I have always, and I believe correctly, considered cohesize/bridging models linear elasticity. This is because whether we apply them to holes or cracks, we are solving the equations of ELASTICITY, with nonlinear boundary conditions along the part(s) of the crack along which a traction-separation law is applied. So the material model is totally elastic. All we did was to augment the elasticity theory with an ad hoc physical condition (inspired by experiments such as Dugdale).

So if I take that point of view, the ratio of crack length to plastic zone size enters the elasticity model, and can predict the behavior of small and long cracks (or small and large holes).

University of Minnesota Civil Engineering Faculty Search

I attach an essay we wrote for a book that will be published by University of Minnesota Press titled "The city, the river, the bridge." The essay is a transcription of part of a public lecture I gave on infrastructure and on the bridge collapse.

After the bridge collapse there were several posts on Imechanica that included speculation about the cause of the collapse, including fatigue crack growth, lack of redundancy, etc.. Our investigation determined the collapse was a result of an undersized gusset plate that reached its plastic limit load. 

The research funding environment we are all experiencing is extremely frustrating, and has the potential for long-term damage to academics and the nation. You may be interested in reading the letter to the Wall Street Journal by two Nobel Prize winners, David Baltimore and Ahmed Zewail.

In a recent discussion it was suggested that it would be useful to perform tension tests on collagen fibrils. We have developed a MEMS-based experimental procedure that is capable of applying very large strains to individual collagen fibrils. The attached paper presents illustrative data; an upcoming paper will present much more data that illustrates the rich behavior of these fibrils during loading and unloading tests.

I registered for iMechanica a few days ago, and found many postings instructive. Here is my first blog entry.

The topics being studied today by mechanicians are very difficult (what I often call "dirty problems"). In fact, often the mechanical theories (actually coupled mechanics, biology, chemistry) required to gain improved understanding are still in their infancy. Mechanicians that have entered fields such as mechanics of biological structures have gotten up to speed by paying the price (hopefully an enjoyable time on a learning curve) of reading large numbers of papers and discipline-based books. Many of these papers are cryptic and, while they may be of high scientific quality, they do not have significant pedagogical value to those entering the field (graduate students for example).