A statistical sampling approach for measurement of fracture toughness parameters in a 4330 steel by 3-D femtosecond laser-based tomography

A new approach using statistically random material volume sampling has been developed to model the variability of fracture toughnesses in steels. A recently developed femtosecond laser-based serial sectioning (FSLSS) technique was utilized to collect 3-D datasets showing the distribution of titanium nitride (TiN) phases in a 4330 high strength steel. Random volumes were sampled from widely spaced regions within the bulk steel specimen. Plastic zone sized volumes were sampled from the 3-D reconstructions to produce statistically representative volume elements containing TiN particles. Fracture toughness was calculated for 48 different plastic zone sized volumes using two different toughness models. Weibull analysis was performed to relate the modeled fracture toughness to the probability of occurrence. Variability in the fracture toughness gave a Weibull modulus of m = 1.4–1.5, similar to the variability measured in 22 bulk sample specimens analyzed by Ruggieri et al. for a similar steel.     

Polymer cryoprotectants in the preservation of biological ultrastructure. I. Low temperature states of aqueous solutions of hydrophilic polymers.

The solid states formed by vitrified and frozen aqueous solutions of some hydrophilic polymers, able to act as biological cryoprotectants, have been studied by differential scanning calorimetry and freeze fracture electron microscopy. Glass transitions, devitrification, recrystallization and melting behaviour of aqueous solutions of polyvinylpyrrolidone, hydroxyethyl starch and dextran have been established. The vitrified polymer solutions exhibit a characteristic microspheral morphology which is not induced by the quench cooling process but is an inherent feature of the solutions themselves.     

Microstructural statistics for fatigue crack initiation in polycrystalline nickel-base superalloys

In advanced engineering alloys where inclusions and pores are minimized during processing, the initiation of cracks due to cyclic loading shifts to intrinsic microstructural features. Criteria for the identification of crack initiation sites, defined using elastic-plastic loading parameters and twin boundary length, have been developed and applied to experimental datasets following cyclic loading. The criteria successfully quantify the incidence of experimentally observed cracks. Statistical microstructural volume elements are defined using a convergence approach for two nickel-base superalloys, IN100 and René 88DT. The material element that captures the fatigue crack-initiating features in René 88DT is smaller than IN100 due to a combination of smaller grain size and higher twin density.     

The preparation,examination and analysis of frozen hydrated tissue sections by scanning transmission electron microscopy and X-ray microanalysis

A method is reported for preparing, examining and analysing frozen hydrated tissue sections using transmission electron microscopy and X-ray microanalysis. Use of this method permits localization and measurement of water soluble or diffusible elements within the hydrated cell matrix. Since any change in total fresh weight of the specimen will affect the concentration of all components, great care has been taken to demonstrate that the mass neither increases nor decreases and to ensure that the tissue remains frozen-hydrated. Criteria for assessing whether or not the tissue remains frozen-hydrated are reported. After quench freezing, 1–2 μm thick sections of mouse liver were cut at 193°K and picked up on a specially designed annular specimen holder covered with an aluminium coated nylon film. Using a transfer device which prevents contamination of the tissue sections while maintaining them at a low temperature (below 143°K), the sections are transferred either to the vacuum evaporator cold stage or the scanning microscope cold stage. The tissue sections may be coated with an aluminium layer to improve electrical and thermal conductivity. The specimens are examined in the scanning transmission imaging mode and analysed using an energy dispersive X-ray analyser. Concentration of intra-nuclear and intracytoplasmic K, P, S and Cl are reported for mouse hepatocytes as ratios of the characteristic radiation to the continuum radiation used as a measure of mass. Ratios for all four elements were higher in the nucleus than the cytoplasm. Examples are given of this method as applied to plant and insect tissue.     

Polymeric cryoprotectants in the preservation of biological ultrastructure. II. Physiological effects.

A study has been made of the physiological effects of three non-penetrating polymeric cryoprotective agents on sixteen different plant and animal cells and tissues. The cryoprotectants, when used at concentrations at which they are effective in preventing ice-crystal formation, generally have a lower toxicity to cells and tissue than similar concentrations of glycerol. The relatively low toxicity of these substances suggests that they would be more suitable as cryoprotectants for morphological and analytical studies than the commonly used low molecular weight compounds.