Mil-Std-810G – Part 6 (Contamination by Fluids)

This is part 6 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers contamination by fluids in 504.1.  Use the contamination by fluids tests to determine if equipment is affected by temporary exposure to contaminating fluids such as may be encountered during its life cycle.  In the case of rugged computers in the military environment, these fluids can include:

• Water and salt water


• Jet fuel (kerosene)


• Gasoline


• Diesel fuel


• Hydraulic fluids


• Lubricating oils


• Solvents and cleaning fluids


• Deicing and antifreeze fluids


• Disinfectant


• Fire extinguishants.

 

Fluids can be intentionally applied in the normal course of operation such as cleaning fluids or there may be inadvertent exposure such as splashing, spillage, or fluids on hands or gloves.

 

The effects of such fluids can include:

• Dissolving or softening paint on the equipment


• Damaging plastic parts


• Conductive effects


• Insulation effects such as leaking across switch contacts


• Gumming up the works such as a full-travel keyboard


• Binding or slackening of moving parts


• Differential contraction or expansion rates or induced strain rates of dissimilar materials


• Changes in electrical and electronic components


• Electronic or mechanical failures due to rapid water or frost formation.


• Excessive static electricity


• Interruption of electrical continuity (such as “grounding” fingers on EMI strips)


• Increase in electrical resistance due to thermo-mechanical “fretting corrosion”

 

In general, it is best to test material samples instead of the entire product.  Painted samples can be used to test impact on the paint or powder coating.  Individual components such as switches and drive carriers can be easily tested.

 

It should be noted that testing for contamination by fluids should be done after other tests for 810G as contamination by the fluids may potentially damage test equipment required for other tests.

 

The tests are not intended to demonstrate suitability of materials in continuous contact with a fluid such as a pump, nor should it be used to demonstrate resistance to electrolytic corrosion.

 

810G includes consideration of temperature effects of exposure to fluids and the operating environment should be evaluated in preparing for the tests.  Many chemicals are much more reactive at higher temperatures and may not have any impact at lower temperatures.

 

Sections of 504.1 include for testing:

• Length of exposure


• Test fluids


• Combination of test fluids


• Test Temperature


• Test item temperature


• Test fluid temperature


• Soak temperature


• Fluid exposure duration


• Methods of application

 

The goal of the testing is to analyze any contamination effects for their immediate or potential (long-term) effects on the proper functioning of the test item or safety during its life cycle.

Mil-Std-810G – Part 6 (Contamination by Fluids)

Mil-Std-810G - Part 5 (Temperature Shock)

This is Part 5 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature) and 502.5 (Low Temperature), both of which have been covered in previous blogs.  In addition, 503.5 covers Temperature Shock. Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 520.3 will be examined in future blogs.  Method 503.5 covers 13 pages of Mil-Std-810G.

 

Use the temperature shock test of 503.5 to determine if materiel can withstand sudden changes in the temperature of the surrounding atmosphere without experiencing physical damage or deterioration in performance.

 

Temperature shock effects on computers and LCDs include:

• Shattering of plastic materials


• Binding of moving parts


• Drive failure


• Cracking from differential expansion (contraction) of dissimilar materials


• Integrated Circuit (IC) bond failure


• Cracking of LCD cover glass materials


• Delamination of the LCD display


• Electronic or mechanical failures due to rapid water or frost formation

 

Method 203.5 includes one test procedure with four variations – essentially in the length of the test and the shock itself. It employs constant temperature at each of the extreme shock conditions because, in many instances, the thermal shock itself so outweighs the other thermal effects that the test may be performed using two constant temperatures. This is particularly the case when more severe shocks are desired, such as for evaluation of safety or initial design, and when extreme values will be used.

 

The tests simulate what happens when you would move equipment from one environment rapidly into a much different environment.  That can be from hot to cold or from cold to hot.  For hot to cold, picture moving from a warm control room to outside in the artic where the temperature might be -30 deg C or lower.  Cold to hot can be as simple as moving from a cool air conditioned room to outside in Texas in the middle of summer where the temperature and humidity are both very high causing immediate condensation on the cold equipment.

 

As with other 810G methodologies, there are no absolute values associated with the different tests.  The tests are designed to simulate performance in an intended environment.  Thus, determining the climatic conditions where the equipment is to be deployed or stored is the first step.  Then the test high and low points can be determined.  503.5 actually recommends using a range of temperatures that reflects the anticipated in-service environment, rather than some arbitrary extreme range.

