TITLE: An In Situ Sensor for Process Control of Fiber Reinforced Composites

Abstract:
(Introduction) Development of novel sensor technology has played an important role in the online analysis of process integrity for the manufacture of high performance composite materials. The behavior of the interface in composite materials dominates the overall mechanical characteristics of the composite material. In order to effectively predict the mechanical performance of the composite, it is critical to quantitatively assess the characteristics (density, stiffness, etc.) of the interface. Current technologies designed for assessment of the interface include destructive testing (fiber push testing [1], thermal mechanical fatigue testing, etc.) in which the interface is degraded or destroyed during the testing process, conventional ultrasonics (shear wave back reflection [21, normal incidence C-scanning [31) in which the material is tested post-process, and embedment of sensors (such as optical fibers [4,5]) in which the sensing system is inlaid within the material for on-line interface integrity and/or interface characterization. However, these current and emerging technologies often contain limitations addressed by the following issues.

1. Can the material/structure be effectively utilized after the test is complete or does the test influence the nature of the interracial region in the composite?
2. Does the test provide on-line interracial integrity data which can be fed back to processing/manufacture for process optimization?
3. Does the sensor / test procedure influence the mechanical properties of the material?
4. How does the sensor data relate to the actual interfacial conditions, i.e. is there a direct or indirect correspondence between sensor data and interfacial behavior?
5. Does the sensor /test procedure provide local or global parameters?

In this work, we describe the feasibility of the multi-functional fiber sensor for specific applications and show the relationship between specific mechanical properties and the detected ultrasonic signal response for selected composite materials. A novel optical interferometric technique has been developed which allows noncontacting coupling for high sensitivity detection at elevated temperatures and pressures.

*This paper was presented and submitted. in similar form. to the 4 Ist Sagamore Confercnce on Intelligent Processing of [vlatcrials. Ply mouth. MA. August 1994 )

Source: Proceedings of the 'NDE applied to Process Control of Composite Fabrication' - Conference, 4-5 Oct 1994 St. Louis, Missouri. Publisher and Organizer: Nondestructive Testing Information Analysis Center (NTIAC) Texas Research Institute Austin, Inc. Austin, Texas [http://www.ntiac.com] [Buying the Proceedings]