Some observations on the assessment of short,sharp cracks at the roots of blunt notches,and their effect on brittle fracture

The paper is concerned with effects of short, sharp quench cracks at the roots of blunt notches on cleavage fracture in a coarse-grained martensitic microstructure. At test temperatures between –196 and –140°C, such cracks control cleavage fracture. The values of local stress intensities calculated by loading such short cracks with the stress field ahead of the blunt notch are closely similar to the values of K _IC measured in long-crack fracture toughness tests. At the test temperature of –100°C, such sharp cracks are blunted out (by ductile crack growth) and appear to play no part in the subsequent failure mechanism, which is now better characterised by values of the local cleavage fracture stress _F ^* , below the notch. At the test temperature of –120°C, a transition region is seen with a large observed scatter in faulure load.In a fine-grained martensitic microstructure tested in the ST-L orientation brittle plates of manganese sulphide inclusions have been shown to promote cleavage fracture at –196°C.

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Résumé Le mémoire est relatif aux effets de fissures de trempe courtes et aiguës dans le found d'entailles arrondies sur la rupture par clivage dans une microstructure martensitique à gross grains. Aux températures d'essai de –196°C et de –140°C, de telles fissures déterminent la rupture par clivage. Les valeurs de concentration locale de la contrainte, calculées en sollicitant ces fissures avec un champ de tension appliqué sur l'entaille arrondie, sont très similaires aux valeurs de K _IC mesurées lors d'essais de ténacité à la rupture sur des fissures longues. A une température de –100°C, les fissures aiguës s'émoussent lors de leur croissance ductile, et n'apparaissent pas jouer un rôle dans le mécanisme de rupture ultérieure, lequel est à présent mieux caractérisé par les valeurs de la tension locale de rupture par clivage _F ^* , au droit de l'entaille.A la température de –120°C, apparaît une zone de transition, avec une grande dispersion de la charge de rupture.Dans une microstructure martensitique à grains fins soumise à essai dans le sens ST-L, des plaquettes fragiles d'inclusion de Sulphure de Manganèse favorisent une rupture par clivage à –196°C.

     

Local approach concepts and the microstructures of steels

The paper describes cleavage fracture models that relate local fracture stresses and fracture toughness values to the sizes of brittle initiating particles. In a “quasi-homogeneous” steel, i.e. one possessing a smooth distribution of small particle sizes, a “typically coarse” particle is present in every sample tested and the failure stress or fracture toughness is single valued. When random experimental errors are included, the single valued function becomes a Gaussian distribution. Spatially heterogeneous microstructures produce quite different distributions and these are discussed with respect to extrapolations to low failure probabilities.     

Population pharmacokinetic modeling in very premature infants receiving midazolam during mechanical ventilation: midazolam neonatal pharmacokinetics

BACKGROUND: Midazolam is used widely as a sedative to facilitate mechanical ventilation. This prospective study investigated the population pharmacokinetics of midazolam in very premature infants. METHODS: Midazolam (100 microg/kg) was administered as a rapid intravenous bolus dose every 4-6 h to 60 very premature neonates with a mean (range) gestational age of 27 weeks (24-31 weeks), a birth weight of 965 g (523-1,470 g), and an age of 4.5 days (2-15 days). A median (range) of four (one to four) blood samples, 0.2 ml each, were drawn at random times after the first dose or during continuous treatment, and concentrations of midazolam in serum were assayed by high-performance liquid chromatography. A population analysis was conducted using a two-compartment pharmacokinetic model using the NONMEM program. RESULTS: Average parameter values (interpatient percent coefficient of variation) for infants with birth weights 1,000 g or less were total systemic clearance (Cl(T)) = 0.783 ml/min (83%), intercompartmental clearance (Cl(Q)) = 6.53 ml/min (116%), volume of distribution of the central compartment (V1) = 473 ml (70%), and volume of distribution of the peripheral compartment (V2) = 513 ml (146%). For infants with birth weights more than 1,000 g they were as follows: Cl(T) = 1.24 ml/min (78%), Cl(Q) = 9.82 ml/min (98%), V1 = 823 ml (43%), and V2 = 1,040 ml (193%). The intrapatient variability (percent coefficient of variation) in the data was 4.5% at the mean concentration midazolam in serum of 121 ng/mL CONCLUSIONS: Serum concentration-time data were used in modeling the population pharmacokinetics of midazolam in very premature, ventilated neonates. Clearance of midazolam was markedly decreased compared with previous data from term infants and older patients. Infants weighing less than 1,000 g at birth had significantly lower clearance than those weighing more than 1,000 g.     

