What is Noise Vibration and Harshness Testing?
Noise Vibration and Harshness testing (NVH testing) is a critical component of any product during its design and development phase. Not only do manufacturers need to meet established requirements laid out by governing bodies such as The Environmental Protection Agency, but also severe noise and vibration are harmful to the human body and can be detrimental to the structural integrity of almost all consumer goods. In order to make products that last longer and sound better, physical testing should accompany all FEA models to ensure proper correlation, as well as give confidence in the design.
With the growing popularity of the electric car, automotive manufacturers will see an ever-increasing need to conduct NVH testing such as Buzz, Squeak & Rattle (BSR). Given the lack of engine noise present, many sounds that may have gone unnoticed may now become a nuisance to customers, leading to complaints and possible returns. Many of the BSR problems can be detected early in the development period with simple testing such as running a component through developed vehicle profiles or sine sweeps on a BSR shaker in an anechoic chamber. These chambers are designed to mimic a "Free Field" in which sound waves are permitted to propagate freely in all directions outwards but not return. This type of testing can be useful in localizing the source or cause of an unwanted sound, allowing manufacturers to modify their designs before the product becomes a warranty issue.
BSR testing can be completed in one of two ways, subjectively or objectively. With a subjective evaluation, typically an individual or panel of individuals will listen to the noise generated by the structure under vibration and assess its perceived characteristics. Likewise, an objective test will utilize actual measurements along with hardware such as microphones to establish noise levels in several useful units including dBA, Sones, and so on.
Another critical aspect of NVH testing is Modal Analysis. Since all structures and mechanisms (including the human body) inherently have resonances to which they vibrate at, it is key to identify and avoid these frequencies whenever possible. When a system is excited at its resonance frequency, the amplitude at which it oscillates is at its maximum and can lead to premature wear of components, fatigue, or even sudden total loss of structural integrity. For example, aircraft manufacturers must comply with FAA Title 14 CFR Part 23, which requires the manufacturer to undergo ground vibration testing of all airframes to identify the structures resonances before an airworthiness certificate is issued. This process is completed on all new airframes, as well as changes to existing designs as any modifications to the structure will change the frequencies at which it resonates.
There are two principal methods in which modal analysis is conducted, either with force input via a modal tuned hammer or an electrodynamic shaker. Selecting the best option for structure excitation and boundary conditions to apply depends upon the structure tested and the specific data set of interest to product designers and developers. Regardless of the excitation method chosen, the primary information extracted is relatively the same, with resonances identified via the Frequency Response Function (FRF), between the force input and acceleration output on the structure.
These and other types of NVH testing offered by Element include:
- Sound Power and Sound Intensity
- Natural Frequency Analysis
- Determination of Rigid Body Properties (CG, Moments & Principal Axis of Inertia)
- Sound Quality
- Order tracking and analysis for rotating machinery
- Transfer Path Analysis
- Static and Dynamic Structural Stiffness
Element experts use industry leading NVH testing methods, hardware, and software to assist our customer in developing safe, quality, compliant, and enjoyable products to bring to the marketplace.
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