Study of Resistance to Helium Swelling of Lithium-Containing Ceramics under High-Temperature Irradiation

The aim of this work was to study resistance to helium accumulation processes in the structure of the surface layer of lithium-containing ceramics and the subsequent destruction and embrittlement processes, depending on radiation fluence. The objects of study were Li2TiO3-type ceramics obtained by thermal sintering. The fluence dependency of changes in the structural and strength properties of ceramics was determined to be in the range from 1018 to 1022 ion/m2, which corresponded to the concentration of implanted helium from 0.01% to 0.8–1 at.%. Irradiation was carried out at a temperature of 700 °C, which made it possible to simulate the processes of radiation damage that were closest to the real conditions in the reactor core. During the studies carried out, it was found that, at irradiation fluences of 1018–1020 ion/m2, the formation of point radiation defects was equaled by the process of thermal annealing of defects, as a result of which the concentration of defects and their effect on the change in the structural and strength properties of ceramics were insignificant. An increase in the concentration of implanted helium in the structure of the surface layer to above 0.5 at.% led to the dominance of radiation damage processes over the annealing of defects and the formation of gas-filled cavities, which negatively affects the strength of ceramics.

An Experimental and Numerical Study on Acoustic Emission in the Process of Rock Damage at Different Stress Paths

The study of the damage process of rock under external loads is good guidance for geotechnical construction design. The differences in rock damage processes and damage modes under different stress paths are rarely reported. To explore the effects of stress paths on rock damage processes, uniaxial compression experiments under three stress paths were conducted. Numerical simulation is also used to simulate the rock acoustic emission (AE) and fracture process. The results of the study indicate that the maximum acoustic emission events are at the peak of stress, and fractures are mainly formed at this stage. The peak of AE energy occurs before the peak of AE events. The damage pattern and fragmentation size of the rock are related to the way the stresses are loaded. It is noticed that there is appearance of a quiet period of AE events prior to the production of significant cracks. Minor damage to the rock is accompanied by the generation of bright white spots in the specimen, which is due to the high tensile or shear stress in the units. When the stress in these units exceeds their strength, the units break down and tiny cracks appear. As the external load increased, the cracks developed and penetrated, and the specimen was damaged. Under cyclic loading and unloading, the number of AE events increased significantly compared with the controlled displacement and controlled stress loading methods, and the radius of the AE circle became larger and the energy also increased, which indicates a greater degree of destruction of the rock under cyclic loading and unloading. The results of the study are of reference significance for rock crack propagation and fracture mode influenced by stress conditions and provide some guidance for construction design under different working conditions.

STABILITY CONSIDERATIONS FOR ELASTIC-PLASTIC PROCESSES WITH DAMAGE

Classical theory of plasticity is fairly complete with flow rules, convexity of yield surfaces, extremum principles, and the uniqueness theorem. For the strain-hardening plasticity, Drucker’s postulates are established and proven based on the plastic-work and energy principles. Plasticity models have been further applied to heterogeneous and cementitious materials with certain degrees of success. In this paper, the stability statements of strain-hardening and strain-softening processes in concrete are examined by utilizing thermodynamic potential functions in the stress space and by applying Euler’s theorem of homogenous functions. It is shown that by specifying a strain-hardening parameter to account for the plastic strains and a damage parameter to represent the effect of microcracking, the dissipation inequality can be used to establish the Drucker’s stability postulate for the plastic flow within the framework of the internal variable theory of thermodynamics. Using the same approach and assuming uncoupling between plastic flow and microcracking, the formation leads to a softening stability statement for damage processes in concrete.

Fundamentals of electro-mechanically coupled cohesive zone formulations for electrical conductors

Motivated by the influence of (micro-)cracks on the effective electrical properties of material systems and components, this contribution deals with fundamental developments on electro-mechanically coupled cohesive zone formulations for electrical conductors. For the quasi-stationary problems considered, Maxwell’s equations of electromagnetism reduce to the continuity equation for the electric current and to Faraday’s law of induction, for which non-standard jump conditions at the interface are derived. In addition, electrical interface contributions to the balance equation of energy are discussed and the restrictions posed by the dissipation inequality are studied. Together with well-established cohesive zone formulations for purely mechanical problems, the present developments provide the basis to study the influence of mechanically-induced interface damage processes on effective electrical properties of conductors. This is further illustrated by a study of representative boundary value problems based on a multi-field finite element implementation.

