scholarly journals Structure of fracture under the joint operation of two mechanisms of local destruction

2020 ◽  
pp. 49-58
Author(s):  
Николай Михайлович Осипенко
Keyword(s):  
Brittle Fracture ◽  
Joint Action ◽  
Ice Sheet ◽  
Compression Axis ◽  
Mechanism Of Formation ◽  
Local Fracture ◽  
Joint Operation ◽  
Model Situation ◽  
Local Destruction ◽  
A Chain

Рассмотрены примеры сценариев хрупкого разрушения, в которых участвуют два механизма локального разрушения - развитие трещин нормального разрыва и компактирование, либо торошение, при сжатии. Работа является продолжением исследований структур разрушения в условиях сжатия [1]. Показано, что в модельной ситуации с цепочкой отверстий в пластине выбор механизма формирования локальных очагов разрушения или их совместного действия зависит от ориентации системы отверстий относительно оси сжатия. Другой пример относится к процессу разрушения ледяного покрова при его сжатии под действием течений и ветровой нагрузки. Рассмотрен вариант разрушения, в котором происходит взаимодействие двух видов разрушения - локализованное в виде трещиноподобного дефекта разрушение при сжатии (торошении) и формирование сопутствующих поперечных разрывов, разбивающих нагружаемый участок ледяного покрова на ряд полос вдоль напряжений сжатия. Examples of brittle fracture scenarios are considered, in which two mechanisms of local fracture participate - the development of normal fracture cracks and compaction, or hummocking, under compression. The work is a continuation of studies of fracture structures under compression [1]. It is shown that in a model situation with a chain of holes in a plate, the choice of the mechanism of formation of local fracture centers or their joint action depends on the orientation of the system of holes relative to the compression axis. Another example relates to the process of destruction of the ice cover when it is compressed under the influence of currents and wind load. The fracture variant is considered, in which two types of fracture interact: the fracture localized in the form of a crack-like defect during compression (hummocking) and the formation of accompanying transverse ruptures dividing the loaded ice sheet section into a series of bands along the compression stresses.

A STUDY OF CUPRENE FORMATION

1937 ◽  
Vol 15b (5) ◽  
pp. 208-223 ◽  
Author(s):  
J. M. Calhoun
Keyword(s):  
Induction Period ◽  
Maximum Rate ◽  
Rapid Rise ◽  
Constant Ratio ◽  
Mechanism Of Formation ◽  
Chain Reaction ◽  
Exponential Equation ◽  
Free Hydrogen ◽  
Rate Of Absorption ◽  
A Chain

The copper oxide catalyzed polymerization of acetylene to cuprene has been studied between 230° and 330 °C. by the flow method. The reaction shows an initial induction period at the lower temperatures followed by a rapid rise to a maximum rate and a more gradual decrease. With increase in temperature the induction period becomes shorter, and the maximum rate attained becomes greater. If commenced at 330 °C. the reaction is explosive. Analysis of the exit gas shows considerable ethylene and some free hydrogen, the amounts increasing with the temperature of the reaction. This indicates that the hydrogen split off in cuprene formation does not bear a constant ratio to the amount of cuprene formed. The yield of cuprene based on acetylene reacting is about 85% of theory, which is 4 to 10% lower than values based on a volume contraction of acetylene alone.An exponential equation has been derived which expresses the rate of absorption of acetylene at 290 °C. over a period of 72 hr. under the conditions of the experiment. The equation is integrated to give the quantity of acetylene absorbed at any time. This makes a prediction of yields possible. The heat of polymerization was calculated from the determined heat of combustion of cuprene. Various theories regarding the mechanism of formation and structure of cuprene are discussed, and the photochemical evidence of a chain reaction is supported.

