## 1 Introduction
presented a work where the main aim was to create a model which was meant to serve as a platform for iterative modifications of a foot prosthesis design by simulating a standardized dynamic mechanical test (ISO/TS 16955), wherein the foot performed a complete roll-over [16]. Table 2 summarizes the literature on the use of FEA for the design and analysis of prosthetic feet characterized by the elastic elements in composite materials. So far, state-of-the-art analyses show that the literature approaches relatively to prosthetic foot design are not based on a systematic methodology. This work aims to introduce a methodology that helps the designer develop their initial idea of a foot prosthesis by combining ergonomic and functional requirements with stiffness and strength requirements and choosing the most suitable materials. In the methodology, two different FE models of the foot prosthesis were built during the first phase (_design phase_, Section 3.1). The first FE model was two-dimensional (2D FE model) and considered the foot prosthesis only in the sagittal plane (Section 3.1.1). The second FE model was three-dimensional (3D FE model); the profile shapes of the elastic elements in the sagittal plane were the ones optimized in the 2D FE analysis (Section 3.1.2). In previously published studies, 3D FEAs have been carried out to perform stiffness optimization of the energy-storing parts [12; 13; 16]. However, when the analysis aims to study the effect of \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Manufacturer** & **Model** & **Website (Access Date)** & **County** \\ \hline Blatchford & Elan & www.blatchford.co.uk (1 November 2021) & UK \\ Blatchford & Elan\({}^{IC}\) & www.blatchford.co.uk (1 November 2021) & UK \\ Filhauer & Raize & www.filhauer.com (1 November 2021) & USA \\ Freedom-Innovations & Kinnex 2.0 & www.freedom-innovations.com (1 November 2021) & USA \\ Ossur & Proprio Foot & www.ossur.com (1 November 2021) & Iceland \\ Ottobock & Empower & www.ottobock.com (1 November 2021) & Germany \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Commercial active and semi-active foot prostheses with composite elastic foot. varying many geometric parameters on the behavior of the prosthesis, 3D FEA is time-consuming. Therefore, the 2D FE model built in the present work is aimed to be used as a tool to determine the effect of the geometry variation on the foot prosthesis behavior in the sagittal plane, reducing the computation time. The 3D FE model was built to perform a more detailed structural analysis, aiming to optimize the stiffness and the strength of the prosthetic device. The optimization was carried out by determining the final material properties to use; therefore, the lamination sequence of the layers of CFRP was used to build the elastic elements. In previous studies, the composite elastic elements have been simplified by simulating them with isotropic properties in 3D FEAs [12; 13; 14]. Simplifying the laminate composites as isotropic materials could lead to high approximated results, both in terms of stiffness and strength points of view. In Section 3.1.2, a guideline to build the 3D FE model is given, also specifying the constraints and the load conditions of the equivalent of ISO 10328 static tests. The second phase of the present methodology is the FE model validations. The 2D and 3D FE models and analyses were subsequently subjected to validation through an ISO 10328-inspired static test (_mechanical test phase_, see Section 3.2). The _design phase_ was carried out by optimizing the stiffness of the ESR foot with static loads; thus, the _validation phase_ was carried out with static tests. Nevertheless, the foot prostheses were loaded dynamically during use. Therefore, it is crucial to understand the behavior of the foot prostheses when they are under dynamic conditions. Two approaches to verify the functionality and study prosthetic feet's behavior when subjected to dynamic loads are proposed.