1. When is an impact test appropriate?
An impact test is appropriate for equipment likely to be used in areas with non-restricted access and where impacts are likely to occur. For equipment destined for areas with restricted access, an impact test may be appropriate but is likely to be of a lower severity.
2. Choice of test apparatus
The part of IEC60068 provides three test method which, as far as is practicable, are intended to give similar results. To obtain repeatable and reproducible results, this test is more dependent on the details of the test apparatus than is usual in IEC60068 standards.
The choice of the test apparatus depends on the orientation of the surface to be tested and on the energy level. Not all methods can be used in every case. It is self-evident that a pendulum hammer can only be used on vertical surface without overhangings. Similarly, the vertical hammer can normally only be used on accessible horizontal surfaces. When the specimen cannot be moved or turned for any reason, the choice is limited. The advantage of the spring hammer is that it can be used in any position, provided there is enough room to apply it correctly and that the specified impact energy does not exceed 2J. For higher energy levels, a spring hammer would be too difficult to handle, and could even be hazardous for the operator.
3. Choice of energy level
The energy of impacts depends on the mass of the striking object and its speed, which may be generated by its fall. Below table gives theoretical energy levels which approximate to values give in the part of IEC60068.
| Energy levels in joules | |||||||
| Height of fall (m) | Speed (m/s) | Mass of striking object (KG) | |||||
| 0.1 | 0.2 | 0.5 | 1 | 2 | 5 | ||
| 0.1 | 1.4 | 0.1 | 0.2 | 0.5 | 1 | 2 | 5 |
| 0.2 | 2 | 0.2 | 0.4 | 1 | 2 | 4 | 10 |
| 0.5 | 3.1 | 0.5 | 1 | 2.5 | 5 | 10 | 25 |
| 1 | 4.4 | 1 | 2 | 5 | 10 | 20 | 50 |
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*The value correspond to blows perpendicular to the specimen surface. *Much higher energies can be encountered in particular situations such as vandalism or in a car accident. In these cases, consideration should be given to the use of additional protection such as barriers or wall. |
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4. Information for testing
The temperature of the specimen may influence of the results of the tests and the relevant specification should take this into account, when applicable.
Impact tests can be specified in sequence with other tests, but attention is drawn to the fact that some standardized tests are required to be performed on new specimens, which excludes previous hammer tests.
The main performance criteria should be derived from how the operational and survival characteristics of the specimen are influenced by mechanical impacts.
The other important aspect is safety, which can be the prime consideration in certain circumstances.
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