Recovery and improvement in low-velocity impact properties of e-glass/epoxy composites through novel self-healing technique S. Zainuddin a,⇑ , T. Arefin b , A. Fahim a , M.V. Hosur a , J.D. Tyson b , Ashok Kumar c , J. Trovillion c , S. Jeelani a,b a Department of Material Science and Engineering, Tuskegee University, Tuskegee, AL 36088, United States b Department of Mechanical Engineering, Tuskegee University, Tuskegee, AL 36088, United States c Construction Engineering Research Laboratory, U.S. Army Engineer Research and Development Center, Champaign, IL 61821-9005, United States article info Article history: Available online 26 September 2013 Keywords: Self-healing agent Hollow glass fibers E-glass/epoxy Low-velocity impact abstract We report the recovery and improvement in low-velocity impact properties of e-glass/epoxy composites achieved through embedding self-healing agent (SHA) filled hollow glass fibers (HGFs). At first, catalytic technique was used to fill bonded HGFs with SHA. The HGFs were then laid on e-glass fibers and the lam- inates were fabricated using vacuum assisted resin infusion molding (VARIM) process. Low-velocity impact tests at two different energy levels were conducted multiple times in the closest proximity to determine the healing efficiency. Results showed significant improvement and recovery in impact prop- erties with 53.6% gain in peak load after second impact in SHA filled HGFs samples in comparison to con- trol samples. A significant gain in energy to peak load was also found in SHA filled samples with 86.6% improvement over control samples. Optical microscopy images of SHA filled HGFs samples showed filling of cracks developed after impact. A distinct damage behavior was observed in control and HGFs embed- ded samples. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Self-healing of materials, such as glass, polymers, and concrete, has been investigated in order to extend the service life of these structures [1–4]. In most of these investigations, the healing pro- cess involved human intervention and thus the materials were not able to heal autonomically. In recent years, polymer compos- ites have been attractive candidate to introduce the autonomic healing concept into modern day engineering materials. Even though several methods have been utilized in self-healing of poly- meric materials [5–9] and fiber reinforced polymers [10–15], the concept of repair by bleeding of enclosed functional agents re- mains a challenge and has gathered wide attention in the scientific community. The first use of hollow glass fibers embedded in a composite laminate was suggested by Bleay et al. [11]. In their study, filled hollow fibers with a resin were released into the damaged area when the fiber was fractured. A two-part epoxy resin was used as the repair medium. The two components was diluted with sol- vent and infiltrated into different plies of a composite based on Hollex S2-glass fiber. Even though the method needed no manual intervention for healing damages, efficient recovery of matrix strength was observed only at elevated temperature. More recently, several self-healing unidirectional glass fiber composites have been developed [13–17]. Trask et al. [18] placed self-healing plies within both glass fiber/epoxy and carbon fiber/epoxy lami- nates. They investigated quasi-static and impact properties and confirmed self-healing. In the work performed by Jones et al. [19], it was shown that solid-state self-healing system was capable of healing transverse cracks and delaminations in a composite. Their system involved a thermoplastic healing agent dissolved in a conventional thermosetting epoxy resin. Through Charpy impact testing, cracks were developed in the resin system before it was self-healed. However, the healing was assisted by heating the frac- tured samples. Woldesenbet and Williams [20] showed that, a con- siderable portion of the tensile strength can be restored by using single hollow fiber filled with releasable healing agent DCPD in polymer matrix composite. When the crack was initiated and prop- agated through the composite breaking the hollow fiber, the heal- ing agent flowed out and filled the gap. Polymerization was facilitated when the healing agent contacts the Grubb‘s catalyst that was coated on the outside surface of the hollow glass fiber. Even though different research groups around the world are en- gaged in developing self-healing materials, problems of localized healing and damage detection in fiber reinforced composites do still exist in most self-healing systems. Use of temperature or cat- alyst stayed highly impractical solution for localized self-healing. Moreover, the application of temperature to overall structure for self-healing is impossible particularly in case of undetected 0263-8223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.compstruct.2013.09.023 ⇑ Corresponding author. Tel.: +1 334 724 4222; fax: +1 334 724 4224. E-mail address: szainuddin@mytu.tuskegee.edu (S. Zainuddin). Composite Structures 108 (2014) 277–286 Contents lists available at ScienceDirect Composite Structures journal homepage: www.elsevier.com/locate/compstruct