On the origins of fatigue strength in crystalline metallic materials.

Metallic materials experience irreversible deformation with increasing applied stress, manifested in localized slip events that result in fatigue failure upon repeated cycling. We discerned the physical origins of fatigue strength in a large set of face-centered cubic, hexagonal close-packed, and body-centered cubic metallic materials by considering cyclic deformation processes at nanometer resolution over large volumes of individual materials at the earliest stages of cycling. We identified quantitative relations between the yield strength and the ultimate tensile strength, fatigue strength, and physical characteristics of early slip localization events. The fatigue strength of metallic alloys that deform by slip could be predicted by the amplitude of slip localization during the first cycle of loading. Our observations provide a physical basis for well-known empirical fatigue laws and enable a rapid method of predicting fatigue strength as reflected by measurement of slip localization amplitude.

Multi-modal Dataset of a Polycrystalline Metallic Material: 3D Microstructure and Deformation Fields.

The development of high-fidelity mechanical property prediction models for the design of polycrystalline materials relies on large volumes of microstructural feature data. Concurrently, at these same scales, the deformation fields that develop during mechanical loading can be highly heterogeneous. Spatially correlated measurements of 3D microstructure and the ensuing deformation fields at the micro-scale would provide highly valuable insight into the relationship between microstructure and macroscopic mechanical response. They would also provide direct validation for numerical simulations that can guide and speed up the design of new materials and microstructures. However, to date, such data have been rare. Here, a one-of-a-kind, multi-modal dataset is presented that combines recent state-of-the-art experimental developments in 3D tomography and high-resolution deformation field measurements.

The origin and stability of nanostructural hierarchy in crystalline solids.

The structural hierarchy exhibited by materials on more than one length scale can play a major part in determining bulk material properties. Understanding the hierarchical structure can lead to new materials with physical properties tailored for specific applications. We have used a combined experimental and phase-field modeling approach to explore such a hierarchical structure at nanoscale for enhanced coarsening resistance of ordered γ' precipitates in an experimental, multicomponent, high-refractory nickel-base superalloy. The hierarchical microstructure formed experimentally in this alloy is composed of a γ matrix with γ' precipitates that contain embedded, spherical γ precipitates, which do not directionally coarsen during high-temperature annealing but do delay coarsening of the larger γ' precipitates. Chemical mapping via atom probe tomography suggests that the supersaturation of Co, Ru, and Re in the γ' phase is the driving force for the phase separation, leading to the formation of this hierarchical microstructure. Representative phase-field modeling highlights the importance of larger γ' precipitates to promote stability of the embedded γ phase and to delay coarsening of the encompassing γ' precipitates. Our results suggest that the hierarchical material design has the potential to influence the high-temperature stability of precipitate strengthened metallic materials.

Forward models for extending the mechanical damage evaluation capability of resonant ultrasound spectroscopy.

Finite element (FE) modeling has been coupled with resonant ultrasound spectroscopy (RUS) for nondestructive evaluation (NDE) of high temperature damage induced by mechanical loading. Forward FE models predict mode-specific changes in resonance frequencies (ΔfR), inform RUS measurements of mode-type, and identify diagnostic resonance modes sensitive to individual or multiple concurrent damage mechanisms. The magnitude of modeled ΔfR correlate very well with the magnitude of measured ΔfR from RUS, affording quantitative assessments of damage. This approach was employed to study creep damage in a polycrystalline Ni-based superalloy (Mar-M247) at 950°C. After iterative applications of creep strains up to 8.8%, RUS measurements recorded ΔfR that correspond to the accumulation of plastic deformation and cracks in the gauge section of a cylindrical dog-bone specimen. Of the first 50 resonance modes that occur, ranging from 3 to 220kHz, modes classified as longitudinal bending were most sensitive to creep damage while transverse bending modes were found to be largely unaffected. Measure to model comparisons of ΔfR show that the deformation experienced by the specimen during creep, specifically uniform elongation of the gauge section, is responsible for a majority of the measured ΔfR until at least 6.1% creep strain. After 8.8% strain considerable surface cracking along the gauge section of the dog-bone was observed, for which FE models indicate low-frequency longitudinal bending modes are significantly affected. Key differences between historical implementations of RUS for NDE and the FE model-based framework developed herein are discussed, with attention to general implementation of a FE model-based framework for NDE of damage.

Post-vaccination symptoms following DTP and DT vaccination.

Post-vaccination symptoms in 6,004 infants given adsorbed Diphtheria Tetanus and Pertussis (DTP) vaccine and 4,024 infants given adsorbed Diphtheria and Tetanus (DT) vaccine have been compared. Although crying, screaming and fever were slightly more frequent after adsorbed DTP than adsorbed DT, attacks of high-pitched screaming, episodes of pallor and hypotonia, convulsions, other neurological disorders and sudden infant death occurred with similar frequency in the two groups. No specific neurological effect attributable to the pertussis component was found.

Symptoms after primary immunisation with DTP and with DT vaccine.

Symptoms after routine primary immunisation of 6004 infants with diphtheria/tetanus/pertussis (DTP) vaccine and 4024 infants with diphtheria/tetanus (DT) vaccine have been compared. After each dose, crying, screaming, and feverishness were more frequent with adsorbed DTP than adsorbed DT, but the difference was small. Attacks of high-pitched screaming, episodes of pallor or cyanosis with limpness, convulsions, and local reactions occurred with similar frequency after both vaccines. There was a considerable increase in local reactions after the 3rd dose with both vaccines. Over 1000 doses of plain DTP (with no aluminium hydroxide adjuvant) were given during the study. Post-vaccination symptoms were more common after the plain than after the 2 adsorbed preparations.

