MIL-STD-810G – Part 15 (Acceleration) Method 513.5

MIL-STD-810G covers steady-state acceleration experienced by material in the service environment. The Method is used to assure material continues to operate after testing.  The Method is also used to assure the material does not become hazardous after exposure to inertial loads experienced in a crash. The method is applicable to material that is installed in aircraft, helicopters, manned aerospace vehicles, air-carried stores, and ground/sea-launched missiles. Method 513.5 is 13 pages long plus a 6 page annex discussing Test Considerations .

 

Method 513.5 includes a note stating that tailoring is essential. A large part of the Method is devoted to tailoring the tests to the material and intended environment.

 

This Method is different from Method 514.6 (Vibration) and Method 516.6 (Shock) in that the acceleration is applied slowly enough with sufficient time allowed to fully distribute the resulting loads through the material and dynamic response of the material is not excited. This method is not adequate for testing aerodynamic loads. Method 501.5 (High Temperature) should be conducted prior to this Method.

 

The effects of acceleration include:

 

1. Structural deflections that interfere with materiel operation.


2. Permanent deformation, structural cracks, and fractures that disable or destroy materiel.


3. Broken fasteners and supports that result in loose parts within materiel.


4. Broken mounting hardware that results in loose materiel within a platform.


5. Electronic circuit boards that short out and circuits that open up.


6. Inductances and capacitances that change value.


7. Relays that open or close.


8. Actuators and other mechanisms that bind.


9. Seals that leak.


10. Pressure and flow regulators that change value.


11. Pumps that cavitate.


12. Spools in servo valves that are displaced causing erratic and dangerous control system response.

 

Section 2 provides formulas for determining g-loads for fighter aircraft because of the high roll and pitch rates and tables of suggested g-loads for other platforms such as helicopters, manned aerospace vehicles, ground-launched missiles, etc. There is also a table of suggested g-loads for the Crash Hazard Acceleration test which goes up as high as 40-g.

 

Required apparatus for testing consists of either a centrifuge of adequate size or a rocket-powered sled.

 

This Method provides for three procedures:

 

1. Procedure I – Structural Test
   
   The item under test is subjected to the specified g-level while not operating. After the test, test the item for proper operation.


2. Procedure II – Operational Test
   
   The item under test is turned on and operating normally while subjected to the g-load.


3. Procedure III – Crash Hazard Acceleration Test
   
   Very high non-operational g-loads are imparted to assure the item under test does not become a hazard during a crash. Items, such as aircrew seats, are tested to ensure they remain attached to the aircraft structure during a crash.

MIL-STD-810G – Part 15 (Acceleration) Method 513.5

MIL-STD-810G – Part 14 (Immersion) Method 512.5

810G covers Emmersion or partial Emmersion in water (or salt water) of equipment. This Method is 7 pages long.

 

This is a rather simple Method. The goal of the tests are to check the item for leaks when submerged in water. There are two Procedures:

 

I. Immersion or submersion

II. Fording

 

Effects of immersion include:

 

1. Fouling of lubricants between moving parts.


2. Formation of electrically conductive paths which may cause electrical or electronic equipment to malfunction or become unsafe to operate.


3. Corrosion due to direct exposure to the water or to the relatively high humidity levels caused by the water.


4. Impairment of the burning qualities of explosives, propellants, fuels, etc.


5. Failure of vehicle engines to operate.

 

For the Immersion test (Procedure I), the item is submerged so the top of the item is 1M below the surface. If the environment anticipates a deeper depth, it may be necessary to use a chamber and pressurize to the test depth, assuring the top of the test item is fully submerged.

 

The Fording test (Procedure II) is primarily targeted at vehicles traversing a body of water or material secured to such vehicles.

 

One facet of the Immersion test to consider is the item under test should be heated 27 deg C above the water temperature. When the item is submerged in the cooler water, it will cool down and the inside pressure will be lower. This may “suck” water into the item. 27 Deg C is specified to simulate solar heating. Otherwise, use 10 deg C as a differential to simulate normal differences between material and water temperature.

 

The Immersion test should last approximately 30 minutes. The Fording test should last an hour.

 

Prior to testing, doors, valves, etc., should be exercised a minimum of 3 times to assure seals are not sticking to the surfaces.

 

After the test, examine the article for leaks. Air bubbles during the test are a good indication of a leak. Weight before and after the test may be a good indication of a leak.

 

As a side note, the immersion test may be used for the rain test. However, rain dynamics can sometimes compromise seals so both rain and immersion tests should be conducted.