Oxidative Free Radicals and Other Species: Selective Messengers with a Reactive Capacity for Unselective Tissue Damage

Oxygen and nitrogen free radicals (RONS) form an exceptionally reactive molecular assembly within eukaryote cells. This perspective article gives a combined overview of different facets of research covering molecular reactivity, resultant tissue damage and final tissue outcomes as they relate to major disease. There is an emphasis on cardiovascular disease, as the damage processes are best liked to the pathology. The overriding importance of inflammation in driving damage across all tissues is highlighted. Brief coverage is also provided of measurement approaches, respectively for antioxidant status, using potentiometry, and voltammetry for selected target species. Whilst damage due to RONS is a common focus, the fundamental importance of RONS to biological signalling is also covered here as an indispensable basis for life. The article thus provides a global overview of this topic for anyone wishing to understand the current status across multiple fronts.

Damage Evolution Analysis in a “Spaghetti” Bridge Model Using the Acoustic Emission Technique

This paper applies the Acoustic Emission (AE) Technique to analyze the damage process in a one-meter span bridge model that was built from spaghetti sticks during a loading test. The AE signals are analyzed in terms of four coefficients that are evaluated as predictors of structure failure, with frequency variation appearing to be the strongest indicator of instability. The AE data are also compared to theoretical predictions that are given by the Bundle Model, confirming that underlying general patterns in damage processes are highly influenced by the geometric distribution of the structure and the loading pattern that is applied to it.

A Review on Multiscale Bone Damage: From the Clinical to the Research Perspective

The investigation of bone damage processes is a crucial point to understand the mechanisms of age-related bone fractures. In order to reduce their impact, early diagnosis is key. The intricate architecture of bone and the complexity of multiscale damage processes make fracture prediction an ambitious goal. This review, supported by a detailed analysis of bone damage physical principles, aims at presenting a critical overview of how multiscale imaging techniques could be used to implement reliable and validated numerical tools for the study and prediction of bone fractures. While macro- and meso-scale imaging find applications in clinical practice, micro- and nano-scale imaging are commonly used only for research purposes, with the objective to extract fragility indexes. Those images are used as a source for multiscale computational damage models. As an example, micro-computed tomography (micro-CT) images in combination with micro-finite element models could shed some light on the comprehension of the interaction between micro-cracks and micro-scale bone features. As future insights, the actual state of technology suggests that these models could be a potential substitute for invasive clinical practice for the prediction of age-related bone fractures. However, the translation to clinical practice requires experimental validation, which is still in progress.

Primary Impacts of the Fungal Toxin Sporidesmin on HepG2 Cells: Altered Cell Adhesion without Oxidative Stress or Cell Death

The fungal metabolite sporidesmin is responsible for severe necrotizing inflammation of biliary tract and liver of livestock grazing on pasture containing spores of Pithomyces chartarum that synthesizes the toxin. The toxin is secreted into bile causing the erosion of the biliary epithelium accompanied by inflammation and damage to surrounding tissues. Toxicity has been suggested to be due to cycles of reduction and oxidation of sporidesmin leading to oxidative damage from the formation of reactive oxygen species. The current work is the first test of the oxidative stress hypothesis using cultured cells. Oxidative stress could not be detected in HepG2 cells incubated with sporidesmin using a dichlorodihydrofluorescein diacetate assay or by use of two-dimensional electrophoresis to search for oxidized peroxiredoxins. There was also no evidence for necrosis or apoptosis, although there was a loss of cell adhesion that was accompanied by the disruption of intracellular actin microfilaments that have known roles in cell adhesion. The results are consistent with a model in which altered contact between cells in situ leads to altered permeability and subsequent inflammation and necrosis, potentially from the leakage of toxic bile into surrounding tissues. There is now a need for the further characterization of the damage processes in vivo, including the investigation of altered permeability and mechanisms of cell death in the biliary tract and other affected organs.