Vibration test engineers seek to create test profiles that reflect the real world. An accurate test profile better ensures that the product can withstand the vibration environments it will experience in its lifetime.
There are several test development methods in which a product’s environment can be replicated using recorded field data. The result is a test profile that closely reflects—or is the equivalent to—its end use.
FDS: Accelerated Random Test
Cracks or deformation can occur gradually and appear after many years. As such, a test standard may call for a test profile that reflects the fatigue that accumulates over the product’s lifetime. The fatigue damage spectrum (FDS) is a test development tool that calculates lifetime fatigue damage using recorded random vibration. It can combine multiple vibration environments and weigh them based on their prevalence in the field environment.
For test purposes, the FDS can be converted into a power spectral density (PSD), and the test duration can be accelerated. The FDS-correlated PSD is a cumulative spectrum that represents the product’s relative damage based on the weighted environments.
SRS: Complex Shock Test
A basic model of the SRS.
Shock testing helps determine a product’s physical and functional performance during and after a shock event. Shock events can range from small, anticipated transient shocks to large, unexpected seismic events.
The shock response spectrum (SRS) is a tool for evaluating the effect of complex shock. It is a mathematical model that allows engineers to examine the theoretical response of their device under test (DUT) to shock. Many industries use SRS for development and testing; in some cases, the required response spectrum (RRS) is a part of the specifications for product qualification.
STAG: Accelerated Sine-on-Random Test
Sinusoidal and random vibrations often occur simultaneously, and a sine-on-random (SoR) test reflects this real-world occurrence. An SoR test is a fitting choice for an environment with dominant sinusoidal vibration mixed with broadband random vibration, such as that of engines, transmissions, gearboxes, electric motors, pumps, bearings, driveshafts, etc.
Sinusoidal vibration drives a frequency at a particular amplitude, while random vibration testing excites the frequency at random amplitudes. If the sinusoidal vibration exceeds the random levels, the test profile should include these sine tones to represent the field environment accurately.
The FDS is an accepted method for creating a random test from field data. However, FDS is not ideal for processing sinusoidal content. In comparison, an SoR test can effectively generate random energy with sine tones superimposed in the background.
STAG dialog in ObserVIEW.
Vibration Research developed Sine Tracking, Analysis and Generation (STAG) to track, accelerate, and generate an SoR test profile that duplicates these environments on a shaker. Combining the resulting sine and random test profiles allows the engineer to analyze, accelerate, and generate a test that represents real-world environments with dominant sinusoidal components.
Why Use Field-recorded Data?
Data from the field offers a realistic look into the product’s operational environment. A test profile that is as close to the end-use environment as possible leads to an efficient testing process and a quality product.
In the end, understanding the operational environment and using recorded data to develop a correlated test is faster and costs less. Upfront knowledge of failure modes and mechanisms with objective pass/fail criteria is essential. Using quality field-recorded data to develop a customer-correlated test mitigates risk and minimizes the probability of issues down the road.
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