MIL-STD 810 Gunfire Shock:
In operational environments where guns are fired, there is a relatively infrequent, short duration transient high rate shock. Gunfire shock tests are performed to ensure that material can structurally and functionally withstand such shock. These tests are performed in gunfire shock testing labs.
Keystone Compliance is a gunfire shock lab with significant experience in MIL-810 gunfire shock testing. Our test engineers have an in-depth knowledge of military gunfire testing standards. This includes MIL-810G gunfire shock and MIL-810H gunfire shock testing standards. This makes Keystone Compliance uniquely qualified to provide gunfire shock certifications for all you commercial, military, and aerospace products.
The following information is extremely technical in nature. It provides a summary of Method 519.8, as derived from the MIL-STD 810H gunfire shock section. Even though the language is from MIL-810H, it applies previous versions of the standard. This includes MIL-STD 810G gunfire shock.
How Ought Method 519.8 Gunfire Shock Be Applied?
Method 519.8 is useful for evaluating the structural and functional performance of material. This material is likely to be exposed to a gunfire shock environment in its life cycle. This Method helps determine a material’s ability to resist a “gunfire schedule” environment without ruining its structural integrity and functional performance. Gunfire schedule refers to the firing rate, the number of rounds fired, and the number of firing events.
The gunfire environment may be considered to be a high rate repetitive shock having form of a substantial transient vibration. This is produced by an airborne gun muzzle blast pressure wave impinging on the material at the gun firing rate. Or by a structure-borne repetitive shock transmitted through structure connecting the gun mechanism and the material. It may also be produced by a combination of these.
When the material surface is closer to direct pressure pulse exposure, several things result. First, the measured acceleration environment is more likely to appear as a repetitive shock environment. In this environment there is a “very short” rise time and rapid decay of material response. Second, the structure-borne repetitive shock contributes less to the overall material response environment.
When the material surface is further from direct pressure pulse exposure, several things result. First the measured acceleration environment is more likely to appear as a structure-borne high rate repetitive shock environment. This is also called substantial transient vibration. This describes some periodic nature that has been filtered by the structure intervening between the gun mechanism and the material.
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.
What are the Effects of Gunfire Shock Testing on Material?
Exposure to a gunfire shock environment may have adverse effects on the in-service operational capability of material. The chance of adverse effects increases with the blast energy of the gun. As well as with proximity of the material to the gun, and the duration of the gunfire shock environment.
Adverse effects on material increase when the gun-firing rate corresponds with natural frequencies of the mounted material. They also increase when the duration of exposure to gunfire shock environment corresponds with natural frequencies of the mounted material. As well as when its sub-harmonics and super-harmonics corresponds with natural frequencies.
What Are the Differences Between Military Gunfire Shock Testing Procedures?
Procedure I is measuring materials input/response time history under TWR. Measured in-service gunfire shock environment for material is replicated under gunfire shock laboratory exciter waveform control. Test
Procedure II is SRS generated shock time history puse sequence unter TWR. This procedure is based on former processing measured gunfire shock. This is based on the SRS applied either to individual gunfire pulses or applied to the overall gunfire pulse sequence. In this procedure, it is assumed that time history information is no longer available for application of Procedure I.
It is critical that percent of critical damping considered in computation of the SRS is known. The gunfire rate of interest must also be defined. The gunfire rate will define a parameter Te. Ideally, the “concentration of energy”, Te will also be provided. If the SRS is applied to individual gunfire pulses some form of “enveloping” the individual SRS estimates may be employed.
In either case a single SRS estimate is obtained. It can be used to generate a single shock pulse time history based upon waveform synthesis or other technology. This single shock pulse time history then can be linked into a shock pulse series and run under TWR. Stochastic variations with departures from single pulse generation are permitted.
Procedure III is stochastically generated material input from preliminary design spectrum under TWR. This procedure is ad hoc. It lacks necessary field measured time trace information. Only time trace forms for design are given.
It is not suggested that testing be performed to these forms for material qualification purposes. This procedure is based on the idea that air-borne or structure-borne gunfire shock is impulsive in nature. Any initial design of material must be on the basis of a repetitive shock pulse. This is as opposed to stationary random vibration with added sine components.
What Gunfire Shock Lab Is Most Trusted for the Best Gunfire Shock Testing?
Looking for the best gunfire shock lab in your area? Contact Keystone Compliance today to work with an expert who understands the requirements of gunfire shock compliance. Keystone has a military gunfire lab, and experienced test engineers. Talk to our experts to develop a streamlined test plan and receive a professional and affordable quote.
As an expert in shock certification, Keystone Compliance has been recognized as one of the best shock labs in the country. Our capabilities include testing to commercial, military, and aerospace shock testing standards. Contact us to learn why so many manufacturers rely on Keystone Compliance to meet their mechanical and aerospace shock testing needs.
There have been several versions of gunfire shock testing procedures in MIL-STD-810 vibration testing. Below is a list of each version and the appropriate method number:
- MIL-STD-810C Test Method 519.2 Gunfire Vibration Aircraft Testing
- MIL-STD-810D Test Method 519.3 Gunfire Testing
- MIL-STD-810E Test Method 519.4 Gunfire Testing
- MIL-STD-810F Test Method 519.5 Gunfire Testing
- MIL-STD-810G Test Method 519.6 Gunfire Testing
- MIL-STD-810H Test Method 519.8 Gunfire Shock Testing