Lec14_Ceramics II - Ceramics II Instructor Prof Bishakh...

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Ceramics - II Instructor : Prof. Bishakh Bhattacharya Dept. of Mechanical Engineering IIT Kanpur India E-mail : [email protected]
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Content Processing of ceramics Ceramic elastic modulus Weibull modulus Hardness Fracture toughness Failure in ceramics
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Unlike metals and glasses , which can be cast from the melt and subsequently rolled, drawn, or pressed into shape, ceramics are made from powders . Ceramics powder is consolidated and densified by sintering . Sintering is a process whereby particles bond and merge under the influence of pressure & heat , leading to shrinkage and reduction in porosity. Expensive fabrication technique due to high cost of mould & die. A similar process in metal manufacturing is referred to as powder metallurgy . Processing of Ceramics Powder particles Sintering begins - Particles coalescence and pore forms Sintering terminates - pores change size and shape Reference: W.D Callister, 7 Ed. Sintering Reference: Engineering Materials 2: Ashby & Jones, 4 th Ed.
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Influence of Porosity There always occur some pores or void spaces between the powder particles even after sintering and subsequent heat treatment. Residual porosity has a negative influence on both the elastic properties and strength. Porosity also leads to :- Reduction in effective load carrying area. Acts as stress concentrators. Modulus of Elasticity for Al 2 O 3 at room temperature Bending strength for Al 2 O 3 at room temperature 𝑉????? ??𝑎𝑐?𝑖?? ?????𝑖?? = 𝑉????? ?? ????? 𝑉????? ?? ???𝑐𝑖??? Reference: W.D Callister, 7 Ed.
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How to measure Ceramic Elastic modulus? Ceramics are not subjected to Tensile testing due to 3 important reasons: Difficult to prepare test specimen as required for tensile testing.
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