Lecture 04

Today’s objectives-Mechanical Properties ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Abrasives ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],http://www.abrasiveengineering.com/eurostus.pdf Almost 3000 tons a day! 700 Sand 550 Glass 600 Steel 80 Nickel 2500 Silicon carbide (SiC) 2100 Alumina (AL2O3) 2100 Tungsten carbide (WC) 800 Quartz (SiO2) 1 Graphite 7000 Diamond (C) Knoop Hardness (100g load) Material 60 1150 550 Super (no gems) 850k 310 580 Loose 70k 850 1600 Coatings 65k 860 450 Bonded tons Europe $ US $ Abrasive use, 2002 http://www.chm.bris.ac.uk/pt/diamond

Stress vs. Strain ,[object Object],[object Object],[object Object],[object Object],Brass Brass strains to 35% = Fracture Strength (stress at failure) Ceramics strain to 0.1%

Fracture strength Callister, Appendix B Note that the fracture strength for ceramics is about 10* better in compression than in tension. Body armor 69 Soda lime glass 13.8-69 Graphite 230-825 SiC (sintered) 1050 Diamond (natural) 800-1400 Diamond (synthetic) 37.3-41.3 Concrete 130 Si [100] cleaved 282-551 Al 2 O 3 (99.9% pure) Strength (MPa) Ceramic

Failure Mechanisms-single xtals ,[object Object],[object Object],[object Object],[object Object],http://www.theimage.com/crystalinfo/crystal_page2.htm

Failure Mechanisms-polycrystals ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Typical mechanical property measurements ,[object Object],[object Object],[object Object],[object Object]

Measuring ceramic mechanical properties ,[object Object],Solution: bend test. Most appropriate for bars, rods, plates, and wafers. Where will cracks form? Which part is under tension and which is under compression?

MEASURING FRACTURE STRENGTH • 3-point bend test to measure room T strength. Adapted from Fig. 12.29, Callister 6e. • Flexural strength: Flexural fracture strength is higher than the tensile fracture strength. Why? Test specimens undergo compressive and tensile loads instead of pure tension. Si carbide Al oxide glass (soda) 550-860 275-550 69 Data from Table 12.5, Callister 6e. circ.

MEASURING ELASTIC MODULUS • Room T behavior is usually elastic, with brittle failure. • Determine elastic (Young’s) modulus according to slope: Adapted from Fig. 12.29, Callister 6e. Si carbide Al oxide glass (soda) 430 390 69 Data from Table 12.5, Callister 6e.

Measured Fracture Strengths ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Fracture Toughness ,[object Object],[object Object],Mode I a 2.7-5 Aluminum Oxide usually greater metals 0.7-1.1 Soda-lime glass 0.2-1.4 Concrete K Ic (MPa*m ½ ) Ceramic

[object Object],[object Object],[object Object],[object Object],[object Object],Fracture Toughness-stress concentration Note: no such stress concentration occurs for compression.

Journal of Irreproducible Results? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Weibull statistics ,[object Object],[object Object],130 MPa Si [100] cleaved 81.8 MPa Si [100] laser scribed

Minimizing Failures ,[object Object],[object Object],[object Object],rated load

Guaranteeing No Failures ,[object Object],[object Object],[object Object],[object Object],rated load

Where failures matter ,[object Object],[object Object],[object Object],[object Object]

Caveat for brittle materials: delayed fracture ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Ceramics at higher temperatures ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Ionic Bonding Slip is impossible: Too much electrostatic repulsion + - + - + - + - + - + -

Improvements for mechanical applications ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

SUMMARY Reading for next class Phase diagrams Chapter sections 12.6, 12.7 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

Lecture 04

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Lecture 04