Composite Smart Materials Ppt.pptx

SELF-HEALING MATERIALS

HARISHSHARRAN.A.K.R 18MD38

INTRODUCTION Self-healing materials are artificial or syntheticallycreated substances which have the built-in ability to automatically repair damage to themselves without any external diagnosis of the problem or human intervention.  In general, cracks are hard to detect at an early stage, and manual intervention is required for periodic inspections and repairs. In contrast, selfhealing materials counter degradation through the initiation of a repair mechanism which responds to the micro-damage.  Some self-healing materials are classed as smart structures, and can adapt to various environmental conditions according to their sensing and actuation properties. 

CLASSIFICATION OF SELF-HEALING MATERIALS  Self-healing materials can be classified according to various criteria. The most general partition is based on matrix material, that is,  Organic matrix  Inorganic Organic matrix could be epoxy resins and other polymers.  Self-healing abilities are incorporated in inorganic materials like metals, ceramics, concrete and asphalt.

 Other

possible classification of the materials could be on basis of healing agent nature:  Monomers and chemical catalysts.  Metals and alloys with low melting temperature.  Shape memory alloys.  Diffusing atoms of different inclusions.  Bacteria. Modern self-healing materials include glass, rubber, plastic and metals.

WORKING OF SELF HEALING MATERIALS Embedded healing agents 

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The best-known self-healing materials have built-in microcapsules (tiny embedded pockets) filled with a glue-like chemical that can repair damage. If the material cracks inside, the capsules break open, the repair material "wicks" out, and the crack seals up. The main body of the material is a solid polymer, while the capsules contain a liquid monomer (one of the basic, endlessly repeated units that makes up the polymer). When the material fails and the capsules break, the monomer mixes with the polymer, more polymerization occurs, and the damage is healed effectively by creating more of the original material to replace the damaged area.

Microvascular materials 

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Embedded healing agents are simple and effective, but they do have a drawback: interrupting the structure of the material with capsules can actually weaken it, potentially increasing the risk of failure The human body doesn't fix damage this way with makeshift repair materials waiting inside every bit of skin and bone in case we happen to cut ourselves or fall over. Instead, our body has an amazingly comprehensive vascular system (a network of blood vessels of different sizes) that transport blood and oxygen for energy and repair. If damage occurs, our blood system simply pumps extra resources to the places where they're needed, but only when they're needed.

Shape-memory materials Shape memory works in a more complex way, typically you need to heat or otherwise supply energy to a material to make it snap back to its original, preferred form.  These materials therefore need some sort of mechanism for delivering heat to the place where damage has occurred.  An embedded network of fiber-optic cables similar to the vascular networks used in other self-healing materials except that, instead of pumping up a polymer or adhesive, these tubes are used to feed laser light and heat energy to the point of failure. That causes them to flip back into their preferred shape, effectively reversing the damage. 

Reversible polymers 

Some of the Polymers break apart to reveal what we might think of as highly "reactive" ends or fragments that naturally try to join up again. Energized by either light or heat, these stray fragments naturally try to rebond themselves to other nearby molecules, effectively reversing the damage and repairing the material. Some break to expose electrically charged ends, which give the broken fragments a built-in electrostatic attraction.

Benefits of self-healing materials:  Minimizing

the production cost of various industrial processes required for repairing damage.  Prolonging the service life of the materials.  Reducing the inefficiency of the materials due to degradation.

CASE STUDY:  This

case study deals with the incorporation of Self healing materials in cables which often cannot be accessed for repair.  The incorporation of self-healing materials would effectively allow these systems to maintain themselves, resulting in lower failure rates, and longer operational lifetimes.  Two 

types of cables discussed here are :

Extruded polymeric cables  Legacy fluid-filled circuits

SELF-HEALING FLUID FLUID-FILLED CABLES Fluid-filled cables (FFCs) exist in most undergrounded power networks as legacy cables.  FFCs are insulated by a layer of tightly lapped cellulosic paper impregnated with a low-viscosity mineral oil. 

Schematic of self-healing material response post-damage

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Gnosys has developed a next-generation of insulation oil that is self-healing and capable of cross-linking in the presence of oxygen. Should a breach in the sheath develop, the insulation oil will react to form a solid plug, thereby preventing the flow of oil. This self-healing fluid (SHF) is intended to replace the existing oil within the cable, thereby conferring self-healing capabilities without requiring wholesale asset replacement.

EXTRUDED POLYMERIC POWER CABLES

As with FFCs, the development of sheath defects can significantly reduce the lifespan of a polymerinsulated cable.  In this case, the danger is due to water passing through the defect and reaching the insulation.  Here, the combination of water and high electrical fields can cause accelerated degradation of the insulation through the formation of dendritic structures known as ‘water trees’.  If allowed to grow, these can eventually cross the insulation and cause its breakdown, resulting in the failure of the cable. 

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Gnosys has carried out extensive investigations into the development of self-healing systems for cable protection. Here, the use of a hydrophilic thermoplastic elastomers (h-TPE) deployed as a discrete layer positioned immediately under the sheath is proposed. Should the sheath be breached and water enter, the h-TPE will swell into the damaged area, closing the breach and preventing further penetration to the insulation.

Example water tree

CONCLUSION  In

conclusion, Gnosys is developing a range of SHFs and materials to meet the requirements of love-lived assets within the power sector.

REFERENCE 

Rhys Rhodes , Ian German, Susmit Basu, Gary C. Stevens , “Self-healing materials for autonomous cable repair”, June 2017.