Vibration testing of components is a critical aspect of design validation in modern engineering. This type of testing ensures that components do not
fail due to fatigue or fasteners do not shake loose in service. The types of testing regimes vary widely, from the simulation of shipping transportation vibrations of white goods, to launch and inflight vibrations of orbital launch systems. The vibrations can be simple single axis sinusoidal waves, or complex three axis recorded vibrations representative of real world conditions. Frequencies can range from 5Hz to 2,000Hz.
Aside from the shaker, key aspects of a vibration testing system is the support tooling, i.e. Head Expander, Slip plate, and the fixture that supports the component. These items need to be stiff, strong, light weight and have good damping characteristics to reduce resonance amplification levels for improved controllability. Magnesium AZ31B-Tool Plate (TP) is an ideal material for these due to its combined physical and mechanical properties. Damping capacity of Magnesium and its Alloys
Damping capacity is a measure of a material’s ability to dissipate elastic
strain energy during mechanical vibration or wave propagation. When ranked according to damping capacity, materials
may be roughly categorized as either high- or low-damping. Low damping materials maybe utilized in musical instruments
where sustained mechanical vibration and acoustic wave propagation is desired. Conversely, high damping materials are
valuable in suppressing vibration for the control of unwanted noise and for the stability of sensitive systems and
Properties of Magnesium Alloys AZ31B- Tool Plate
AZ31B-TP has a density of 0.064 lbs/inch 3 (1.78g/cm3) which is over 30% lower than aluminum alloys. AZ31B-TP suitable for vibration fixtures and with good damping capacity has a tensile yield strength of 19Ksi, ultimate tensile strength of 35Ksi, elongation of 10% and a Young’s Modulus of 45Gpa.
The low density and high damping capacity make AZ31B-TP the material of choice for vibration test fixtures. Fixtures
fabricated from AZ31B-TP exhibit higher resonant frequencies relative to equivalent aluminium structures. This allows
testing to be carried out at higher frequencies and shorter test times, reducing testing costs. The low density of the
materials leads to fixtures with lower weights. This has several benefits. Firstly, vibration test machines are limited to a
maximum force that they can exert. As F=ma and high acceleration enables higher frequencies with in a defined
displacement, the reduced mass of a magnesium fixture increases the overall envelope of operation of any give vibration
test bed. This can allow multiple parts to be run in the same test, greatly reducing the overall cost.
AZ31B-TP is free machining i.e. cutting fluids are not required. The material generates chips during machining that allow it to be machined at very high speeds. Furthermore, magnesium’s free machining characteristics reduces wear of the cutting tools, greatly increasing tool life. AZ31-B TP is weldable and is stable after subsequent stress relieving. This allows complex fixturing to be fabricated and precision machined.