Use the gunfire shock lab test to evaluate the performance of a material likely to be exposed to a gunfire shock environment in its lifetime. As a certified military testing lab, we realize the importance of MIL-STD gunfire shock testing. Meeting the MIL-810 testing requirements can be difficult. Keystone Compliance understands the challenges and guides companies through the process.
Our pricing is competitive and we offer volume discounts. Thus, our proven process helps avoid product launch delays. Keystone Compliance partners with customers to achieve MIL-810 standard product compliance. Our accurate test reports are delivered quickly. We have a reputation of helping customers achieve their MIL-STD product certifications.
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The Importance of MIL 810 Gunfire Shock Compliance Testing
MIL-STD-810 Gunfire shock tests are performed to provide confidence that material can withstand relatively infrequent, high rate repetitive inputs. These inputs can be found in working environments during the firing of guns.
The gunfire shock method 519 environment may be considered to be a high rate repetitive shock.
Repetitive shock applied to a complex multi-modal material system will cause the material to respond in two ways. First it will respond at forced frequencies imposed on the material from the external excitation environment. Second, it will respond to the material’s resonant natural frequencies either during or immediately after application of the external excitation.
Such a response may cause:
- Material failure from increased or decreased friction between parts, or general interference between parts.
- Changes in material dielectric strength, loss of insulation resistance, and/or variations in magnetic and electrostatic field strength.
- Materiel electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. Sometimes circuit card contaminants with the potential to cause short circuits are dislodged under material response to a gunfire environment.
- Permanent mechanical deformation of the material due to overstress of material structural and non-structural members.
- Collapse of mechanical elements of the material because the ultimate strength of the element is exceeded.
- Faster fatiguing of materials a.k.a. low cycle fatigue.
- Potential piezoelectric activity of materials.
- Material failure due to cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.
Selecting MIL-810 Method 519 Gunfire Shock Compliance Testing
After reviewing the requirements and test reports, the following must be used to confirm the need for this MIL-STD 810 compliance test. This sequence should be placed with other MIL-810 methods. Exposure to a gunfire shock environment has the potential to produce adverse effects. Effects take into account the integrity of all materials including in-service capability.
The gunfire firing rate and the duration of gunfire shock environment exposure that correspond with natural frequencies of the mounted material will magnify the adverse effects on the material’s overall integrity.
Information on the Standard
Placing this shock testing method among other MIL-STD-810 test methods will depend on the types of testing. This includes design development, qualification, endurance testing and more. Normally, test method 519, the gunfire shock test would come in the beginning of the test sequence. This includes after other shock tests have been performed.
If the gunfire shock environment is deemed severe, perform the MIL-STD 810 lab test first. However, if deemed less severe than vibration testing, the gunfire shock tests may be deleted from the testing.
It is never acceptable to naturally conclude that the MIL-STD 810 test levels are less severe than mechanical shock tests. Methods for comparing severity of shock cannot be used to assess the harshness of test levels between gunfire and simple mechanical shock.
It is important to note that the standard shock environment may affect material performance. Especially when material is tested simultaneously to other environmental conditions.
MIL-STD-810 Standard Gunfire Shock Testing Procedures
The gunfire shock compliance test contains three procedures. In many cases, one or more procedures will apply to material being tested.
Be sure to consider the following information prior to choosing a procedure:
- Measured material response available and unavailable
- Purpose of the material to determine the functions to be performed on the material
- Natural exposure circumstances
- Data required to document the test environment
- The procedure sequence.
Procedure I – Measured Material Input/Response Time History Under TWR – This procedure measures in-service gunfire shock environment for material that is replicated under laboratory exciter waveform control to achieve an exact reproduction of the measured in-service gunfire shock environment.
Procedure II – SRS Generated Shock Time History Pulse Sequence under TWR – This procedure is based on former processing measured gunfire shock in terms of the SRS applied either to individual gunfire pulses or the SRS applied to the overall gunfire pulse sequence. It is critical that the percent of critical damping considered in computation of the STRS and gunfire rate of interest must be known and defined. This procedure will be required if measurement time history is inaccessible.
Procedure III – Stochastically Generated Material Input From Preliminary Design Spectrum Under TWR – This procedure is ad hoc, lacking necessary field measured time trace information, and a last resort to providing guidelines for design material to resist a gunfire shock environment. Procedure III may be used to predict the gunfire repetitive shock environment.
Limitations Regarding the MIL-810 gunfire shock test
This 810-test Method provides limited information with regard to the prediction of input levels to material. This is based only on the gun parameters and the geometrical configuration between the gun and material.
It may not be possible to replicate some service gunfire response environments. This may be because of impedance mismatches, particularly laboratory fixture limitations or other physical constraints. In addition, this military standard test method:
- Does not provide guidelines for separating air-borne from structure-borne excitation input to material.
- Does not provide guidance on techniques for isolation of material from the source of excitation.
- Does not include provisions for performing gunfire tests at high or low temperatures. Perform tests at standard ambient temperature unless otherwise specified.
- Is not intended to simulate blast pressure or acoustic effects on material as a result of exposure to gunfire environments.
- In general, it provides limited guidance on material response to gun excitation from simultaneous firing of more than one gun.
Keystone Compliance Provides Gunfire Shock 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-STD-810 gunfire shock testing, Keystone has a full scope of expertise including solar radiation, fungus, freeze-thaw, and humidity.
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