Secured Cargo

MIL-STD-810: Vibration Testing Category 9 – Aircraft – Helicopter

MIL-STD-810: Vibration Testing Category 7 – Aircraft – Jet

MIL-STD-810: Vibration Testing Category 8 – Aircraft – Propeller

MIL-STD-810: Vibration Testing Category 12 – Fixed Wing Jet Aircraft

MIL-STD-810: Vibration Testing Category 15 – Aircraft Stores

MIL-STD-810: Vibration Testing Category 20 – Ground Vehicles – Ground Mobile

MIL-STD-810: Vibration Testing Category 24 – Minimum Integrity Tests (MIT)

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IEC 60068 Explained: A Deep Dive into Vibration Testing Standards

What is IEC 60068 Vibration Testing?

IEC 60068-2 is a subset of the broader IEC 60068 series, which sets out international test standards for various environmental tests on products, equipment, and components. Included within the IEC 60068-2 series are the vibration test standards:

• IEC 60068-2-6 Environmental testing Part 2-6: Test Fc: Vibration (sinusoidal)
• IEC 60068-2-64 Environmental testing Part 2-64: Test Fh: Vibration, Broadband Random, and Guidance

DES has extensive experience performing many vibration tests to IEC 60068-2-6 and IEC 60068-2-64.  We are A2LA accredited to those standards. 

Why perform IEC 60068 Vibration Testing?

• All products will likely experience some vibration during their lifetime from shipping and transportation.  Thus, some level of vibration testing is valuable. 
• For items being sold outside of the USA, the results from vibration testing to IEC 60068-2-6 and IEC 60068-2-64 are accepted worldwide.  
• IEC 60068-2-6 and IEC 60068-2-64 can be used to evaluate the reliability and performance of products that will be exposed to vibration environments.
• They are useful to assess the durability and performance of connectors exposed to harsh conditions such as military, automotive, and space environments.  During the vibration, the connectors are monitored for intermittent electrical contact with specialized equipment provided by DES. 
• Manufacturers can validate the structural integrity of items and identify possible degradation under different vibration conditions. 
• Automotive and aerospace suppliers can evaluate the reliability, durability, and performance of their components that are subjected to intense vibration during their lifetime.
• IEC 60068-2-6 and IEC 60068-2-64 can be used to investigate structural dynamic characteristics for items used in spacecraft programs.
• Testing to these standards can simulate the stresses that occur during the life of a product giving confidence in its performance and longevity.
• Products can be developed to function and withstand vibration exposures encountered during their life cycle.
• Companies can evaluate the durability and performance of components, equipment, and articles during transportation and service vibration.

IEC 60068-2-6: Sinusoidal Vibration Test Standard

IEC 60068-2-6 is a test standard for Sinusoidal Vibration Testing.  It defines a procedure for testing specimens to sinusoidal vibrations over a specified frequency range for a given duration.  It is applicable (but not limited) to products or components that are subjected to harmonic vibrations such as rotating, pulsating, or oscillating forces that occur in ships, aircraft, land vehicles, rotorcraft, machinery, space applications, and seismic events. 

Much of the IEC 60068-2-6 specification deals with controlling the test parameters.  Other parts cover various test severities such as the vibration amplitude, frequency ranges, and durations.  It is up to the user to choose which test severities are applicable to their products.  Annex A in IEC 60068-2-6 gives some guidance on testing.  Annexes B and C provide examples of severities based on different applications.  The user must also specify whether the specimen shall be functional during the vibration test or whether it can be functionally tested before and after. 

IEC 60068-2-6 endurance testing can be accomplished either by endurance by sweeping or endurance at fixed frequencies.  Endurance by sweeping is performed by continuously sweeping or varying the sinusoidal vibrations from the lowest to the highest to the lowest frequencies for a chosen number of sweep cycles.  Endurance at fixed frequencies is completed by subjecting the specimens to a sine dwell at the product resonances for a fixed duration and vibration amplitude.

Contact DES today to discuss your IEC 60068-2-6 vibration testing requirements with one of our experts.

