American Scientist

To the Editors:

Congratulations to Victor Li on his excellent article about fracture of concrete “ Can Concrete Be Bendable? ” in the November–December issue. Studies of that material’s fracturing are now on the same plane as the well-developed studies of metals and plastics. I would especially like to congratulate Dr. Li for showing a beautifully designed and executed “four point bending jig” in Figure 1 of the article. This apparatus makes the bending moment, and thus the bending stress field, uniform between the loading points. My mentor Frank A. McClintock and I—as well as all others he trained—have advocated this method as the standard for bending tests. I am very glad to see Dr. Li’s use of it.

C. A. Berg
Professor Emeritus, Mechanical Engineering
Northeastern University
Boston, MA

Dr. Li responds:

Many thanks to Dr. Berg for his kind comments on my article. Many researchers contributed to our current knowledge on the fracture behavior of concrete materials, including Drs. Z. Bazant and S. Shah at Northwestern University, Dr. Y-W. Mai at the University of Sydney in Australia, and the late Dr. A. Hillerborg at Lund University in Sweden. My research group has built on this knowledge in deliberate tailoring of the microstructure so that the common brittle fracture mode of concrete is suppressed, giving preference to a ductile damage-tolerant deformation mode when the material is overloaded.

I am also delighted to read the reference to Frank A. McClintock in Dr. Berg’s note. The late Dr. McClintock was a colleague of mine when I taught at MIT in the 1980s. I count him as a friend from whom I learnt a great deal about mechanics and materials.