Vibration Testing Fixtures
Case Study – Controlling Fixture Resonances
Resonances are great for musical instruments, but except for some very specialized vibration applications, resonances should be avoided in vibration fixtures.
Almost anything that requires vibration testing also requires a fixture to attach the product to the vibration table. Frequently, little consideration is given to the effects of the fixture on the outcome of the vibration test.A poorly designed vibration testing fixture can either magnify or dampen the vibration energy which the product under test receives.As a result, a good product can fail because of the amplification effect of a resonant fixture and conversely a bad product can pass because of under testing when a fixture exhibits dampening.
The ideal vibration fixture would mimic the mechanical and impedance characteristics of the actual mounting location of the DUT. Since this is really difficult to achieve and even more difficult to repeat between test facilities, the accepted industry standard for vibration fixtures is resonance-free performance.
A poor fixture design will exhibit multiple resonances as well as damping at different frequencies. Each resonance can easily amplify the energy transmitted into the DUT by a factor of 10 or more. In extreme cases or with heavier DUTs, much of the force capacity of the shaker will be used solely to try and control this amplified energy. On the other hand, frequency ranges where the fixture damping the vibration energy, the fixture can reduce the acceleration energy recieved by the DUT by 90% or more. Each of these characteristics makes it difficult or impossible to control a vibration test PSD with the typical +/- 3 dB tolerance.
Where the client cannot supply a fixture for a vibration test, our in-house vibration fixture design team can design and fabricate one to suit your product, the frequency range and the test environment. Our experience ranges from small solid cube fixtures to large complex structures weighing as much as 450 kg.
Each vibration testing fixture we deliver includes a qualification report describing the dynamic response characteristics for each product mounting location.
Design, FEA analysis and fabrication in either aluminum or magnesium.
Analysis and qualification of resonant performance per GMW14906.