 

The four test variations are:

• Procedure I-A One-way shock(s) from constant extreme temperature.  Appropriate for material that is likely to be exposed only rarely to thermal shock in one direction, perform at least one shock for each appropriate condition, i.e., low to high temperature, or vice-versa.


• Procedure I-B Single cycle shock from constant extreme temperature. For materiel that is likely to be exposed to only one thermal shock cycle (one in each direction), perform one shock for each appropriate condition, i.e., low-to-high temperature, and one in the opposite direction


• Procedure I-C Multi-cycle shocks from constant extreme temperature. Appropriate for systems that may be subjected to multiple temperature shock events.  A minimum of three shocks is specified.


• Procedure I-D Shocks to or from controlled ambient temperature. Essentially the same as I-C except the shock is to ambient instead of extreme hot and cold temperatures.

 

The tests should consider the deployed state of the equipment.  Perhaps the systems are mounted in transit cases which will slow the internal temperature changes.  On the other hand, a transit case may maintain an internal temperature which will suddenly change when the covers are removed.

 

The tests involving ambient require a single chamber.  Tests to extreme high and low temperatures require two chambers where the equipment is moved from one chamber to the other.  There is test equipment providing two side by side chambers with a divider between them allowing the equipment to be shuttled between the different temperatures automatically.

 

Chassis Plans has demonstrated experience working with customers to design rugged systems appropriate for any environment including rapid temperature changes.

Mil-Std-810G - Part 5 (Temperature Shock)

Mil-Std-810G - Part 4 (Low Temperature)

This is Part 4 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature) which was discussed in a previous blog, 502.5 (Low Temperature) and 503.5 (Temperature Shock). Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 520.3 will be examined in future blogs.  Method 502.5 covers 6 pages of Mil-Std-810G.

 

This method is not intended for testing materiel to be installed in and operated in unpressurized aircraft, since such materiel would usually be tested according to Method 520.3.

 

Low temperature effects on computers and LCDs include:

• Failure of the system to boot


• Drive failure


• Drive won’t spin due to internal frost


• Stiffening of shock mounting devices


• Change in vibration and shock dynamic response


• Cracking of surface coatings


• Cracking from differential expansion (contraction) of dissimilar materials


• Change in electrical properties of electronic components


• Integrated Circuit (IC) bond failure


• LCD will not operate due to sluggish or frozen liquid crystal material


• Delamination of the LCD display


• Excessive static electricity

 

As with Method 501.5 for High Temperature, with a few exceptions, the Methods for low temperature do not place absolute limits on the devices to be tested.  There is no specification delineating a minimum temperature of 0 deg C, for example.  Thus, a manufacturer stating their device has been tested per Mil-Std-810G for operation between 0 and 50 deg C has written their own test method.

 

The limitations for 502.5 specify the Method is appropriate for short term (months as opposed to years), even distributions of cold throughout the test item.  For the purposes of testing, time is allowed for the test item to stabilize in temperature.

 

Within 502.5 are three procedures:

• Procedure I – Storage


• Procedure II – Operation


• Procedure III – Manipulation

 

In general, companies will publish both storage and operating temperature specifications but rarely, if ever, Manipulation for computers or LCDs.  Use Procedure III to investigate the ease with which the equipment can be set up and disassembled by personnel wearing heavy, cold-weather clothing.  In the case of computers, the use of gloves might be an impediment to operating the systems.

 

Testing for cold simulates conditions in selected regions or for worldwide use.  Note that Antarctica is excluded from consideration by international treaty restrictions for military equipment. On the other hand, testing for civilian use in Antarctica is appropriate.  Solar loading is not considered an issue so testing at constant temperatures is allowed.

 

There are three cold test environments:

 

Basic Cold covers most of Europe; Northern contiguous US; Coastal Canada; High-latitude coasts (e.g., southern coast of Alaska); High elevations in lower latitudes and ranges from -21 to -31 deg C for ambient air temperature and -25 to -33 deg C for induced environment (storage and transit).

 

Cold covers Canada, Alaska (excluding the interior); Greenland (excluding the “cold pole”); Northern Scandinavia; Northern Asia (some areas), High Elevations (Northern and Southern Hemispheres); Alps; Himalayas; Andes and ranges from -37 to -46 deg C for ambient and -25 to -33 deg C for induced environment (storage and transit).

 

Severe Cold covers the Interior of Alaska; Yukon (Canada); Interior of Northern Islands; Greenland ice cap; Northern Asia and specifies a single temperature of -51 deg C.

