Pyroshock Testing Techniques

Browsing the ANSI Webstore can lead to some interesting things, along with some confusion when trying to understand what exactly a particular standard does, or even what the words in its title describe. For example, look at IEST-RP-DTE032.2: Pyroshock Testing Techniques, a standard by the Institute of Environmental Sciences and Technology (IEST), an organization that focuses primarily on the topic of contamination control. It is difficult to deduce exactly what this recommended practice refers to, especially if you do not know the meaning of pyroshock. From just looking at the word, it seems that it has something to do with fire and electricity, but that is not likely true. Whatever the case, it sounds remarkably intriguing, and it is worth some further exploration.

A pyroshock, which is also referred to as a pyrotechnic shock, occurs after there is an explosive event near a structure that leaves “a high-frequency and high-magnitude material stress phenomenon that propagates throughout the structure”. The example the standard gives of this is an explosive charge to separate two stages in a multi-stage rocket. These are classified as far-field, mid-field, and near-field pyroshocks, having varying impacts on a nearby structure depending on its distance from the explosive event.

Figure 1 from IEST-RP-DTE032.2 demonstrates the typical acceleration-time history for a pyroshock. It shows the initial pulse that comes from the explosion, followed by a calmer after-period.

A low-velocity pyroshock is rarely damaging to structural integrity and is generally considered mild. However, the high-frequency energy emissions are now known to harm electronic systems. IEST-RP-DTE032.2 is used to test any items or systems that must be able to withstand a pyroshock while they are in use. Different tests are necessary for the three classifications of pyroshock, with a near-field test requiring frequency control up to 10 kHz for amplitudes greater than 10,000 g, a mid-field test requiring 3 kHz to 10 kHz for amplitudes less than 10,000 g, and a far-field test requiring frequency control less than 3 kHz for amplitudes less than 10,000 g. These are dependent on the proximity of the structure to the source of the explosive event, and will provide data that can determine the potential impact.

The standard also provides calculations that can be used to target corrupted pyroshock data, which has been acquired in some laboratory environments and can lead to inaccurate testing. It looks in-depth at several other variables that could affect the impact of a pyroshock, recommending them to be considered during testing. Industries like aerospace and defense require technology that is in close range to explosive events. Being able to test structures and electronic systems prior to their use in direct proximity to these events is indispensable to predict their performance and durability.
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