Experimental study on dynamic behavior of woven carbon fabric laminates using in-house piezoelectric sensors

Piezoelectric Polyvinylidene fluoride (PVDF) nanofibers are produced through the electrospinning process and then characterized to examine their morphology, crystal structures, and thermal behavior for usage as an in-house strain sensor. Characterization results confirm that electrospinning of PVDF fibers promotes the formation of beta-phase which is an electro-active phase for piezoelectricity. Load controlled dynamic flexural tests are performed on woven carbon fabric composites with embedded and surface mounted PVDF sensors to study the capability of these sensors for monitoring the fatigue life of composite materials. The correlation factor for PVDF sensors is obtained through comparing the output voltage of PVDF sensor and strain measurement by video extensometer. It is shown that the PVDF based sensor is able to monitor the strain history and damage progression in woven carbon fabric laminates under fatigue loading condition. Moreover, the strain field acquired by the surface mounted PVDF sensor can clearly capture the three distinct stages of overall fatigue life of woven carbon fabric laminated composite material. This result is validated by the strain measurement with the video extensometer during tests. It is important to emphasize that surface mounted PVDF sensors do not show any sign of detachment from the surface of the specimen or malfunctioning during the test. SEM analysis of fractured surfaces of composite specimens show vivid delamination and fiber pullouts through the thickness, thus indicating gradual growth of damage in laminates.