Effects of high energy radiation on the mechanical properties of epoxy/graphite fiber composites

Studies on the effects of high energy radiation on graphite fiber reinforced composites are summarized. Studies of T300/5208 and C6000/PMR15 composites, T300 fibers and the resin system MY720/DDS (tetraglycidyl-4,4'-diaminodiphenyl methane cured with diaminodiphenyl sulfone) are included. Radiation dose levels up to 8000 Mrads were obtained with no deleterious effects on the breaking stress or modulus. The effects on the structure and morphology were investigated using mechanical tests, electron spin resonance, X-ray diffraction, and electron spectroscopy for chemical analysis (ESCA or X-ray photoelectron spectroscopy). Details of the experiments and results are given. Studies of the fracture surfaces of irradiated samples were studied with scanning electron microscopy; current results indicate no differences in the morphology of irradiated and control samples

Effects of high energy radiation on the mechanical properties of epoxy/graphite fiber reinforced composites

Publications and theses generated on composite research are listed. Surface energy changes of an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T-300 graphite fiber and T-300/5208 (graphite fiber/epoxy) composites were investigated after irradiation with 0.5 MeV electrons. Electron spin resonance (ESR) investigations of line shapes and the radical decay behavior were made of an epoxy based on tetraglycidyl diaminodiphenyl methane (TGDDM)/diaminodiphenyl sulfone (DDS), T-300 graphite fiber, and T-300/5208 (graphite fiber/epoxy) composites after irradiation with Co(60) gamma-radiation or 0.5 MeV electrons. The results of the experiments are discussed

Effects of high energy radiation on the mechanical properties of epoxy graphite fiber reinforced composites

The effects of high energy radiation on mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites are assessed so that durability in space applications can be predicted. A listing of composite systems irradiated along with the maximum radiation dose applied and type of mechanical tests performed is shown. These samples were exposed to 1/2 MeV electrons

The effects of energetic proton bombardment on polymeric materials: Experimental studies and degradation models

This report describes 3 MeV proton bombardment experiments on several polymeric materials of interest to NASA carried out on the Tandem Van De Graff Accelerator at the California Institute of Technology's Kellogg Radiation Laboratory. Model aromatic and aliphatic polymers such as poly(1-vinyl naphthalene) and poly(methyl methacrylate), as well as polymers for near term space applications such as Kapton, Epoxy and Polysulfone, have been included in this study. Chemical and physical characterization of the damage products have been carried out in order to develop a model of the interaction of these polymers with the incident proton beam. The proton bombardment methodology developed at the Jet Propulsion Laboratory and reported here is part of an ongoing study on the effects of space radiation on polymeric materials. The report is intended to provide an overview of the mechanistic, as well as the technical and experimental, issues involved in such work rather than to serve as an exhaustive description of all the results

The effects of electron and gamma radiation on epoxy-based materials

Specimens of graphite/epoxy composites and epoxy resins were exposed to electron and gamma radiation, followed by mechanical property and fundamental measurements. Measurement techniques included: scanning electron microscopy, X-ray diffraction analysis, and electron spin resonance spectroscopic analysis. Results indicate little or no change in flexural properties of miniature specimens of a graphite/epoxy composite and no change in failure mode at the fiber-resin interface and in the crystallinity of the fiber and the resin. Some doubt in the observation of stable flexural properties is cast by electron paramagnetic resonance spectra of a relatively large number of radiation-generated radicals. These generally lead to a change in cross-linking and in chain-scissioning which should alter mechanical properties

Corporate social responsibility in emerging markets:case studies of Spanish MNCs in Latin America

Purpose – This paper aims to analyse corporate social responsibility (CSR) initiatives in emerging markets (EMs) from developed countries-based multinational companies (MNCs). Design/methodology/approach – The analysis is based on eight case studies with data collected through in-depth interviews with senior managers of the companies representing 85 per cent of the Spanish foreign investments in Latin America. Findings – The findings tend to indicate that instrumental theories of CSR seem to apply for Western MNCs operating in EMs. CSR initiatives from these companies seem to be guided by instrumental theories, as they use these initiatives as a strategic tool to achieve economic objectives, seek a positive relation between them and their financial performance and use them to strengthen their reputation. Research limitations/implications – The results of this article resulted from an in-depth analysis of case studies with data collected from a carefully selected theoretical sample with data analysed by following well-established methods like coding, triangulation and pattern matching. This combination was designed to minimise possible concerns in these areas, and as a consequence to strengthen the research design and, therefore, the conclusions of the paper. Measures were taken to minimise possible concerns in this area. The companies were selected for theoretical, not statistical, reasons with the aim to replicate or extend emergent theories, which is one of the main objectives of the research. Practical implications – Companies are using CSR in EMs as a strategic tool to achieve economic objectives (the main principle behind instrumental theories). MNCs seek a positive relation between CSR initiatives in EMs and their financial performance (also a key principle within instrumental theories). Companies in the sample develop CSR initiatives, including those in EMs, to increase their legitimacy as part of their global reputation rather to deal with host country challenges. Finally, MNCs actively manage stakeholders to strengthen their local reputation as a means to improve financial performance. Social implications – Instrumental theories of CSR seem to apply for Western MNCs operating in EMs. These findings highlight the need to continue the study of CSR from Western MNCs in Ems, as the vast majority of academic literature relates to the characteristics of social responsibility initiatives in developed economies. Originality/value – Instrumental theories apply in a global market for MNCs; in this case, Spanish companies operating in more than 30 countries with a global strategy in CSR and similar objectives. </jats:sec

Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites

The effects of high energy radiation on the mechanical properties and on the molecular and structural properties of graphite fiber reinforced composites were assessed so that the durability of such composites in space applications could be predicted. Investigative techniques including ESR and infrared spectroscopy, ESCA, contact angle measurements, and dynamic and static mechanical testing (3-point bending and interlaminar shear) were employed. The results using these different techniques are individually described, and the implications of the data are discussed. The proposed plan of work for the next fiscal year is outlined

Bioturbation and particle transport in Carolina slope sediments: A radiochemical approach

In situ tracer experiments investigated short-term sediment mixing processes at two Carolina continental margin sites (water depth = 850 m) characterized by different organic C fluxes, 234Th mixing coefficients (Db) and benthic assemblages. Phytoplankton, slope sediment, and sand-sized glass beads tagged with 210Pb, 113Sn, and 228Th, respectively, were placed via submersible at the sediment-water interface at both field sites (Site I off Cape Fear, and Site III off Cape Hatteras). Experimental plots were sampled at 0, 1.5 days, and 90 days after tracer emplacement to examine short-term, vertical transport. Both sites are initially dominated by nonlocal mixing. Transport to the bottom of the surface mixed layer at both sites occurs more rapidly than 234Th-based Db values predict; after 1.5 days, tagged particles were observed 5 cm below the sediment-water interface at Site I and 12 cm below at Site III. Impulse tracer profiles after 90 days at Site III exhibit primarily diffusive distributions, most likely due to a large number of random, nonlocal mixing events. The Db values determined from 90-day particle tagging experiments are comparable to those obtained from naturally occurring 234Th profiles (~100-day time scales) from nearby locations. The agreement between impulse tracer mixing coefficients and steady-state natural tracer mixing coefficients suggests that the diffusive analogue for bioturbation on monthly time scales is a realistic and useful approach. Tracer profiles from both sites exhibit some degree of particle selective mixing, but the preferential transport of the more labile carbon containing particles only occurred 30% of the time. Consequently, variations in the extent to which age-dependent mixing occurs in marine sediments may depend on factors such as faunal assemblage and organic carbon flux