Complex stamp forming of advanced thermoplastic composites

The inherent advantages of thermoplastics over the traditional thermoset composite systems are well recognized in the aeronautics community. The main advantages are the much faster processing and the higher toughness. The current advanced thermoplastic material systems provide excellent mechanical performance but their main disadvantage is the difficult processing. Ideally, future aircraft subcomponents with complex shapes can be readily formed on the basis of pre-consolidated tailored laminates based on uni-directional plies. However, to exploit the full potential of thermoplastic composites models are to be developed in order to predict the process feasibility and product performance in an early stage of development. This paper addresses a number of steps to increase the accuracy of stamp forming simulations and highlights promising results for identifying intra-ply shear and tool-ply behavior of thermoplastic composites. A comparison of the forming behavior of a doubly curved reference part with simulations will be presented. The paper concludes with remarks on necessary future researc

Communications Biophysics

Contains report on one research project.National Institutes of Health (Grant 2 PO1 MH-04737-06)Joint Services Electronics Programs (U.S. Army, U.S. Navy, and U.S. Air Force) under Contract DA 36-039-AMC-03200(E)National Science Foundation (Grant GK-835)National Aeronautics and Space Administration (Grant NsG-496

Adhesion and electronic structure of graphene on hexagonal boron nitride substrates

We investigate the adsorption of graphene sheets on h-BN substrates by means of first-principles calculations in the framework of adiabatic connection fluctuation-dissipation theory in the random phase approximation. We obtain adhesion energies for different crystallographic stacking configurations and show that the interlayer bonding is due to long-range van der Waals forces. The interplay of elastic and adhesion energies is shown to lead to stacking disorder and moir\'e structures. Band structure calculations reveal substrate induced mass terms in graphene which change their sign with the stacking configuration. The dispersion, absolute band gaps and the real space shape of the low energy electronic states in the moir\'e structures are discussed. We find that the absolute band gaps in the moir\'e structures are at least an order of magnitude smaller than the maximum local values of the mass term. Our results are in agreement with recent STM experiments.Comment: 8 pages, 8 figures, revised and extended version, to appear in Phys. Rev.

Retaining Raised Fibrils and Microfibrils on Oak Fiber Surfaces

Drying of spruce softwood kraft fibers treated with hexamethyldisilazane (HMDS) has been found to: (1) maintain fibrils and microfibrils in a raised position on fiber surfaces, (2) raise fibrils and microfibrils that had been dried down on fiber surfaces, and (3) increase strength properties of handsheets made from dried fiber. The question whether shorter thick-walled hardwood fibers behave similarly is examined in the present study of the effect of HMDS-drying on oak kraft pulp fibers. The effects of HMDS-drying, air-drying, and paper-machine-drying were evaluated by observing the surfaces of refined hardwood kraft pulp fibers. Using scanning electron microscopy, the fiber surfaces of these dried fibers were compared with those of never-dried fiber whose morphology was preserved by critical point drying. In addition, air-dried and paper-machine-dried fibers were examined after rewetting and HMDS-treatment to recover fibrils and microfibrils. Overall strength properties were considerably greater when handsheets were made from pulps treated with HMDS than from pulps that were dried in air or on the paper machine

Extended conjugated microporous polymers for photocatalytic hydrogen evolution from water

Conjugated microporous polymers (CMPs) have been used as photocatalysts for hydrogen production from water in the presence of a sacrificial electron donor. The relative importance of the linker geometry, the co-monomer linker length, and the degree of planarisation were studied with respect to the photocatalytic hydrogen evolution rate

Structure of Pit Border in Pinus Strobus L.

Sections fro111 white pine trccs were studied by electrori lllicroscopy in a search for the organization of cell wall layers in the pit border. Depending on the developmental stage of the trachcids, or perhaps on technical imperfections, differences appeared in the pit border within the same tree species. From an electron micrograph of a mature latewood tracheicl, a diagram was reconstructed that appears to be the most representative structure for the pit border in white pine