Self-Healing Composites

SELF-HEALING COMPOSITES

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A report submitted for the partial fulfillment of the requirement for the seminar classes in 2nd semester (SESSION: JAN-JUN 2016) of Master of Technology in Production Engineering of NIT, Patna

Report Submitted by:

PETTA AVINASH

Roll no: 1535001

Under The Guidance of

Dr. S.K. Roy

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DEPARTMENT OF MECHANICAL ENGINEERING

NATIONAL INSTITUTE OF TECHNOLOGY

PATNA (BIHAR) -800005

ACKNOWLEDGEMENT

I am very much thankful to respected Professor Dr. S.K. ROY for his generous guidance, help and suggestions. To be honest it is the kind of devotion that he showed for our presentations has inspired me to complete this presentation sincerely. I always found his helpful hand wherever I needed it.

I express my sincere thanks to my classmates and department of Mechanical Engineering for giving me all essential helps required for this presentation.

contents:

• Introduction
• Definition of composite
• Self-healing composites
• Capsule based self-healing composites
• Assessment of self-healing efficacy
• Objectives
• Limitations
• Conclusion
• References

INTRODUCTION

For centuries, man has been searching for and creating tougher and more durable structural materials.

However, from the perspective of other natural creatures, protection and defense are not fulfilled only by their hard coats or shells, but also adaptively as in the healing of the human skin and the regeneration of the lizard’s tail [5]. It is simple observation that many natural systems can self-heal, it is equally simple observation that animals usually achieve this via a ‘bleeding’ mechanism [2].  Inspired by this design, intelligent material systems defined as self-healing composites have been developed. They are capable of automatic recovery and adaptation to environmental changes in a dynamic manner, unlike traditional tough and static composites. Through self-healing, it is expected that safety and reliability will improve, the cost of maintaining artificial composites will decrease and material life will be extended. This area has rapidly developed for more than a decade and seen a number of significant achievements [5].

WHAT ARE COMPOSITES?

            A composite material [1] is made by combining two or more materials to give a unique combination of properties. The final properties of composite materials are better than constituent material properties.

•  Typically, composite material is formed by reinforcing fibers in a matrix resin as shown in figure.       [pic 4]

SELF-HEALING COMPOSITES

Self-healing materials [4] exhibit the ability to repair themselves and to recover functionality using the resources inherently available to them. They are inspired by biological systems such as the human skin which are naturally able to heal themselves.

Self-healing is a three step process [4]:

• The first step involves triggering action immediately after the damage occurs.

• The second step is the transportation of materials to an affected region.
• The third step involves the chemical repair process.

Capsule based self-healing composites

• In the natural biological world, the unit that carries out self-healing is the cell, in which different liquids accomplish specific functions. Inspired by this design, artificial small capsules capable of bridging gaps when a crack occurs have been developed using encapsulation technique [5].
• In capsule-based self-healing materials, small capsules containing a liquid able to fill and close cracks are embedded under the material surface [5].
• Microencapsulation self-healing involves the use of a monomer, dicyclopentadiene (DCPD), stored in urea-formaldehyde microcapsules dispersed within a matrix [2].
• When the microcapsules are ruptured by a progressing crack, the monomer is drawn along the fissure where it comes into contact with a dispersed particulate catalyst (Ruthenium based “Grubbs” catalyst), initiating polymerization and thus repair [2].

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(a) Basic method of the microcapsule approach

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(b) ESEM image showing ruptured microcapsule

source : R S Trask et al., Self-healing polymer composites mimicking nature to enhance performance, Publisher: IOP publishing ltd., volume 2, issue 1.

Assessment of self-healing efficacy [5] 

Sustainable healing consists of three main aspects: healing efficiency/healing strength, healing rate and healing capability.

• Healing rate and efficiency represent the rate of curing and the strength of the repaired material respectively.
• Healing capability relates to the size of the damaged area and the range of materials that can be healed.
• In addition, sustainable healing implies the ability to undergo multiple healing cycles and ideally, means that the healing rate, healing efficiency and haling capability remained unchanged throughout.

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