 

MIL-STD-810G – Part 14 (Immersion) Method 512.5

MIL-STD-810G – Part 13 (Explosive Atmosphere) Method 511.5

810G covers equipment operated in an Explosive Atmosphere. Method 511.5 is 8 pages long. This Method is performed to:

 

1. Demonstrate the ability of materiel to operate in fuel-air explosive atmospheres without causing ignition, or


2. Demonstrate that an explosive or burning reaction occurring within encased materiel will be contained, and will not propagate outside the test item.

 

This method applies to all materiel designed for use in the vicinity of fuel-air explosive atmospheres associated with aircraft, automotive, and marine fuels at or above sea level. Procedure II specifically relates to atmospheres in a space in which flammable fluids or vapors exist, or can exist, either continuously or intermittently (e.g., in fuel tanks or within fuel systems).

 

The Method provides for two Procedures:

 

I – The item under test operating in an explosive atmosphere without igniting the air/fuel mixture environment.

II – Determine the ability of the test item to contain an explosion or flame that is the result of an internal malfunction.

 

The test involves placing the item under test inside a chamber that is filled with an explosive mixture of air and n-hexane. N-hexane is specified because its ignition properties in flammable atmospheres are equal to or more sensitive than the similar properties of 100/130-octane aviation gasoline, JP-4 and JP-8 jet engine fuel.

 

The chamber is maintained at the maximum temperature the item may experience. Also, altitude is simulated as appropriate. The energy required to ignite a fuel-air mixture increases as pressure decreases.

 

For Procedure I, operate the item in an explosive atmosphere to determine if it will ignite the mixture.

 

For Procedure II, introduce an explosive mixture into the test item and ignite that mixture. Assure the resulting explosion is contained inside the test item and does not ignite the explosive mixture in the chamber.

 

MIL-STD-810G – Part 13 (Explosive Atmosphere) Method 511.5

Mil-Std-810G – Part 12 (Sand and Dust) Method 510.5

810G covers exposure of equipment to dry blowing sand and dust. Think Afghanistan. As with Method 509.5 for Salt Fog exposure, Blowing Sand and Dust is one of the more commonly performed tests. Method 510.5 covers 13 pages. This is one of the shorter duration Methods and can be finished in a day.

 

Dust is defined as particles measuring less than 150um and sand measures in the range of 150 to 850um. There are specs for size distribution within that range for the test dust or sand.

 

Dust exposure is examined for the ability of the item under test to resist vents being clogged, penetration through cracks, crevices, bearings and joints and to evaluate the effectiveness of filters.

 

Sand exposure is designed to test the item for its ability to be stored and operated in blowing sand conditions. Blowing sand can be very erosive, easily stripping the finish from an item allowing subsequent corrosion or operational failure. Blowing sand can quickly render optical devices unusable.

 

This method is not used to evaluate in-flight material such as air frames, propellers, helicopter rotors, etc. due to the velocities involved. This Method is also not used to evaluate the build-up of electrostatic charge. Some care should be exercised with the equipment regarding ESD. Blowing sand and dust can impart a fairly high charge on an item and subsequent handling of the item may cause damage from a discharge. Assure the item and operator are grounded before handling during or after a test.

 

Blowing sand and dust is usually associated with hot-dry regions though it can be experienced in most other regions depending on the season and weather. In addition, military operations can generate large quantities of loose sand and dust which can be picked up by the wind or, potentially, rotorcraft or other aircraft.

 

The effects can include:

 

1. Abrasion and erosion of surfaces.


2. Penetration of seals.


3. Degradation of electrical circuits.


4. Obstruction/clogging of openings and filters.


5. Physical interference with mating parts.


6. Fouling/interference of moving parts.


7. Reduction of thermal conductivity.


8. Interference with optical characteristics.


9. Overheating and fire hazard due to restricted ventilation or cooling.


10. Wear (increased fretting due to imbedding between mating surfaces).


11. Increased chaffing between non-mating contacting surfaces.


12. Weight gain, static/ dynamic balance.

 

Because of potential damage to an article, Humidity, Salt Fog and Fungus Growth testing should be accomplished prior to Blowing Sand and Dust testing. Also consider the corrosive effects of dust or dust residue since salt and highly alkaline materials may be present in the end-use environment.

