Development of an On-Line, In-Situ, Fiber-Optic Void Sensor

• Published in: Journal of thermoplastic composite materials 1994-07, Vol.7 (3), p.219-229
• Main Authors: Klosterman, D.A., Saliba, T.E.
• Format: Article
• Language: English
• ISSN: 0892-7057; 1530-7980
• DOI: 10.1177/089270579400700304

Porosity is a common defect introduced during the molding of composite laminates, particularly with thick, complex, or high-production-rate parts. The deleterious effect of voids on the mechanical properties of composites has been well documented. Clearly, improved process control is needed to minimize voids. To this end, work has been initiated to develop an in-situ sensor for void detection that is nonintrusive, nondestructive, simple, reliable, of reasonable cost and able to withstand harsh curing en vironments. Initial development of an intensity-based fiber optic sensor using refractive in dex changes is summarized. The many factors that affect the sensor response are dis cussed, but the refractive index of the resin is found to be the only non-extraneous factor that affects light guidance in the sensor. Further, it is concluded that changes in the resin degree of cure and temperature can account for changes in the resin refractive index. An experimental approach for sensor calibration and operation is proposed, including description of an image analysis study to relate sensor signal to void size and distribution. A theoretical approach is also proposed that is based on a model for the sensor response given the state of the resin.