Development of upper bound technique for analysis of fracture in metal forming

Summary An attempt is made to modify the plasticity theory for compressible materials and then to derive the upper bound theorem or the second extremum principle which incorporate normal velocity discontinuity; this discontinuity is considered to be a measure of fracture. The theorem is applied to predict the occurrence of fracture, central bursting in extrusion or drawing. The occurrence of fracture appears to depend on the value of the parameters in the theorem; these parameters may be related to ductility or workability of the material in question. The upper bound technique is then applied to multi-stage extrusion of a carbon steel for which the values of the parameters are given with some assumptions. It is thus shown that the stage at which central bursting occurs agrees with experimental results and that it apparently depends on the extrusion condition.

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Ein obere-schranken-konzept zur bestimmung von bruchvorgängen bei der umformung von metallen

Übersicht Es wird der Versuch unternommen, mit einer modifizierten Plastizitätstheorie für kompressible Werkstoffe den Obere-Schrankensatz bzw. das zweite Extremum-Prinzip herzuleiten, wenn die Normalgeschwindigkeit auf Sprungflächen unstetig ist. Diese Unstetigkeit wird als Indikator von Bruchvorgängen angesehen. Angewandt wird diese Hypothese auf die Vorhersage des Bruchs, d. h. der Materialtrennung im Kern beim Durchdrück- bzw. Durchziehverfahren. Das Auftreten von Brüchen erweist sich als abhängig von den Parametern des Ansatzes. Diese Parameter lassen sich mit der Umformbarkeit des Materials in Zusammenhang bringen. Angewandt wird das Obere-Schranken-Konzept auf das mehrstufige Durchpressen eines Kohlenstoff-Stahls, für den die Parameterwerte mit Hilfe einiger Parameterwerte festgelegt werden. Davon ausgehend wird gezeigt, daß die Preßstufe bei Materialtrennung mit experimentellen Ergebnissen übereinstimmt und offensichtlich von den Durchpreßbedingungen abhängt.

     

Optical and electromagnetic characteristics of clay�Ciron oxide nanocomposites

Fe-pillared bentonite clay-based nanoadsorbent was synthesized by the thermal aging technique. The characteristics of the nanocomposite were detected by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), thermal gravimetric analysis (TGA), scanning electron microscope (SEM), electron dispersive X-ray spectrometer (EDX), reflectance spectrophotometer (RS), and electromagnetic transition instrument (ETI). The TGA result demonstrated that the Fe particles generated on the clay surface can significantly improve the thermal stability of clay particles. The SEM and EDX results showed the presence of chemical elements of Fe, Al, and Si on the surface of clay. In this research, the successful synthesis of Fe-pillared clay nanocomposite can be concluded from the FTIR spectra.     

A Simple One‐Pot Synthesis of N‐Alkyl‐2,5‐diaryl‐1,3‐dioxol‐4‐amines

An efficient procedure for the synthesis of N‐alkyl‐2,5‐diaryl‐1,3‐dioxol‐4‐amines 3 via a one‐pot reaction of aromatic aldehydes 2 and alkyl isocyanides 1 at room temperature in good yields is described (Scheme 1, Table).     

Solvent‐free synthesis of new 2,4,6‐triarylpyridines catalyzed by a Brønsted acidic ionic liquid as a green and reusable catalyst

Some new 4‐(aryl)‐2,6‐di‐2‐naphthylpyridines and 4‐(aryl)‐2,6‐di‐2‐thienylpyridines have been prepared through three‐component condensation of 2‐acetylnaphthalene or 2‐acetylthiophene, aromatic aldehydes, and ammonium acetate in presence of 1‐(4‐sulfonylbutyl) pyridinium hydrogensulfate [(CH₂)₄SO₃HPy][HSO₄], a Brønsted acidic ionic liquid as a green and reusable catalyst in solvent‐free conditions. Also some new 4,4'‐(1,4‐phenylene)‐bis‐(2,6‐di‐aryl pyridine) was prepared. J. Heterocyclic Chem., (2011).     

Highly efficient enzymatic synthesis of 3'-deoxyapionucleic acid (apioNA) having the four natural nucleobases

The synthesis of the 3'-deoxyapionucleoside 3'-triphosphates (apioNTPs) having the four natural nucleobases and their enzymatic incorporation into a DNA-DNA primer-template have been tried. Therminator DNA polymerase was shown to incorporate these apioNTPs effectively giving 43mer DNA-apioNA chimera.     

Control of the Solid‐State Chiral Optical Properties of a Supramolecular Organic Fluorophore Containing 4‐(2‐Arylethynyl)‐Benzoic Acid

The solid‐state chiral optical properties of a 4‐(2‐arylethynyl)‐benzoic acid/amine supramolecular organic fluorophore can be controlled by changing the arylethynyl group of the achiral 4‐(2‐arylethynyl)‐benzoic acid component molecule rather than the chirality of the amine component molecule.     

Changes in Hip and Knee Muscle Strength in Patients Following Total Hip Arthroplasty

Objective: To investigate changes in hip and knee muscle strength in patients before and after total hip arthroplasty (THA) in comparison with that in healthy adults. Methods: The study included 21 women who underwent unilateral THA (THA group) and 21 age-matched healthy women (healthy group). Maximal isometric strengths of hip flexors, extensors, and abductors, and knee extensors and flexors were measured before surgery and at 4 weeks and 6 months after surgery. Results: Before surgery, muscle strength on both sides, except for hip flexors on the uninvolved side, was significantly lower in the THA group than the corresponding muscle strength in the healthy group. Up to 6 months after THA, strength of all muscle groups on both sides was significantly improved compared with their preoperative status, although the knee extensor strength on the involved side temporarily worsened at 4 weeks. However, the strength of hip extensors and knee extensors on the involved side, and hip abductors on both sides in the THA group remained below that in the healthy group. Conclusions: Our results suggest that rehabilitation specialists should consider increasing the focus on the uninvolved side and encourage patients to continue strength training beyond 6 months after surgery.