The Random Vibration Test: An In-depth Look at IEC 60068-2-64

IEC 60068-2-64 is a procedure for Random Vibration Testing of components, products and equipment.  Random vibration occurs in transportation environments, vehicles, aircraft, aerospace, military environments, etc.  Random vibration tests can also be useful for evaluating the general robustness and durability of products and components.  IEC 60068-2-64 defines requirements for subjecting specimens to broadband random vibration tests over a specified frequency range for a given duration.  It is primarily intended for specimens that are unpackaged, however, a packaged product can be tested using transportation vibrations. 

The first part of IEC 60068-2-64 covers controlling the test parameters.  Subsequent parts of IEC 60068-2-64 list various test severities such as the Grms value of acceleration, the frequency range, and the duration of testing.  Similar to IEC 60068-2-6, the user chooses what test severities to apply to their products and if the specimen shall be functional during the vibration test or whether it should be functionally tested before and after.  Annex A in IEC 60068-2-64 provides examples of severities based on different applications.  Annexes B and C provide information and guidance. 

An optional low-level vibration response investigation (sometimes called a resonance scan or modal survey) can be performed before and after the random vibration in each axis.  The vibration response investigation can be either a sinusoidal vibration sweep or random vibration applied for a short duration.  In either case, the vibrations should be low level to avoid damaging the test specimen but high enough to excite resonances.  

Completing the Vibration Test

Once all the severities are chosen in either IEC 60068-2-6 or IEC 60068-2-64, the testing is performed along three perpendicular axes, one at a time.  Upon completion of the vibration test, DES will promptly deliver a detailed test report that includes the customer’s name and address, the test dates, a summary of the test procedure, chosen severities, equipment & measuring system calibration information, operational test data, test observations & results, color pictures of the vibration test setup and color pictures of any failures. 

Secure your product’s market success with DES’s comprehensive random vibration testing services. Contact us now and let’s get started.

DES Your Go-To for IEC 60068 Compliant Vibration Testing

Choosing the right partner for your vibration testing needs is crucial. At Delserro Engineering Solutions, we offer a comprehensive suite of services designed to ensure your products meet the stringent IEC 60068 standards. Here’s why DES should be your first choice:

• Customized Solutions: We design and fabricate your vibration test fixtures tailored to your specific needs.
• Precision and Care: Our test setup process is meticulous, incorporating control and response accelerometer placement, correct bolt torque application, and organized cable routing.
• Quality Assurance: As an accredited laboratory, we adhere to IEC 60068-2-6 and IEC 60068-2-64 test standards, ensuring quality and compliance.
• Advanced Facilities: With our state-of-the-art testing facilities and equipment, we are equipped to handle a wide range of vibration test requirements.
• Extensive Experience: Our team has a broad range of experience in vibration testing, including products used in outer space, rockets, missiles, automotive and truck environments, military environments, and medical environments.

Contact DES today to discuss your vibration testing requirements with one of our experts. 

If you want to learn more about different types of vibration testing, please read these related blog articles:

• Sinusoidal and Random Vibration Testing Primer
• Mixed Mode: Sine on Random Vibration Testing
• Extreme Combined Temperature & Vibration Testing

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Meeting these requirements separately would alone be a challenge for any lab.  Meeting these requirements concurrently requires specialized equipment and test setup.  Good insulation is an obvious concern for this test.  The lab must ensure that heat isn’t transferred to the armature of the shaker or else costly damage can occur to the shaker system.  Extreme temperature accelerometers are also necessary if a lab wants to obtain accurate acceleration data.  DES was able to perform this test with successful results and overcome the challenges associated by utilizing their combined temperature and vibration chamber, Figure 1.

For more information on Combined Temperature and Vibration Testing or other testing services, contact DES or call 610.253.6637.

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Category 4 of Method 514.7 Vibration testing details the transportation random vibration environmental conditions from cargo interaction with vehicle suspension and structures with road and surface discontinuities.  “This environment may be divided into two phases, truck transportation over US highways, and mission/field transportation.  Mission/field transportation is further broken down into two-wheeled trailer and wheeled vehicles categories.”

