Characterization of fatigue behavior of long fiber reinforced thermoplastic (LFT) composites

Fatigue behavior of long fiber reinforced thermoplastic composites (polypropylene/20 vol.% E-glass fiber) is presented in terms of stress – number of cycles to failure curves. Samples tested along longitudinal direction showed a higher fatigue life than the transverse samples which can be explained by the preferential orientation of the fibers along the longitudinal direction developed during the processing. Fatigue life decreased with increase in frequency. Hysteretic loss and temperature rise were measured; they depended on the stress amplitude as well as the cyclic frequency. Long fiber reinforced thermoplastic composite showed a lower temperature rise compared to unreinforced PP because long fiber reinforced thermoplastic has higher thermal conductivity than unreinforced PP and thus faster heat dissipation to the surroundings occur. The hysteretic heating also led to decrease in the modulus of long fiber reinforced thermoplastic as a function of number of cycles due to the softening of the matrix during fatigue cycling and depended on stress amplitude and frequency of the test.     

Titania-coated glass microballoons and cenospheres for environmental applications

Functional titania coatings on glass microballoons (GMBs) and cenospheres have a broad range of potential environmental applications, primarily in purification of drinking water and treatment of industrial wastewater. The heterogeneous photocatalytic capabilities of titania films and particles have been extensively examined in the literature as effective alternatives to current technologies. Although the chemistry of titania films for photocatalysis has been studied, titania-coated GMBs have not yet been extensively considered and the materials science aspects of the titania-GMB and titania-cenosphere systems have not been addressed. We have examined the microstructure, morphology, and mechanical properties of titania coatings on both cenospheres and commercially produced GMBs. Scanning electron microscopy was used to examine coating coverage and defects. Energy dispersive X-ray spectroscopy and Raman spectroscopy were used for element and phase identification, respectively. Hardness and modulus measurements of the titania coatings and the GMB and cenosphere materials were done by nanoindentation. Additionally, the photocatalytic activity of the titania-coated GMB system was tested on Procion Red dye using two different types of mixing, a magnetic stirrer and an aeration bubbler apparatus. The titania coatings showed good coverage and retention except in the case of magnetic stirring, where significant coating loss was observed.     

Management of actinide waste inventories in nuclear phase-out scenarios

The improvement of the “radiological cleanliness” of nuclear energy is a primary goal in the development of advanced reactors and fuel cycles. The multiple recycling of actinides in advanced nuclear systems with fast neutron spectra represents a key option for reducing the potential hazard from high-level waste, especially when the fuel cycle is fully closed. Such strategies, however, involve large inventories of radiotoxic, transuranic (TRU) nuclides in the nuclear park, both in-pile and out-of-pile. The management of these inventories with the help of actinide burners is likely to become an important issue, if nuclear energy systems are eventually phased out, i.e. replaced by other types of energy systems.     

Thermal Degradation of Fiber Coatings in Mullite-Fiber-Reinforced Mullite Composites

The thermal degradation behavior of single-layer BN and of double-layer BN/SiC chemically vapor-deposited fiber coatings in mullite-fiber-reinforced mullite composites was investigated by means of transmission electron microscopy after processing and heat treatment of the composites at 1000°, 1200°, and 1300°C for 6 h in air. The single-layer BN coatings were ˜0.7 mu m thick and consisted of turbostratic BN with (0001) basal planes lying parallel to the surfaces of the fibers plus nanosized areas that had no preferential orientation. This microstructure remained unchanged up to 1000°C; however, distinct coarsening of the randomly oriented BN crystallites occurred in the temperature range of 1000°-1200°C. The single-layer BN coatings were stable against oxidation, up to 1200°C. At higher temperatures, degradation of the coatings via oxidation occurred. Double-layer BN/SiC coating systems consisted of BN that was 0.08 mu m thick and SiC layers that were 0.16 mu m thick and deposited onto the mullite fibers. The turbostratic BN was highly anisotropic and did not undergo any microstructural change, up to 1300°C. The outer SiC layer of the double-layer coating system improved the oxidation resistance of BN in the 1200°-1300°C temperature range, despite a partial oxidation of SiC to SiO₂.     

Refined Monte Carlo analysis of the H.B. Robinson-2 reactor pressure vessel dosimetry benchmark

Refined analysis, based on use of the Monte Carlo code MCNPX-2.4.0, is presented for the “H.B. Robinson-2 pressure vessel dosimetry benchmark”, which is a part of the Radiation Shielding and Dosimetry Experiments Database (SINBAD). First, the performance of the Monte Carlo methodology is reassessed relative to the reported deterministic results obtained with DORT. Thereby, the analysis is accompanied by a quantitative evaluation of the optimal energy cut-off value for each of the in- and ex-vessel dosimeters that were employed. Second, a more realistic definition of the neutron source is implemented than proposed in the benchmark. Thus, the current procedure for power-to-neutron-source-strength conversion, as also for explicitly considering the burnup-dependent fuel assembly-wise average fission neutron spectrum, is found to affect the calculated values significantly.     

