Micro CT Image-based Simulations of Concrete under High Strain Rate Impact using a Continuum-Discrete Coupled Model

A continuum-discrete coupled modelling approach is developed in LS-DYNA to simulate complicated fragmentation phenomena of concrete under high strain-rate impact, using realistic mesoscale finite element models converted from micro X-ray computed tomography (XCT) images. In this approach, the Johnson Holmquist concrete (JHC) constitutive law based on continuum damage plasticity is used to simulate plasticity and crushing of elements, while a node-split method with contact is used to simulate discrete fracture between elements. This avoids using the popular element erosion technique, which suffers from unreal losses in mass and energy, especially under dynamic loadings with high strain rates. After the new approach is validated, extensive Monte Carlo simulations (MCS) of 93 2D FE models and one 3D model from XCT images of a 37.2mm concrete cube, consisting of aggregates, mortar, interfaces, and pores, are conducted under compressive impact with strain rates ranging from 0-1000/s and different end friction conditions. It is demonstrated that the developed modelling approach can simulate realistic failure mechanisms such as discrete fracture propagation under strain rates of 0-200/s and immediate crushing, fragmentation and prilling under higher strain rates of 500-1000/s. The predicted compressive dynamic increase factor of strength (CDIF)–strain rate curve is found well within the range of experimental data and very close to other empirical curves. Quantitative statistical calculations show that the meso-structure is the main contributor to the dynamic strength increase or reduction when the strain rate is lower than 10/s, but the inertial effect becomes dominant when the strain rate is higher than 100/s. The end friction confinement makes only 3-5% difference.