Event Scheduled for Dec 4, 2009

Event: 1:30 PM, BPB Rm 130: School of Engineering Distinguished Lecture:

Location: BPB 130

Time: 02:00 pm

Details of Event:
Abstract: Based on probabilisitic atomisitic analysis, the lecture addresses some problems vital for the resilience of structures made of quasitbrittle materials such as concrete, fiber composites, coarse-grained ceramics, rocks, sea ice and bone, or any brittle material when used in micro- or nano-scale devices. For brittle as well as ductile materials, the type of probability distribution of structural strength is size and shape-independent. Analyzing the random growth of atomistic fracture and the multiscale transition to material scale, Bažant shows that, on the scale of the representative volume element of material, the probability distribution of strength is Gaussian, with a grafted remote Weibullian tail. For increasing structure size, the Weibullian portion gradually spreads into the Gaussian core and, for very large sizes, the distribution becomes purely Weibullian. Presenting an atomistic derivation of the power law for creep crack growth, Bažant further shows that a similar change of distribution occurs for structure lifetime. Numerous experimental results support the theory. One practical consequence is that the safety factors for large quasibrittle structures, e.g. concrete structures, airframes or ship hulls made of composites, and ceramic micro-devices, must depend on their size and shape. Another is that the lifetime can be predicted from tests of size effect on the mean short-time strength and of creep crack growth rate. Finally, Bažant points out an interesting mathematical analogy that explains lifetime anomalies for the latest nano-scale dielectrics.

BIO-SKETCH: Born and educated in Prague (Ph.D. 1963), Bažant joined Northwestern in 1969, where he has been W.P. Murphy Professor since 1990 and simultaneously McCormick Institute Professor since 2002, and Director of Center for Geomaterials (1981-87). He was inducted to National Academy of Sciences, National Academy of Engrg.and Am. Acad. of Arts & Aci., as well as Italian Nat. Acad. (dei Lincei), Austrian Acad. of Sciences, Czech Acad. of Engrg., Spanish Royal Acad. of Eng., Eur. Acad. of Sci. & Arts, and Istituto Lombardo. An ASCE Hon. Member and Illinois Registered Structural Engineer, he received six honorary doctorates (Prague, Karlsruhe, Colorado, Milan, Lyon, Vienna), ASCE von Karman, Newmark, Croes Medals and Lifetime Achievement Award, SES Prager Medal, ASME Warner and Nadai Medals (and selected for 2009 Timoshenko Medal), RILEM L'Hermite Medal, Torroja Medal, etc. He authored six books: Scaling of Structural Strength, Inelastic Analysis, Fracture and Size Effect, Stability of Structures, Concrete at High Temperatures, and Concrete Creep. With H-index 47 and >11,000 citations, he is one of top 100 ISI Highly Cited Scientists in engineering (www.ISIhighlycited.com).

References:
Bažant, Z.P. (2002). Scaling of Structural Strength. 2nd updated ed., Elsevier, London 2005.
Bažant, Z.P., and Planas, J. (1998). Fracture and Size Effect in Concrete and Other Quasibrittle Materials. CRC Press.
Bažant, Z.P. (2004). “Scaling theory for quasibrittle structural failure.” Proc., Nat. Acad. of Sciences 101 (37), 14000—14007.
Bažant, Z.P., and Pang, S.-D. (2006). “Mechanics based statistics of failure risk of quasibrittle structures and size effect on safety factors.” Proc. of the National Academy of Sciences 103(25), 9434-9439.
Bažant, Z.P., Le, J.-L., and Bazant, M.Z. (2008). “Size effect on strength and lifetime distributions of quasibrittle
structures implied by interatomic bond break activation.” Proc., 17th European Conference on Fracture (ECF-17), held at Technical University Brno, Brno, Czech Rep., J. Pokluda et al., eds., pp. 78-92.
Bažant, Z.P., Le, J.-L., and Bazant, M.Z. (2008). “Scaling of strength and lifetime distributions based on atomistic fracture mechanics.” Proc. of the Nat. Academy of Sciences, 106 (28), 11484-11489.
Pang, S.-D., Bažant, Z.P., and Le, J.-L. (2009). Statistics of strength of ceramics: finite weakest-link model and necessity of zero threshold.” Int. J. of Fracture 154, 131-145.
Le, J.-L., and Bažant, Z.P. (2009). “Strength Distribution of Dental Restorative Ceramics: Finite Weakest-Link Model with Zero Threshold.” Journal of Dental Materials, 25, 641--648.
Le, J.-L., Bažant, Z.P. and Bazant, M.Z. (2009). “Subcritical Crack Growth Law and Its Consequences for Lifetime Statistics and Size Effect of Quasibrittle Structures. J. of Physics D: Applied Physics 42, 214008.

Sponsored By: Mechanical Engineering

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