 

Note that there are frequencies of occurrence that certain low temperatures may be experienced.  For example, there is a 20 percent chance of going to -51 deg C and a 1 percent chance of going all the way down to -61 deg C.  For extended storage such as years in areas that experience extreme cold, there is a chance the material may experience temperatures approaching -65 deg C.

 

Testing time for storage of 4 hours at a stabilized temperature is generally considered adequate for nonhazardous or non-safety-related equipment.  Some items such as explosives may continue to degrade over time at low temperatures and should be tested further as appropriate.

 

Note that Method 502.5 does not mention humidity.  Because the humidity is so low, essentially non-existent at these low temperatures, static electric generation does become an issue and must be considered.  As a side note, it is much more important to practice safe static electric remediation procedures at low temperatures including use of wrist straps, grounding points, non-static generating packaging and wiping cloths, etc.  Users may have a Styrofoam coffee cup handy trying to keep warm and Styrofoam can generate very high static fields.

 

The test itself is rather anti-climatic.  The device under test is placed in a chamber, powered down, and the temperature lowered to the desired value.  Generally the rate of change in the chamber is limited to 3 deg C per minute to prevent thermal shock.  Soak at the storage temperature for 4 hours, then raise the chamber temperature to the operating temperature, let the item stabilize internally at that temperature, then power it on and check operation.

 

Chassis Plans is versed in low temperature operation of rugged military grade computers and LCDs and can provide remediation such as extended temperature components or heaters as required.  There are multiple options for products such as rugged LCDs to enable low temperature operation.

 

 

Mil-Std-810G - Part 4 (Low Temperature)

Mil-Std-810G - Part 3 (High Temperature)

This is Part 3 of a series delving into the intricacies of Mil-Std-810G.

 

810G covers temperature in 501.5 (High Temperature), 502.5 (Low Temperature) and 503.5 (Temperature Shock). Method 520.3 details testing which combines temperature, humidity, vibration and altitude interactively.  Methods 502.5 and 520.3 will be examined in future blogs.  Method 501.5 covers 12 pages of Mil-Std-810G.

 

High temperature effects on computers and LCDs include:

• Exceeding the published high temperature limits for the components such as processors and chip sets causing damage


• Exceeding operating limits on components inside the power supply such as transformers


• Intermittent operation as the processors automatically slows down in a protective mode


• Intermittent operation as power supply modules shut down in a protective mode


• Reduced component life


• The screen on LCDs can turn black at elevated temperatures


• Glue creep or failure

 

With a few exceptions, the Methods for temperature do not place absolute limits on the devices to be tested.  There is no specification delineating a maximum temperature of 50 deg C, for example.  Thus, a manufacturer stating their device has been tested per Mil-Std-810G for operation between 0 and 50 deg C has written their own test method.

 

The limitations for 501.5 specify the Method is appropriate for short term (months as opposed to years), even distributions of heat throughout the test item.  For the purposes of testing, time is allowed for the test item to stabilize in temperature.

 

Within 501.5 are three procedures:

• Procedure I – Storage


• Procedure II – Operation


• Procedure III – Tactical Standby to Operational

 

In general, companies will publish both storage and operating temperature specifications but rarely, if ever, tactical standby to operational for computers or LCDs. The term “tactical” is used to identify materiel that is not in storage, but is in a standby operational configuration, and as such is subjected to extended non-operational conditions immediately prior to operation.

 

Humidity is usually not a factor in high temperature testing.  However, climatic conditions should be considered. Identify the appropriate climatic conditions for the geographic areas in which the materiel will be operated and stored. There are two climatic categories where high temperatures are typically encountered: Hot Dry and Basic Hot.

 

Basic Hot is applicable to many parts of the world, extending outward from the hot dry category of the southwestern United States, northwestern Mexico, central and western Australia, Saharan Africa, South America, southern Spain, and southwest and south central Asia.  The ambient air temperature is specified at 30-43 deg C (86 to 110 deg F) and induced at 30-63 deg C (86 to 145 deg F).  Induced temperature is a result of heat loading from sun exposure, for example.  Humidity ranges from 5% at 63 deg C (induced) to 44% at 31 deg C (induced).    As can be seen, the target area is hot and dry!

 

Hot Dry covers Southwest and south central Asia, southwestern United States, Saharan Africa, central and western Australia, and northwestern Mexico.  The ambient temperature is specified at 32 to 49 deg C (90 to 120 deg F) and induced at 33 to 71 deg C (91 to 160 deg F).  Humidity ranges from 1% to 7%.  Really hot and really dry.