Truck Transportation over US Highways Vibration Testing

This vibration test method is used when products or equipment will be transported by large trucks tractor-trailers commonly seen on US highways.  The truck transportation over US highways random vibration profile is designed to simulate 1609 km (1000 miles) on interstate highways.  The random vibration profile along each axis can be seen in the plot below in Figure 1.  The length of this profile is 60 minutes per axis for each 1000 miles of transportation.  For example to simulate 2000 highway miles, the vibration test duration would be 2 hours per axis x 3 axes = 6 hours total.

Two-wheeled Trailer Vibration Testing

The two wheeled trailer (TWT) random vibration profile is a subcategory under the Two-wheeled trailer and wheeled vehicles category.  This vibration test method is used when products or equipment will be transported by two-wheeled trailers across paved, secondary, and cross-country road surfaces.  The random vibration profile simulates the cargo conditions of a two-wheeled trailer from the forward supply point to the using unit.  The length of travel to be simulated is 51.5 km or 32 miles.  The length of this vibration profile is 32 minutes per axis and can be seen in the plot below in Figure 2.  The vibration test duration would have to be increased accordingly for longer lengths of travel.

A typical two-wheeled trailer is shown in Figure 3.

Composite Wheeled Vehicle Vibration Testing

The composite wheeled vehicle (CWV) random vibration profile is another subcategory under the Two-wheeled trailer and wheeled vehicles category.  The vibration profile simulates the cargo conditions of transport by trucks or semitrailers across paved, secondary, and cross-country road surfaces.  The random vibration profiles along each axis can be seen below in Figure 4.  The length of travel to be simulated is 800 km (500 mi) from the port staging area to the forward supply point.  The length of this vibration profile is 40 minutes per axis for each 500 miles of transport.

Composite Wheeled Vehicles are military vehicles.  A typical Composite Wheeled Vehicle is shown in Figure 5.

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MIL-STD-810 is a public military test standard that is designed to assist in the environmental engineering considerations for product design and testing.  For the purposes of this blog series we will focus on Method 514.7, titled Vibration.  This section defines the environmental vibration conditions a material or product may experience during the product life cycle and translates these conditions into replicable test procedures.  Unfortunately, unless you’re familiar with this document, this section or any section for that matter may seem a little daunting.  This blog will hopefully provide some guidance into navigating your way through it.

The best place to start is Table 514.7-I which can be found shortly after the table of contents of Method 514.7.  This table basically acts as a summary for the section and directs you to the specific annex to look for the applicable environmental vibration category for your product.  Before you jump to the test profiles, there are some definitions and details worth pointing out.  The different types of test procedures, called out in the last column of the table, are defined further on in this section.  This is important because some of the test procedures require different or unusual test setups which may be more suitable to your product’s environmental vibration exposure.

Test I: General Vibration

This condition applies to material/products “to be transported as secured cargo or deployed for use on a vehicle.  This procedure applies to ground vehicles as well as fixed and rotary wing aircraft.  For this procedure, the test item is secured to a fixture or a vibration exciter, and vibration is applied to the test item as an input.

Test II: Loose Cargo Transportation

This condition applies to material/products “to be carried in/on trucks, trailers, or tracked vehicles and not secured to (tied down in) the carrying vehicle.  The test severity is not tailorable, and represents loose cargo transport in military vehicles traversing rough terrain.”  Essentially, worst case scenario.  For this procedure, the test item is not secured to the vibration exciter, and is free to move during the test.  Typically a fence is built around the vibration table to prevent the product from falling off of the table.

Test III: Large Assembly Transportation

This condition applies to “large assemblies of material installed or transported by wheeled or tracked vehicles.  It is applicable to large assemblies or groupings forming a high proportion of vehicle mass, and to materiel forming an integral part of the vehicle.”

Test IV: Assembled Aircraft Store Captive Carriage and Free Flight

This condition applies to “fixed wing aircraft carriage and free flight portions of the environmental life cycles of all aircraft stores, and to the free flight phases of ground or sea-launched missiles.”

Test procedures I and IV use standard laboratory vibration shakers while test procedures II and III require more specialized equipment.  For the most part, most of the categories in Table 514.7-I call for test procedures I and IV which most test laboratories should have and therefore can be configured to those test profiles.

