Vibration Testing Insights

07 Jul 2020

What You Need to Know To Pull Off a Vibration Test

Vibration testing is an integral part of many testing and development programs for a variety of products, such as automobiles, aerospace, appliances, electronics, machinery, electronic equipment, and industrial components.  These evaluations can provide insights into structural soundness, continued use, fatigue, failure modes and more.  To successfully use vibration testing, it is important to understand what vibration is, variations of the testing and how to implement and understand the assessments.

Simply put, vibration is the physical repetitive motion of some object either about or in relation to another point of reference. Vibration can occur in six different directions when not constrained.  This is referred to as degrees of freedom. The first three are around the traditional orthogonal axes--X, Y, Z— that depict height, width, and depth.  Additionally, there are three rotational directions around the orthogonal axes, referred to as yaw, pitch and roll, respectively.

There are two primary types of controlled vibration utilized for testing and evaluation:

1. Sinusoidal or sine vibration, which replicates simple harmonic motion and is considered the simplest form of vibration.  It is measured on a single axis and has the shape of a sine wave, which is where it gets its name. Because of this shape, it has distinct peaks and frequencies. These evaluations, which can be performed as sine dwells or sine sweeps, provide data on peaks and amplitudes—the maximum displacement (acceleration or deceleration)—over a period of time, also providing information on frequency rates.  This testing is useful for evaluating effects of continued use, fatigue or structure related to consistent, repeated use.  The peaks and amplitudes identify stress points and the frequency of issues.
2. Random vibration is motion that is not determined, or predicted, over a period of time. Thus, random vibration offers variations that are not seen in sine vibration and, as such are useful when the future events of vibration is not known. For example, random vibration may be present when a car passes over a rough or uneven surface or air passes over an airplane wing, causing the wing to vibrate. As seen in these examples, these are often real-world occurrences. Indistinct frequencies and phase changes occur.  There are multiple domains in which random vibration can be categorized and measured. The two most common are: time, which measures acceleration versus a point in time, and frequency, where acceleration is measured versus a rate of time, showing how much of the signal lies within each given frequency band, over a range of frequencies.

Vibration testing is a part of many standards for many industries.  Some examples include ISO 16750-3, IEC 60068-2-64 and SAE J1455 and J2380 for the automotive industry; RTCA DO 160 and MIL STD 810G in aerospace; ANSI C135-31 for roadway/area lighting; ASTM D4169 for packaging; and for military equipment and products, MIL STD 810G and MIL STD 202H.

Before embarking on vibration testing, consider what type of test needs to be run. This will depend on the product being tested and the information needed.  Consider as well how many samples are available, fixture types, parameters and breakpoints. 

Get more insights into vibration testing in our webinar recording and stay tuned for a second blog on this subject, looking at fixtures needed for vibration testing.