Scientific and Technical Aerospace Reports Volume 38 July 28, 2000

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COMPOSITE MATERIALS
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20000062451 Saclay Research Centre, Inst. National des Sciences et Techniques Nucleaires, Gif-sur-Yvette, France
Regular multi-sequences copolymers study at interfaces and in solution
Leclerc, E.; Nov. 15, 1996; 189p; In French; In English
Report No.(s): DE98-732050; FRCEA-TH-590; No Copyright; Avail: Department of Energy Information Bridge
In this study, the conformations which are taken by multi-sequences copolymers in various situations are described. The phase
diagram of copolymers near an interface defined by two non-miscible liquids has been given, respectively for a strongly adsorbing
interface and for a weakly adsorbing interface. The passage between these two extreme conditions has revealed the existence of
many intermediate conditions. Copolymers have also been studied with several solvents of different quality. The formation of
folded structures described by micellar structures has been studied according to the size of the respective sequences in a ’good’
solvent and in a ’bad’ solvent. The obtaining of ’flower’ micelles is due to very strict conditions on the solvent quality and on the
sequences size. The phase diagram of the different micellar structures has been established. Along with this theoretical study,
experimental work has been developed on a model protein: the (beta) casein. The main characteristic parameters of the aggregates
formed by the protein have been established by experiments of small angle neutrons scattering. The interactions which are present
between macromolecules are strongly attractive at low concentration (formation of micelles) and repulsive when the concentration
increases. Some resemblances exist between the micelles formed by the copolymers and the aggregates formed by the (beta)
casein.
NTIS
Sequencing; Copolymers; Interfaces; Solubility
20000063379 NASA Glenn Research Center, Cleveland, OH USA
A New Local Failure Model with Application to the Longitudinal Tensile Behavior of Continuously Reinforced Titanium
Composites
Bednarcyk, Brett A., Ohio Aerospace Inst., USA; Arnold, Steven M., NASA Glenn Research Center, USA; May 2000; 36p; In
English
Contract(s)/Grant(s): NCC3-650; RTOP 242-23-52
Report No.(s): NASA/TM-2000-210027; E-12224; NAS 1.15:210027; No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
A new model for local fiber failures in composite materials loaded longitudinally is presented. In developing the model, the
goal was to account for the effects of fiber breakage on the global response of a composite in a relatively simple and efficient manner.
Towards this end, the model includes the important feature of local stress unloading, even as global loading of the composite
continues. The model has been incorporated into NASA Glenn’s Micromechanics Analysis Code with Generalized Method of
Cells (MAC/GMC) and was employed to simulate the longitudinal tensile deformation and failure behavior of several silicon carbide
fiber/titanium matrix (SiC/Ti) composites. The model is shown to be quite realistic and capable of accurate predictions for
various temperatures, fiber volume fractions, and fiber diameters. Further- more, the new model compares favorably to Curtin’s
(1993) effective fiber breakage model, which has also been incorporated into MAC/GMC.
Author
Titanium; Fiber Composites; Tensile Deformation; Silicon Carbides; Micromechanics
20000064104 Mississippi State Univ., Dept. of Aerospace Engineering, Mississippi State, MS USA
Design Optimization and Residual Strength Assessment of a Cylindrical Composite Shell Structure, May 1999 - Apr. 2000
Rais-Rohani, Masoud, Mississippi State Univ., USA; [2000]; 17p; In English
Contract(s)/Grant(s): NAG1-2038; No Copyright; Avail: CASI; A03, Hardcopy; A01, Microfiche
A summary of research conducted during the specified period is presented. The research objectives included the investigation
of an efficient technique for the design optimization and residual strength assessment of a semi-monocoque cylindrical shell structure
made of composite materials. The response surface methodology is used in modeling the buckling response of individual skin
panels under the combined axial compression and shear loading. These models are inserted into the MSC/NASTRAN code for
design optimization of the cylindrical structure under a combined bending-torsion loading condition. The comparison between
the monolithic and sandwich skin design cases indicated a 35% weight saving in using sandwich skin panels. In addition, the residual
strength of the optimum design was obtained by identifying the most critical region of the structure and introducing a damage
in the form of skin-stringer and skin-stringer-frame detachment. The comparison between the two skin design concepts indicated
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