Once you have determined the application type and test procedure your product/material falls under, you can move on to determining your test profile.  There are a variety of types of vibration profiles that are defined in Annexes B through E of MIL-STD-810 depending on the expected environmental vibration exposures of your product.  General definitions of the different types of vibration profiles can be found in Annex A of MIL-STD-810G Change 1, Method 514.7, however, more detailed understanding of sinusoidal, random and mixed vibration profiles can be found in the associated links as well as below.

Sinusoidal Vibration Testing

Sinusoidal & Random Vibration Testing Primer

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These tests demonstrate the unique capability of Delserro Engineering solutions.  Not many labs are equipped to perform combined temperature and vibration testing at the extreme temperatures of this test or are able to produce the high levels required for random vibration and shock testing.

For more information on Combined Temperature and Vibration Testing or other vibration testing services, contact DES or call 610.253.6637.

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As you can imagine, the stresses of this test can be relatively severe and justifiably so due to the nature of aeronautical environments.  However, vibration is not the only stress aircraft equipment is tested for.  Environmental stresses such as altitude, temperature and shock are also typically seen by most aircraft equipment.   All of these stresses play a role in reducing a product’s reliability.  Therefore, it is important for aircraft equipment manufacturers to test to the proper specifications in order to ensure proper safety when flying.  DES can help you decide what test specifications are best for your product based on their considerable experience and knowledge.

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DES recently performed package testing per ASTM standard, ASTM D7386-12.  The test included shipping vibration testing which was conducted on DES’s Unholtz Dickie ED Shaker System.  ASTM D7386-12 requires packages to withstand random vibration levels of approximately ½ Grms over the frequency range 1 – 200 Hz.  This test is meant to simulate environments these packages could see in the field.  It is extremely important for manufacturers to test the effectiveness of their package designs prior to product shipment.  Shipping environments can put a lot of stress on products.

Improper package design can cause products to fail when the customer receives the product.  Environments such as high altitude, temperature, humidity, vibration and shock are common for most packages.  High return rates due to damage during shipment can cripple a company’s bottom line.  Prevent this from happening and send DES your packages to test!

Other package testing standards DES is capable of include (but not limited to):

• ISTA 1 Series
• ISTA 2 Series
• ISTA 3 Series
• ASTM D3580 Vibration (Vertical Linear Motion) Test of Products
• ASTM D4169 Performance Testing of Shipping Containers and Systems
• ASTM D4728 Random Vibration Testing of Shipping Containers
• ASTM D7386 Performance Testing of Packages for Single Parcel Delivery Systems
• ASTM D999 Vibration Testing of Shipping Containers

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If you have not done so yet, please check out Part 1 – Defining your project and  Obtaining a Quote.

You obtained quotes from a couple of vibration test labs.  Your next task is to select a vibration test lab to perform your vibration test.  Your selection should not be based upon price alone.  Factors that should affect which lab you choose are capability, cost, timing, location, quality, and other special requirements.

Most importantly, the test lab must be capable of running your test.  Running a successful vibration test is not easy.  A good vibration test lab will make it look easy, but running a vibration test requires significant knowledge of vibration theory, fixture design, testing skills, and a skilled operator to run the vibration test equipment.

Of course, cost and timing should be a significant part of your decision.  If one quote is considerably lower than the other quotes, then you should question that lab to see if they misunderstood the project requirements.

Location can be important if you need to haul bulky support equipment to the test lab.  It can also be important if witnesses need to travel and be present during the test.

The lab should have up to date calibrated vibration test equipment.  If you have never used them before and this is a large project, then it would be a good idea to schedule a visit to review their equipment and capabilities.  If your company has special quality or other requirements, then review them with the lab.  Special requirements could be handling, lifting or Electro Static Discharge (ESD).

Planning & scheduling your test

After you have selected a lab, it is time to schedule your vibration test.  First contact the test lab to inquire about their vibration test schedule.  The test lab may be backed up with large projects and may need some time to schedule your test.  DES has multiple shakers with a goal to reduce scheduling time as much as possible.

