Assessing impact resistance of concrete-based materials
This thesis presents the impact behavior of different types of concrete-based materials. Local impact effects of 34 g steel projectiles on concrete panels with nominal thicknesses of 2.54 cm and 3.81 cm were investigated. The objective was to stop the projectile (penetration resistance) or to minimize the damage (enhance strain capacity). To achieve these goals three approaches were implemented. These included changing the thickness of the panels, modifying concrete properties through fiber reinforcements and reducing damage by protecting the concrete with external layers (Polypropylene or Zylon fabric), which were either tightly bonded or loosely attached to the concrete panels.
It was found that the thickness of concrete panels has a significant effect on penetration resistance. Moreover, in the case of panels protected by fabric, they can effectively catch the debris and hold the scabbed crater from the rear face of the targets. Also, it was observed that having the loosely attached fabric on the rear face was more effective in absorbing the energy and catching the projectile and debris.
Subsequently, to investigate the damage, a Motionless Laminography (MLX®) technique was employed. This technique provides the ability to look through an object layer by layer. These 2D images can be mathematically reconstructed to produce a 3D map of the objects x-ray absorption. The MLX® images revealed that the back crater cone forms due to radial cracks followed by circumferential cracks. Hence, reinforcing concrete with fibers proved to be effective in increasing the impact resistance by inhibiting these cracks. Significant decrease in the damage zone, and increase in the penetration resistance was observed by including two or more types of fiber, i.e. PVA micro-fibers combined with steel macro-fibers. However, it was also observed that fiber length together with compressive strength of concrete is very important parameters in improving the impact resistance in this case.
Finally, Bayesian framework was employed to update one of the analytical models for predicting concrete failure under impact loading, based on the experimental data in the literature and the experiments in this study. The new updated model introduces the effect of panel thickness into the available formulation. For smaller thicknesses, the improved model predicts failure more accurately.
0548: Mechanical engineering
0794: Materials science