Effect of plastic material properties on the limiting state of a finite-stiffness cable

The work of finite-stiffness cable cross-sections in transverse bending is examined. The material is assumed to be rigid-and elastoplastic. The equation for limit curves is derived. Calculation results are presented. __________ Translated from Problemy Prochnosti, No. 5, pp. 132–140, September–October, 2007.     

Autoclave for investigating the influence of high-temperature aqueous media on the resistance of structural materials to crack initiation

Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fiziko-Khimicheskaya Mekhanika Materialov, Vol. 30, No. 3, pp. 127–130, May – June, 1994.     

Effect of low temperature on plastic deformation in structural materials in a complex state of stress

The results of experimental studies of elastoplastic deformation in structural materials of different grades in a complex state of stress at low temperatures are analyzed. It is shown that the degree of the effect of temperature and force conditions on the character of materials’ strain hardening at low temperature depends on their nature and structural state. The principal hypotheses and postulates that form the basis of the modern plasticity theories are examined for low temperatures. Two new models are introduced to describe the elastoplastic deformation of quasi-brittle and metastable materials under the simple loading with consideration for the effect of low temperatures on their structural state and mechanical properties.     

Fracture resistance of a structural steel as characterized by the strength of the plastic stress singularity

Fracture resistance, characterized by the strength of the plastic stress singularity, was determined at failure load and crack length using three-dimensional elastic-plastic finite-element analysis of 29 A36 steel fracture specimens that had been tested at –50°F. This measure of fracture resistance was insensitive to specimen size, geometry, parent plate, and heat, provided that the specimens were either of full plate thickness or were taken from the mid-thickness of parent plates. On the other hand, the fracture resistance of full-thickness plates was not reliably estimated from fracture specimens taken from the thickness 1/4 point or near the surface of the parent plates. The computed variation in crack-front through-thickness response at 10% of maximum load was confirmed by comparison with elastic results. Elastic-plastic response at maximum load, including the tendency to more extensive yielding in smaller specimens, was similar to that indicated by other authors. Several parameter studies demonstrated the insensitivity of the results to the finite-element mesh design.

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Résumé On a déterminé, à la charge de rupture, la résistance à la rupture caracterisée par la résistance de la singularité en contrainte plastique et la longueur de la fissure en utilisant une analyse par élément fini à trois dimensions élasto-plastique de 29 éprouvettes de rupture en acier A.36 essayées à –50°F. Cette mesure de la résistance à la rupture a été trouvée insensible à la dimension de l'éprouvette, à sa géométrie, à la tôle de base et à la chaleur pour autant que les éprouvettes soient prises en pleine épaisseur ou soient prélevées à mi-épaisseur des tôles. D'autre part, la résistance à la rupture de tôles en plein épaisseur n'a pu être estimée de manière fiable à partir d'éprouvettes de rupture prises au quart-épaisseur ou au voisinage de la surface des tôles de base. La variation calculée de la réponse du front de fissure au travers de l'épaisseur à 10% de la charge maximum a été confirmée en comparant les résultats élastiques. La résponse élasto-plastique à charge maximum comportant la tendance à une plastification plus intense dans des éprouvettes plus petites a été trouvée similaire à celle indiquée par d'autres auteurs. Diverses études paramétriques ont démontré l'insensibilité des résultats par rapport au type de réseau d'éléments finis choisi.

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Nomenclature K _pc weighted through-thickness average of the plastic stress singularity strength at failure - P applied load, kN - R radial extent of singular crack-front elements, mm - l through-thickness extent of singular crack-front elements, mm - load-point deflection, mm - _ep VonMises equivalent stress, MPa - _ys 0.2% offset yield strength, MPa     

Optimization of large structures subjected to dynamic loads with the multiplier method

The multiplier method for optimization of large-scale mechanical and structural systems subjected to dynamic loads is investigated. A large-scale dynamic response optimization problem is formulated and solved in several alternate ways using the first- and second-order forms of the equations of motion. Results are compared with those obtained with the sequential quadratic programming algorithm—a primal method. In all the cases investigated, the multiplier algorithm is more efficient than the primal method. Therefore, it is concluded that the multiplier method is more appropriate for dynamic response optimization of large-scale problems.     

Statistical scatter of fracture toughness in the ductile-brittle transition of a structural steel

The statistical scatter of fracture toughness in the ductile-brittle transition temperature range was experimentally examined on a 500 MPa class low carbon steel. Fracture toughness tests were replicatedly performed at −60 °C, −20 °C and −10 °C. The tests at −60 °C resulted in a single modal Weibull distribution with a shape parameter of 4 for the critical stress intensity factor converted from J-integral, whereas the Weibull distributions of the critical stress intensity factor at −20 °C and −10 °C showed a bilinear pattern with an elbow point, which caused a wider scatter than that at −60 °C. Such scatter transition behavior was discussed with reference to stable crack initiation. A model of the statistical scatter transition has been proposed in this work and the model reasonably explains the experimental results.     

Determining the stiffnesses of structural components with a periodic structure

An approach to the computation of the stiffnesses of periodic components, which is reduced to the problem of determining the stress-strain state of a single cell under special boundary conditions, is confirmed; this makes it possible to perform cell calculations by numeric methods using a computer. Examples of one-dimensional (shaped plating) and two-dimensional (three-layer honeycomb panel) periodicity are given.Translated from Problemy Prochnosti, No. 1, pp. 82–86, January, 1990.