Density-Graded Cellular Solids: Mechanics, Fabrication, and Applications

Cellular solids have gained extensive popularity in different areas of engineering due to their unique physical and mechanical properties. Recent advancements in manufacturing technologies have led to the development of cellular solids with highly controllable microstructures and properties modulated for multiple functionalities at low structural weights. The concept of density gradation in cellular solids has recently gained attention due to its potentials in opening new doors to the development of lightweight structures that offer optimal physical and mechanical properties without compromising their favorable characteristics. Herein, a comprehensive insight into the fundamental concepts, fabrication, and current and potential applications of density-graded cellular solids in various areas of science and engineering is provided. Cellular solids are broadly classified into two main categories: foams and lattice structures. An overview of the fundamental concepts in each category is presented, followed by details on the characterization approaches and some of the most novel processing techniques utilized in fabricating the structures. The uses of density-graded structures in load-bearing, acoustic, and biomedical applications are highlighted. The state of the art in each category and the current trends in application-specific optimization of density-graded structures are discussed. The review concludes with an outlook of the future directions in this exciting field.