Severity of whooping cough in England before and after the decline in pertussis immunisation.

Since the decline of pertussis immunisation, hospital admission and death rates from whooping cough have fallen unexpectedly. Although this might be taken to indicate that the disease is becoming less severe, a comparison of admissions and deaths in England and Wales before and after the decline in immunisation suggests that several factors other than disease severity--a shift in the social class distribution of the disease, an increase in the proportion of milder cases notified, and improved care--were responsible for this. The severity of attacks and the complication rates in children admitted to hospital were virtually unchanged. Very young infants, those from disadvantaged families, and children with chronic illness were at greatest risk.

Infection of the central nervous system by Listeria monocytogenes: a review of 54 adult and juvenile cases.

The clinical features in 54 juvenile and adult patients with Listeria monocytogenes infection of the central nervous system are described. Thirty-one of the patients had pre-existing chronic disease; the remainder were previously healthy. Twenty of the patients, the 'meningo-encephalitic group' developed focal neurological signs. The remaining 34, the 'meningitic group' exhibited no focal signs other than those caused by increased intracranial pressure. The 'meningitic group' differed from the 'meningo-encephalitic group' in that the cerebrospinal fluid white cell count, protein and glucose levels were markedly more abnormal and the prognosis worse. Evidence of septicaemia was found only in the 'meningitic group'. Meningo-encephalitis may represent a modified response to listerial infection typified by granulomatous rather than a suppurative response. The predominance of this response that was demonstrated in females may indicate partial immunity, the result of previous Listeria monocytogenes colonisation of the female genital tract. Listeria monocytogenes infection is treatable and should be considered in patients with meningitic or encephalitic illness. Repeated blood cultures may be required to establish the diagnosis.

Pyrexia after diphtheria/tetanus/pertussis and diphtheria/tetanus vaccines.

The temperatures of 587 children were taken before and after diphtheria/tetanus/pertussis (DTP) or diphtheria/tetanus (DT) vaccine. Only slight temperature increases were found but these were notably more frequent after plain than adsorbed DTP vaccine preparations and the frequency increased with each successive dose.

Measles control in the United Kingdom.

In the United Kingdom measles vaccine is known to be highly effective, but only half of the children of eligible age are vaccinated. Many doctors are doubtful about the risks and benefits of measles vaccination. Although serious reactions are rare, convulsions occur in one per 1,000 children vaccinated in England, and malaise after vaccination is common. Insufficient effort seems to have been made to convince family doctors of the undoubted value of the vaccine. In the few areas where motivation is high, good vaccination rates have been achieved. The introduction of measles vaccination 14 years ago has markedly reduced disease incidence to approximately 75% of the preimmunization level. So far regular surveys have not suggested any tendency for the proportion of susceptible individuals among the older population to increase.

A 7-year survey of disorders attributed to vaccination in North West Thames region.

Voluntary reporting of vaccine reactions was intensified in a single large region for 7 years Anaphylaxis and collapse, convulsion, and neurological disorder were reported most frequently after diphtheria/tetanus/pertussis (DTP). The greater frequency of recorded reactions after DTP than after DT could have been due to bias caused by the adverse publicity accorded to pertussis vaccine, since no major difference was found when the immunisation histories of children admitted to hospital with such conditions were compared. No convincing evidence that DTP caused major neurological damage emerged from this large and lengthy study.

Surveys of rubella antibodies in young adults and children.

22 000 serum samples from university students and young adult blood donors collected between 1969 and 1980 were tested for antibody to rubella virus. Of the women born in 1956 and after (i.e., those eligible for rubella vaccine at school) the proportions seronegative ranged from 3% to 6% in different years, compared with 12-20% in men of the same age groups. Serum samples from schoolchildren were also tested: 40-50% of girls and boys aged 10-11 years were seronegative--percentages similar to those before the introduction of vaccine. However, only 2-6% of 15-year-old girls (who would have been offered vaccine) were seronegative compared with 20-30% of 15-year-old boys. These results indicate that the rubella vaccination programme in the U.K. is having a significant impact on the immunological status of young women of childbearing age but that a large number of women remain potentially susceptible.

Consequences of confirmed maternal rubella at successive stages of pregnancy.

Over a thousand women with confirmed rubella infection at different stages of pregnancy were followed up prospectively. Two-thirds of the women were multiparous. Pregnancy continued in 40%, and the infants were followed up after birth both clinically and serologically. The frequency of congenital infection after maternal rubella with a rash was more than 80% during the first 12 weeks of pregnancy, 54% at 13-14 weeks, and 25% at the end of the second trimester. The infection rate then rose again to reach a high figure in the last month. Follow-up was to 2 years of age--the findings in infected children being compared with those in children who had escaped infection. Rubella defects occurred in all infants infected before the 11th week (principally congenital heart disease and deafness) and in 35% of those infected at 13-16 weeks (deafness alone). No defects attributable to rubella were found in 63 children infected after 16 weeks. Continued surveillance of cases of confirmed rubella during pregnancy is recommended as an additional way of monitoring the effect of rubella vaccination.