Materials 2021, 14, 6645. https://doi.org/10.3390/ma14216645 www.mdpi.com/journal/materials Article Efficient Design of Thin Wall Seating Made of a Single Piece of Heavy-Duty Corrugated Cardboard Berta Suarez *, Luisa M. Muneta, Gregorio Romero and Juan D. Sanz-Bobi Mechanical Engineering Department, Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid, C/José Gutiérrez Abascal, 2, 28006 Madrid, Spain; luisa.mtzmuneta@upm.es (L.M.M.); gregorio.romero@upm.es (G.R.); juandedios.sanz@upm.es (J.D.S.-B.) * Correspondence: b.suarez@upm.es Abstract: Corrugated cardboard has waved cores with small flutes that prevent the use of detailed numerical models of whole structures. Many homogenization methods in the literature overcome this drawback by defining equivalent homogeneous plates with the same mechanical behaviour at a macro-mechanical scale. However, few homogenization works have considered complete struc- tures, focusing mainly on beams or plates. For the first time, this study explores the application of homogenization approaches to larger structures as an aid in their design process. We also consid- ered triple-wall boards rather than single- and double-wall configurations commonly addressed in the literature. To this end, we adapted the homogenization methods proposed by Talbi and Duong to analyze thin-walled stools made of triple-wall corrugated cardboard. Using a progressive design process, we performed an efficient stool design by removing material zones with lower stresses, with 35% less material, 35% lower vertical deflections, and 66% lower stresses than the initial design. Unlike other corrugated cardboard stools, this design comprises just one folded piece instead of three, thus saving storage space. These results demonstrate the utility of homogenization techniques as an aid in the design process of whole structures made of corrugated cardboard. Further research will consider buckling analysis. Keywords: composite sandwich structures; thin-walled structures; anisotropic material; corrugated core; homogenization approach; first-order shear deformation theory; FSDT; FEM simulation; finite element analysis; design process 1. Introduction Finite element analysis (FEA) greatly facilitates the design process of many products, avoiding the construction of failed prototypes. Concerning products made of corrugated cardboard, this advantage is not so evident since it is inexpensive and easy to handle, so that prototypes have low economic and time costs. In this paper, the authors aim to show that FEA can also be very useful when designing products made with this material. The main advantage is not to avoid prototyping, but to guide the design stages towards more efficient solutions. Likewise, it could help to choose the most suitable type of cardboard for each product, avoiding the need to gather an extensive assortment of materials to test different prototypes. In this work, we applied FEA to a piece of furniture made of corrugated cardboard to achieve a more efficient design. To define the material properties, we adapted the ho- mogenization methods proposed by Talbi [1] and Duong [2], as described in Section 2.3. Conventional furniture designs often rely on traditional knowledge in handicraft manufacturing. Moreover, their structural elements are often intentionally oversized. However, FEA becomes an essential tool when dealing with unconventional furniture made of thin-wall structural elements. In [3–9], we can find some studies on the FEA of wood furniture. Other previous research studies also considered other materials, such as Citation: Suarez, B.; Muneta, L.M.; Romero, G.; Sanz-Bobi, J.D. Efficient Design of Thin Wall Seating Made of a Single Piece of Heavy-Duty Corrugated Cardboard. Materials 2021, 14, 6645. https://doi.org/10.3390/ma14216645 Academic Editors: Tomasz Garbowski, Tomasz Gajewski and Jakub Krzysztof Grabski Received: 18 September 2021 Accepted: 30 October 2021 Published: 4 November 2021 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and insti- tutional affiliations. Copyright: © 2021 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).