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Impact events on composite structures that may cause damage can be readily detected and located using sensors that respond to the resulting impact stress waves as they propagate. This capability can be used as an alert to maintainers or operators who use the structures that an incident has occurred. However, for this capability to be truly useful it must include the capacity to determine automatically if the impact has caused damage. This will avoid the situation where a follow up inspection of the impact site reveals that no damage has been caused (no-fault found). This paper reports results from impact tests on glass and carbon composite, structural test specimens in which impact sensor data has been processed to reveal clear features that allow discrimination between damaging and non-damaging impacts.

An essential part of the SHM validation effort is to check the presence and adequacy of the methods required to validate the correct functionality of each SHM task, which can be targeted at detecting structural faults. The ultimate proof of the correct functionality is validation evidence, e.g. crack detection evidence, observed during the operation of the aircraft. However, the occurrences of structural faults such as cracks are infrequent, and hence, years of flight tests might be required to collect validation evidence; small numbers of flights would be only sufficient to prove the system's “fitness for flight” and would be insufficient to prove “fitness for purpose”. Validation evidence can be collected during laboratory tests by inducing faults in structural specimens and examining the SHM detection capability.