If any special support equipment is required for the test, then it may take time to gather this equipment and to set it up.  If rental equipment is required, then the time to ship the equipment from the rental company must be considered.  Most importantly, significant time may be required to design and manufacture special fixtures.

Much or all of the planning could fall on the test labs shoulders if they are supplying everything.  Expediting schedules is always an option, but you will likely have to pay more.  It is important to know what each party is responsible to supply.  For instance if assembly is required, who will supply the bolts?  It is a lousy situation for all involved, to plan a test for weeks ahead and then to find that you are missing something during the test setup.  Good communication with the test lab is very important!

Fixture Design and Manufacture

Most vibration test labs can design and make fixtures.  Sometime you may have in-house fabrication capabilities.  However, you may not have the experience to design good vibration test fixtures.  Designing good vibration test fixtures requires specialized knowledge.

The vibration test fixtures should be stiff and light weight.  They should have a high natural frequency.  It is preferable that all resonances fall above the test frequency range, but many times that is not possible especially when testing to high frequencies of 2,000 to 3,000 Hz.  A good rule of thumb is to make natural frequencies as high as possible without adding too much weight.  Easier said than done!  When designing vibration test fixtures, many more bolts are required than for static loading to securely join the fixture to the vibration table and increase the fixture resonances.  Good materials for vibrating test fixtures are aluminum and magnesium.

Figure 1.  Fixture Cube Designed by DES

Computer analysis software such as Finite Element Analysis (FEA) is a great tool for estimating fixture resonances during fixture design.  If the lab is designing your fixture, inquire if they have FEA capability.

Test setup

Setting up the vibration test on the shaker is the responsibility of the test lab.  If the requirements are for your product to be operationally functional tested, then that may fall on your shoulders.  It is very common for DES’s customers to bring support equipment to functional test their specialized products during the test.  Many labs including DES, can also provide support equipment, but it if your product is very specialized, then it probably makes more sense for you to be responsible for this task.  Again, good communication with the test lab is very important to determine the responsibilities for each party.

The test setup may also involve a trial run with the fixtures alone to scan for severe resonances.  This is a good idea especially when testing to high frequencies of 2,000 to 3,000 Hz.  Control problems could occur if the fixtures have a severe resonance in the frequency range of the test causing the shaker controller to abort.  Sometimes (but not always) a large resonance can be “notched out” meaning that the test acceleration levels are reduced significantly at frequencies a little higher or lower than the resonance.  Note that some test specifications will not allow for notching.

Running the vibration test

Finally you are ready to run your vibration test.  Before starting the shaker, all support equipment and the DUT should be operated to verify that it is working acceptably.

Before the vibration testing begins, the shaker controller will first go through a “self-check” to make sure that the amplifier and the vibration accelerometers are connected and producing signal.  It is looking for a “closed loop” between the controller, the amplifier and the control vibration accelerometers.  Once the “self-check” is successful, the operator will start the vibration shaker.  A skilled operator is taught to start up at low vibration levels.  This is typically -12 (≈1/4 of full level) to -6dB (≈1/2 of full level) below the full vibration level (which is 0 dB).  Thus if anything such as a loose bolt was missed during the setup, it can be caught before reaching full level.  So it may take a couple of minutes to ramp up to full level even for an error free setup.  Once at full level, the shaker controller will be constantly adjusting the vibration table to meet the specification.  This is called running in “closed loop”.  The definition of “closed loop” control is contained below.  (Note, in some special cases the shaker can be run in “open loop”, meaning that the controller will not adjust the shaker, but that is a subject for another discussion).  There are abort limits in the controller software to automatically stop the test in case an accelerometer or cable breaks.  Also, if a failure occurs in the product or fixture, it will probably cause an abrupt change in the control accelerometer outputs causing the controller to abort the vibration test.  In addition, a skilled operator knows that a change in the audible sound coming from the vibration test could be a sign of an imminent failure.

Now the shaker starts moving.  What do you need to worry about?  At this point, if everyone did their homework, then the only thing to worry about would be if vibration fatigue causes a failure in your product or if your product does not operate properly.