 

Method 510.5 provides two procedures:

Procedure I – Blowing Dust (less than 150um)

Procedure II – Blowing Sand (150 to 850um)

 

As you will recall, MIL-STD-810G is not a set of tests to pass or not pass but a document guiding the creation of test procedures which are agreed upon between the vendor and customer as to the intended environment. Therefore, part of the process for Method 510.5 is to identify the climatic conditions appropriate for the geographic areas in which the material will be operated and stored. Specific test conditions should be based, if possible, on field data. Method 510.5 offers guidance which can be used in the absence of field data.

 

The test itself, while straight forward, can be brutal.

 

For Blowing Dust, the item under test should be maintained at its high operating or storage temperature. Humidity should be maintained below 30 percent. The air velocity for the test should be a minimum of 300 +/-200 feet/min with a higher velocity of 1750 +/-250 feet/min typical of desert winds. Use local conditions if they are more representative of the intended environment. The dust should have a chemical composition similar to the dust found in the intended environment. For example, in arid regions, soluble salts are common and can cause fouling, corrosion, and electrical shorts. If possible, actual dust from the region should be used in the test. The goal is to have as realistic test as possible.

 

The item under test should be rotated to assure all surfaces face the blowing dust.

 

The test duration should be at least 6 hours at ambient temperature with an additional 6 hours at the high storage or operational temperature.

 

For Blowing Sand, the test is very similar regarding temperature and humidity. However, the velocity is increased to 40-65 mph (3500-5700 ft/sec). The material should be common silica sand. As with Dust testing, it is preferred to match the properties of the sand found in the end-use environment to the test sand. There are 90 deserts in the world, each with different particle size distributions.

 

The quantity of sand in the air during the test is determined by the expected environment:

 

1. For materiel likely to be used close to helicopters operating over unpaved surfaces: 2.2 ± 0.5 g/m3.


2. For material never used or exposed in the vicinity of operating aircraft, but which may be used or stored unprotected near operating surface vehicles: 1.1 ± 0.3 g/m3.


3. For material that will be subjected only to natural conditions: 0.18 g/m3, -0.0/+0.2 g/m3.

 

The item under test should be oriented so that the most vulnerable surface faces the blowing sand. Rotate the item every 90 minutes if more than one vulnerable surface exists.

 

The Blowing Sand test should last 90 minutes per vulnerable face.

 

For Blowing Dust, evaluate the item for binding, clogging, seizure, etc. Does it operate correctly? Check air filter operation to assure the filters are up to the task.

 

For Blowing Sand, evaluate the item for abrasion and operation. Examine protective coatings and seals. Does the item operate correctly?

 

Chassis Plans has taken our military chassis and displays through Blowing Sand and Dust testing and can work with the customer to put a plan in place for 810G compliance.

 

Mil-Std-810G – Part 12 (Sand and Dust) Method 510.5

Mil-Std-810G – Part 11 (Salt Fog) Method 509.5

This is part 11 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers accelerated corrosion using salt fog in Method 509.5.  This method comprises 10 pages. This is one of the more commonly performed tests and is definitely required for items sold to the Navy or for use in coastal areas. Salt is one of the most pervasive chemical compounds in the world. It is found in the oceans and seas, the atmosphere, ground surfaces, and lakes and rivers. It is impossible to avoid exposure to salt.

 

The purpose of Method 509.5 is to assess the effectiveness of protective coatings and finishes on materials. All unprotected metals will corrode if not protected with some finish such as plating or paint. Finishes can also have pinholes or cracks allowing salt to reach the underlying material, causing corrosion. The Method can also be applied to determine the effects of salt deposits on the physical and electrical aspects of the assembly.

 

The effects of a corrosive environment include:

 

1. Corrosion effects such a electrochemical reaction, stress corrosion, and the formation of acidic/alkaline solutions


2. Electrical effects such as impairment of electrical material due to salt deposits, production of conductive coatings causing short circuits, and corrosion of insulating materials.


3. Physical effects such as clogging or binding of moving parts and blistering of paint as a result of underlying electrolysis.

 

Use Method 509.5 for screening purposes only to evaluate the effectiveness and quality of protective coatings and finishes. Either coupons (samples) or the final assembly can be evaluated. The Method is not representative of the natural environment but is a good indicator of potential problem areas. In general, only apply this Method to material that will experience significant exposure to high levels of salt in the atmosphere, such as ship board applications.

 

The Method lists six limitations as follows:

 

1. There is no relationship between this test and any real world exposure duration.


2. It has not been demonstrated that a direct relationship exists between salt fog corrosion and corrosion due to other media.


