Bridging Scales in Plasticity

Though there has certainly been a high level of progress in the use of these methods to model structure (microstructure in particular) in materials, the allied task of exploiting these microstructures to explore the properties of materials remains as one of the important current challenges. 

As was noted earlier in the present chapter, one of the key ways in which an effective description of material response can be constructed is through the construction of defect dynamics approaches in which the fundamental degrees of 

In chap. 8 we developed many of the fundamental tools needed to examine the behavior of one or several dislocations. However, an equally challenging and important problem is the statistical problem posed by a collection of large numbers of dislocations. We made a certain level of progress in confronting the statistical questions that attend the presence of multiple interacting dislocations in the previous chapter, and now revisit these questions from the standpoint of the hierarchical approaches being described here and in particular in terms of the variational approaches to defect dynamics introduced in section 12.3.2. 

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The towers of the George Washington Bridge were modeled in celluloid at a scale of 140 to 1 in order to study the distribution of strain. Even though these were distorted models, it was subsequently found that predicted values were within 10% of those measured later on the actual structure. The Hoover Dam was modeled at a scale of 240 to 1 before construction, in order to identify and study points of stress concentration. The canyon walls were modeled in concrete while the dam was made of plaster E = 90,000 psi) which is a convenient modeling material for brittle materials. The water pressure on the dam was modeled, using mercury in plastic bags. 

One of the most promising bottom-up approaches in nanoelectronics is to assemble 7i-conjugated molecules to build nano-sized electronic and opto-electronic devices in the 5-100 nm length scale. This field of research, called supramolecular electronics, bridges the gap between molecular electronics and bulk plastic electronics. In this contest, the design and preparation of nanowires are of considerable interest for the development of nano-electronic devices such as nanosized transistors, sensors, logic gates, LEDs, and photovoltaic devices. 

Most recently, plastic lumber has broken into two potentially large-scale apphcations—aplastic railroad ties and bridges. Plastic rail ties have been used for some time in Japan, where wood is scarce, but... 

This computational imbalance motivated development of the Plastic Domain Decomposition (PDD) method described in this paper. Developed PDD is applied to a large scale seismic soil-foundation-structure (SFS) interaction problem for bridge systems. It is important to note that the detailed analysis of seismic SFSI described in this paper is made possible with the development of PDD as the modeling requirements (finite element mesh size) were such that sequential simulations were out of questions. 

Recycled plastic railroad ties have very large scale potential. A number of test projects with a few ties each were carried out between 1996 and 1997. In 1998, the Chicago Transit Authority became the first commercial purchaser, buying 250 ties for a test on its elevated train line. U.S. Plastic Lumber has been one of the major prodncers of these materials, and it claims that they have twice the fife span of wood ties. Polywood produces RPL for railroad ties as well as for bridges and boardwalks from a blend of polyethylene and poly-... 

FESEM images of SWNT/epoxy fracture surface (a) Pulled out CNT bundles as long as 30-40 can be seen. Plastic deformation of the matrix is obvious. Scale bar is 2fj,m. (b) Fracture surface in lower magnification. The failure modes of the composite portion include SWNT pullout, matrix cracks bridged by SWNT. Scale bar is 10 / m. 

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