Most vibration tests are performed along three orthogonal axes, but only one axis at a time.   Time will be needed when changing from one axis to another especially when switching from a horizontal to vertical axis.  Fixtures will need to be unbolted from the table and the lab may need to disconnect from the horizontal slip table, rotate the shaker vertically and then install a vertical head expander.  So if your vibration test is 8 hours in total duration, plan for extra time to switch axes which could mean that your test takes more than 1 day.  The time required to switch to a different axis could be less than 1 hour to 1 day depending upon the size of the product, the complexity of the test fixtures and the support equipment.

Hurray!  Your test completed, your product operated smoothly and no structural failures occurred.  Now it is time to clean up and for the lab to provide a test report.

The definition of running in closed loop is the following:  The vibration controller sends a drive signal to the amplifier.  The amplifier powers the shaker using the drive signal causing it to vibrate.  The vibration levels are sensed by the control accelerometers.  The output from these accelerometers is fed back to the controller.  The controller then adjusts the drive signal to make the vibration levels match the test specification. 

Test report

The vibration test lab should provide a thorough, accurate, well written test report with prompt delivery as a final step.  The test report should include:

1. Photographs of test set-up
2. Location of accelerometers
3. List of test equipment used and calibration status
4. Summary of the test procedure
5. Plots of vibration data
6. Visible observations of the product after the test and summary of the product operational test results (if product was operational during the test)
7. Photographs of any product failures

In conclusion, running a successful vibration test is difficult.  A good vibration test lab will make it look easy, but there are many specialized skills and knowledge required.  We hope that this two part article will help you gain perspective from a vibration test lab’s point of view and to understand what information that you need to provide to perform a successful vibration test.  Most importantly, good communications is essential for a positive experience.  DES looks forward to performing your next vibration test!

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Part 1 – Defining your project and Obtaining a Quote

Vibration testing is a very specialized field, not very well understood by many.  There are different types of vibration and there are an enormous number of vibration test specifications.  Vibration testing equipment is very expensive to purchase forcing many companies to hire a vibration test lab to fulfill their vibration testing requirements.  So what should you expect when Choosing A Vibration Test Lab?

You contact a lab to obtain a quote for vibration testing.  The lab replies with many questions.  You ask yourself, why does the lab ask so many questions just to prepare a quote?  The answer is that details matter and can significantly affect the vibration test time and cost.  This article is written from a vibration test lab’s point of view to help explain what information is needed to perform a successful vibration test.

Before contacting the lab, it might help to ask yourself, what is the purpose of your test? Do you need to comply with customer qualification requirements, improve your product reliability, estimate life expectancy, perform package testing, etc.?  It is more effective to contact the lab after your goals are clear.  It is also helpful if you can prepare a list of requirements or a statement of work or a test plan.  The following are questions that a vibration test lab may ask you:

1. What are the vibration test specifications?
2. What is the size and weight of the product or Device Under Test (DUT), what does it look like and how many samples need to be tested?
3. How will the DUT be mounted?
4. Does the DUT need to be powered and monitored during the test?
5. Do you need response accelerometers on the DUT?
6. Are combined environments (such as temperature) and vibration required?
7. Are any other unique requirements needed for the vibration test?

1. What are the vibration test specifications?

There are many different vibration test specifications and test parameters that need to be defined.  A few common test standards are: MIL-STD-810, MIL-STD-883, MIL-STD 167, RTCA DO-160, IEC 60068-2-64, and IEC 60068-2-6.  However there are many more.  The types of vibration can be random, sinusoidal (sine), sine dwell, sine on random, random on random, sine on random on random.  The most common types of vibration testing services conducted by vibration test labs are sinusoidal and random.  A decision will have to be made as to what type of vibration is needed and if a test specification applies.  Some other test parameters that need to be defined are: acceleration or G level, frequency range, how many axes to be tested, duration per axis, sinusoidal sweep rate and number of sweeps for sine testing, random vibration PSD profile or sine vibration curve.