3. This test has does not imply the material will survive under all corrosive conditions.


4. This test is unreliable for predicting the service life of materials in corrosive conditions.


5. Effects of humidity and fungus growth are not represented in this test.


6. This test is not intended to be used for sample or coupon testing in lieu of assemblage testing.

 

The Method requires a 5% (+/-1%) salt fog be produced and circulated (with minimal air velocity) around the item under test. Condensation should not be allowed to drip onto the test items. This is a fog test, not a salt water exposure test. The test is recommended to last 48 hours with a 48 hour drying time although an alternating 24 hour test cycle (24 fog, 24 drying, 24 fog, 24 drying) has proven to be more destructive. The test temperature is specified as 35 deg C which has been historically accepted and is not necessarily indicative of the actual environment. Alternate temperatures can be used as appropriate.

 

In general, test samples from the salt fog test should not be used in other tests. If only one sample is available or a sample must be reused for other tests, in terms of a schedule, humidity and fungus growth testing should be performed before the salt fog test and sand and dust testing after the salt fog test.

 

After the test, the item should be inspected for physical, electrical and corrosion effects. There can be surprising results. We tested a sample rear panel with a nickel finish compared to a zinc plated finish. As it turned out, the more expensive nickel had apparent pinholes in the finish and failed miserably while the much less expensive zinc coating showed only a light surface corrosion with no damage to the underlying metal.

 

Chassis Plans has worked with various customers to define test procedures, as required by MIL-STD-810G, to validate our rugged rackmount computer systems and displays.

 

Mil-Std-810G – Part 11 (Salt Fog) Method 509.5

Mil-Std-810G – Part 10 (Fungus Growth) Method 508.6

This is part 10 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers fungus growth in Method 508.6.  This method comprises 11 pages plus a 1 page annex on decontaminating equipment after the tests and a 1 page annex on fungus-inert materials.

 

The purpose of Method 508.6 is to assess the extent to which materiel will support fungal growth and how any fungal growth may affect performance or use of the materiel. The primary objectives of the fungus test are to determine:

 

1. if the materials comprising the test object, or the assembled combination of same, will support fungal growth, and if so, of what species.


2. how rapidly fungus will grow on the materiel.


3. how fungus affects the materiel, its mission, and its safety for use following the growth of fungus on the material.


4. if the material can be stored effectively in a field environment.


5. if there are simple reversal processes, e.g., wiping off fungal growth.

 

Because some other tests in 810G such as salt fog, sand and dust, or humidity can change the results of a fungus test, those tests should be conducted on a sample after the fungus test is complete. It is imperative the sample be decontaminated after the fungus tests.

 

Electronic equipment is typically manufactured using fungus-resistant material such as fiberglass, metal, plastic, etc. Materials affected by fungus such as fabrics are not typically used in electronic equipment. However, fungus growth can still have detrimental effects on electronic circuitry.

 

The detrimental effects of fungus growth can include:

 

• Natural material – products such as paper, natural fibers, fabric, etc., are most susceptible as they can feed the fungus. Other organic materials such as adhesives, grease, oils, etc. and leather are susceptible.


• Synthetic materials – PVC formulations, some polyurethanes, plastics with organic fillers and paints or varnishes with susceptible constituents.

 

Effects of indirect attack include:

 

• Fungal growth on surface deposits of dust, grease, or other contaminants can cause damage to the underlying material.


• Metabolic waste products of the fungus (organic acids) can cause corrosion of metals, etching of glass, or staining or degrading of plastics and other materials.


• Fungus growth can bridge sensitive circuitry changing the electrical properties.


• Fungus can affect optical systems by adversely affecting light transmission through the system or block delicate moving parts.

 

The Method includes a warning note that 1) highly-specialized techniques are required for the analysis and 2) simple analysis is not sufficient and testing should be performed.

 

Fungus growth can have a negative health impact as many people are very sensitive to mold and fungus.

 

This is a long test, lasting 28 days as a minimum, to allow germination, break-down of carbon-containing molecules, and degradation of the material. In addition, it is recommended the test be extended to 84 days to fully evaluate the impact of fungus growth.

 

The Method identifies five different varieties of fungus which are known to affect different materials and are distributed worldwide. Other species can be introduced as required.  It is recommended to only use 5 or 6 species for testing. The more dominant species will prevail in testing and adding additional species will only add to the cost without additional degradation to the underlying material.

 

The test requires a relatively sophisticated chamber to maintain the desired humidity and temperature as these greatly impact fungus growth. The chamber needs to be vented and filtered to release pressure changes and to filter fungus spores from the discharge.

