A novel device patented by Intel and called WISP (Wireless Identification and Sensing Platform) is modified to interface with a conventional foil resistance strain gage. The wireless, battery-free, digital device communicates with and is powered by an Ultra-High Frequency (UHF) RFID (Radio Frequency Identification) reader. The standard Intel WISP has been modified with the addition of a PCB (printed circuit board), which act as the analog interface with the strain gage. The so-called WISPs/g (for strain gage) has been utilized during uniaxial tension tests on carbon fiber composite specimens to compare accuracy and repeatability with conventional wired strain gage and extensometer. Validation of the technology is performed with a structural test, whereby four independent WISPs/g devices are positioned on the surface of a carbon fiber composite flat panel subjected to quasi-static indentation. Measurements are compared to the predictions of a NASTRAN finite element model (FEM) and show excellent agreement. Applications of this technology include strain measurement during static airframe tests, as well as on-board real-time strain measurements during test flight and certification of new aircraft.

Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. This study analyzes in detail the meso-structure of this class of materials, which exhibit point-to-point variations associated with the random chip distribution, by means of destructive and non-destructive inspections, in the attempt to identify characteristic traits that can yield insight in its quality and performance. Results show that several types of defects can be encountered within the molded panel, such as macro-voids, fiber kinking and swirling, or resin-rich areas. However, it is found that failure may or may not occur in proximity of these hot spots, independently from their size and location, even for specimens containing the circular hole. Therefore it appears that for this class of materials conventional ultrasonic inspection and defect classification may not be suitable as criteria for part acceptance or rejection.

Two carbon-fiber-reinforced composite cylinders were tested in bending.One cylinder, the baseline cylinder, consisted of 0 • , 90 • and ±45 • plies, whereas the other cylinder, called the variable-stiffness cylinder, contained plies with fiber orientations that varied in the circumferential direction, which caused a variation in laminate stiffness.The cylinders were optimized for maximum buckling load carrying capability under bending. 1 Simulations showed that the variable-stiffness cylinder was able to redistribute the applied loads around the circumference, resulting in lower strain values at both the tension and the compression side of the cylinder and an improvement of the buckling load by 18 percent compared to the baseline cylinder.The purpose of the bending test was to show that the improvements obtained in the analytical results could also be achieved experimentally.The baseline cylinder was tested first to serve as a benchmark for the variable-stiffness cylinder.The finite element model was adjusted based on the baseline cylinder tests to represent the experimental conditions correctly.The model took into account the flexible connection between the cylinder and the test fixture, the test mechanism and geometric imperfections present in the cylinder and showed good agreement with the experimental results.The variable-stiffness cylinder was tested twice: first oriented in the direction it was designed for and later rotated 180 degrees about the cylinder axis, such that the loading direction on the cylinder was reversed.The predicted global response and strain distributions for both configurations corresponded well with the experimental data.The flexible boundary conditions and the geometric imperfections affected the load and strain distributions of the baseline and the variable-stiffness cylinders, but the relative improvements of the variablestiffness cylinder in the preferred orientation with respect to the baseline cylinder were not affected.Follow-up tests of the cylinders including cutouts or induced damage are planned in the future.

Recent composite technology research and development efforts have focused on discontinuous carbon fiber/epoxy molding systems derived from chopped aerospace-grade unidirectional tape prepreg. Although the average elastic modulus of this material has been shown to be as high as that of the continuous tape quasi-isotropic benchmark, experimental measurement by means of strain gage or extensometer has shown variation as high as 20%. Digital Image Correlation can be used successfully to obtain a full-field strain measurement, and it shows that a highly non-uniform strain distribution exists on the surface of the specimen, with distinct peaks and valleys. This pattern of alternating regions of high and low strain gradients, and which exhibit a characteristic shape and size, can be described in terms of Random Representative Volume Element (RRVE). The RRVE proposed here exhibits random elastic properties, which are assigned based on stochastic distributions. This approach leads to the analysis method proposed here, which is designed to compensate for the fact that traditional methods cannot capture the experimentally observed variation in modulus within a specimen and among different specimens. The method utilizes a randomization process to generate statistical distributions of fractions and orientations of chips within the RRVE, and then applies Classical Laminated Plate Theory to an equivalent quasi-isotropic tape laminate to calculate its average elastic properties. Validation of this method is shown as it applies to a finite element model that discretizes the structure in multiple RRVEs, whose properties are generated independently of the neighboring ones, and then are solved simultaneously. The approach generates accurate predictions of the strain distribution on the surface of the specimen.

