What Environmental Tests Should Defence Product Do?

Military industry mainly refers to the industrial departments, factories and other military supply units that mainly serve the national defense construction and directly provide the troops with weapons, equipment and other military supplies. Defence products mainly include:

weapons industry	aviation industry	shipbuilding industry
electronics industry	nuclear industry	aerospace industry

Features of Defense Products

The main task of the defense industry is to produce weapons and other military products. Weaponry is a special consumer product, and its direct use is to meet the needs of the military, which determines that the national defense industry has different characteristics compared with the civilian industry:

① The country plays an important role. The country is the maker of the production plan of the defense industry, and also the consumer of the products of the defense industry. The products of the defense industry are generally ordered and consumed directly by the military.

② Capital and technology intensive. The establishment of the national defense industry and the production of weapons and equipment require huge investment. In the national defense industry, there are generally the most advanced science and technology and more outstanding scientific and technological personnel.

③ Product cost is high and expensive.

④ The alternation of peace and war has a direct impact on the planning and production of the defense industry. In peacetime, the demand for military products is small, but in wartime, the demand is large.

⑤ High confidentiality and stricter management.

⑥ Most of the main enterprises are distributed in strategically deep areas to ensure wartime security.

Reliability testing is an activity to evaluate the functional reliability of defense products in all environments such as expected use, transportation or storage during the specified life span. It is to expose the product to natural or artificial environmental conditions, to evaluate the performance of the product under the environmental conditions of actual use, transportation and storage, and to analyze the degree of influence of environmental factors and its mechanism of action. Defense products are critical to users, so environmental testing is also essential. This passage mainly introduce the following tests.

LOW PRESSURE (ALTITUDE) TEST

Use low pressure (altitude) tests to determine if materiel can withstand and/or operate in a low pressure environment and/or withstand rapid pressure changes.

Application

Use this method to evaluate materiel likely to be:

a. stored and/or operated at high ground elevation sites.

b. transported or operated in pressurized or unpressurized areas of aircraft.

c. exposed to a rapid or explosive decompression and, if so, to determine if its failure will damage the aircraft or present a hazard to personnel.

d. carried externally on aircraft.

Having selected this method and relevant procedures, it is necessary to complete the tailoring process by selecting specific parameter levels and special test conditions/techniques for these procedures based on requirements documents, Life Cycle Environmental Profile, Operational Environment Documentation, and information provided with this procedure. From these sources of information, determine the functions to be performed by the materiel in low pressure environments or following storage in low pressure environments.

Determine the test parameters such as test pressure and temperature, rate of change of pressure (and temperature if appropriate), duration of exposure, and test item configuration.

Test pressure and temperature

Base determination of the specific test pressures and temperatures on the anticipated deployment or flight profile of the test item.

a. Ground areas. If measured data are not available, temperatures may be obtained for appropriate ground elevations and geographical locations from STANAG 2895. The highest elevation currently contemplated for NATO ground military operations (materiel operating and nonoperating) is 4,570m with an equivalent air pressure of 57 kPa.

b. Transport aircraft cargo compartment pressure conditions. The test pressure used for each of the four procedures in this method will vary greatly for each test item. There are many different types of cargo transport aircraft on which materiel could be transported and many different types of pressurization systems.

Aircraft have different service ceilings (“normal” altitude for cruise) and the normal service ceiling may not be achievable for very heavy equipment. Most pressurization systems provide outside atmospheric pressure in the cargo compartment (no pressure differential between the inside and outside of the aircraft) up to a particular altitude, and then maintain a specific pressure above that altitude. The pressure inside the cargo department is known as “cabin altitude.” Subject the test item to the most likely anticipated conditions.

Unless the materiel has been designed for transport on a particular aircraft with unique cabin altitude requirements, use the following guidance:

(1) For Procedures I and II, use 4,572m (15,000 ft) for the cabin altitude (corresponding pressure in a standard atmosphere: 57.2kPa or 8.3 psia).

(2) For Procedures III and IV, use 2,438m (8,000 ft) for the initial cabin altitude (75.2kPa or 10.9 psia), and 12,192m (40,000 ft) for the final cabin altitude after decompression (18.8kPa or 2.73 psia).

c. Transport aircraft cargo compartment temperature conditions. The range of temperatures associated with the various low pressure situations varies widely, primarily depending on the capabilities of the environmental control system within the cargo compartment of the various aircraft. Obtain the test temperatures from measured data or from appropriate national sources.

Test Facility.

LIB Altitude Test Chamber

Step 1. Place the test item in its storage or transport configuration and install it in the testchamber.

Step 2. If appropriate, stabilize the test item to the required temperature.

Step 3. Adjust the chamber air pressure to that which corresponds to the required test altitude,at an altitude change rate as specified in the test plan.

Step 4. Maintain the conditions for a minimum of one hour unless otherwise specified in the test plan.

Step 5. Adjust the chamber air to standard ambient conditions at the rate specified in the test plan.

Step 6. Visually examine the test item to the extent possible and conduct an operational check.

Document the results.

TEMPERATURE AND HUMIDITY TEST

Use high temperature tests to obtain data to help evaluate effects of high temperature conditions on materiel safety, integrity, and performance. Use this method to evaluate materiel likely to be deployed in areas where temperatures are higher than standard ambient.

Effects of high temperature environments.