Mechanisms of regulation of the number of cells in the cell chain of diatoms

2019 ◽  
pp. 8-22
Author(s):  
Aleksey V. Fedorov ◽  
Anna V. Lifanchuk
Keyword(s):  
Mathematical Model ◽  
Cell Division ◽  
Simple Mathematical Model ◽  
Mechanism Of Formation ◽  
Division Rate ◽  
The Difference ◽  
A Chain ◽  
Number Of Cells

We proposed hypothesis that describes the mechanism of formation and disintegration of cell chains, according to which the number of cells in a chain is determined by the difference in the rates of cell division and the separation of chains into individual cells, and the maximum number of cells in the chain is achieved at the highest division rate. Experiments showed that the addition of phosphorus stimulates the formation of longer chains. We developed a simple mathematical model of the dynamics of the number of cells in cell chains.

scholarly journals STUDY ON BRITTLE FRACTURE OF STEEL UNDER PLASTIC STRAIN BASED ON LOCAL FRACTURE APPROACH

2000 ◽  
Vol 65 (536) ◽  
pp. 151-156 ◽  
Author(s):  
Tadao NAKAGOMI ◽  
Susumu MINAMI ◽  
Hiroshi SHIRASAKI ◽  
Satoru ARAI
Keyword(s):  
Brittle Fracture ◽  
Plastic Strain ◽  
Local Fracture

General discussion

1989 ◽  
Vol 327 (1596) ◽  
pp. 631-633
Keyword(s):  
Design Of Experiments ◽  
Joint Action ◽  
Experimental Methods ◽  
Probability Of Failure ◽  
Imperial College ◽  
The Other ◽  
Major Theme ◽  
Statistical Tools ◽  
Nuclear Plants ◽  
A Chain

A. C. Atkinson ( Imperial College ,London, U.K. ). A major theme of this meeting has been the necessity of considering the joint action of several factors. Experimental methods in which one factor is changed at a time have been shown to fail because of the frequent occurrence of important interactions between factors. It is therefore particularly disturbing that Dr Ballard’s paper on reliability in nuclear plants is confined to consideration of the failure of components in isolation. Since the failure of one component can drastically change the environment in which the other components work, one failure may trigger a chain of failures. The accident at Three Mile Island illustrates this. Of course, the compound probability of failure is still found by multiplying probabilities together, but these are conditional rather than unconditional, and they can be very different. Will Dr Ballard please comment? I now turn to direct consideration of the design of experiments. The basic statistical tools for the design of multifactor experiments with quantitative variables have been available for 30 years. One continuing development since then has been the increasing use of computers in both design and analysis.

scholarly journals Brittle fracture in structural steels: perspectives at different size-scales

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140126 ◽  
Author(s):  
John Knott
Keyword(s):  
Brittle Fracture ◽  
Fracture Stress ◽  
Structural Integrity ◽  
Materials Testing ◽  
Local Fracture ◽  
Cooperative Movement ◽  
Test Pieces ◽  
Conclusion Section ◽  
Local Fracture Stress ◽  
Size Scales

This paper describes characteristics of transgranular cleavage fracture in structural steel, viewed at different size-scales. Initially, consideration is given to structures and the service duty to which they are exposed at the macroscale , highlighting failure by plastic collapse and failure by brittle fracture. This is followed by sections describing the use of fracture mechanics and materials testing in carrying-out assessments of structural integrity. Attention then focuses on the microscale , explaining how values of the local fracture stress in notched bars or of fracture toughness in pre-cracked test-pieces are related to features of the microstructure: carbide thicknesses in wrought material; the sizes of oxide/silicate inclusions in weld metals. Effects of a microstructure that is ‘heterogeneous’ at the mesoscale are treated briefly, with respect to the extraction of test-pieces from thick sections and to extrapolations of data to low failure probabilities. The values of local fracture stress may be used to infer a local ‘work-of-fracture’ that is found experimentally to be a few times greater than that of two free surfaces. Reasons for this are discussed in the conclusion section on nano -scale events. It is suggested that, ahead of a sharp crack, it is necessary to increase the compliance by a cooperative movement of atoms (involving extra work) to allow the crack-tip bond to displace sufficiently for the energy of attraction between the atoms to reduce to zero.

scholarly journals STUDY ON BRITTLE FRACTURE OF WELDED JOINT WITH WELD DEFECTS BASED ON LOCAL FRACTURE APPROACH

2006 ◽  
Vol 71 (610) ◽  
pp. 169-176 ◽  
Author(s):  
Tadao NAKAGOMI ◽  
Yusuke TATSUMI
Keyword(s):  
Brittle Fracture ◽  
Welded Joint ◽  
Local Fracture ◽  
Weld Defects

scholarly journals Regio- and stereospecific assembly of dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidines] from simple precursors using a one-pot procedure: synthesis, spectroscopic and structural characterization, and a proposed mechanism of formation