An Analysis of Motivation Constructs with First‐Year Engineering Students: Relationships Among Expectancies,Values, Achievement,and Career Plans

Background Researchers have identified many factors affecting undergraduate engineering students' achievement and persistence. Yet, much of this research focuses on persistence within academia, with less attention to career plans after graduation. Furthermore, the relative influence of expectancy‐versus value‐related beliefs on students' achievement and career plans is not fully understood. Purpose (Hypothesis ) To address these gaps, we examined the relationships among the following motivation constructs for female and male first‐year engineering students: (a) expectancy‐related constructs that included engineering self‐efficacy (i.e., a judgment of one's ability to perform a task in engineering) and expectancy for success in engineering (i.e., the belief in the possibility of success in engineering); (b) value‐related constructs that included identification with engineering (i.e., the extent to which one defines the self through a role or performance in engineering) and engineering values (i.e., beliefs related to engineering interest, importance, and usefulness); (c) engineering achievement; and (d) engineering career plans. Design /Method Participants included 363 first‐year engineering students at a large state university. The students completed an online survey instrument in the first and second semester of their first year. Results Students' expectancy‐ and value‐related beliefs decreased over the first year for both men and women. Men reported higher levels for expectancy‐related beliefs than women. Expectancy‐related constructs predicted achievement better than the value‐related constructs, whereas value‐related constructs predicted career plans better for both men and women. Conclusions Expectancy‐ and value‐related constructs predicted different outcomes. Thus, both types of constructs are needed to understand students' achievement and career plans in engineering.     

Molecular structure development in silsesquioxane−urethane thin film hybrids: A small-angle neutron scattering investigation

The small-angle neutron scattering (SANS) technique was used to investigate the molecular structure in situ of the synthesis of a series of polyhedral oligomeric silsesquioxane (POSS)-based polyurethane hybrid materials with respect to the reaction time, and the hybridization chemistry. In order to tailor the material properties for application in thin film coatings of metal surfaces, the effect on the hybrid structure was investigated of a selected end-capping agent (silane[N-ethyl-3-trimethoxysilyl-2-methylpropanamine]; A-Link35) and chain extension agent (poly[ethylene glycol-ran-propylene glycol]). The structure of the POSS-urethane hybrid in solution was observed to vary between fully or partially solvated polymer chains (radius of gyration R _g~20–40 Å), and larger collapsed structures (R _g >100'sÅ). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48772.     

PETROLEUM GEOLOGY AND FUTURE HYDROCARBON POTENTIAL OF THE IRISH SEA

The East Irish Sea Basin is hydrocarbon prolific with ten gasfields, two oilfields and another eight gas or oil discoveries. Production is from a widespread Triassic fluvioaeolian reservoir (the Ormskirk Sandstone) which is sealed by salt-prone mudstones. Three episodes of hydrocarbon generation occurred from a rich, Namurian-age source rock during deep burial in the Late Carboniferous-Early Permian, in the Early Jurassic and in the Late Cretaceous. All of the discoveries are in structural traps which are controlled to some degree by N-S trending normal faults probably active in the Late Jurassic. Consequently, the third (Cretaceous) phase of hydrocarbon generation is the most important. Another phase of uplift and erosion occurred in the Early Tertiary leading to the almost complete removal of Cretaceous and Jurassic strata. This event led to significant primary and tertiary migration as a result of overpressuring in the source rock and gas expansion within the reservoir. Although similar good quality Triassic reservoir occurs in other basins in the Irish Sea, rift-related uplift and erosion in the Middle Permian caused the widespread removal of potential Carboniferous source rocks in these areas, severely limiting the chance of hydrocarbon charge.     

Effect of pre-strain on grain size distributions in 316H austenitic stainless steel

An experimental study addressing the effect of tensile deformation on recrystallized grain size has been undertaken to explore the conditions leading to abnormal grain growth in Type 316H austenitic stainless steel. Following a solution heat treatment, a Type 316H stainless steel has been subjected to various tensile deformations up to a maximum of approximately 50% strain and then heated at a temperature of 1150 °C for 0.5 h followed by furnace cooling. A fraction of abnormally large grains is observed following a prior strain of approximately 20%. The results are presented, in terms of standard statistical analysis, and also graphically. The graphical presentation provides a clear, visual appreciation of uni- and bi-modal distributions, which may be of general help in other analyses of this nature.     

Variability of hydroxyapatite-coated dental implants

Uniformity, surface roughness, and chemical phase structure are all important features of implant coatings. While the first two variables are important for implant placement, the phase structure affects implant fixation. This study examined the coating morphology and the amount, size, and distribution of crystalline regions of press-fit and screw-type dental implants. Implants obtained from five commercial vendors were sectioned sagittally, mounted, and polished to reveal the coating microstructure. The crystalline phase content varied depending on the implant supplier; however, general trends were observed. Amorphous regions were predominantly found at the metal interface and decreased toward the outside of the coating, producing a crystallinity graded coating. The distal end of the implant, where heat build-up was more likely during the coating procedure, displayed a higher crystalline content and larger crystalline regions. Similarly, the thread apex consisted of more of a crystalline phase. The results of this study of coating microstructure may be used to improve the quality and performance of implants and may help to explain different in vivo responses to the many available varieties of hydroxyapatite-coated dental implants.