Environmental conditions, classification and methods of test
Title & Task
PT 60068-2-86 Environmental testing – Part 2-86: Tests-Test Fx: Multi-Exciter and Multi-Axis Shock and Vibration Testing
This part of IEC 60068 demonstrates the adequacy of specimens to resist dynamic loads without unacceptable degradation of its functional and/or structural integrity when subjected to the specified random vibration and shock test requirements adopting the use of multi exciter and/or multi-axis stimulation. The test procedure has significant similarity to the general-purpose vibration test procedures of IEC 60068-2-64: Random and IEC 60068-2-6: Sine and encompasses the same range of vibration excitation types. The laboratory test environment may be derived from field measurements on materiel or may be based on an analytically generated specification.
Broad band random vibration and shocks may be used to identify accumulated stress effects and the resulting mechanical weakness and degradation in the specified performance. This information, in conjunction with the relevant specification, may be used to assess the acceptability of specimens.
This standard is applicable to specimens which may be subjected to vibration of a stochastic nature resulting from transportation and/or operational environments, for example in aircraft, space vehicles and land vehicles. It is primarily intended for unpackaged specimens, and for items in their transportation container when the latter may be considered as part of the specimen itself. However, if the item is packaged then the item itself is referred to as a product and the item and its packaging together are referred to as a test specimen. This standard may be used in conjunction with IEC 60068-2-47:2005, for testing packaged products.
If the specimens are subjected to vibration of a combination of random and deterministic nature resulting from transportation or real-life environments, for example in aircraft, space vehicles and for items in their transportation container, testing with pure random or in a single axis at a time may not be enough. See IEC 60068-3-8:2004 for estimating the dynamic vibration environment of the specimen and based on that, selecting the appropriate test method.
Although primarily intended for electrotechnical specimens, this standard is not restricted to them and may be used in other fields where desired (see Annex A).
PURPOSE AND JUSTIFICATION INCLUDING THE MARKET RELEVANCE, WHETHER IT IS A PROPOSED HORIZONTAL STANDARD (GUIDE 108) AND RELATIONSHIP TO SAFETY (GUIDE 104), EMC (GUIDE 107), ENVIRONMENTAL ASPECTS (GUIDE 109) AND QUALITY ASSURANCE (GUIDE 102):
In the early 1970s, the first multishaker vibration tests were completed for the following requirements:
Simulation of a real-world environment that cannot be decomposed axis by axis.
Tests on structures of large dimension or mass.
Since then, more and more multi-shaker/multi-axis tests are being specified, particularly in the aerospace and automotive industries to better replicate the vibration environment recorded during transportation or use. It is believed that multiaxial testing offers the most conservative and realistic real-world simulation, as multiaxial testing will better excite all modes of the structure simultaneously.
Many problems can occur when materiel is exposed to a multi-axis dynamic environment. These environmental effects can also occur in single axis environments, but damage may be unique to the multi-axis environment, such as a rotational induced failure.
However, it is only in recent years that some National Standards have been issued. Despite this there is still some way to go for these Standards to reach a suitable maturity to match other testing techniques.