2020 ◽  
Vol 76 (8) ◽  
pp. 779-785
Author(s):  
Pablo Romo ◽  
Jairo Quiroga ◽  
Justo Cobo ◽  
Christopher Glidewell
Keyword(s):  
Hydrogen Bonds ◽  
High Resolution Mass Spectrometry ◽  
Synthesis And Characterization ◽  
Mechanism Of Formation ◽  
One Pot ◽  
X Ray ◽  
A Chain ◽  
Definition Of ◽  
Resolution Mass

The synthesis and characterization of three new dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidine] compounds are reported, together with the crystal structures of two of them. (3RS,1′SR,2′SR,7a′SR)-2′-(4-Chlorophenyl)-1-hexyl-2′′-sulfanylidene-5′,6′,7′,7a′-tetrahydro-2′H-dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidine]-2,4′′-dione, C28H30ClN3O2S2, (I), (3RS,1′SR,2′SR,7a′SR)-2′-(4-chlorophenyl)-1-benzyl-5-methyl-2′′-sulfanylidene-5′,6′,7′,7a′-tetrahydro-2′H-dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidine]-2,4′′-dione, C30H26ClN3O2S2, (II), and (3RS,1′SR,2′SR,7a′SR)-2′-(4-chlorophenyl)-5-fluoro-2′′-sulfanylidene-5′,6′,7′,7a′-tetrahydro-2′H-dispiro[indoline-3,3′-pyrrolizine-1′,5′′-thiazolidine]-2,4′′-dione, C22H17ClFN3O2S2, (III), were each isolated as a single regioisomer using a one-pot reaction involving L-proline, a substituted isatin and (Z)-5-(4-chlorobenzylidene)-2-sulfanylidenethiazolidin-4-one [5-(4-chlorobenzylidene)rhodanine]. The compositions of (I)–(III) were established by elemental analysis, complemented by high-resolution mass spectrometry in the case of (I); their constitutions, including the definition of the regiochemistry, were established using NMR spectroscopy, and the relative configurations at the four stereogenic centres were established using single-crystal X-ray structure analysis. A possible reaction mechanism for the formation of (I)–(III) is proposed, based on the detailed stereochemistry. The molecules of (I) are linked into simple chains by a single N—H...N hydrogen bond, those of (II) are linked into a chain of rings by a combination of N—H...O and C—H...S=C hydrogen bonds, and those of (III) are linked into sheets by a combination of N—H...N and N—H...S=C hydrogen bonds.

A hard choice for Tomasello

2020 ◽  
Vol 43 ◽  
Author(s):  
Philip Pettit
Keyword(s):  
Joint Action ◽  
The Other ◽  
Hard Choice ◽  
Margaret Gilbert ◽  
Michael Bratman ◽  
Human Sense ◽  
Sense Of Obligation

Abstract Michael Tomasello explains the human sense of obligation by the role it plays in negotiating practices of acting jointly and the commitments they underwrite. He draws in his work on two models of joint action, one from Michael Bratman, the other from Margaret Gilbert. But Bratman's makes the explanation too difficult to succeed, and Gilbert's makes it too easy.

Social epistemic actions

2020 ◽  
Vol 43 ◽  
Author(s):  
Giovanni Pezzulo ◽  
Laura Barca ◽  
Domenico Maisto ◽  
Francesco Donnarumma
Keyword(s):  
Social Interaction ◽  
Joint Action ◽  
Niche Construction ◽  
Cultural Practices ◽  
Learning Processes ◽  
Epistemic Actions ◽  
Target Article ◽  
Online Social Interaction

Abstract We consider the ways humans engage in social epistemic actions, to guide each other's attention, prediction, and learning processes towards salient information, at the timescale of online social interaction and joint action. This parallels the active guidance of other's attention, prediction, and learning processes at the longer timescale of niche construction and cultural practices, as discussed in the target article.

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