Optical fiber sensor based life cycling monitoring and quality assessment of carbon fiber reinforced polymer matrix composite structures

Optical fiber sensors are very useful to monitor the internal strain and temperature in composites during manufacturing and assembly as well as in practical operations. The authors have been using both multi-point and distributed strain monitoring techniques to characterize the internal state of composite structures. This paper reports some recent developments of life cycle monitoring and quality control of aerospace composite structures. Specifically, distributed sensing for large-scaled parts, through-thickness strain monitoring for complex-shaped parts, and direction-dependent cure shrinkage monitoring are described, highlighting wide applicability of embedded optical fiber sensors for intelligent process monitoring and quality assessment of composite parts.

1. Introduction

Even though carbon fiber reinforced plastic (CFRP) is being used in almost all modern aerospace structures as a primary structural material, it is still difficult to precisely manufacture large-scale CFRP structures and ensure their structural integrity during operation. There is an urgent need to develop innovative sensing techniques to monitor the internal states of composite structures and utilize the obtained data to improve safety, structural design, processing technologies and maintenance methods. Within the systems developed so far, optical fiber sensors have attracted considerable attention [1]. They possess sufficient flexibility, strength, and heat resistance to be embedded relatively easily into composite laminates during the fabrication. Embedded sensors continuously monitor the composite manufacturing process itself, in-service usage, and damage (Fig. 1, [2]). By combining all the information obtained by the sensing network, we can accurately evaluate the internal state of the structure throughout its life. We call this technology “Life Cycle Monitoring” of composite structures. This paper reports some recent developments of our work. Figure 1.

Life cycle monitoring of composite structures [2].