## 1 Introduction
investigated the effects of using foam-filled sandwich panels on the energy absorption and impact resistance of rail vehicles. The results showed that polyurethane foam filling can significantly increase crushing strength and energy absorption capacity. However, the weight of the car body increased by only 2% [21]. Reducing the cost of composites while improving their properties remains an attractive motivation in the field of composite development [22]. Fiber Metal Laminates (FMLs) have shown significant potential for optimizing structures by combining metal sheets and Fiber-Reinforced Plastic (FRP) composite laminates to provide a range of benefits from each material group. Thus, FMLs offer an excellent opportunity for creating lightweight structures [23]. The properties and failure modes of FMLs were studied by [PERSON] et al. Figure 1: Components of the sandwich panel. They performed three-point bending tests to analyze the bending behavior of CARbon fiber-Reinforced composites/Aluminum Laminates (CAR-ALLs) with different composite/metal layer configurations [24]. [PERSON] et al. investigated the impact behavior of SiRALs (aluminum laminates reinforced with sisal fibers) and evaluated the influence of fiber orientation on performance [25]. Numerous studies have investigated the use of sandwich composite structures in railway [15; 16; 17; 18; 19; 20; 21]. However, in terms of weight and cost optimization of the train floor, few have attempted to provide an accurate analytical model that can offer the optimal configuration of honeycomb cores and face sheets from a variety of possible combinations to achieve the best trade-off between weight reduction and cost efficiency. In this study, we elaborate an integrated approach to make new contributions, as described below:  
1. Material selection: In this study, different types of aluminum (Al) honeycomb cores are used in combination with different combinations of Fiber Metal Laminates (FMLs) as face sheets. This particular combination of materials and structural components had not been investigated in the literature before. 2. Cost and weight optimization: The elaborated optimization procedure in this study focuses on weight and cost, since only a limited number of previous studies have investigated the relationship between weight and cost reduction simultaneously. 3. Flexible design: A wide range of design variables is used in our study to investigate a larger number of feasible designs and determine the optimal sandwich construction. 4. Structural integrity: The optimization method used in this study effectively satisfies the specified constraints on the strength of the sandwich structure and the behavior of the final sandwich structure. 5. New optimization algorithm: The application of the NCGA algorithm for the structural optimization of floors for high-speed trains represents a new contribution that is not represented in the literature. This highlights the ability of the NCGA algorithm to achieve optimal designs that balance weight reduction and cost efficiency. The paper is organized as follows: Section 2 provides a basic description of the investigated train floor, while Section 3 explains the materials used in the examined sandwich structures and their mechanical properties. The optimization problem and the mathematical models for objective functions, design constraints, and design variables are discussed in Section 4. Section 5 describes the creation of a finite element model for the optimal designs. The structural optimization results are presented in Section 6. Finally, Section 7 highlights the main conclusions of this study.