Test method 515 acoustic testing evaluates a material’s resistance to a specified acoustic environment. As a certified military testing lab, we realize the importance of MIL-STD-810 acoustic testing. We understand the challenges and guide companies through the process. Meeting the MIL-STD-810 standard requirements can be difficult.
Keystone Compliance provides comprehensive reports shortly after completion of the MIL 810-testing. Our accurate test reports are delivered quickly. We are in constant communication throughout the entire test process. Thus, our proven process helps avoid product launch delays.
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The Importance of MIL-STD Acoustic Noise Compliance Testing
The acoustic method 515 test is performed to determine the adequacy of material to resist specific acoustic environments without unacceptable degradation of its functional performance and/or structural integrity. Method 515, is applicable to systems, and units that must function and/or survive in a severe acoustic noise environment.
Not only is the acoustic noise method 515 applicable to systems, sub-systems etc. It is also applicable to material located where noise excitation is used. This is in combination with, or in preference to mechanical vibration excitation for the simulation of aerodynamic turbulence.
How Method 515 of MIL 810 Testing Affects Products
The acoustic noise environment is created by any mechanical or electromechanical device. This device is capable of causing large airborne pressure fluctuations. When pressure fluctuations impact material, a transfer of energy takes place.
This takes place between the energy in the surrounding air to strain energy in the material.
The transfer of energy will result in the vibration of material. Because of the large amplitude and broad frequency range, the measurement of material response is important.
The following list is not intended to be completely inclusive. It provides examples of problems that could occur when material is exposed to an acoustic noise environment.
- Component acoustic and vibratory fatigue.
- Component connecting wire fracture.
- Failure of wave guide components.
- Intermittent operation of electrical contacts.
- Cracking of small panel areas and structural elements.
- Optical misalignment of the item.
- Loosening of small particles that may become lodged in circuits and mechanisms.
- Excessive electrical noise.
Information on the MIL-STD 810 Testing
Like vibration, the effects of acoustically induced stresses may affect material performance. Material performance is affected under other environmental conditions, such as, temperature, humidity, pressure, electromagnetic, etc.
When it is required to evaluate the effects of acoustic interferences, it is recommended to expose a single test item under all the relevant environmental conditions in turn. Consider an order of the tests that are compatible with the life cycle and sequence guidance in the individual methods.
The choice of MIL-810 test and military standard test procedures are governed by the in-service acoustic environments and test purpose. Note the environments from consideration of the Life Cycle Environmental Profile as described in the passages above.
This MIL-STD 810 lab method includes three different MIL-810 acoustic test procedures. To determine which of the following shock testing methods would be appropriate, consider:
- The operative purpose for the material.
- The natural exposure circumstances.
- The test data required to determine if the operative purpose of the material has been met.
- The procedure sequence within the MIL-STD-810 acoustic noise test method. If more than one of the enclosed procedures is applied to the same test item, the less damaging procedure is conducted first.
Procedure I – Diffuse Field – This procedure states 2 concepts:
- Uniform Intensity Acoustic Noise. This is a shaped spectrum of acoustic noise that impacts all the exposed material surfaces.
- Direct Field Acoustic Noise. This uses normal incident plane waves to impact directly on all exposed test article surfaces without external boundary reflections.
Procedure II – Grazing Incidence Acoustic Noise – Generally, Procedure II includes a high intensity, rapidly fluctuating acoustic noise. The noise has a shaped spectrum that impacts the material surfaces in a particular direction.
Procedure III – Cavity Resonance Acoustic Noise – The intensity and frequency content of the acoustic noise spectrum is governed by the relationship between geometrical configuration of the cavity and the material within the cavity.
Types of Acoustic Noise Within This MIL-810 Standard Method
Uniform Intensity Acoustic Noise – This MIL-STD 810 compliance test is applicable to material or structures that have a function or survive within an acoustic noise environment. Such as that produced by aerospace vehicles, power plants, and other high intensity acoustic noise. Acoustic tests are not required if the material is exposed to broadband random noise at a sound pressure level less than 130 dB.
Direct Acoustic Field Noise – A direct field is generated by audio drivers. These drivers are arranged to encircle the test article. Two different control schemes can be used to perform a direct field test.
Method one is known as Single Input. Method one uses a single drive signal to all acoustic drivers with multiple control microphones. Method two is known as Multiple Input. This method produces a different field that is much more uniform than the SISO field.
Grazing Incidence Acoustic Noise – Grazing incidence acoustic noise is generated in a duct. The duct is known as a progressive wave tube. Normally, wide band random noise with a shaped spectrum is directed along the duct.
Cavity Resonance – Cavity Resonance is generated when a cavity is excited by the airflow over it. This causes oscillation of the air within the cavity at frequencies dependent upon the cavity dimensions and the aerodynamic flow conditions.
Limitations of the MIL-STD-810 Test Standards
When considering this acoustic lab testing method, there are some important notes to consider. Technical limitations restrict the production and control of laboratory acoustic environments. Therefore, laboratory acoustic fields can be significantly different from many of the real fluctuating pressure loading classes as “acoustic”.
Keystone Compliance Provides Expert Acoustic Noise Testing Services
Keystone has a full lab of test equipment which permits us to provide short lead times on scheduling. Our team strives to give our customers more time and energy on product development instead of testing. In addition to MIL-810 acoustic compliance testing, Keystone has a full scope of expertise including fungus, solar radiation, and freeze-thaw.
Ready to get started? We are. Contact us to see why so many companies work with us to achieve their military standard testing needs.