The predictive capability of a class of rate-type constitutive equations for describing the behaviour of frictional dilatant materials is tested in plane strain compression experiments. The examination is restricted on shear band bifurcation states, where small deviations of the deformations from rectilinear extensions can be assumed. For predicting correctly both the state of bifurcation and the shear band inclination, the incipient shear modulus parallel to the geometric axis has to be estimated as the modified secant modulus. In addition a second hardening modulus, related to incipient contraction during the process of shear band formation, must be considered. On teste la possibilité de prevoir le comportement de matériaux possédant frottement et dilatance à partir de quelques lois rhéologiques du type rate. On se limite au cas d'un état de bifurcation avec bandes de cisaillement, où l'on peut supposer que les déviations par rapport à l'extension rectilinéaire sont petites. Pour prévoir correctement l'état de bifurcation et l'inclinaison de la bande de cisaillement on doit evaluer le module initial de cisaillement parallélement á l'axe géométrique par le module sécant modifié, et en doit introduire aussi un deuxième module decrivant la contractance initiale.
The trap-door problem with dry sand is treated in a statical analysis based upon model test kinematics. Integration of the equilibrium conditions along horizontal slices and introducing the mean value for the vertical stresses yields a differential equation for the trap-door force. Concerning the constitutive response of sand a statical model of a moving shear band is proposed as an internal boundary. Solutions for the trap-door force for the active and passive modes and for the ultimate and residual states are discussed.
With the recent rise in the demand for additive manufacturing (AM), the need for reliable simulation tools to support experimental efforts grows steadily. Computational welding mechanics approaches can simulate the AM processes but are generally not validated for AM-specific effects originating from multiple heating and cooling cycles. To increase confidence in the outcomes and to use numerical simulation reliably, the result quality needs to be validated against experiments for in-situ and post-process cases. In this article, a validation is demonstrated for a structural thermomechanical simulation model on an arbitrarily curved Directed Energy Deposition (DED) part: at first, the validity of the heat input is ensured and subsequently, the model's predictive quality for in-situ deformation and the bulging behaviour is investigated. For the in-situ deformations, 3D-Digital Image Correlation measurements are conducted that quantify periodic expansion and shrinkage as they occur. The results show a strong dependency of the local stiffness of the surrounding geometry. The numerical simulation model is set up in accordance with the experiment and can reproduce the measured 3-dimensional insitu displacements. Furthermore, the deformations due to removal from the substrate are quantified via 3D-scanning, exhibiting considerable distortions due to stress relaxation. Finally, the prediction of the deformed shape is discussed in regards to bulging simulation: to improve the accuracy of the calculated final shape, a novel extension of the model relying on the modified stiffness of inactive upper layers is proposed and the experimentally observed bulging could be reproduced in the finite element model.
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