Unstable fracture criterion in a power-law hardening material

A fracture criterion for a pre-cracked plate subjected to large deformation is presented in a power-law hardening material based on the energy conservation law. First Hencky equations are applied to a non-linear elastic model in a small strain to derive the criterion and the theory is extended to a large strain case with the aid of numerical analysis. The criterion is expressed as a relation between a crack length and a remote fracture strain, and it is identical with Griffith's criterion when the power exponent is unity.Large strain and stress fields near a crack tip are also assessed. Experiments with pre-cracked steel plates well verify the theory, that is, the criterion based on elastic analysis appears to apply to an actual plastic material. The transition from the brittle fracture to the present unstable ductile fracture and a physical implication of the reduction of area in tension test are discussed.

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Résumé On présente un critère de rupture pour une tôle préfissurée soumise à une grande déformation dans une matériau durcissant suivant une loi parabolique et en se basant sur une loi de propagation de l'énergie. Les premières équations de Hencky sont appliquées à un modèle élastique non linéaire pour des déformations de faible amplitude en vue de dériver un critère, et la théorie est étendue au cas des grandes déformations à l'aide d'analyse numérique. Le critère est exprimé comme une relation entre la longueur de la fissure et une déformation à la rupture lointaine, et il est identique au critère de Griffith lorsque l'exposant de la loi de durcissement du matériau est l'unité.Les déformations en amplitude et les champs de contrainte au voisinage de l'extrémité de la fissure sont également prises en considération. Des expériences réalisées avec des tôles d'acier préfissurées vérifient la théorie de manière satisfaisante, c'est-à-dire que le critère basé sur l'analyse élastique apparait applicable à un matériau se comportant de façon plastique. La transition de la rupture fragile à une rupture ductile instable et les implications physiques de la striction lors de l'essai de traction sont discutées.

     

Intraparticle ion exchange mass transfer accompanied by instantaneous irreversible reaction

A model is proposed for intraparticle mass transfer of ion exchange coupled with instantaneous irreversible reaction. The theoretical equations are der     

Mechanical behaviour of brittle materials under hydrostatic pressure (on torsion of chalk cylinders)

Torsion tests were carried out on black-board chalk under hydrostatic pressures of up to 4·0 kgf/mm² in order to investigate the pressure effect on the deformation and fracture of brittle materials. Chalk, which is very weak (the tensile strength is about 0·1 kgf/mm²), was chosen as test material because the ratio of the applied hydrostatic pressure to the tensile strength of the material could be easily raised to high values.It is shown that there is a distinct difference in the characteristics of deformation and fracture between specimens under a pressure which is higher than a critical value of 0·3 kgf/mm² and those under a pressure less than that value. It is also shown that under relatively high pressure a macroscopic crack is formed around the twist angle yielding the maximum torque and thereafter it propagates helically with increase of twist angle.     

Tunneling of quasiparticles between two weakly coupled systems of superfluid helium

Quasiparticle tunneling in a weakly coupled system of liquid helium is theoretically studied, in analogy with normal electron tunneling of superconductor junctions. Chemical potential difference in this case is to be created across the junction by a superfluid flow parallel to the junction. Calculation shows that a collimated beam of quasiparticles would show several divergences of tunneling current at specific angles of incidence or at specific values of superfluid velocity, while no divergence is expected for the integrated current, which is an important difference from the case of superconductor junctions.     

Adsorption and desorption of complex metal ions in polyviologen or its polyion complexes with poly(sulphonate)s by the control of a given potential

Complex anions and a complex cation were concentrated electrostatically in the domain of polyviologen by the control of a given potential. Pyrolytic graphite electrodes were coated with polyviologen or the polyion complex of polyviologen with poly (sulphonic acid) for the concentration of complex anions or the complex cation, respectively. In an aqueous solution in which Mo(CN)^4?₈ and Fe(CN)^4?₆ coexisted, the polyviologen-coated electrode predominantly concentrated Mo(CN)^4?₈. Furthermore, the Mo(CN)^4?₈ incorporated in the film was desorbed by reducing the charge density of polyviologen. The desorption rate was proportional to the charge density of polyviologen which depended on a given potential. On the other hand. Ru(NH₃)³⁺₆ was adsorbed in the domain of the polyion complex of polyviologen with poly (sulphonic acid) and it was desorbed completely in a few seconds by reducing the overall charge density of the polyion complex. Generally, reversible adsorption-desorption of multivalentions could be performed by changing the given potential if redox-active sites were fixed or chemically bonded in the polymer matrix. Redox-active polymers were stabilized by polyion complex formation with oppositely charged polyelectrolytes.     

Change of monochloroacetic acid to biodegradable organic acids by hydrothermal reaction

The feasibility of biodegradability improvement induced from the structural conversion of refractory pollutants by hydrothermal reaction was investigated. Monochloroacetic acid (MCAA) was selected as a preliminary material represented for linear hydrocarbon structured refractory pollutants. Under the tested conditions, MCAA was partially destructed and then converted to biodegradable reaction products by hydrolysis, dehydration and thermal decomposition. The identified products were glycolic acid, citric acid and formic acid. Total organic carbon (TOC) reduction during the structural conversion did not exceed 24%, except the results at the reaction conditions of 350 degrees C and 17 MPa. However, Produced biodegradable organic acids were reduced by thermal decomposition with increasing reaction temperature and time. At the reaction temperature of 250 and 300 degrees C, biodegradability (BOD/COD(Cr)) was reached at 0.51 in 6.9 min and 0.52 in 7.4 min despite the presence of dissociated chlorine ions. The detachment of recalcitrant chlorine ion from MCAA and the production of biodegradable organic acids by hydrothermal reaction were directly related to the biodegradability improvement of reaction products.     

Simultaneous determination of residual fourteen kinds of beta-lactam and macrolide antibiotics in bovine muscles by high-performance liquid chromatography with a diode array detector

Residues of 14 kinds of beta-lactam and macrolide antibiotics in bovine muscles were extracted with acetonitrile and the extract was partitioned with n-hexane to remove fat. High-performance liquid chromatography was carried out on a TSK-gel ODS-80TM column using gradient elution with acetonitrile-0.05% trifluoroacetic acid and the drugs were quantitated by diode array detection. The recoveries of the drugs from bovine muscles spiked at 0.1 ppm were over 63% and each quantitation limit was 0.04 ppm.