Surface roughness characterization of Nicalon and HI-Nicalon ceramic fibers by atomic force microscopy

The behavior of ceramic composites is governed by the nature of the fiber/matrix interface. Fiber surface roughness is a key parameter in the behavior at the fiber/matrix interface (e.g., debonding, interfacial sliding) and the overall behavior of a composite. Using an atomic force microscope (AFM), quantitative surface roughness values of ceramic fibers can be obtained, with an uncertainty of 1nm. The AFM technique was used to obtain surface roughness profiles and analysis on Si-C-O and Si-C fibers (Nicalon, and a new, virtually oxygen-free Si-C fiber, HI-Nicalon). The latter fiber had a slightly higher roughness amplitude, which may be caused by differences in processing. Although the differences in roughness between the fibers were small, the calculated radial strain and radial normal stress in composites reinforced with HI-Nicalon were higher than in those reinforced with Nicalon. This result indicates that small changes in the roughness of a fiber can significantly affect the debonding and sliding properties between the fiber and matrix.     

A clinical trial comparing primary stenting of the infarct-related artery with optimal primary angioplasty for acute myocardial infarction: results from the Florence Randomized Elective Stenting in Acute Coronary Occlusions (FRESCO) trial

OBJECTIVES: This study sought to compare stenting of the primary infarct-related artery (IRA) with optimal primary percutaneous transluminal coronary angioplasty (PTCA) with respect to clinical and angiographic outcomes of patients with an acute myocardial infarction. BACKGROUND: Early and late restenosis or reocclusion of the IRA after successful primary PTCA significantly contributes to increased patient morbidity and mortality. Coronary stenting results in a lower rate of angiographic and clinical restenosis than standard PTCA in patients with angina and with previously untreated, noncomplex lesions. METHODS: After successful primary PTCA, 150 patients were randomly assigned to elective stenting or no further intervention. The primary end point of the trial was a composite end point, defined as death, reinfarction or repeat target vessel revascularization as a consequence of recurrent ischemia within 6 months of randomization. The secondary end point was angiographic evidence of restenosis or reocclusion at 6 months after randomization. RESULTS: Stenting of the IRA was successful in all patients randomized to stent treatment. At 6 months, the incidence of the primary end point was 9% in the stent group and 28% in the PTCA group (p=0.003); the incidence of restenosis or reocclusion was 17% in the stent group and 43% in the PTCA group (p=0.001). CONCLUSIONS: Primary stenting of the IRA, compared with optimal primary angioplasty, results in a lower rate of major adverse events related to recurrent ischemia and a lower rate of angiographically detected restenosis or reocclusion of the IRA.     

Non-invasive diagnosis of venous thromboembolism in outpatients

BACKGROUND: We designed a simple and integrated diagnostic algorithm for acute venous thromboembolism based on clinical probability assessment of deep-vein thrombosis (DVT) or pulmonary embolism (PE), plasma D-dimer measurement, lower-limb venous compression ultrasonography, and lung scan to reduce the need for phlebography and pulmonary angiography. METHODS: 918 consecutive patients presenting at the emergency ward of the Geneva University Hospital, Geneva, Switzerland, and H?pital Saint-Luc, Montreal, Canada, with clinically suspected venous thromboembolism were entered into a sequential diagnostic protocol. Patients in whom venous thromboembolism was deemed absent were not given anticoagulants and were followed up for 3 months. FINDINGS: A normal D-dimer concentration (<500 microg/L by a rapid ELISA) ruled out venous thromboembolism in 286 (31%) members of the study cohort, whereas DVT by ultrasonography established the diagnosis in 157 (17%). Lung scan was diagnostic in 80 (9%) of the remaining patients. Venous thromboembolism was also deemed absent in patients with low to intermediate clinical probability of DVT and a normal venous ultrasonography (236 [26%] patients), and in patients with a low clinical probability of PE and a non-diagnostic result on lung scan (107 [12%] patients). Pulmonary angiography and phlebography were done in only 50 (5%) and 2 (<1%) of the patients, respectively. Hence, a non-invasive diagnosis was possible in 866 (94%) members of the entire cohort. The 3-month thromboembolic risk in patients not given anticoagulants, based on the results of the diagnostic protocol, was 1.8% (95% CI 0.9-3.1). INTERPRETATION: A diagnostic strategy combining clinical assessment, D-dimer, ultrasonography, and lung scan gave a non-invasive diagnosis in the vast majority of outpatients with suspected venous thromboembolism, and appeared to be safe.