Stiffened structures materials

Studies performed at the University of Missouri-Rolla in conjunction with Rockwell Scientific have shown FSP to produce a hne-grain-size material and create low-temperature, high-strain-rate superplasticity in aluminum and titanium alloys. The PNNL is currently investigating the application of this FSP-induced superplasticity in the fabrication of large, integrally stiffened structures. 

Huybrechts SM, Hahn SE, Meink TE. Grid-stiffened structures a survey of fabrication, analysis and design methods. In Proceedings of 12th international conference on composite materials (ICCM), Paris France 1999. 

Thermoplastic adhesives are not ordinarily recommended for use at above 66°C, although they can be used up to 90°C in some applications. These materials have poor creep resistance and fair peel strength. They are used mostly in stressed joints and designs with caps, overlaps, and stiffeners. The materials most commonly bonded are non-metallic material, especially wood, leather, plastics, and paper. With the exception of some hot-melt adhesives, thermoplastic adhesives are not generally used for structural applications. Examples of thermoplastic adhesives are shown in Table 4.2. ... 

Injection molding processing involves both a molten flow phase and a solidification phase. The major challenges of constitutive modeling of the liquid-solid transition involve two related topics. First, one needs to eonsider how the flow and thermal history influence the structure of the fluid. Seeondly, one needs to understand how the ehanges in the internal strueture stiffen the material. There are some investigations on the topics for semicrystaUine materials and a variety of approaches or models have been proposed by different authors. Most of these results are reviewed by Tanner and Qi (2005) and Pantani et al. (2005). However,... 

Vaicaitis, R. and Lyrintzis, C. S., Response of Discretely Stiffened Structures, AIAA/ASME/ASCE/AHS 28th Structures, Structural Dynamics Materials Conference Paper No. 87-0914, Monterey, California, April 6-8, 1987. 

Under this programme 25% of the stiffeners and adjacent plate material in bulk carriers will be examined with thickness measurements being taken at upper, lower and mid points in both face and web plates of the stiffeners and associated end brackets. The extent of thickness measurement applied to transverse bulkheads has also been increased. In addition. Classification has revised the scantling requirements for new buildings to nominate thicker material in the bottom structure and at the transverse watertight bulkheads of the No 1 cargo holds. 

Work on analysis of the common structural shell element made of composite materials is very extensive. Contributions will be mentioned that parallel the developments in Chapter 5 on plates. Some of the first analyses of laminated shells are by Dong, Pister, and Taylor [6-44] and the monograph by Ambartsumyan [6-36]. Further efforts include the buckling work on laminated shells by Cheng and Ho [6-45] and on eccentrically stiffened laminated shells by Jones [6-46]. 

For composite stiffeners, all shapes are builtup from individual layers of material. Of course, some stiffener shapes can be produced by roll forming or pultrusion, for example, and then fastened to panels. Or, the stiffened panel could be made in a single operation involving the placement, usually by hand, of individual laminae of various dimensions in positions such that a builtup structure results. Stiffeners can be fastened to panels by bonding, stitching, or mechanical fastening. 

What kinds of configurations are possible for composite structures The most obvious is that of a fiber-reinforced laminate. With a laminate, we can change laminae orientations, stacking sequence, and laminae materials to arrive at a suitable structure. We can stiffen the laminate, or we can put a sandwich core in the middle of those laminae. We can do all of those possibilities, but recognize that we will also have, in vir-tuaiiy any structure, some kind of hoie or a cutout for some reason. Thus, we must have a procedure to place an appropriate amount of reinforcement around those cutouts so that ioad can be transferred around them. Without that reinforcement, the structure cannot do the job it is required to do. These various possibie configurations are shown in Figure 7-38. 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

Glucose molecules can link together into chains, with each ring tethered to the next by a bridging oxygen atom. In one form, this is cellulose, the stiff material that gives the stalks of plants and the trunks of trees their structural strength. Chitin, a variation on cellulose, is an even stiffen material that forms the exoskeletons of crustaceans such as crabs and lobsters. 

As a start to a tetralogy on dendrimers, the volumes Dendrimers and Den-drimers II have already appeared in print. This mini-series continues now with the latest volume Dendrimers III and will be completed by the fourth volume Dendrimers IV within the next few months. Volume III offers dendrimers based on novel design concepts leading to highly stiffened and shape persistent dendritic structures as well as to new families of rather soft and floppy dendrimers and focuses on new functional properties and materials aspects. As an example, the question of host-guest interactions with dendrimers, whose existence has been under intense debate for a long time, finds its final - and positive - answer in this volume. As a consequence, dendrimers clearly represent a subset of supramolecular chemistry. 

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