Abstract
AbstractCurrent high strain rate testing procedures generally rely on the split Hopkinson bar (SHB). In order to gain accurate material data with this technique, it is necessary to assume the test sample is in a state of quasi‐static equilibrium so that inertial effects can be neglected. During the early portion of an SHB test, it is difficult to satisfy this assumption making it challenging to investigate the elastic–plastic transition for metals. With the development of ultra‐high speed imaging technology, the image‐based inertial impact (IBII) test has emerged as an alternative to the SHB. This technique uses full‐field measurements coupled with the virtual fields method to identify material properties without requiring the assumption of quasi‐static equilibrium.The purpose of this work is to develop the IBII method for the identification of elasto‐plasticity in metals. In this paper (part 1), the focus is on using synthetic image deformation simulations to analyse identification errors for two plasticity models, a simple linear hardening model and a modified Voce model. Additionally, two types of virtual fields are investigated, a simple rigid body virtual field and the recently developed sensitivity‐based virtual fields. The results of these simulations are then used to select optimal processing parameters for the experimental data analysed in part 2.
Highlights
The behaviour and failure mechanisms of metals are often dependent on strain rate
The requirement that the sample must undergo uni-axial deformation and one dimensional wave propagation strongly limits the stress-states which can be tested with the traditional split Hopkinson bar (SHB) technique
In the interest of reducing computational time and increasing the strain increment for the return-mapping algorithm (RMA) the data can be down-sampled such that every third frame is included in the cost function
Summary
The behaviour and failure mechanisms of metals are often dependent on strain rate. These differences are critical when designing structures or components that are subjected to impact or blast loads. The requirement that the sample must undergo uni-axial deformation and one dimensional wave propagation strongly limits the stress-states which can be tested with the traditional SHB technique This makes it difficult to fully characterise the yield surface at high strain rates for the case of anisotropic plasticity. For the IBII test, the assumption of plane stress with uniform kinematic fields through-thickness is used since the specimens under consideration are thin and only loaded in plane using an edge-on impact configuration Using these assumptions and neglecting the influence of body forces, equation 1 can be rewritten as: Wa∗cc σ : ε∗dS − T · u∗dl + ρ a · u∗dS = 0. The cost function is minimised by updating the constitutive model parameters, noting that for each iteration the stress reconstruction must be performed to calculate the internal virtual work
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