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Ceramic Properties (Bonding (Covalent & Ionic Bonding Cons…
Ceramic Properties
Bonding
Covalent *
Metallic
VDW
Ionic
*
Ionic Radius
Affects crystal structure
Packing
Charge
Affects crystal structure
High Bond Strength Result
High Elastic Modulus
High MP
Good Chemical Stability
Covalent & Ionic Bonding Cons
Brittleness
Poor Electrical Conductivity
High Rigidity
Low Thermal Conductivity
Strength
Theoretical vs Real Strength Discrepancy
Inherent Flaws in microstructures
Processing Stages
Powder Raw Material
High Localised Stress Concentrations
Lead to Catastrophic Failure
Cracks & Flaws
Silicate-Based Compounds
Subcritical Crack Growth
Crack Propagation (Stress)
Under Low Loads
Threshold Region: Threshold Value (Kth)
Region 1: Power-Law Growth Region
Region 2
Region 3: Fast Fracture
Humidity
Temp
Lower than expected
Factors
Porosity
Grain Size
~ Flaw Size
Small Grains => Small Flaws => Higher Strength
Tests
Uniaxial Tensile Strength
4/3-Point Bending
Theta
Strengthening Mechansims
Reduce Flaw Size
Increase Fracture Toughness
Theoretical
Tests
Compressive
Tensile
Bending
Toughening Mechanisms
Crack Deflection
More New Surface
Crack Propagation
Direction Change
More Energy Consumed
Increase Distance Travelled
Crack Bridging
Crack not fully open
Fibers
Elongated Grains
Overcome
Fiber Strength
Adhesion btwn matrix & fiber
Transformation Toughening
Sintering Additives
R-Curve Behaviour
Reliable Strength Measurement
Crack Propagation Tolerance
Does not follow Griffith Model
Elastic Modulus/Young's Modulus (Fig 8)
Factors
Porosity
Brittle Fracture
Low/Medium Temp
Microstructure
Processing Determines
Machining
Sintering
Types
Viscous Flow
Liquid Phase Sintering
Solid State Sintering
Drying
Forming