4(%3)3 - Ecole nationale supérieure de chimie de Montpellier

intensity factor (K IMax ) experienced. During fatigue-type damage crack propagation is related to both K IMaxand the change in K I during cycling (K). Either the fractured surfaces of the crack must be resealed orthe growth of the crack must be stunted or checked to effectuate the healing process of the polymer. Anumber of so called extrinsic mechanisms 11,14 are proposed to mitigate the crack growth (Figure– 1.3) 13 .Figure– 1.3: The proposed extrinsic mechanisms for crack growth retardation in a material 13,14 , a) Crack deflection,b) Wedging – debris induced crack retardation, c) Wedging – surface roughness induced crack deflection, d)Bridging – fiber toughening, e) Zone shielding – microcrack toughening, f) Zone toughening – transformationtoughening, g) Zone shielding – crack field formation, h) Wedging and bridging – fluid pressure induced crackclosureAll traditional and self-healing approaches are based on these mechanisms and generally involvedissipation of energy away from the propagating crack tip via a mechanical change behind the crack tip.1.2 SELF HEALING MATERIALS IN GENERALAn ideal self-healing material (polymeric) should have an in-built capability to repeatedly sense,respond and repair from damage it suffered while recovering most of its primal properties within a shorttimeframe. From here, healable polymeric materials can be broadly classified into two classes:Autonomous self-healing materials in which the healing process is triggered by the damage itselfwithout need of any other external stimulus and the materials is able to attain pristine material’sproperties; Non-Autonomous self-healing materials in which healing is triggered and executed in3