Classification and Quantification of Matrix Micro-cracks in Composite Structures

Fiber reinforced composites have been widely used in aerospace applications due to their functional properties such as high strength-to-weight ratios. But many challenges are yet to be overcome in order to have more confidence on the performance of composites structures. Particularly, composites have different failures types and modes that make the damage prediction and propagation a very challenging subject. The current work will focus on developing structural health monitoring (SHM) techniques for inspection to reduce maintenance costs and increase aircraft safety by understanding and identifying damage types. The steps in implementing a successful Structural Health Monitoring System are to: 1) Locate damage, 2) Identify damage type, 3) Quantify damage and 4) Estimate remaining life. Stanford’s Structures and Composites Lab has developed Structural Health Monitoring techniques based on ultrasonic Lamb wave [1] propagation via the use of piezoelectric sensor networks. Using the sensor network in its active sensing mode, damage in a composite structure can be monitored. But the current state-of-the-art detection methods can only detect changes in sensor signal but do not distinguish among damage types or quantify the damage. Knowing the type of damage and quantifying it would provide the inputs needed for physics based prognostic models (lifetime estimation) which would predict the remaining life of the structure for its safe use.