# Double-Bend and Semi-Spherical Energy Deflectors' Blast Load Efficiency--A Comparative Study
## 1 Introduction
Furthermore, the development of various printing methods has made it possible to produce various structures, including auxetic structures with a negative Poisson's ratio [22; 23]. The impedance of soil is significantly greater than that of air, so the ejected soil action causes more deformation and damage to energy-absorbing panels than does blast wave action. This effect was studied experimentally [24; 25] and numerically [24; 25; 26]. One of the first published studies of V-shaped plates for blast resistance was performed using a ballistic pendulum [27]. The V-shaped plates with deflection angles from 60\({}^{\circ}\) to 180\({}^{\circ}\) loaded with blast waves from the detonations of small charges (2.5-13 g) were tested. [PERSON] and [PERSON] showed that with decreasing deflector angles, the effectiveness of the deflector increases, as a more significant portion of the blast wave is reflected. This research, conducted experimentally and numerically, was continued by [PERSON] et al. [28]. In addition to confirming the earlier results, their study showed that an increase in the impulse (smaller distance or more significant charge) results in more deflection of the V-shaped plates. It was also found that the deflection of V-shaped plates is less for plates characterized by a smaller angle. [PERSON] et al. [29] studied various modifications of plates with the dilation angle of 154\({}^{\circ}\) loaded with an impact of granular material slugs driven by a blast wave from the detonation of 1 g PETN [29; 30]. They also determined the Head Injury Criterion (HIC) index for the analyzed cases. The use of a V-shaped plate allowed for an approximately 100-fold reduction in acceleration and a similar reduction in HIC index values. [PERSON] studied not only the process of momentum transfer to the plate for non-deformable plates with angles of 90\({}^{\circ}\) and 120\({}^{\circ}\), but also the effect of soil hydration on this process [31]. Increasing the density of the sand by hydration increased the momentum transferred, whereas decreasing the deflector angle decreased the momentum. In turn, numerical analyses reflecting a real structure loaded with a blast wave from the detonations of charges with masses of 14, 17, and 21 kg showed that a deflector with an opening angle of 160\({}^{\circ}\) is inferior to a flat plate [32]. [PERSON] et al. studied, using the finite element method coupled with the smoothed particle method, the effects of centric and non-centric blast wave loadings of a V-shaped plate and U-shaped plate [33]. In all the cases analyzed,the V-shaped plate better dispersed blast waves for any loading. An aluminum foam sandwich panel with V-shaped and double-V-shaped face plates was studied by [PERSON] and others [34] using the finite element method implemented in AUTODYN software. The use of aluminum foam increased the performance of the V-shaped panel. On the other hand, for the double-V-shaped face panel, the results depended on the proper selection of the stiffness of the front and back panel sides. [PERSON] and [PERSON] used Ls-Dyna software to study blast wave interactions with multiple-V-shaped deflectors [35]. Studies showed that usage of the multi-V-shaped deflectors results in an increase in the force peak in comparison with a single-V-shaped deflector. As can be seen from the literature review, to date the main focus of deflector research has been on V-shaped deflectors. Multi-V-shaped systems have also been investigated; however, the results for these have not been satisfactory. For this reason, in this paper we focus on two different shapes, namely semi-spherical and double-bend. A number of these types of deflectors with different characteristic dimensions were selected for the study, and the effects of these dimensions on their performance was determined using a ballistic pendulum test stand. The carried-out tests proved that the selected deflectors are characterized by higher energy dispersion capacity than the traditional V-shape while maintaining identical external dimensions.