Measurement of Fracture Toughness in Ceramics

This lecture is designed to give guidelines for meaningful fracture toughness testing for ceramics. Often, the young scientist is confused by the wealth of methods available. This lecture is meant to describe advantages and disadvantages of the various techniques presented and to provide some depth such as stress fields around indentations, weight function method etc. All methods described are suitable to obtain one toughness value as well as to obtain the whole R-curve. Crack geometry and specimen geometry effects will be highlighted.

  1. Handbook solutions: short vs. Long cracks
  2. Testing devices
  3. Long cracks in CT specimen
  4. Long cracks in bend bars (single edge notcheed beam (SENB) single edge pre-cracked beam (SEPB) and single edge V-notched beam (SEVNB) )
  5. Indentation methods: Indentation crack length (ICL) and indentation strength bending (ISB)
  6. Short cracks in bend bars: short crack in flexure (SCF)
  7. Measuring crack opening displacement and obtaining crack tip toughness and the crack closure stresses.
  8. Measuring subcritical crack growth (v-K curves)
  9. Temperature dependent toughness
  10. Case studies: Effect of macroscopic plastic yielding in ferroelastics on the toughness measurement

Toughening Mechanisms in Ceramics

This lecture is designed to classify and describe the separate toughening mechanisms

  1. The crack tip cohesive zone
  2. Process zone mechanisms in general
  3. Transformation toughening
  4. Microcrack toughening
  5. Ferroelastic toughening
  6. Crack bridging in general
  7. Crack bridging using fibers and whiskers
  8. Crack bridging using ductile particles

Strength of ceramics

This lecture describes the way ceramics fail, the determination of fracture origins, the modelling of fracture origins, the first microcracking event, the technique of acoustic emission and the propagation of the critical flaw until instability.

  1. Fractography and classification of defects
  2. Microcracking
  3. Models for stress concentrator and critical flaw
  4. Model experiments on the strength of ceramics
  5. Strength as a function of grain size
  6. Strength as a function of density
  7. Strength for nanocrystalline materials
  8. Strength for metal-ceramic composites

Processing and sintering of ceramics, particularly nanocrystalline ceramics

This lecture describes the problems encountered when processing nanocrystalline ceramics, the theory of sintering in an atomistics prospective as well using a continuummechanical approach.

  1. Slip casting of ceramics
  2. Sintering models for ceramics
  3. Influence of grain size on sintering
  4. Constraint sintering: Sintering thin films and sintering layered materials
  5. Processing of functionally graded materials: gradient in porosity and metal-ceramic gradient materials.

Actuator materials

Piezoceramics are increasingly used for actuators such as for inkjet printers, valve control in Diesel engines, thread guides etc.. The mechanics of these materials including their electromechanical coupling has not yet been fully clarified. Also, since the need to perform for about 109 cycles, the long term reliability is not yet understood.

  1. Applications for actuators
  2. Mechanical properties of ferroelectric and ferroelastic materials
  3. Constraint cracking at electrode edges
  4. Damage mechanisms in actuators after long cycling
  5. Interaction between domain walls and defects