 

Cyclic temperature exposure should be considered.  Generally, 7 cycles is sufficient for Procedure I – Storage and 3 cycles for Procedure II – Operation.

 

A situation to be aware of and which needs careful attention and control is run-away chamber temperature during testing.  A high power computer may generate more heat than the chamber can cool resulting in unanticipated high temperatures beyond the scope of the testing.

 

Chassis Plans rugged military grade computers are designed to function in high temperature environments for high power systems.  Included are multiple high velocity fans, optimized air flow paths, and Chassis Plans’ proprietary SysCool®  Intelligent Fan Controller.

Mil-Std-810G - Part 3 (High Temperature)

MIL-STD-810G – Part 21 (Gunfire Shock) Method 519.6

MIL-STD-810G covers Gunfire Shock in Method 519.6. Method 519.6 is comprised of 17 pages with the following annexes:

 

A – Guidelines for Procedure I (11 pages)

B – Guidelines for Procedure II (21 pages)

C – Guidelines for Procedure III (12 pages)

D – Sine-on-Random Spectrum Prediction (10 pages)

E – Guidelines for Gunfire Shock Test Scaling (7 pages)

 

Gunfire shock tests are performed to provide a degree of confidence that materiel can structurally and functionally withstand the relatively infrequent, short duration transient high rate repetitive shock input encountered in operational environments during the firing of guns. Exposure to a gunfire shock environment has the potential for producing adverse effects on the structural and functional integrity of all materiel including in-service operational capability. The probability of adverse effects increases with the blast energy of the gun, proximity of the materiel to the gun, and the duration of the gunfire shock environment. The gunfire firing rate and the duration of gunfire shock environment exposure that correspond with natural frequencies of the mounted materiel (along with its subharmonics and superharmonics) will magnify the adverse effects on the materiel’s overall integrity.

 

The gunfire environment may be considered to be a high rate repetitive shock having form of a substantial transient vibration produced by (1) an air-borne gun muzzle blast pressure wave impinging on the materiel at the gun firing rate, (2) a structure-borne repetitive shock transmitted through structure connecting the gun mechanism and the materiel, and/or a combination of (1) and (2).

 

Some of the effects of Gunfire Shock include:

 

1. changes in materiel dielectric strength, loss of insulation resistance, variations in magnetic and electrostatic field strength;


2. materiel electronic circuit card malfunction, electronic circuit card damage, and electronic connector failure. (On occasion, circuit card contaminants having the potential to cause short circuits may be dislodged under materiel response to gunfire environment);


3. permanent mechanical deformation of the materiel as a result of overstress of materiel structural and non-structural members;


4. collapse of mechanical elements of the materiel as a result of the ultimate strength of the element being exceeded.


5. accelerated fatiguing of materials (low cycle fatigue);


6. potential piezoelectric activity of materials; and


7. materiel failure as a result of cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.

 

This is a very complicated Method in that the effects of air pressure pulse is combined with shock through the structure with distance from the gun having a significant impact on which input has more effect. In addition, predicting material response may be impossible.

 

The Method relies heavily on Method 525 (Time Waveform Replication).

 

There are three procedures:

 

Procedure I –

Measured in-service gunfire shock environment for materiel is replicated under laboratory exciter waveform control (Method 525 TWR) to achieve a near exact reproduction of the measured in-service gunfire shock environment.

 

Procedure II –

This procedure is based upon either (1) direct stochastic generation of time traces appropriate for Method 525 that are “equivalent” in severity to in-service measured time trace information, or (2) a procedure that may be justified for properly distributing uncertainty, and for conservative testing (but in accordance with the principles of random process theory).

 

Procedure III –

This procedure is ad hoc, lacking necessary field measured time trace information, and a last resort to providing guidelines for design of materiel to resist gunfire shock environment. Only time trace forms for design are given, and it is not suggested that testing be performed to these forms for materiel qualification purposes.

 

Gunfire Shock testing is performed on a shake table with the ability to follow test waveform inputs.

MIL-STD-810G – Part 21 (Gunfire Shock) Method 519.6

MIL-STD-810G – Part 20 (Acidic Atmosphere) Method 518.1

MIL-STD-810G covers exposure to an Acidic Atmosphere in Method 518.1. Acidic atmospheres are of increasing concern, especially for materiel in the vicinity of industrial areas or near the exhausts of fuel burning devices. Method 518.1 is comprised of 7 pages.

 

This Method is used to determine the resistance of materials and protective coatings to corrosive atmospheres. This Method is appropriate for materiel likely to be stored or operated in areas where acidic atmospheres exist, such as industrial areas or near the exhausts of any fuel-burning device.

