Single-axis Vibration Testing

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Single-axis vibration testing is the traditional method of vibration testing. A test engineer exposes a test item to a single-axis excitation and then rotates and re-mounts it to test the subsequent orthogonal axes.

A single-axis test assumes that the vibration of each axis is independent. Because of its historical prevalence, single-axis testing is a common method, and many test standards are modeled after it.

When to Use Single-axis Testing

Many test standards call for a single axis sine, random, or shock test. Additionally, engineers can accomplish many test goals with a single-axis test. It is an accessible test method that, at minimum, requires one shaker and basic software (although engineers can use advanced applications if desired).

With a single-axis shaker, a test engineer can determine the resonant frequency of a test item from a sine sweep test. They can then run a sine dwell or random test to bring the product to failure. A single-axis system can run classical and complex shock tests, mixed-mode vibration, accelerated test profiles, fatigue tests, and more. In fact, many engineers will find single-axis systems to be more than sufficient for their testing needs.

Constraints

A single-axis test cannot always capture the multi-directional vibrations of complex structures. Single-axis testing is more time-consuming than its multi-axis counterpart and does not account for the interaction of excitation paths and combined loading. What test items might pass in a single-axis test may fail in service.

However, there is still more technological advancement needed. Multi-axis equipment is more expensive and is not prevalent in every industry. Many testing standards still require single-axis tests, although some test labs are choosing to perform multi-axis testing to improve product quality.

It is important to note that these are simply constraints of single-axis testing; it is still an acceptable vibration testing method.

Frequency Rating

As Clyde Harman and Michael B. Pickel note in the research paper “Multi-Axis Vibration Reduces Test Time,” most servo-hydraulic shaker systems are limited to several hundred hertz. There are multi-axis shakers on the market capable of handling high-frequency tests. However, many industries are still limited to a single axis for tests that exceed standard shaker limits.

As the point of lab testing is to avoid the cost and time it takes to test in the field, single-axis testing will prevail until technology advances and multi-axis testing becomes more prevalent.