N. Eswara Prasad et al. Engineering Fracture Mechanics 71(2004) 2589-2605 [7-10). These properties include, high melting point combined with high thermal shock resistance and xcellent thermal as well as electrical insulating properties [8, 10]. However, the mechanical properties of lica material in the monolithic form are far from acceptable levels. Silica, in its bulk form, has low strength (both tensile and flexural) and extremely low fracture toughness as compared to several structural ceramic materials [8]; thus, needing significant improvements so that it can be accepted for any structural application. One of the means of achieving improved mechanical properties is by using either two-or three- dimensional(designated commonly as 2D- and 3D, respectively) networks of continuous fibres as rein- forcements to the ceramic-matrix material leading to newer structural materials, known as"continuous fibre-reinforced, ceramic-matrix composites(CFCCs)". Numerous studies have been conducted in the last two decades on the fibre/whisker toughening of this class of ceramics. These studies have been compre- hensively reviewed by Evans [2] as well as by Becher [4] and later, by Faber [6]. However, to the best of our knowledge, there are no fracture toughness/energy studies reported so far for the silica-silica CFCCs During the fracture process of a CFCC, various events/developments take place in the three regions of the fracture, namely the wake of the crack, at the crack tip and finally in the region of process zone ahead of the crack tip These influence the net enhancements in the fracture resistance of a CFCC. They include some or most of the following [2, 3, 5 1. Local increase in the stress level with the application of external loading 2. relative displacement of matrix/interface elements 3. matrix microcracking, leading to matrix failure(with or without significant crack path meandering, i.e rack deflection and/or branching) 4. debonding of matrix/fibre interface(with or without significant frictional forces), fibre pull-out and fibre breakage in the crack tip process zone, 6. frictional sliding of the fibres along the matrix/fibre interfaces, 7. loss of residual strain energy These processes/stages, schematically shown in Fig. 1, result in significant energy dissipation through frictional events in the wake and process zones, acoustic emission and fibre debonding, pull-out and breakage. Contributions from these stages of crack tip and fibre reinforcements interactions, with or ULL-oUT FRIC TIONAL DISSIPATION ENERGY DISSIPATED ACOUSTIC WAVES MATRIX CRACK RESIDUA SURFACES STRESS-FREE LOSS OF RESIDUAL Fig. l. Schematic showing various events and processes of crack bridging mechanism in fibre-reinforced composites(from Ref. 2). Note that the crack extension process essentially involves matrix microcracking, fibre/matrix debonding, fibre fracture and fibre pull[7–10].These properties include, high melting point combined with high thermal shock resistance and excellent thermal as well as electrical insulating properties [8,10].However, the mechanical properties of silica material in the monolithic form are far from acceptable levels.Silica, in its bulk form, has low strength (both tensile and flexural) and extremely low fracture toughness as compared to several structural ceramic materials [8]; thus, needing significant improvements so that it can be accepted for any structural application.One of the means of achieving improved mechanical properties is by using either two- or three￾dimensional (designated commonly as 2D- and 3D-, respectively) networks of continuous fibres as rein￾forcements to the ceramic–matrix material leading to newer structural materials, known as ‘‘continuous fibre-reinforced, ceramic–matrix composites (CFCCs)’’.Numerous studies have been conducted in the last two decades on the fibre/whisker toughening of this class of ceramics.These studies have been compre￾hensively reviewed by Evans [2] as well as by Becher [4] and later, by Faber [6].However, to the best of our knowledge, there are no fracture toughness/energy studies reported so far for the silica–silica CFCCs. During the fracture process of a CFCC, various events/developments take place in the three regions of the fracture, namely the wake of the crack, at the crack tip and finally in the region of process zone ahead of the crack tip.These influence the net enhancements in the fracture resistance of a CFCC.They include some or most of the following [2,3,5]: 1.Local increase in the stress level with the application of external loading, 2.relative displacement of matrix/interface elements, 3. matrix microcracking, leading to matrix failure (with or without significant crack path meandering, i.e., crack deflection and/or branching), 4.debonding of matrix/fibre interface (with or without significant frictional forces), 5.fibre pull-out and fibre breakage in the crack tip process zone, 6.frictional sliding of the fibres along the matrix/fibre interfaces, 7.loss of residual strain energy. These processes/stages, schematically shown in Fig.1, result in significant energy dissipation through frictional events in the wake and process zones, acoustic emission and fibre debonding, pull-out and breakage.Contributions from these stages of crack tip and fibre reinforcements interactions, with or Fig.1.Schematic showing various events and processes of crack bridging mechanism in fibre-reinforced composites (from Ref.[2]). Note that the crack extension process essentially involves matrix microcracking, fibre/matrix debonding, fibre fracture and fibre pull￾out. 2590 N. Eswara Prasad et al. / Engineering Fracture Mechanics 71 (2004) 2589–2605