High temperatures may temporarily or permanently impair performance of materiel by changing physical properties or dimensions of the material(s) of which it is composed. The following are examples of problems that could result from high temperature exposure that may relate to the materiel being tested. Consider the following typical problems to help determine if this method is appropriate for the materiel being tested. This list is not intended to be allinclusive.

a. Parts bind from differential expansion of dissimilar materials.

b. Lubricants become less viscous; joints lose lubrication by outward flow of lubricants.

c. Materials change in dimension, either totally or selectively.

d. Packing, gaskets, seals, bearings and shafts become distorted, bind, and fail causing mechanical or integrity failures.

e. Gaskets display permanent set.

f. Closure and sealing strips deteriorate.

g. Fixed-resistance resistors change in values.

h. Electronic circuit stability varies with differences in temperature gradients and differential expansion of dissimilar materials.

i. Transformers and electromechanical components overheat.

j. Operating/release margins of relays and magnetic or thermally activated devices alter.

k. Shortened operating lifetime.

l. Solid pellets or grains separate.

m. High pressures created within sealed cases (projectiles, bombs, etc.).

n. Accelerated burning of explosives or propellants.

o. Expansion of cast explosives within their cases.

p. Explosives melt and exude.

q. Discoloration, cracking or crazing of organic materials.

r. Outgassing of composite materials.

Test duration.

For constant temperature exposure, soak the test item until its temperature has stabilized and maintain the test temperature at least two hours following stabilization. For cyclic exposure, determine the test duration based on an estimate of the number of cycles required to satisfy the design requirements and the guidance below. The duration of high temperature exposure may be as significant as the temperature itself.

Because Procedures I and II could expose the test items to cyclic temperatures, the number of cycles is critical. (Cycles are 24-hour periods unless otherwisespecified.)

a. Procedure I - Storage. The number of cycles for the storage test is set at a minimum of seven to coincide with the one percent frequency of occurrence of the hours of extreme temperatures during the most severe month in an average year at the most severe location. (The maximum temperature occurs for approximately one hour in each cycle.) When considering extended storage, critical materials, or materials determined to be very sensitive to high temperature, increase the number of cycles to assure the design requirements are met.

b. Procedure II - Operation. The minimum number of cycles for the operational exposure test is three.

This number is normally sufficient for the test item to reach its maximum response temperature. A maximum of seven cycles is suggested when repeated temperature response is difficult to obtain.

Humidity.

Generally, relative humidity (RH) control during high temperature tests is not necessary. In special cases, extremely low RH may have a significant effect on some materiel during high temperature testing. If the materiel has special characteristics that could be affected by extremely low RH, use the values for RH shown in tables 501.4-I and -II.

Test Facility.

LIB Temperature and Humidity Test Chamber

Controls.

a. Temperature. Unless otherwise specified in the test plan, if any action other than test item operation (such as opening the chamber door) results in a significant change of the test item temperature (more than 2℃ (3.6℉)) or chamber air temperature, re-stabilize the test item at the required temperature before continuing the test. If the operational check is not completed within 15 minutes, reestablish test item temperature/RH conditions before continuing.

b. Rate of temperature change. Unless otherwise specified, use a rate of temperature change not exceeding 3℃ (6℉) per minute to prevent thermal shock.

These cycles were obtained from AR 70-38, 1 August 1979, and essentially conform to those in MIL-HDBK-310 and NATO STANAG 2895. These values represent typical conditions throughout a typical day in this climatic category. "Induced Conditions" are air temperature levels to which materiel may be exposed during storage or transit situations that are aggravated by solar loading.

Humidity control during high temperature testing is generally not necessary. Use these values only in special cases.

Data were originally recorded in ℉ and converted to ℃. Hence, table data conversion may not be consistent.

Procedure

Step 1. Place the test item in its storage configuration.

Step 2. Adjust the chamber environment to the appropriate test conditions for the start of the test period and maintain for the specified time following temperature stabilization of the test item.

Step 3.

a. For cyclic storage, expose the test item to the temperature (and humidity, if applicable)conditions of the storage cycle for at least seven cycles (if 24-hour cycles are used, this would be a total of 168 hours) or as specified in the test plan. If noted in the test plan, record the thermal response of the test item.

b. For constant temperature storage, maintain the test temperature at least two hours following test item temperature stabilization (see Part One, paragraph 5.4). The additional two hours will help ensure unmeasured internal components actually reach stabilization. If not possible to instrument internal components, base any additional soak time on thermal analysis to ensure temperature stabilization throughout the test item.

Step 4. At the completion of the constant temperature soak or the last cycle, adjust the chamber air temperature to standard ambient conditions and maintain until the test item temperature is stabilized.

Step 5. Conduct a visual examination and operational checkout of the test item and record the results for comparison with pretest data.

Summary

Most of the above data comes from MIL STD 810, which is a testing standard created by the United States Department of Defense to ensure the durability and reliability of military equipment in various environmental conditions. The standard covers a wide range of environmental factors, including temperature, humidity, shock, vibration, and altitude, among others. It is essential for a product in development to meet MIL-STD-810 compliance to ensure that it can withstand harsh conditions and perform optimally in the field.

Products that meet MIL-STD-810 compliance are considered to be of higher quality, more reliable, and more durable, providing customers with greater confidence in their performance in challenging environments.

Altitude	Temperature	Humidity	Vibration
Thermal Shock	Rain	Sand & Dust	Salt Fog/Spray
Materials Testing	Immersion	Solar Radiation	Mechanical Testing

These are the tests included in the standard. All of them are tests for defence product.To improve your product reliability and durability, which test and the chamber do you need? LIB will provide you with the professional solution. Contact us now.