Many times all of the test parameters above are well defined in a test specification such as MIL-STD-810.  However sometimes they are not and then you will need to provide these details to the test lab.  The reason is that the details do matter and can significantly affect the test time and cost.  For instance a sine sweep from 10 to 2,000 Hz at a rate of 1 octave per minute takes approximately 7.5 minutes.  Performing the same sweep at a rate of 60 Hz/minute will take approximately 33 minutes.  So if you need to perform 10 sweeps per axis x 3 axes, the time to complete each test will be approximately 225 minutes (3.75 hours) at a rate of 1 octave/minute vs. 990 minutes (16.5 hours) at a rate of 60 Hz/minute.  Obviously a test that takes 16.5 hours to complete will cost more than one that takes only 3.75 hours.

Test requirements such as G level and random vibration PSD profile greatly affect the overall difficulty of the test.  Testing at high G levels for larger, heavier products may be beyond the capabilities of some vibration test equipment.  The frequency range of the test will affect the design of the vibration test fixtures.

2. What is the size and weight of the product or Device Under Test (DUT), what does it look like and how many samples need to be tested?

The lab is going to ask you to provide the dimensions of the DUT and the mounting foot print.  This information is required to assess vibration test fixtures and also to determine if the DUT will fit on the vibration shaker table.  A drawing or sketch or picture with some overall dimensions is very helpful.  Ideally the DUT should be mounted to a rigid vibration table or fixture.  It is not a good idea for the product to hang over the sides of the table because that could affect its vibration response.  The size and weight will also affect how many products can fit on the table simultaneously or if multiple groups need to be tested.

That leads into the question of how much does the DUT weigh?  This is important because it may be easier for a vibration shaker to test a 200 pound product at 1 G than a 10 pound product at 20 G’s, (neglecting handling!!).  Vibration shakers are rated for maximum force.  The maximum force is determined from the formula

Force = Mass (or Weight) x Acceleration

The units for Mass are usually pounds or kilograms and Acceleration units are usually G’s or m/s².  Someone inexperienced with vibration testing might think that the same amount of force is required to test a 200 pound DUT at 1G and 10 pound DUT at 20G because the forces are equal using F=MA.  It is important to note that the Mass is not only from the DUT’s but is also from the moving masses of the shaker and fixtures per the formula below:

MASS or Weight = weight of shaker armature + shaker table (slip table or head expander or cube or angle fixtures etc.) + DUT fixture + DUT’s + weight of any other adapter fixtures or significant added moving weight.

For example, let’s say the 200 and 10 pound products will use the same test fixtures and will be used on the same vibration shaker.  Using the assumed weights in the table below, the total moving weight is 425 pounds for the 200 pound product and 235 pounds for the 10 pound product.

Don’t stress too much.  You will only need to provide the weights of components that you are supplying such as the product to be tested, the DUT fixture weight if you are supplying this fixture, and any other significant moving weights that you are supplying such as heavy cables.  The test lab will calculate the required shaker force.The total force required for the shaker is 425 pounds for the 200 pound product and 4,700 pounds for the 10 pound product.  The required shaker force is more than 10 times greater for a product weighing 10 times less!!  The 4,700 pounds of force required for the 10 pound product may overload some small to medium shakers.

Let’s briefly explain the parts involved.  The vibration shaker armature is part of the electrodynamic shaker.  Typically a magnesium head expander is bolted to the armature when testing in a vertical configuration, Figure 1.  A magnesium slip table is bolted to the armature when testing in horizontal configurations, Figure 2.  (Note, we will refer to the head expander or slip table as a vibration table.) These tables have a generic hole pattern.  Usually an adapter plate is used to adapt the mounting pattern of the product to the magnesium shaker tables.

3. How will the DUT be mounted?

The mounting hole pattern of your product will probably not match the hole pattern of the vibration test lab’s tables.  So an adapter plate or DUT fixture will be required as seen in Figures 1 and 2.  The DUT fixture will need to be bolted to the test lab’s vibration table.  Then the product will be mounted to the DUT fixture.  Test labs will not drill holes in their vibration tables because they are expensive specialized fixtures usually made with magnesium.  The DUT fixture is typically an aluminum plate with two sets of hole patterns.  One pattern matches the vibration table while the other pattern matches the product mounting.  To reduce cost and lead-time, DES has generic aluminum adapter plates available and will add holes to fit your product.  Bars and threaded rods can be used to attach products to the vibration shaker for products that do not have mounting holes such as a cell phone.  So the DUT fixture is a cost that will have to be accounted for by you or the test lab.  This cost is usually non-recurring.

