Rockfall is a phenomenon which, when uncontrolled, may cause extensive material damage and personal injury. One of the structures used to avoid accidents caused by debris flows or rockfalls is flexible barriers. The energy dissipating devices which absorb the energy generated by rock impact and reduce the mechanical stresses in the rest of the elements of the structure are an essential part of these kinds of structures. This document proposes an overview of the performance of energy dissipating devices, as well as of the role that they fulfil in the barrier. Furthermore, a compilation and a description of the dissipating elements found in literature are proposed. Additionally, an analysis has been performed of the aspects taken into account in the design, such as experimental (quasi-static and dynamic) tests observing the variation of the behaviour curve depending on the test speed and numerical simulations by means of several finite element software packages.

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This paper illustrates the experimental test procedure and results of two flexible barriers of low and medium energy, the so-called IBT-150 and IBT-500. For this purpose, ETAG 027 European Guideline is used. All the requirements for the tests performance are followed and the two energylevel tests performance requirements have been fulfilled in both rockfall barriers. Numerical modeling helps to understand and predict the behavior of these barriers with different configurations drastically reducing the costs of performing real tests. The results of the real test on IBT-150 and IBT-500 have been taken as references to validate two numerical models using Abaqus Explicit software. Afterwards, a presentation of some alternatives of the barrier IBT-150 are stated, which allow a more economical design removing some components that do not affect the energy level of 150 kJ set by the manufacturer. Also, a parametrical analysis of the IBT-500 numerical model has been performed varying the geometrical characteristics, such as the net grid dimension, the diameter of the perimeter cable, the length of the functional modules and its height. The aim of this analysis is the enhancement of maximum energy capacity of the barrier related with the amount of material used to build it. Following the ETAG recommendation, the maximum energy level (MEL) test is achieved if the barrier is able to retain the block. Thus, the MEL level for each numerical model was determined by increasing the initial speed of the block until it trespasses the barrier.

In this paper a fracture assessment in additive manufactured acrylonitrile butadiene styrene (ABS) fracture specimens containing U-notches is performed. We performed 33 fracture tests and 9 tensile tests, combining five different notch radii (0 mm, 0.25 mm, 0.50 mm, 1 mm and 2 mm) and three different raster orientations: 0/90, 30/−60 and 45/−45. The theory of critical distances (TCD) was then used in the analysis of fracture test results, obtaining additional validation of this theoretical framework. Different versions of TCD provided suitable results contrasting with the experimental tests performed. Moreover, the fracture mechanisms were evaluated using scanning electron microscopy in order to establish relationships with the behaviour observed. It was demonstrated that 3D-printed ABS material presents a clear notch effect, and also that the TCD, through both the point method and the line method, captured the physics of the notch effect in 3D-printed ABS. Finally, it was observed that the change in the fracture mechanisms when introducing a finite notch radius was limited to a narrow band behind the original defect, which appeared in cracked specimens but not in notched specimens.

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