Influence of engineered interfaces on residual stresses and mechanical response in metal matrix composites

Because of the inherent coefficient of thermal expansion (CTE) mismatch between fiber and matrix within metal and intermetallic matrix composite systems, high residual stresses can develop under various thermal loading conditions. These conditions include cooling from processing temperature to room temperature as well as subsequent thermal cycling. As a result of these stresses, within certain composite systems, radial, circumferential, and/or longitudinal cracks have been observed to form at the fiber matrix interface region. A number of potential solutions for reducing this thermally induced residual stress field have been proposed recently. Examples of some potential solutions are high CTE fibers, fiber preheating, thermal anneal treatments, and an engineered interface. Here the focus is on designing an interface (by using a compensating/compliant layer concept) to reduce or eliminate the thermal residual stress field and, therefore, the initiation and propagation of cracks developed during thermal loading. Furthermore, the impact of the engineered interface on the composite's mechanical response when subjected to isothermal mechanical load histories is examined

The Role of Fear of Failure in Competitive Anxiety and the Mediating Role of 2 x 2 Achievement Goals in Female High School and Collegiate Runners

The purpose of this study was to (a) examine the role of general FF on competitive anxiety and (b) determine if achievement goals mediated the relationship between general FF and anxiety. The participants for the study included 77 female athletes NCollege = 60; NHighSchool = 17). Participants completed a questionnaire packet containing the Competitive State Anxiety Inventory-2 (CSAI-2; Martens, Vealey, & Burton, 1990), the Achievement Goal Questionnaire for Sport (AGQ-S; Conroy, Elliot, & Hofer, 2003) and the Performance Failure Appraisal Inventory (PFAI; Conroy, 2001). A correlational analysis revealed a significant relationship between fear of failure (FF) and the intensity of cognitive anxiety (r = 0.50, p \u3c .01), but a significant relationship did not emerge between FF and the intensity of somatic anxiety. A significant negative correlation was found between FF and the direction of cognitive anxiety (r = -0.35, p \u3c .01). The results for FF and the direction of somatic anxiety did not reveal a significant relationship (r = -0.05, p = 0.69). FF was not related to either the intensity or direction of self-confidence respectively, (r = -0.18, p = 0.15; r = -0.18, p = 0.17). Avoidance achievement goals partially mediated the relationship between FF and anxiety. MAv goals partially mediated the relationship between FF and the intensity and direction of cognitive anxiety. PAv goals partially mediated the relationship between FF and the intensity of cognitive anxiety. The findings highlight the importance of examining multiple factors that contribute to competitive anxiety

Chemical etching and organometallic chemical vapor deposition on varied geometries of GaAs

Results of micron-spaced geometries produced by wet chemical etching and subsequent OMCVD growth on various GaAs surfaces are presented. The polar lattice increases the complexity of the process. The slow-etch planes defined by anisotropic etching are not always the same as the growth facets produced during MOCVD deposition, especially for deposition on higher-order planes produced by the hex groove etching

Materials International Space Station Experiment (MISSE) 5 Developed to Test Advanced Solar Cell Technology Aboard the ISS

The testing of new technologies aboard the International Space Station (ISS) is facilitated through the use of a passive experiment container, or PEC, developed at the NASA Langley Research Center. The PEC is an aluminum suitcase approximately 2 ft square and 5 in. thick. Inside the PEC are mounted Materials International Space Station Experiment (MISSE) plates that contain the test articles. The PEC is carried to the ISS aboard the space shuttle or a Russian resupply vehicle, where astronauts attach it to a handrail on the outer surface of the ISS and deploy the PEC, which is to say the suitcase is opened 180 deg. Typically, the PEC is left in this position for approximately 1 year, at which point astronauts close the PEC and it is returned to Earth. In the past, the PECs have contained passive experiments, principally designed to characterize the durability of materials subjected to the ultraviolet radiation and atomic oxygen present at the ISS orbit. The MISSE5 experiment is intended to characterize state-of-art (SOA) and beyond photovoltaic technologies

Be-implanted (GaAl)As stripe geometry lasers

GaAl)As double-heterostructure stripe geometry lasers have been fabricated using Be ion implantation. Pulsed threshold currents as low as 21 mA have been found. The light-vs-current characteristics were kink-free up to 10 mW output power and the measured differential quantum efficiency was 45%

Evaluation of Cellulose Ethers for Conservation

Describes the chemical character of cellulose ethers as a general class of polymers and establishes an approximate ranking of the relative stability of each generic chemical subclass

A monolithically integrated optical repeater

A monolithically integrated optical repeater has been fabricated on a single-crystal semi-insulating GaAs substrate. The repeater consists of an optical detector, an electronic amplifier, and a double heterostructure crowding effect laser. The repeater makes use of three metal semiconductor field effect transistors, one of which is used as the optical detector. With light from an external GaAlAs laser incident on the detector, an overall optical power gain of 10 dB from both laser facets was obtained

The GaAs solar cells with V-grooved emitters

Geometrically structured surfaces have become increasingly important to solar cell efficiency improvements and radiation tolerance. Gallium arsenide solar cells with a V-grooved front surface which demonstrate improved optical coupling and higher short-circuit current compared to planar cells were fabricated. GaAs homojunction cells were fabricated by organometallic chemical vapor deposition (OMCVD) on an n+ substrate. The V-grooves were formed on the surface with an anisotropic etch, and an n-type buffer and p-type emitter were grown by OMCVD, followed by ohmic contacts. Reflectivity measurements show significantly lower reflectance for the microgrooved cell compared to the planar structure. The short circuit current of the V-grooved solar cell is consistently higher than that of the planar controls