 

The method goes into great detail on cleaning the test items and the chamber. In addition, while the fungi used in the tests are not typically harmful to humans, some people may have or may develop allergies or other reactions so good housekeeping and handling precautions should be observed.

 

As mentioned earlier, this is a sophisticated test and requires trained personnel and specialized laboratory equipment such as a centrifuge to properly administer the test. The fungal spores need to be prepared and tested for viability. Control strips of cotton are prepared and hung adjacent to the test specimen to be exposed as much as possible to the conditions the specimen is seeing.

 

After the test period, the material under test is analyzed for the fungus species, extent of growth, impact on the underlying material, long range effect the growth could have on the material, and the specific nutrients supporting the growth.

 

Chassis Plans has worked with various customers to define test procedures, as required by MIL-STD-810G, to validate our rugged rackmount computer systems and displays.

 

Mil-Std-810G – Part 10 (Fungus Growth) Method 508.6

Mil-Std-810G - Part 9 (Humidity)

This is part 9 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers humidity in Method 507.5.  This method comprises 21 pages.

 

The purpose of Method 507.5 is to determine the resistance of material to the effects of a warm, humid environment.  It is applicable to material that is likely to be stored or deployed in areas in which high levels of humidity occur.   The essence of 507.5 is hot and humid.  Effects on electronics can include break down of insulators as they absorb moisture or condensation when a cold object is brought into contact with a warmer humid environment.

 

The method may not reproduce all the humidity effects associated with the natural environment nor is this method applicable to low humidity situations.

 

There is not specific method that addresses low humidity.  However, for completeness, low humidity exposure should be considered.  The usual side effect of low humidity is static electricity build-up and subsequent discharge causing spurious operation or material damage to sensitive electronic devices.  MIL-HDBK-263B is the reference for Electrostatic Discharge Control.

 

Warm, humid conditions can occur year-round in tropical areas, seasonally in mid-latitude areas and in material subject to changes in pressure, temperature, and relative humidity.  Material enclosed in non-operating vehicles can experience high internal temperature and humidity conditions.

 

Specifically, this method does not address:

• Condensation resulting from changes of pressure and temperature for airborne or ground materiel.


• Condensation resulting from black-body radiation (e.g., night sky effects).


• Synergistic effects of solar radiation, humidity, or condensation combined with biological and chemical contaminants.


• Liquid water trapped within materiel or packages and retained for significant periods.


• This method is not intended for evaluating the internal elements of a hermetically sealed assembly since such materiel is air-tight.

 

Method 520.3 should be considered in conjunction with Method 507.5 to explore the synergistic effects of temperature, humidity and altitude.

 

The effects of high humidity can include:

 

a. Surface effects, such as:

1. Oxidation and/or galvanic corrosion of metals.


2. Increased chemical reactions.


3. Chemical or electrochemical breakdown of organic and inorganic surface coatings.


4. Interaction of surface moisture with deposits from external sources to produce a corrosive film.


5. Changes in friction coefficients, resulting in binding or sticking.

 

b. Changes in material properties, such as:

1. Swelling of materials due to sorption effects.


2. Other changes in properties.
   
   (a) Loss of physical strength.
   
   (b) Electrical and thermal insulating characteristics.
   
   (c) De-lamination of composite materials.
   
   (d) Change in elasticity or plasticity.
   
   (e) Degradation of hygroscopic materials.
   
   (f) Degradation of explosives and propellants by absorption.
   
   (g) Degradation of optical element image transmission quality.
   
   (h) Degradation of lubricants.

 

c. Condensation and free water, such as:

1. Electrical short circuits.


2. Fogging of optical surfaces


3. Changes in thermal transfer characteristics.

 

In addition to “Natural”, Method 507.5 provides for two Procedures: Induced and Aggravated.  Natural simulates a natural environment.  Induced simulates a natural environment for storage and transit.  Aggravated exposes the test item to more extreme temperature and humidity levels than those found in nature but for shorter durations.  The Natural test criteria was selected to mimic Majuro, Marshall Islands with a temperature range of 88 to 105 degrees F. and relative humidity (RH) of 59% to 88% for the Hot Humid test.  Cycle B2 (High RH) provides for lower temperatures but RH up to 100%

 

The test duration is recommended to be a minimum of 45 cycles for non-hazardous materials to 180 days for Induced testing for hazardous material.  Hazardous materials are those in which a failure may cause damage to adjacent material or injury or death to a user.  The purpose of the higher cycle counts is to establish confidence in the testing.

Mil-Std-810G - Part 9 (Humidity)