National Repository of Grey Literature 5 records found  Search took 0.01 seconds. 
An experimental investigation of yield surfaces anisotropies
Štefan, Jan ; Parma, Slavomír ; Marek, René ; Plešek, Jiří ; Feigenbaum, H. P. ; Ciocanel, C.
This contribution is dedicated to a rigorous experimental procedure for evaluation of yield surfaces of common metallic materials. This yield surface tracing procedure employs thin-walled tubular specimens to identify individual yield points of the material under arbitrary combinations of axial load and torque. A yield point is identified on the basis of a prescribed threshold for the effective plastic strain that is being continuously and fully automatically evaluated throughout the test. The experimental results generated with this tracing method are promising, leading to shapes of the yield surfaces conform with the von Mises criterion. The proposed methodology can effectively capture the YS shape.
Numerical solution of a secular equation for rayleigh waves in a thin semi-infinite medium made of a composite material
Červ, Jan ; Adámek, V. ; Valeš, František ; Parma, Slavomír
The traditional way of deriving the secular equation for Rayleigh waves propagating along the stress-free edge of a thin semi-infinite composite is presented. It means that it is necessary to find a general steady-state solution that vanishes at infinity. The secular equation is then obtained by vanishing of the surface traction at the stress-free edge. For the solution of such secular equation it is necessary to precompute some roots of characteristic quartic equation. The method shown in this paper, based on displacement formulation, leads to the so-called implicit secular equation. The numerical approach to the solution is shown.
Numerical calibration of material parameters of selected directional distortional hardening models with combined approach using both distorted yield surfaces and stress-strain curves
Hrubý, Zbyněk ; Plešek, Jiří ; Parma, Slavomír ; Marek, René ; Feigenbaum, H. P. ; Dafalias, Y.F.
The plastic strain induced anisotropy is a well-known phenomenon in manufacturing and directional distortional hardening represents a very promising way to capture real plastic behavior of metals. Many papers were published in the past typically extending the von Mises yield criterion with directionally dependent internal variable and defining yield point at the basis of plastic strain offset. Material parameters of these models were typically calibrated at the basis of deformed yield surfaces only, which – as revealed – could lead to certain discrepancies in simple stress-strain response. Presented paper introduces a numerical calibration approach taking both distorted yield surfaces and stress-strain curves information into account. Besides the calibration procedures, innovative applications of experimental techniques such as the acoustic emission for an acquisition of yield inception and plastic straining, convexity of the models, or numerical implementation of these models are discussed.
Experiments in directional distortional hardening—determination of mechanical properties of the S355J0 grade structural steel
Parma, Slavomír ; Ciocanel, C. ; Seiner, Hanuš ; Hrubý, Zbyněk
In order to carry out comprehensive experiments in the research of directional distortional hardening phenomenon, some basic mechanical properties of S355J0 structural steel are determined. Particularly, attention is payed to the determination of elastic properties of the material, determination of anisotropy of the material induced by the manufacturing technology of specimens, and determination of elasto-plastic behavior of the material. Elastic properties of the material are measured via an ultrasound method, elasto-plastic behavior is analyzed from the tensile and torsional testing. Conclusions of the report are intended for design and evaluation of the comprehensive experiments mentioned.
Identification of Parameters of the Feigenbaum-Dafalias Directional Distortional Hardening Model
Parma, Slavomír ; Plešek, Jiří ; Hrubý, Zbyněk ; Marek, René ; Feigenbaum, H. P. ; Dafalias, Y.F.
Distortion of yield surface was observed in numerous experiments with various types of metals. The distorted surface shows high curvature in the direction of load and flattening in the opposite direction. Feigenbaum and Dafalias (2008) proposed a new phenomenological model to capture this phenomenon. In sum, Feigenbaum-Dafalias directional distortional model includes six independent material parameters to be identified. The present paper describes an identification algorithm for parameters of the model.

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