Side-grooved Charpy impact testing: Assessment of splitting and fracture properties of high-toughness plate steels.

The fracture properties and susceptibility to crack-divider delamination (or splitting) of three commercially produced high-toughness X70 pipeline steels are evaluated with Charpy impact test samples modified to incorporate side grooves. Temperature-dependent impact data are compared with standard Charpy V-notch (CVN) and drop weight tear test data (DWTT). It is shown that the modified geometry prevents the accumulation of plastic deformation at upper shelf energy temperatures and improves the accuracy of impact properties measurements. It also promotes splitting, mirroring the splitting behavior assessed with DWTT samples. To demonstrate the effects of splitting on fracture characteristics and impact energies, steels with similar tensile properties but different splitting susceptibilities are considered. Splitting severity is maximum close to the ductile-brittle transition temperature. However, the effect of splitting on impact energy is minimum at such temperature, as this type of delamination increases energy absorption at lower temperatures and decreases it by a similar extent at higher temperatures. This finding is discussed by examination of force-displacement curves from the instrumented impact tests.

A new mechanism of strain transfer in polycrystals.

At the grain boundaries of plastically deforming polycrystals, strain transfer mechanisms can accommodate the shear strain carried by slip bands and mechanical twins to prevent stress build-ups and damage. So far, only the accommodation obtained through slip (and twinning) alone has been considered in the mechanism known as slip (and twin) transfer. Here, a strain transfer mechanism that also requires the rotation of the crystal lattice is demonstrated. A region of accumulated slip develops perpendicular to the active slip plane in the impinged grain. The slip gradients enable a localized lattice rotation that accommodates the shear strain in the incoming band, preventing the build-up of interfacial stresses. The mechanism operates preferentially at the boundaries between highly misoriented grains. Facilitating strain transfer at these interfaces opens up new possibilities to improve the mechanical properties of polycrystals, as discussed.

Reduced partitioning of plastic strain for strong and yet ductile precipitate-strengthened alloys.

When a material that contains precipitates is deformed, the precipitates and the matrix may strain plastically by different amounts causing stresses to build up at the precipitate-matrix interfaces. If premature failure is to be avoided, it is therefore essential to reduce the difference in the plastic strain between the two phases. Here, we conduct nanoscale digital image correlation to measure a new variable that quantifies this plastic strain difference and show how its value can be used to estimate the associated interfacial stresses, which are found to be approximately three times greater in an Fe-Ni2AlTi steel than in the more ductile Ni-based superalloy CMSX-4®. It is then demonstrated that decreasing these stresses significantly improves the ability of the Fe-Ni2AlTi microstructure to deform under tensile loads without loss in strength.

Stable Speckle Patterns for Nano-scale Strain Mapping up to 700 °C.

The digital image correlation (DIC) of speckle patterns obtained by vapour-assisted gold remodelling at 200 - 350 °C has already been used to map plastic strains with submicron resolution. However, it has not so far proved possible to use such patterns for testing at high temperatures. Here we demonstrate how a gold speckle pattern can be made that is stable at 700 °C, to study deformation in a commercial TiAl alloy (Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB2). The pattern is made up of a uniformly sized random array of Au islands as small as 15 nm in diameter, depending on reconstruction parameters, with a sufficiently small spacing to be suitable for nano-scale, nDIC, strain mapping at a subset size of 60 × 60 nm2. It can be used at temperatures up to 700 °C for many hours, for high cycle fatigue testing for instance. There is good particle attachment to the substrate. It can withstand ultra-sound cleaning, is thermally stable and has a high atomic number contrast for topography-free backscatter electron imaging.

The influence of menopause and habitual smoking upon serum zinc, serum copper and the cardiovascular and immune parameters of women.

One hundred and thirty-three women in general good health were divided into two groups, according to menopausal status. The pre-menopausal group (n=106) was further subdivided into non-smokers (n=76) and smokers (n=30). All of the post-menopausal women were non-smokers (n=27). The determination of blood pressure (BP) and the collection of fasting blood samples were performed in the early morning hours. Habitual smoking increased the number of blood lymphocytes and monocytes in pre-menopausal women. The post-menopause group demonstrated an increase in BP, in serum cholesterol and triglycerides and a reduction of the serum zinc/copper (Zn/Cu) ratio. Serum Zn was positively correlated with serum glucose levels in the pre-menopausal group, regardless of smoking habit, but was negatively correlated in postmenopausal women. This may suggest that menopause induces changes in Zn metabolism and/or in insulin Serum Cu - particularly in smokers - was significantly correlated with blood lymphocytes. This may suggest an effect of smoking on the immune system via an alteration of Cu metabolism, including the synthesis and/or the release of ceruloplasmin, a known marker of inflammation. Moreover, serum Copper levels of both the pre- and the post-menopausal groups were significantly correlated with mean and diastolic B.P. while the serum Zn levels of the pre-menopausal group was significantly correlated solely with diastolic BP, implying that the metal plays a physiological role in some mechanism of blood pressure regulation. In the pre-menopausal non-smokers subgroup and the post-menopausal group, there was a weak, but statistically significant (p<0.01), correlation between systolic and mean BP, and blood lymphocytes levels. These data may be explained by a neuroendocrine influence, related partially to the morning hours.