MICROCRACK PROPAGATION AND MICROSTRUCTURAL PARAMETERS OF FATIGUE DAMAGE

Abstract— Modern approaches to microstructural analysis of fatigue in metallic materials consider the density and the total length per unit area of propagating surface microcracks as useful indicators of fatigue damage. Such parameters, when observed on a carbon steel studied in a previous paper, have a dispersion similar to that of fatigue life and they are linearly correlated with fatigue endurance.
The aim of this paper is to extend the research on fatigue damage in the already studied carbon steel and to examine the scatter of crack propagation rate together with the evolution of surface cracks during fatigue life. The final aim of this work is to study how these two factors are correlated with fatigue life distribution in order to evaluate the effectiveness of damage detection methods.     

Inferences in probability logic

We define a particular fuzzy logic, able to manage information that is probabilistic in nature. In this logic the probabilistic theories are suitable fuzzy sets of formulas that turn out to be lower envelopes while only the complete probabilistic theories coincide with the probabilities.     

Serum dioxin levels in Seveso, Italy, population in 1976

On July 10, 1976, an explosion at a chemical plant near Seveso, Italy, released a mixture of chemicals, including 2,3,7,8-tetrachlorodibenzo-p-dioxin and 2,4,5-trichlorophenol. As a result, several thousand people in the Seveso area may have been exposed to those chemicals. At that time, human exposure assessment was based primarily on soil levels of 2,3,7,8-tetrachlorodibenzo-p-dioxin. Medical examinations of this potentially exposed population and control subjects were begun in 1976 and in some cases continued until 1985. In 1988, we began assessing human exposure in this population by measuring 2,3,7,8-tetrachlorodibenzo-p-dioxin in small volumes of serum specimens remaining from the medical examinations. As expected, we found that the median serum dioxin levels were highest among people who lived closest to the explosion and were progressively lower among groups living farther away. These measurements have allowed us to assess exposure more accurately among individuals in this population and to relate exposure to various health effects. We found that some individuals in the exposed population had among the highest serum dioxin levels ever reported, yet chloracne was the only unequivocal effect found; cancer risks are still being investigated. We also found that other individuals with as high or higher serum dioxin levels did not develop chloracne. We also found that the serum half-life of dioxin in this population was 7-8 years, which agrees with other findings although we do report some differences in the serum half-life of TCDD for women and children. We also observed an increase in the percentage of female newborns to parents who resided in Zone A at the time of the explosion, and we also report on the 1976 serum dioxin levels in people who later developed cancer.     

Determination of selenium in Italian rices by differential pulse cathodic stripping voltammetry

The total selenium content in white, black, red rice and white rice hull samples, grown in Northern Italy cultivars, has been determined using the differential pulse cathodic stripping voltammetry (DPCSV) on the hanging drop mercury electrode (HDME), in the presence of Cu(II). The digestion was performed in open vessel through a combination of wet acid/dry ashing with Mg(II) salts. The calibration curve was linear in the concentration range 0.15–8 ppb, the detection limit was estimated to be 0.07 ppb, and the recovery was in the range 85–102%. Reproducibility was from 1.9% to 9.0% (RSD, n = 4). Rice samples were analyzed by the standard addition method and the results were compared with those obtained by a spectroscopic technique (HG-ICP-AES). The proposed procedure, sensitive, inexpensive, easy-to-handle and precise can be successfully applied for the determination of selenium in nutritional products. The resulting selenium contents in different Italian rice varieties were: 20.1 ± 1.8 ppb (white), 53.0 ± 1.0 ppb (red), 26.7 ± 1.3 ppb (black), 45.3 ± 4.1 ppb (white rice hull).     

A comparison of Mode III threshold under simple shear and RCF conditions

A novel experimental method, previously developed by the authors, has been applied in order to promote Mode III co-planar crack propagation in a bearing steel. The method consists in out-of-phase multiaxial fatigue tests, adopting a stress history typical of sub-surface RCF, onto specimens containing micro-notches that were previously subjected to Mode I pre-cracking at R = −2. Three defect sizes, expressed in terms of Murakami’s √area parameter, equal to 630 μm, 315 μm and 220 μm were considered. The experimental data clearly show that the threshold conditions for out-of-phase tests is lower than in simple torsional tests, thus promoting the shear growth. This enhanced damage mechanism, which cannot be described neither in terms of fatigue criteria nor in terms of crack driving force at the crack tip, is characterised by intense plastic deformation and rubbing of the crack lips with an opening of the crack faces. In order to compare the multiaxial and torsional fatigue test results the effect of this type of opening on the friction of the crack faces will be investigated.     

Proteolysis of beta-casein as a marker of Grana Padano cheese ripening

Proteolysis has a critical role in defining the typical organoleptic characteristics of Grana Padano, a well-known Italian cheese. During the ripening process, hydrolysis of beta-casein produces different fragments, the most abundant and widely studied of which are gamma-caseins, three polypeptides containing the HOOC-terminal portion of beta-casein. By sodium dodecyl sulfate-PAGE and a specific anti-beta-casein monoclonal antibody, two beta-casein-derived bands were identified in Grana Padano cheese: betaa and betab. Thanks to the identification of the amino acid sequences, it was shown that: a) betaa contains gamma1-casein [beta-casein (29-209)] and the correlated peptide [beta-casein (30-209)]; b) betab contains gamma2-casein [beta-casein (106-209)] and gamma3-casein [beta-casein (108-209)]. The production of betaa and betab by the three enzymes most involved in cheese proteolysis (pepsin, chymosin, and plasmin) was evaluated by performing in vitro digestions. A significant correlation between abundance of some polypeptides and ripening process was shown.     

The IKEA effect in collective problem‐solving: When individuals prioritize their own solutions

To improve problem‐solving performance, individuals can rely on social learning. This approach is constrained by an individual's social network, which influences the efficiency of the problem‐solving process. To date, research disagrees on what kind of network structure is preferable, providing support for efficient network structures, as well as for inefficient networks. However, studies implicitly assume that solvers always imitate superior solutions, an assumption that lacks empirical grounding. We propose a simple derivation of an existing simulation framework by incorporating a known cognitive bias (‘IKEA effect’), whereby individuals are assumed to prioritize individual information. This effect allows inefficiencies to be embodied at the individual microlevel, reducing the need for inefficiencies at the structural macrolevel. Simulation results explain discrepancies in previous results, illustrating how more realistic microlevel assumptions substantially impact macrolevel outcomes.