# Improving the Impact Resistance of Anti-Ram Bollards Using Auxetic and Honeycomb Cellular Cores
## 1 Introduction  
Every year, around 1.3 million people's lives are cut short as a result of traffic accidents. Non-fatal injuries affect between 20 and 50 million more people, with many of them resulting in disability as a result of their injuries. Individuals, their families, and nations suffer significant economic losses as a result of road traffic injuries. Losses can be estimated to constitute 3% of a country's GDP [1, 2]. Vehicle barriers can be placed around the perimeter of a protected area to prevent vehicular accidents. Such barriers are frequently used as bollards. This is because, as compared to other barrier systems, they may easily blend in with other architectural features and cause fewer disturbances to building's functionality. Hollow steel tubes are employed in a wide range of barrier system applications where deformation-induced energy absorption is required [3]. The use of anti-vehicle barriers is critical in terms of protecting structures. They have the potential to block vehicles from passing through to other assets. The public, on the other hand, is less concerned about the use of bollards these days. Some believe that the use of bollards is inefficient and that they are only used for aesthetic reasons. As a result, most buildings do not employ bollards for security. Moreover, mounted bollards may be inappropriate in some locations. Some bollards around buildings are not stiff enough and, hence, cannot withstand strong impacts. Likewise, as a form of building protection, some important and historic structures require the installation of impact-resistant-type bollards [4]. Security bollards are used to defend buildings and personnel from intentional attacks or accidents as a cost-effective option. Hence, bollardscan provide effective perimeter security by prohibiting vehicles from reaching pedestrian sidewalks or restricted zones, as well as collisions with structures. Common forms of ballard applications include governmental buildings, storefront security, and traffic control. Bollards can be either crash or non-crash-resistant, and they can be fixed, removable, or retractable, depending on the application. Crash-resistant ballards should be certified through a crash test in line with an established standard. Anti-ram bollards are widely utilized because of their straightforward installation, resulting in minimal disruption and ease of integration into existing architectural features. The ability to manufacture bollard systems in a variety of shapes and sizes also helps to reduce installation and maintenance costs. Costs are kept low while the essential level of protection is maintained. Anti-ram bollard systems, which comprise mild steel tubes, are usually embedded into concrete foundations to provide the necessary stiffness and strength to withstand significant vehicle impacts. Because of their stiffness and energy-absorbing properties, thin-walled tubes are usually utilized in bollard designs [5; 6]. Vehicle security barriers (VSBs) are evaluated using a variety of standards. The International Organization for Standardization (ISO), in its latest standard, ISO 22343-1:2023 [7], specifies the essential impact performance requirement for a vehicle security barrier (VSB) and testing methods used to rate its performance when subjected to a single impact by a test vehicle not driven by a human being. This ISO standard supersedes the well-known previous version (IWA 14-1) published in 2013. Publicly Available Specification PAS 68:2013 [8] defines the standard method to be used to test the impact performance and protection rating of a VSB when impacted by different categories of UK vehicles traveling at specified speeds. The American Society for Testing and Materials, ASTM F2656 [9], defines the method to be used for impact testing and assigning performance ratings for a VSB when impacted by different categories of vehicles.