Knut Andreas Meyer

The stability of a 3D concrete printed structure during fabrication depends on the ability of the fresh concrete to carry the weight of the subsequently deposited layers. This ability is referred to as buildability and it depends on a local reversible buildup process in the fresh material after deposition. Structural-scale simulations commonly relate this buildup process to the deposition age alone, omitting its dependence on the deformation history and the reversible nature of the process. In contrast to these approaches, this work presents a thermodynamically consistent viscoplastic constitutive model for Shotcrete 3D Printing material, in which a single internal structural variable governs the buildup over time and the breakdown under plastic deformation of both the yield stress and the elastic stiffness. A flocculation strain is introduced to keep the stress constant at constant total strain while the elastic stiffness increases during flocculation. The model is implemented in an open-source finite element framework with layer-by-layer activation in the reference configuration. Numerical examples are presented to examine the behavior of the internal variables and to demonstrate the model on a double-curved wall, where the placement of additional supports is obtained from the predicted displacement field.

In this paper, we analyze one specific assumption used in many cyclic plasticity models: The dependence of the yield surface evolution on the accumulated plasticity, i.e., the time-integrated plastic multiplier. In carefully designed experiments, we measure this scalar variable and track the yield surface evolution. We measure this scalar variable in carefully designed experiments and track the yield surface evolution. Our results show that this variable is insufficient to describe the isotropic or distortional hardening of the investigated steel, invalidating the commonly used assumption. The results highlight requirements for developing and verifying new isotropic and distortional hardening laws.

Rolling contact loading induces severe plastic deformations and initiates cracks near the rail surface. Prevention of such rolling contact fatigue cracks requires a better understanding about the mechanical behavior of the deformed material in this region. Even so, current rail standards do not consider the plasticity-induced changes to mechanical behavior. They only evaluate the mechanical performance of virgin rail steels under uniaxial loading conditions, which is not representative for the material's performance after years of service. This study proposes a new method for fatigue life evaluation of deformed material under loading conditions similar to rolling contact loading. Both virgin and predeformed test bars with a circumferential notch were subjected to strain-controlled torsional fatigue loading to evaluate the influence of axial loading, predeformation, and torsional loading direction. Superimposed compressive axial loads increase the fatigue life without affecting the torque response. The predeformed test bars exhibited longer lives, an effect we attribute to the combination of different torque responses, hardening, and anisotropy.