Mechanical Properties of Ceramics

In this presentation, a brief description of Young's Modulus, Hardness and Fracture Toughness is discussed, also an experimental way to determine the above mentioned properties is also discussed.

1. MECHANICAL PROPERTIES OF CERAMICS SHARAD WALIA MECHANICAL ENGINEERING UPES, DEHRADUN

2. WHAT ARE CERAMICS…? A Ceramic is a non metallic solid material comprising an inorganic compound of metal, non-metal and metalloid atoms, primarily hold in ionic or covalent bonds. The word Ceramics comes from a GREEK word KERAMICOS means “burnt stuff.”

3. A brief description about Mechanical Properties of Ceramics Here some general mechanical properties of ceramics are described: BRITTLE HIGH HARDNESS HIGH ELASTIC MODULUS HIGH DENSITY LOW DUCTILITY LOW

4. HARDNESS Hardness is defined as the ability of a material to resist plastic deformation, usually by indentation. It is the property of a material which gives it the ability to resist being permanently deformed when a load is applied. So, greater the hardness of the material, the greater resistance it has to deformation.

5. HARDNESS Cont… Hardness implies high resistance to deformation and is associated with LARGE Modulus of Elasticity. Hardness is affected by POROSITY in the surface and as well as sub-surface, the GRAIN SIZE of the microstructure and the grain boundary phases of a material.

6. MICROHARDNESS Microhardness refers to the testing of hardness of materials by using small applied loads . Microhardness testing, with applied loads under 10N , is typically used for smaller samples, thin specimens, plated surfaces or thin films.

7. YOUNG’S MODULUS Young’s modulus is also known as Elastic Modulus . It is defined as the ratio of stress below the proportional limit to the corresponding strain. It is the measure of rigidity of stiffness of a material. The greater the modulus, the stiffer the material, in other words, the elastic strain resulting from the application of the resulting stress is smaller.

8. FRACTURE TOUGHNESS In metallurgy, fracture toughness refers to a property which describes the ability of a material containing crack to resist further fracture. It is a quantitative way of expressing a material’s resistance to brittle fracture . Brittle fracture is a characteristic of material with less fracture toughness.

9. INSTRUMENTED TESTING The determination of the mechanical properties like Young’s Modulus and Hardness, carried out using INSTRUMENTED MICROHARDNESS TESTING MACHINE. In instrumented indentation the microhardness testing machine perform continuous measurement and the results are automatically generated which can be obtained from the system. Fracture toughness is further calculated from the radial crack lengths generated in the specimen.

10. Cont… In the determination of Young’s Modulus and Hardness a load of 1N was used and for the calculation of fracture toughness a load of 2N was used. Vicker’s indentation method, using square pyramidal indenter, was used for the measurements. The system after recognizing the load vs. indentation curve calculate stiffness (S) from the unloading part of the curve at h max .  

11. A typical load vs. indentation curve

12. Cont… Using stiffness value, Reduced modulus is evaluated by the system using Also the reduced modulus is given by where E and ν represent Young’s Modulus and Poisson’s ratio of the indenter (i) and sample (s), respectively.  

13. Cont… The Hardness of the sample is given by The contact area, A is an experimentally determined function of the contact depth ( h c ) . The contact depth ( h c ) is related to the total displacement, h of the indenter. w here P max is the peak load and ε is a constant related to the geometry of indenter.  

14. Cont… The calculation of fracture toughness is done using the average radial crack lengths generated during indentation as per the given equation. where α is the geometry factor, E is the Young’s Modulus, H is the hardness, P is the applied load and c is the radial crack length.  

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