By:
Suzanne Phillips - Akron
The Fixture group at MGA Research is
responsible for the design, fabrication and certification of
high quality fixtures used for a variety of tests including
quasi-static structural, dynamic impact, durability, and
vibration applications. The characteristics of the fixture
design are critical to producing a fixture that will
withstand the test without affecting the test results. One
type of fixture design is not suitable for all types of
testing. For example, fixtures used for structural testing
must typically withstand high forces without deflecting or
breaking. These fixtures are typically fabricated from
structural steel and can be relatively heavy. The main
concern with vibration test fixtures is weight (due to the
total force capabilities of the vibration machine), and
resonance issues that may interfere with test results.
Although fixtures are often tested to assure that they will
meet the specific requirements for the test, the use of
Finite Element Analysis (FEA) can address many potential
issues at the design level of the project.
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FEA
Analysis of Fixture Showing Resonance Expected at
Approx. 1500 Hz |
FEA
Analysis of Fixture Showing No Resonance Above Approx.
2000 Hz |
To verify a fixture design before it is built,
the design engineer uses FEA software to analyze the fixture
CAD model to assure that it will meet the design criteria
for a specific test. For example, many vibration tests
require that the fixture be “resonance free” at frequencies
of up to 2000 Hz. Using the FEA software, the design for
the fixture can be analyzed to determine not only the
frequency at which resonance may occur, but also the
location on the fixture where reinforcement can be used to
eliminate this resonance. After the fixture is built,
resonance sweep tests are conducted to assure that there is
no resonance within the specified test range.
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