4. Does the DUT need to be powered and monitored during the test?

If the DUT needs to be powered and monitored during the test, then clearly this will require support equipment.  This can be a simple or very complicated task.  One complicated setup for a past test took DES months of planning.  It required 3 phase electric, cooling water flowing through the product, and many measurements to be made during the vibration test.

Power can be simply provided from 120 alternating current (AC) single phase wall outlets or it can require complex high voltage 3 phase power from the facility or power supplies. Sometimes AC power requires special frequencies such as 400 Hz for some military equipment.  This is provided from special AC power supplies.  Direct Current (DC) power can be provided from DC power supplies or batteries.

Another important consideration will be if the DUT needs to be electrically loaded during the test.  This can be resistive loading from components such as heaters.  The loading can be inductive from AC motors.  DES has previously built a 6 foot tall test rack of resistors to draw a high load through a product.  On another test, DES had large blowers on the floor to load an air conditioning unit for a rail car.

Monitoring can be from simple visual observations or it can require complex measurements.  Typical monitoring equipment are data loggers, digital multi-meters and oscilloscopes.  Different kinds of sensors can be used to provide monitoring data such as thermocouples or speed sensors.

The big question is who will provide this equipment.  Test labs can typically provide most needed equipment at added cost.  Nobody has every piece of test equipment, but there are test equipment rental companies that provide calibrated test and measurement equipment.

5. Do you need response accelerometers on the DUT?

Some test specifications such as RTCA DO-160 require a resonance scan on the DUT.  This involves installing response accelerometers on the DUT, then performing a resonance scan with low level accelerations (usually 0.5 or 1G) over a frequency range such as 10 to 2,000 Hz.  Or perhaps you are interested in examining the response of your product under vibration loading.  Response accelerometers are usually small and are typically attached to the product with an adhesive such as superglue, Figure 3.  They are not used for control.  Control accelerometers are typically mounted in the DUT fixture.

If you want or need response accelerometers, it is helpful to specify this up front.  While installing response accelerometers on the DUT is typically not a big task (however it can be!), there may be some cost added for this effort.  It does take extra time to install response accelerometers, take pictures for documentation in the report, setup extra data acquisition channels and process a resonance search plot for inclusion in a test report, Figure 4.

6. Are combined environments (such as temperature) and vibration required?

Obviously vibration testing in combined environments is much harder and will be more costly than testing at room temperature.  For now, let’s consider combined temperature and vibration testing.  First, there is some time and effort involved in setting up the chamber over the shaker, Figure 5.  While it varies from lab to lab, the vibration table will be inside the chamber or the table will be flush with the floor of the chamber.  The chamber will be fixed.  There will be space between the chamber and the vibration table.  A rubber membrane will be used to seal the chamber to the vibration table.  The vibrations will occur inside the chamber in a confined workspace.

Many chambers only fit over the shaker when it is oriented vertically and do not fit over a horizontal slip table.  If that is the case, then different types of fixtures are required since testing in 3 axes requires rotating the fixtures, not moving the fixtures from a vertically mounted table to a horizontal slip table, Figure 6.

Also, special charge mode accelerometers are needed for working in extreme temperature environments because standard accelerometers will drift under these conditions.  Accelerometers should be mechanically mounted because many adhesives do not stand up to extreme temperatures.

7. Are any other unique requirements needed for the vibration test?

Unique requirements can be very challenging.  Unique requirements could be mechanical loading, internal pressure, fluid flow, etc.  For mechanical loading, it is preferred to use a spring or bolt mechanism to apply a steady load to keep weight to a minimum.  DES has also performed vibration tests with internal pressure applied to products and fluid flowing through heat exchanger products.  Adding extra weight to vibration tests can demand much more force from the shaker.  Testing with fluids may cause sloshing and extra risk of spillage onto expensive shakers.

Vibration test labs are more than happy to help you with your vibration test requirements.  But please do understand that some effort is needed on your part to define your vibration test requirements.  Good communications is essential for a positive experience.  DES looks forward to hearing from you!

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