Assumethaty 1 answer 2 2 1 k ic 1 75 1 0003m 3mm ac

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Unformatted text preview: Three variables must be considered when looking at the possibility of fracture of a material • The Griffith Criterion says that a material fails when: KI KIC applied stress intensity factor • Design stress: design c or GI material fracture toughness K IC Y a • Maximum allowable flaw size: 20 GIc 1 K IC ac designY 2 • A typical steel structure has a fracture toughness of about KIc 75 MPa‐m1/2 If the structure is designed to withstand a stress of 750 MPa, how big do flaws in the material have to be to pose a threat? Assume that Y 1 • Answer: 2 2 1 K IC 1 75 1 0.003m 3mm ac 750 (100) designY – The largest tolerable flaws in many engineering structures are of this dimension 21 100 KIc (MPa · m 0.5 ) 70 60 50 40 30 Graphite/ Ceramics/ Semicond Polymers C-C (|| fibers) Steels Al alloys Mg alloys Al/Al oxide(sf) 2 Y2 O 3 /ZrO 2 (p) 4 C/C ( fibers) 1 Al oxid/SiC(w) 3 Si nitr/SiC(w) 5 Al oxid/ZrO 2 (p) 4 Glass/SiC(w) 6 10 Diamond Si carbide Al oxide Si nitride 3 0.7 22 0.6 0.5 PET PP PVC 2 1 1 Ti alloys 20 7 6 5 4 Composites/ fibers PC <100> Si crystal <111> Glass -soda Concrete PS Polyester Glass 6 increasing Metals/ Alloys K metals c comp Kc poly K cer K c c Based on data in Table B5, Callister 6e. Composite reinforcement geometry is: f = fibers; sf = short fibers; w = whiskers; p = particles. Addition data as noted (vol. fraction of reinforcement): 1. (55vol%) ASM Handbook, Vol. 21, ASM Int., Materials Park, OH (2001) p. 606. 2. (55 vol%) Courtesy J. Cornie, MMC, Inc., Waltham, MA. 3. (30 vol%) P.F. Becher et al., Fracture Mechanics of Ceramics, Vol. 7, Plenum Press (1986). pp. 61-73. 4. Courtesy CoorsTek, Golden, CO. 5. (30 vol%) S.T. Buljan et al., "Development of Ceramic Matrix Composites for Application in Technology for Advanced Engines Program", ORNL/Sub/85-22011/2, ORNL, 1992...
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