Session: 03-03-01: Damage, Fatigue, and Fracture I

Paper Number: 108435

108435 - Self-Healing of Fatigue Delamination in Thermoset Composites Using Thermoplastic Healants 

In this study, fatigue testing under mode-I loading was carried out on double cantilever beam (DCB) specimens, and subsequent healing of the delamination was investigated. Due to the susceptibility of laminated composites to delamination, fatigue delamination is one of the crucial damage modes in laminated composites that may result in catastrophic structural failure. Hence, it is necessary to investigate and quantify the delamination crack growth behavior due to fatigue loading and explore methods to heal the delamination. Therefore, DCB specimens of a carbon fiber-reinforced thermoset polymer (CFRP) composite containing thermoplastic healants were manufactured. Mode-I fatigue delamination experiments were carried out for virgin (initial case) and up to seven repeated healing cycles. The main objective of using thermoplastic healants, i.e., polycaprolactone (PCL) and shape memory polymer (SMP), was to close and then heal the cracks formed during fatigue loading and retain the fatigue life of the DCB specimen. The in-situ self-healing was achieved by activating macro fiber composite (MFC) actuators bonded to the DCB specimen, where the high-frequency vibration of the actuator provides the heat necessary to close the cracks using thermoplastic healants. The in-situ self-healing was triggered using MFCs after 5000 initial loading cycles to allow initial crack extension. The DCB specimen was then loaded up to half a million cycles to study the effect of healing on delamination growth and, ultimately, fatigue life. 

      The DCB Mode-I fatigue experiments were performed by following the ASTM D6115-97 standard under displacement control mode for a displacement ratio of 0.1 and a frequency of 5 Hz. First, the virgin (unhealed) DCB specimens were tested under mode-I fatigue loading through 500,000 fatigue cycles, and the corresponding delamination length referred to as virgin delamination length, was recorded. Subsequently, after self-healing, the DCB specimen was fatigue-loaded up to 500,000 cycles, and the predicted fatigue durability was calculated for the delamination growth equal to the virgin delamination length. The Paris law parameters were extracted from the experimental data of the virgin and healed specimens, and the results were repeatable.

Hence, the preliminary results demonstrate that delamination can be healed efficiently, which was found to be repeatable. As a result of self-healing, significant crack closure was observed, and the fatigue crack growth rate was considerably reduced. More tests must be performed on DCB fatigue specimens to have a statistically significant data set. These findings can help extend the service life of laminated composites and result in significant repair cost savings.

Presenting Author: Nilesh Vishe The University of Alabama

Presenting Author Biography: Mr. Nilesh J. Vishe received his Master’s in Aerospace Engineering from the Indian Institute of Technology Kharagpur, India. He is currently a Graduate Research Assistant in the Department of Aerospace Engineering and Mechanics at the University of Alabama. Mr. Vishe’s research interests are fatigue analysis, structural health monitoring, post-buckling analysis, and multi-disciplinary design optimization, mainly of composite structures. Before joining as a Ph.D. student at the University of Alabama, he worked as a Project Research Assistant in the Advanced Composites Division at CSIR-NAL in India. He is an associate member of the Aeronautical Society of India. He is a student member of AIAA and the American Society for Composites.

Authors:

Nilesh Vishe The University of Alabama
Sameer Mulani The University of Alabama
Samit Roy The University of Alabama