Embedded PVF₂ sensors for impact and damage detection in sandwich composites

It is well understood that composite sandwich structures have poor out-of-plane impact resistance. As a result, health monitoring and damage detection schemes are of interest to ensure the integrity of these structures by eliminating the necessity of overly frequent inspection schedules. For this reason, this study examines the effectiveness of piezoelectric polyvinylidene fluoride (PVF₂) film sensors embedded within the facesheet of a sandwich panel in detecting low-velocity impact and damage. In these experiments, four sensors are constructed and located in the corners of a rectangular test coupon and an instrumented dropped-weight impact test apparatus is utilized to record the sensor and impact force signals during the impact event. Results of the experiments demonstrate that the sensors are capable of producing high-level signals at low levels of impact energy, irrespective of the location of impact. Furthermore, comparisons between the contact force and sensor data show that the sensors are capable of indicating if and when impact damage occurs during the low-velocity impact event. The time-of-arrival information derived from each sensor is also utilized to determine if the location of impact can be found. Finally, the prospective use of these sensors for health monitoring of composite aerospace structures is discussed.