 

Note this method is not a replacement for the salt fog method, nor is it suitable for evaluating the effects of hydrogen sulfide that readily oxidizes in the test environment to form sulfur dioxide. Caution: Although salt fog chambers are usually used for this test, introducing an acidic or sulfur dioxide atmosphere in a salt fog chamber may contaminate the chamber for future salt fog tests.

 

Some problems as a result of an acidic environment include:

 

1. Chemical attack of surface finishes and non-metallic materials.


2. Corrosion of metals.


3. Pitting of cement and optics.

 

This Method should be applied late in a products test cycle. Also, separate items should be tested for Salt Fog.

 

Two test durations are suggested. For infrequent periods of exposure, three 2-hour spraying periods with 22 hours storage after each is sufficient. To represent approximately 10 years natural exposure in a moist, highly industrial area, or a shorter period in close proximity to vehicle exhaust systems, particularly ship funnel exhausts where the potential acidity is significantly higher, four 2-hour spraying periods with 7 days storage after each is sufficient.

 

The actual test is similar to Method 509.5 (Salt Fog) in that the acid solution is atomized into a fog and blown through a test chamber.

 

MIL-STD-810G – Part 20 (Acidic Atmosphere) Method 518.1

MIL-STD-810G – Part 19 (Pyroshock) Method 517.1

MIL-STD-810G covers Pyroshock in Method 517.1. Pyroshock is a high intensity, short duration shock event caused by the detonation of a pyrotechnic device on adjacent structures. Pyroshock is a physical phenomenon characterized by the overall material and mechanical response at a structure point from either (a) an explosive device, or (b) a propellant activated device. Method 517.1 is comprised of 23 pages.

 

Method 517.1 is not intended to test material exposed to external explosions.

 

Use this method to evaluate materiel likely to be exposed to one or more pyroshocks in its lifetime.

 

In general, the pyroshock sources may be described in terms of their spatial distribution – point sources, line sources and combined point and line sources. Point sources include explosive bolts, separation nuts, pin pullers and pushers, bolt and cable cutters and pyro-activated operational hardware. Line sources include flexible linear shape charges (FLSC), mild detonating fuses (MDF), and explosive transfer lines. Combined point and line sources include V-band (Marmon) clamps.

 

Pyroshocks are generally within a frequency range between 100 Hz and 1,000,000 Hz, and a time duration from 50 microseconds to not more than 20 milliseconds. Acceleration response amplitudes to pyroshock may range from 300 g to 300,000 g.

 

Pyroshock usually exhibits no momentum exchange between two bodies (a possible exception is the transfer of strain energy from stress wave propagation from a device through structure to the materiel). Pyroshock results in essentially no velocity change in the materiel support structure.

 

The characteristics of pyroshock are:

1. near-the-source stress waves in the structure caused by high material strain rates (nonlinear material region) propagate into the near-field and beyond;


2. high frequency (100 Hz to 1,000,000 Hz) and very broadband frequency input;


3. high acceleration (300 g to 300,000 g) but low structural velocity and displacement response;


4. short-time duration (< 20 msec);


5. high residual structure acceleration response (after the event);


6. caused by (1) an explosive device or (2) a propellant activated device (releasing stored strain energy) coupled directly into the structure; (for clarification, a propellant activated device includes items such as a clamp that releases strain energy causing a structure response greater than that obtained from the propellant detonation alone);


7. highly localized point source input or line source input;


8. very high structural driving point impedance (P/v, where P is the large detonation force or pressure, and v, the structural velocity, is very small). At the pyrotechnic source, the driving point impedance can be substantially less if the structure material particle velocity is high;


9. response time histories that are random in nature, providing little repeatability and substantial dependency on the materiel configuration details;


10. response at points on the structure that are greatly affected by structural discontinuities;


11. materiel and structural response that may be accompanied by substantial heat and electromagnetic emission (from ionization of gases during explosion).

 

Examples of electronic problems associated with pyroshock follow, but the list is not intended to be all-inclusive.

1. materiel failure as a result of destruction of the structural integrity of microelectronic chips;


2. materiel failure as a result of relay chatter;


3. materiel failure as a result of circuit card malfunction, circuit card damage, and electronic connector failure. On occasion, circuit card contaminants having the potential to cause short circuits may be dislodged under pyroshock.


4. materiel failure as a result of cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.

 

MIL-STD-810G – Part 19 (Pyroshock) Method 517.1