4. Interfaces matrix Reinforcement (fiber, … ) Interface : between any two phase Coherent : one-to-one correspondence between atomic sites semicoherent : increasing size of the crystals → elastic strain energy > interfacial energy leading to a lowering of the free energy of the system by dislocation at the interface →interface containing dislocations to accommodate the large interfacial strains→ Thus having only a partial atomic registry: semicoherent Incoherent :semicoherent still futher increase in crystal sizes→ dislocation density at the interface increases→it is no possible to specify individual atomic positions at the interface : incoherent A phase, lattice B phase Coherent semicoherent

a : ideal planar inreface b : more likely real inreface 4.1 Wettability and bonding wettability is the term used to describe the extent to which a liquid would spread on a solid surface Q: surface energy Q LS +Q LV cos ⊖ = Q SV 180 ⁰ - the drop assume a spherical and no wetting occurs 0 ⁰ - contact angle represents perfect wetting 0 ⁰ < ⊖ <90 ⁰ - a partial wetting occurs Good bonding implies that atomic or molecular bonds are formed uniformly all along the interface !

4.2 The interface in composite The reason the interface in a composite is of great importance is that the internal surface area Occupied by the interface is quite extensive 4.3 interations at the interface Interfacial zone having multiple interfaces resulting from the formation of different intermetallic Compounds, interdiffusion,and so. The difference in the expansion coefficients of the two components can give rise to thermal stresses Of such a magnitude that the softer(generally the matrix) will deform plastically 4.4 types of bonding at the interface Mechanical bonding-any contraction of the matrix onto a central fiber would result in a gripping of The latter by the former Chemical bonding- dislocation and wettability bonding: the implies that surface should be treated to re-move any impurites reaction bonding: transport of atoms that is, this atomic transport is controlled by diffusional processes

The reaction products as well the reaction rates can vary Depending on the matrix composition,reaction time, and temperature 4.5 tests for measuring interfacial strength Single fiber test three- point bend tests indentation method