Blast Analysis – How Can We Model Concrete Subjected to a Contact Charge?

Abstract

In a world with increasing numbers of conflicts, wars and overall increased tension, the need for safety design of buildings and structures increases as a result. Accurate numerical model is an efficient way of predicting the material behavior of structures, thus providing valuable data for design.

This master's thesis provides a comprehensive investigation how concrete plates subjected to contact blasts accurately can be numerically modeled using FEM. The investigations are done through a parametric study of vital parameters of the numerical model. Initially, the study presents possible material models and methods for modeling blast loads in LS-DYNA.

The research begins with an investigation into mesh sensitivity. Here, the refinement of the mesh resulted in a more detailed and accurate model, while being limited by computational power for further refinements. The next area of focus was the damage parameters, revealing that the α- and β-parameters significantly influenced damage propagation with α showing an inverse relationship with damage and the β showing a direct relationship. Conversely, the final damage parameter, μ_(n,min), demonstrated minimal impact on the model.

The study also delves into the effects of particle resolution, finding that increased particle resolution led to more accurate damage propagation, much like the mesh density. Lastly, the research investigated the scalability of the numerical model, comparing it with the experimental work of Torsæter and Tronvoll [1]. The numerical model displayed representative damage patterns not only for the most investigated case with a 50.00 g C4 charge but also for other charge amounts. Despite some discrepancies with the experimental results, the numerical model using the finer mesh and particle resolutions, reduced α-value and increased β-value, provided the most accurate outcomes.

Limitations in comparable experimental data for validation was noted, as well as challenges in precise crater measurements.

In conclusion, this thesis offers insights into concrete behavior with various parametric configurations, contributing to the design of more resilient structures. It highlights the importance of parameter choice and model refinement in achieving realistic simulation results and highlights areas for further research and refinement.

Keywords: Contact Blast; LS-DYNA; Modified Holmquist-Johnson-Cook- Model; Particle Blast Method; Parametric Study