Vibration Test Fixtures – Why worry about them?

The Importance of  Vibration Test Fixtures

For most projects, the design of vibration test fixtures is often left to the last minute.  Regardless of your industry, vibration testing is one of the most important tools in product test and evaluation.  A well designed fixture will provide ample rigidity to prevent resonances that can result in product over test.  It will help provide confidence that the vibration encountered by the unit under test is representative of the required spectrum.

Using you own

Using your own vibration test fixture as opposed to using one from a test facility has many benefits.  Fixtures laying around test labs are often drilled out and adapted for any number or customers’ immediate requirements.  If retesting is required, having your own fixture assures you of a more repeatable test regardless of the test facility you may use.  The same fixtures can also be used for shock testing where rigidity and strength are requirements.  Using vibration test fixtures in environmental chamber tests for can facilitate proper orientation of equipment and prevent accidental damage to interconnected test items during removal from the chamber.

Designing your Fixture

Rigidity is the major consideration in vibration fixture design.  A microscopic deflection in any part of the fixture can result in alarming resonances and nulls.  Aluminum is an excellent material for vibration test fixtures as it provides the required rigidity while minimizing weight.  The US Government’s Department of Defense has substantial research available for US Companies to use for designing a vibration test fixture.

Consider the intended orientations of test items and provide mounting holes for test items so that they can be easily installed and removed.  Time goes by quickly in the lab.  Use through-bolt for mounting the test item as threads in the fixture will fatigue over time. Provide ample through holes for mounting the fixture to the test equipment, especially if you plan to conduct multi-axis (X,Y,Z) testing.

Validate your Fixture

Before using your vibration fixture in testing it is beneficial to perform a resonance scan  to check for any unwanted responses.  This is accomplished by attaching multiple accelerometers to the fixture, and sending low-level random signals that cover the frequency range of your intended test.

CVG Strategy Experts

Our experts at CVG Strategy have extensive experience in Environmental/Dynamic and EMI/EMC testing for a number of industries and products, both military and commercial.  CVG Strategy specializes in Independent Developmental Testing and Evaluation including development of Test Plans, Test Procedures, Test Witnessing and Troubleshooting.

CVG Strategy is a consultancy offering coaching, mentoring, training and program development focused on areas including Business Process Improvement, ITAR and Export Compliance, Cyber Security and Quality Management Systems.  For any additional questions, please contact us now!

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