MIL-STD 810 Pyroshock
Pyroshock tests involve explosive, or propellant-activated devices known as pyrotechnic devices. Military pyroshock testing ensures that material can withstand infrequent shock effects. These shock effects are caused by detonating a pyrotechnic device on the materials mounting structure.
This test experimentally estimates the material’s fragility level in relation to pyroshock. This is so shock mitigation procedures may be employed to protect the material’s structural and functional integrity.
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The following information is extremely technical in nature. It provides a summary of test method 517.3 pyroshock as derived from the MIL-810 pyroshock section. Even though the language is from MIL-810, it applies previous versions of the standard. This includes military standards like MIL-STD 810H pyroshock and MIL-STD 810G pyroshock.
How ought Pyroshock Testing be Applied?
Pyroshock is often referred to as pyrotechnic shock. “Pyroshock” is the localized intense mechanical transient response of material caused by the detonation of a pyrotechnic device on adjacent structures.
A number of devices are capable of transmitting such intense transients to a material. In general, the sources may be described in terms of their spatial distribution. These include 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 shaped charges (FLSC), mild detonating fuzes (MDF), and explosive transfer lines. Combined point and line sources include V-band (Marmon) clamps.
The loading from the pyrotechnic device may be accompanied by the release of structural strain energy. This energy is from structure preload or impact among structural elements. This is a result of the activation of the pyrotechnic device. Use this Method to evaluate material likely to be exposed to one or more pyroshocks in its lifetime.
Pyroshocks are generally within a frequency range between 100 Hz and 1,000,000 Hz. They tend to be at a duration from 50 microseconds to not more than 20 milliseconds. Acceleration response amplitudes to pyroshock may range from 300 g’s to 200,000 g’s. The acceleration response time history to pyroshock will, generally, be very oscillatory, and have a substantial rise time, approaching 10 microseconds.
Generally, pyroshocks generate material stress waves. This excites material to respond to very high frequencies with wavelengths on the order of sizes of micro-electronic chip configurations. Firing of the pyrotechnic device brings about little velocity change in the structure.
Structural resonances of material below 500 Hz will normally not be excited. Therefore the system will undergo very small displacements with small overall structural/mechanical damage. The pyroshock acceleration environment in the neighborhood of the material depends on the configuration of the material and the intervening structure.
The material or its parts may be in the near-field, mid-field or far-field of the pyrotechnic device. The pyroshock environment in the near-field is the most severe. That in the mid-field or far-field is less severe.
In general, some structure intervenes between the material and location of the pyrotechnic device. This results in the “mid-field,” and “far-field.” Experts agree on classifying pyroshock intensity according to the characteristics of “near-field,” “mid-field,” and “far-field.” This document reflects this consensus for three regions according to simulation techniques as “near-field,” “mid- field,” and “far-field.”
What are the Effects of Military Pyroshock Testing?
In general, pyroshock has the potential for producing adverse effects on all electronic materials. The level of adverse effects generally increases with the level and duration of the pyroshock. It decreases with the distance from the source of the pyroshock.
Sometimes material stress waves with the same wavelengths as the natural frequency of microelectronic components within the material, are produced. In these cases adverse effects are enhanced. In general, the structural configuration merely transmits the elastic waves. It is unaffected by the pyroshock.
Examples of problems associated with pyroshock are:
- Material failure as a result of destruction of the structural integrity of micro-electronic chips.
- Material failure as a result of relay chatter.
- Material 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.
- Materiel failure as a result of cracks and fracture in crystals, ceramics, epoxies, or glass envelopes.
This list is not intended to be all-inclusive.
How do you select the Proper Procedure for Best Pyroshock Testing?
There are five types of pyroshock test procedures.
Procedure I is Near-field with an Actual Configuration. In this procedure pyroshock for the near-field environment is replicated. This is done using the actual material, and the associated pyrotechnic shock test device configuration.
Procedure II is Near-field with a Simulated Configuration. In this procedure the pyroshcock near-field environment is replicated. Again this is done using the actual material, but the associated pyrotechnic shock test device is isolated from the test item.
This is done by mounting it on the back of a flat steel plate. Normally this will minimize testing costs because fewer material configurations and/or platforms associated with the test item will be damaged. This can be used for repeated tests at varying pyroshock levels.
Procedure III is Mid-field with a Mechanical Test Device. A mechanical device is used to replicate pyroshock for the mid-field environment. It simulates the pyroshock peak acceleration amplitudes and frequency content.
Procedure IV is Far-field with a Mechanical Test Device. A mechanical device is used to replicate pyroshock for the far-field environment. It simulates the pyroshock peak acceleration amplitudes and frequency content.
Procedure V is Far-field with an Electrodynamic Shaker. An electrodynamic shake is used to replicate pyroshock for the far-field environment. It simulates the comparatively low frequency structural resonant response to the pyroshock.
What Pyroshock Laboratory Should You Trust?
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There have been several versions of pyroshock testing procedures in MIL-STD-810 pyroshock testing. Below is a list of each version and the appropriate method number: