Health monitoring of composite structures subjected to low-velocity impact with surface-bonded CNT buckypaper sensor arrays

The early detection of damage on composite structures can provide a basis and support for use in maintenance. This work presents the results of an experimental investigation concerning the low-velocity impact damage of composite structures based on buckypaper (BP) sensor arrays. Based on the results of a tensile test and load-unload cycle, the BP sensors show high linearity and good stability. Electrical conductive networks that act as in-situ impact damage sensors are provided by well-dispersed carbon nanotubes (CNTs). Electrical resistance decreases with repeated impact load and elastic deformation and damage evolution can be identified from the resistance change. The resistance change ratio of BP sensors after impact is decreased from 0 to -0.95. Throughout the test, BP sensors did not fail until the surface of the composite structure showed obvious damage. Meanwhile, a C-scan was used to measure and record the internal and external damage to composite structures. Compared with the C-scan, experimental results show that this method is feasible, it can detect small barely visible impact damage (BVID) flaws and it is especially fit for the damage evaluation of composite materials subjected to low-velocity impact. This work contributes to the health monitoring of composite structures using BP sensors and could be useful for applying an in-situ impact damage assessment system to real composite structures in the near future.