THIS COLLECTION OF articles was selected from the Proceedings Volume of the 22nd Annual American Society for Composites Technical Conference for inclusion in this special issue of the Journal of Composite Materials. The Conference featured seven Technical Tracks, which included a honorary session for Dr. T. Kevin O’Brien, one on Analysis and Laminate, one on Manufacturing and Processing, one on Bonded Joints and Repairs, one on Nanocomposites, and one on New Technologies. The articles collected here represent some of the most significant contributions presented at the Conference in these seven areas. The conference featured keynotes from Boeing Commercial Airplanes, Air Force Research Laboratory, Adam Aircraft and Bentley Motors. Pioneers in the making gave insight in ‘Evolution of Aircraft Composites’ in a special panel session, which was then be followed by another special panel where leading industry and regulatory agency representatives discussed ‘Future Challenges for Aircraft Composites’. The conference also featured an AFOSR-sponsored workshop on Processing of Mutifunctional

The elastic behavior and failure response of discontinuous carbon fiber/epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Commercial applications for this type of material form already exist, such as Hexcel HexMC®. Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/width ratio, and hole size yields fundamental information on the behavior of this material.

A modal test and analysis are done for two fiber-placed composite cylinders. One of the cylinders consists of a traditional layup, whereas the other one contains plies with varying fiber orientations. The shells were originally designed for maximum load carrying capability under pure bending and built using advanced fiber placement. The modal test is carried out to determine the correlation between the experimental stiffness of the shells and the analytical stiffness. Modal analysis is carried out using ABAQUS, and eigenfrequencies and eigenmodes are compared with the experimental results. Also the physical frequency response is simulated and the results in the form of power spectral densities for displacements, velocities and accelerations are compared to the test results. Overall a good agreement between analytical and experimental results is shown, both for the baseline and the variable-stiffness shell, indicating an accurate prediction of the stiffness for the tested laminate configurations.

*† ‡ The elastic behavior and failure response of discontinuous carbon fiber/ epoxy laminates produced by compression molding of randomly-oriented preimpregnated unidirectional tape is characterized. Complex relationships between unnotched and notched tensile strengths are observed, and show this material to be particularly notch-insensitive. A parametric study on the effect of specimen thickness, width, diameter/ width ratio, and hole size yields fundamental information on the behavior of this material.

The Semantic Web consists of many RDF graphs nameable by URIs. This paper extends the syntax and semantics of RDF to cover such Named Graphs. This enables RDF statements that describe graphs, which is beneficial in many Semantic Web application areas. As a case study, we explore the application area of Semantic Web publishing: Named Graphs allow publishers to communicate assertional intent, and to sign their graphs; information consumers can evaluate specific graphs using task-specific trust policies, and act on information from those Named Graphs that they accept. Graphs are trusted depending on: their content; information about the graph; and the task the user is performing. The extension of RDF to Named Graphs provides a formally defined framework to be a foundation for the Semantic Web trust layer.

The Semantic Web consists of many RDF graphs nameable by URIs. This paper extends the syntax and semantics of RDF to cover such named graphs. This enables RDF statements that describe graphs, which is beneficial in many Semantic Web application areas. Named graphs are given an abstract syntax, a formal semantics, an XML syntax, and a syntax based on N3. SPARQL is a query language applicable to named graphs. A specific application area discussed in detail is that of describing provenance information. This paper provides a formally defined framework suited to being a foundation for the Semantic Web trust layer.

Many approaches to writing RDF in XML have been proposed. The revised standard RDF/XML still has many known problems. It is not intrinsically difficult to have a clear serialization of RDF in XML, and we present a simple solution. We add the ability to name graphs, noting that in practice this is already widely used. We use XSLT as a general syntactic extensibility mechanism to provide human friendly macros for our syntax.

RDF/XML does not layer RDF on top of XML ina useful way. We use a simple direct representation of the RDF abstract syntax in XML. We add the ability to name graphs, noting that in practice this is already widely used. We use XSLT as a general syntactic extensibility mechanism to provide human friendly macros for our syntax. This provides a simple serialization solving a persistent problem in the Semantic Web.

The Semantic Web consists of many RDF graphs nameable by URIs. This paper extends the syntax and semantics of RDF to cover such Named Graphs. This enables RDF statements that describe graphs, which is beneficial in many Semantic Web application areas. In this paper, we explore the application area of Semantic Web publishing: Named Graphs allow publishers to communicate assertional intent, and to sign their graphs; information consumers can evaluate specific graphs using task-specific trust policies, and act on information from those Named Graphs that they accept. Graphs are trusted depending on: their content; information about the graph; and the task the user is performing. The extension of RDF to Named Graphs provides a formally defined framework to be a foundation for the Semantic Web trust layer.

The Metia Framework defines a set of standard, open and portable models, interfaces, and protocols facilitating the construction of tools and environments optimized for the management, referencing, distribution, storage, and retrieval of electronic media; as well as a set of core software components (agents) providing functions and services relating to archival, versioning, access control, search, retrieval, conversion, navigation, and metadata management.