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Application of modified Ritchie-Knott-Rice criterion to cellular automata

Janus-Gałkiewicz Urszula, Neimitz Andrzej

Journal of Theoretical and Applied Mechanics

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2019

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Vol. 57 nr 3

577--590

EN

In this paper, the cellular automata model is applied to analyse cleavage and ductile fracture in front of a crack in three-point-bend specimens made of Hardox-400 steel. The research programme was composed of experiments followed by fractographic and numerical analyses. On the basis of microscopic observations, the sizes of cells used in the automata were determined. The algorithm enabled mapping of the two-dimensional crack surface as well as a simulation of temperature-dependent failure mechanisms by defining transition rules based on the modified Ritchie-Knott-Rice cleavage fracture criterion. The critical stress values were estimated and verified by the cellular automata model.

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Crack habits in metal/hydrogen interactive systems

Katz Y.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 73, nr 2

144--150

EN

Purpose: In terms of structural integrity aspects, interactive insights into metal/hydrogen systems become self-explanatory. In fact, ample of local critical events are involved namely, from sub-critical slow crack growth up to a total delayed failure. Design/methodology/approach: Mainly, crack-tip vicinity characterization became essential from both, chemical and mechanical factors, as related to the complicated aspects of crack stability. Note that the interactive situation has been currently investigated, imposing as such new local conditions. In fact, the current study adopted a highly comprehensive methodology in view of fracture physics. Thus, the material selection included iron-based (Fe-3%Si) and zinc single crystals. For the sake of background only, polycrystalline austenitic stainless steels were also investigated regarding hydrogen interaction affecting mechanical properties. Hydrogen charging has been performed either by electrolytic cathodic charging or, by high temperature/pressure gaseous methods. Fracture mechanics methodology was mainly implemented by utilizing external or internal hydrogen interaction procedures. Experimentally, research activities have been conducted by novel techniques, such as ultra-high visualization techniques and by using basic plasticity information like crack-tip dislocation emission and structures. Findings: Enhanced crack extension was established and the slow subcritical crack extension was traced in physically well-defined crack systems. Fracture mode transitions occurred due to the deformation/environment interaction. For example, in iron-based single crystals the unique cleavage mode emphasized the embrittlement impact. The broadness of the current study enabled a more local fundamental approach aimed to understand the crack-path habits. Here, the role of the crack-tip shielding beside the crack arrest potentials have been considered. Research limitations/implications: The dominating micro-mechanisms of hydrogen-related fracture have been thoroughly reviewed in the literature. Despite the remarkable research efforts involving coupled theory and physical findings, critical experiments still remain the key issue in order to establish more of any basic general concepts. Clearly, the hydrogen/deformation interactions have many facets involving broad service implications. Practical implications: The issue of hydrogen embrittlement or the possible decrease of fracture resistance causing severe mechanical degradation requires special attention. Originality/value: The current investigation includes nano-mechanical probes on top of surface probe microscopy. This technique offered additional critical experiments aimed to resolve the scaling relationship. Moreover, the study assisted to reveal local/global insights related to the interaction conditions involved. One of the values to be mentioned resulted even from the subcritical crack path input. The crack path habits with hydrogen interaction served as critical information. In this context, crack path findings supported the assessment of the possible viable micro-mechanical interactive embrittlement models. Basically, the crack path and the crack-tip front varied with the different crack systems. The important role of plasticity in the cleavage mode formation has been substantiated. Alluded to the above implies that critical experiments might eventually provide the building blocks for modeling efforts that can truly simulate and anticipate embrittlement events. It is demonstrated that huge gaps in knowledge exist preventing appropriate bridging of scales. This has often led to controversy when addressing multiple affected microstructures. This multiplicity occurs due to numerous second phases and interfaces that can interact in various modes with aggressive environment affecting both localized flow and fracture. Only by breaking the microstructure down to its individual building blocks can the scale bridging be appropriately dealt with.

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Wpływ łupności na stan naprężenia i deformacji w górotworze

Patyńska R.

WUG : bezpieczeństwo pracy i ochrona środowiska w górnictwie

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2006

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nr 6

48-49

PL

Uznając za istotną rolę czynnika naturalnego - struktury górotworu i wzajemnego usytuowania płaszczyzn osłabionej spoistości górotworu, w generowaniu wstrząsów o wysokiej energii - dotychczas nie opracowano wiarygodnego modelu deformacji i naprężenia w górotworze, który pozwoliłby w pełni korelować wyniki badań nad sejsmicznością obszaru i tektoniką regionalną. Określenie charakteru takich związków w oparciu o przedstawiony model geomechaniczny stanu naprężeniowo-deformacyjnego górotworu , może pozwolić na szacowanie zasięgu zjawisk sejsmicznych, a tym samym zastosowanie odpowiednich metod profilaktycznych.

EN

Although the role of natural factors - rock mass structure and interacting location of planes of weakened rock mass cohesion - played in generating high energy tremors has generally been accepted, a reliable model of rock mass state of stress and deformation which could allow the results of the studies on seismicity and regional tectonics of the area to be fully correlated has not been developed, as jest. Therefore, defining the nature of such relationships from the presented geomechanical model of stress-strain relations of rock masses will allow assessment of the extent of effects of seismic events and use of the appropriate preventive measures.

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Acid-Catalyzed Cleavage of Some Chromone, Coumarin and Pyrone Derivaties of Aminomethylphosphonic Acid. Products and Kinetics of the ReactionB

Boduszek B., Latajka R., Walkowiak U.

Polish Journal of Chemistry

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2001

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Vol. 75, nr 1

63-69

EN

Treatment of chromone-2, coumarin-4 and pyrone-2 derivatives of N-benzylaminomethylphosphonic acid with strong mineral acids leads to formation of the corresponding heterocyclic amines and phosphoric acid. Kinetic studies of this cleavage reaction demonstrate that protonation has a remarkable influence on a cleavage of C-P bonds. In aq. H2SO4, cleavage of the acids 1-3 exhibits a kinetic dependence on [H+]. The measured solvent isotope effect (kH/kD) was about 1.5 for the 1 and 2 and only 1.1 for the 3. The existence of the isotope effect shows that protons are involved on the rate-determining step. The data obtained suggest that the protonated phosphonate molecule is split by a dissociative mechanism with A-SE2 character and this is combined with an elimination of the phosphonate group as a positive-charged phosphorus moiety.