Modeling Of Strain Rate Effects Research Articles

Modeling of strain rate effect on the pseudoelastic behavior of NiTi SMA using a simple thermomechanical coupling model

NiTi SMA represents a popular group of metals with interesting properties like pseudoelasticity and a high energy dissipative capacity. Indeed, NiTi alloys, presents an interesting damping capacity due to solid-solid phase transformation. Such characteristics allow them to be used in many civil engineering fields mainly as actuators and damping devices. However, because of their complex behavior, the design process of these applications seems to be complicated and consequently, needs to build accuracy numerical models. One of these already existing models is the micromechanical Likhachev model. It seems to be very attractive thanks to its general formulation, numerical efficiency and model parameters relatively easy to determine. This paper concerns the numerical simulation of the pseudoelasticity behavior of NiTi wires dedicated to the application of damping devices, at different stress and strain rates. A thermomechanical coupling is introduced in the Likhachev formulation in order to simulate the thermomechanical behavior of NiTi under strain control. In this paper the model is adapted to a strain-controlled formulation, and 1D simulation is achieved using FORTRAN code. Parameters model are identified thanks to SiDoLo software and the corresponding results are presented and discussed. A good agreement with experimental data is found for the two formulations.

Discrete Modeling of Strain Rate Effect in Concrete Fracture

Concrete fracture can be simulated in static regime, however, it is a dynamical process. For very slow loading rates, the kinetic energy is negligible compared to the energy dissipated by fracturing, and the influence of inertia can be neglected. In all other cases, neglecting the influence of inertia forces can lead to improper results. With increasing loading rate, increase in strength and energy dissipation as well as changes in crack pattern can be observed. The contribution presents dynamical simulations of experiments on concrete specimens under various displacement rates, from very slow, quasi-static, to high displacement rates. The simulations are calculated using discrete particle model, the material is represented by a system of interconnected ideally rigid polyhedral particles. The solution of equations of motion is calculated using implicit time integration Newmark scheme. The constitutive behavior of the material is strain rate independent. For high strain rates the influence of inertia forces dominates and is mainly responsible for increase in loading forces as well as for change in the crack pattern and crack branching. The results obtained with the model are compared to experimental data from literature.

Modeling of strain rate effects for concrete with viscoelasticity and retarded damage

Especially the tensile strength of concrete may by far exceed the quasistatic values under high strain rate conditions. Due to present knowledge this is predominantly caused by the higher resistance of water in the capillary system of concrete on one hand and by the limited speed of the evolution of micro and macro cracks on the other hand. This contribution combines a viscoelastic approach for the first case with a gradient damage approach for the second, whereby damage is retarded due to inertial effects under high strain rates. The combined material law includes quasistatic behavior as a special case and covers dynamic material behavior up to a strain rate in a magnitude of 103 s−1. The material law is implemented in a Finite Element Method and first of all applied to uniaxial wave propagation problems. Thus, typical experimental results for dynamic tensile strength increase factors may be reproduced within a calibration procedure for the three dynamic material parameters of the material law. Furthermore, the structural behavior of a plain concrete beam under impact loading is investigated. The effects of structural mass inertia and the material's strain rate sensitivity to the dynamic load bearing capacity are exemplarily outlined. Finally, it is demonstrated how the dynamic load bearing capacity depends on load duration beneath load amplitude.

Constitutive modeling of strain rate effects in nanocrystalline and ultrafine grained polycrystals

We present a variational two-phase constitutive model capable of capturing the enhanced rate sensitivity in nanocrystalline (nc) and ultrafine-grained (ufg) fcc metals. The nc/ufg-material consists of a grain interior phase and a grain boundary affected zone (GBAZ). The behavior of the GBAZ is described by a rate-dependent isotropic porous plasticity model, whereas a rate-independent crystal-plasticity model which accounts for the transition from partial dislocation to full dislocation mediated plasticity is employed for the grain interior. The scale bridging from a single grain to a polycrystal is done by a Taylor-type homogenization. It is shown that the enhanced rate sensitivity caused by the grain size refinement is successfully captured by the proposed model.