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Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Svárovský, Jiří ; Parma, Slavomír ; Štefan, Jan ; Ciocanel, C. ; Feigenbaum, H. P. ; Marek, René ; Klepač, Vilém ; Plešek, Jiří
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.
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Use of advanced kinematic hardening rules for prediction of multiaxial ratcheting
Klepač, Vilém ; Parma, Slavomír ; Feigenbaum, H. P. ; Marek, René ; Plešek, Jiří ; Svárovský, Jiří
The cumulation of plastic deformation due to cyclic loading, so called ratcheting, is considered as critical process for purpose of simulation. For this reason, many of advanced models of plasticity have been developed to capture the evolution of material during the load reversals. Historically, these models are based on concept of multicomponent back-stress, that provides the prediction of phenomenon of kinematic hardening (KH) [Chaboche 1979]. The key for accurate prediction is, besides well designed model, identification of model parameters. To present results on prediction of multiaxial ratcheting by FEA, the multicomponent Armstrong-Frederick with a threshold with r Modification was implemented via the UMAT interface of Abaqus Standart. Model parameters were identified on experimental data presented in [Hassan, Kyriakides 1992] and [Hassan et. al. 1992]. To prove the performance of the model subroutine, other numerical examples will be presented and their computational costs will be discussed.
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Development of autonomous experimental setup to investigate directional distortional hardening under biaxial loading
Svárovský, Jiří ; Parma, Slavomír ; Štefan, Jan ; Ciocanel, C. ; Feigenbaum, H. P. ; Klepač, Vilém ; Marek, René ; Plešek, Jiří
Plastic deformations alter the shape of the yield surface in the stress space. Models for predicting the shape of the yield surface according to the direction of loading are being developed. Experimental data are the key factor in development and validation of phenomenological models, such as the model of directional distortional hardening cited in this study. The objective of this paper is to present the experimental setup for investigation of the directional distortional hardening. A new autonomous method was developed using an axial-torsional testing machine and the Labivew 2017 graphical programming environment to monitor the yield surface in axial stress – shear stress space. A suitable yield condition in form of effective plastic strain was used for the determination of the yield points. Initial yield surface obtained by this method shows promising agreement with von Mises model of the yield surface. Several outstanding yield points were measured which disrupt the assumption of the yield surface convexity. Therefore, possible shortcomings caused by the methodology are being investigated.
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