## 1 Introduction  
By the year 2035, about two billion vehicles are expected to be used regularly around the world [1]. The majority of these vehicles will be gasoline-powered. With concerns about climate change and greenhouse gas (GHG) emissions, many governments are encouraging the use of electric vehicles (EVs). For instance, the Norwegian government incentivizes the use of EVs through different types of tax-cuts [2]. Such policies have made a positive impact, as Norway currently has the highest sale of EVs per capita with EVs being one-third of all cars sold in 2018 [3]. From sourcing the raw materials to manufacturing and maintenance, modern EVs produce just half of the GHG emissions over their lifetime compared to their average traditional counterparts [4]. Not only do EVs have lower GHGemissions but they also have good performance making them lucrative purchases. Some of the high-end EV models that came out in 2019 can travel between 300 to 600 km per charge [5]. High-capacity rechargeable batteries and lightweight materials are two of the most important factors behind the success of modern EVs [6; 7]. Unlike lead-acid based batteries in traditional cars that are mainly used for starting up the engines, batteries in EVs have more functions and require additional protection from tempering and accidents. Increasing the adoption of EVs everywhere means that there are more chances of EVs being involved in crashes, and these new types of batteries can pose different types of risks. Reports indicate that some lithium-ion batteries can spontaneously burst into flames while others can catch fire in accident causing fatalities [8; 9]. Hence, more research and development are needed in improving protection systems for batteries in EVs as they come with new and unique challenges. EVs can be of different types such as a plug-in hybrid electric vehicle (PHEV), range-extended electric vehicle (REEV), battery electric vehicle (BEV), and fuel cell electric vehicle (FCEV) [10; 11; 12]. The PHEVs and the REEVs have combustion engines along with electric motors, while the BEVs and FCEVs can run without a combustion engine. Based on the load-carrying capacity, the required speed, and the driving conditions among other factors, these vehicles can have different battery capacities and other design parameters. For a long time, the automobile depended on lead-acid based batteries. However, these batteries are too heavy to be used in powering long-range consumer vehicles. Today, some EVs use nickel-metal hydride (Ni-MH) based batteries, while most other EVs use lithium-ion based batteries as the de facto power source [13]. Typically, the batteries are packed together into modules [6]. Power consumption for typical consumer EVs can vary between 11 to 15 kWh/100 km [14]. Batteries in EVs are placed either at the center of the car or at the rear as illustrated in Figure 1[15]. The battery modules are protected through multi-layer casings (Figure 2). Typically, there is an aluminum underbody protection, aluminum extrusion ring for crash absorption, steel tub with flanges and inner walls for the battery modules, and a steel housing cover [16]. Battery casings are designed taking into account the different challenges related to the safety, thermal runway, electric discharge, and mechanical vibrations [17; 18]. The focus of this study is limited to the aluminum crash structure as shown in Figure 2. The aim is to replace this crash structure with cellular structures. Most automobiles instead use tubular structures for crashworthiness [19; 20; 21; 22; 23]. With EVs becoming more popular, lightweight metal cellular structures are regaining interest as promising materials for the crashworthiness of the battery housing. Figure 1: Illustration of an electric vehicle with the battery installed at the rear [15]. Metallic cellular structured materials are basically material with pores and have a density less than the material bulk density, depending on the porosity levels [24].