Lightweight porous foams have been of particular interest in recent years, since they have a very unique set of properties which can be significantly different from their solid parent materials. These properties arise from their random porous structure which is generated through specialized processing techniques. Their unique structure gives these materials interesting properties which allow them to be used in diverse applications. In particular, highly porous Al foams have been used in aircraft components and sound insulation; however due to the difficulty in processing and the random nature of the foams, they are not well understood and thus have not yet been utilized to their full potential. The objective of this study was to integrate experiments and simulations to determine whether a relationship exists between the relative density (porous density/bulk density) and the mechanical properties of open-cell Al foams. Compression experiments were performed using an Instron Universal Testing Machine (IUTM) on ERG Duocel open-cell Al foams with 5.8% relative density, with compressive loads ranging from 0-6 MPa. Foam models were generated using a combination of an open source code, Voro++, and MATLAB. A Finite Element Method (FEM)-based software, COMSOL Multiphysics 4.3, was used to simulate the mechanical behavior of Al foam structures under compressive loads ranging from 0-2 MPa. From these simulated structures, the maximum von Mises stress, volumetric strain, and other properties were calculated. These simulation results were compared against data from compression experiments. CES EduPack software, a materials design program, was also used to estimate the mechanical properties of open-cell foams for values not available experimentally, and for comparison purposes. This program allowed for accurate prediction of the mechanical properties for a given percent density foam, and also provided a baseline for the Al foam samples tested via the IUTM method. Predicted results from CES EduPack indicate that a 5.8% relative density foam will have a Young’s Modulus of 0.02-0.92 GPa while its compressive strength will be 0.34-3.37 MPa. Overall results revealed a relationship between pores per inch and selected mechanical properties of Al foams. The methods developed in this study can be used to efficiently generate open-cell foam models, and to combine experiments and simulations to calculate structure-property relationships and predict yielding and failure, which may help in the pursuit of simulation-based design of metallic foams. This study can help to improve the current methods of characterizing foams and porous materials, and enhance knowledge about theirproperties for novel applications.

Organic composite materials can be readily found in our daily life, such as plywood used in construction industry and bamboo composites as indoor and outdoor flooring materials. These organic composite material systems consist of cellulose fibers bonded with each other through adhesives, leading to a bonded system with a gradient structure that possesses a unique structural behavior which has a great potential to be used as load-bearing building materials. In view of the manufacturing process of such composite material systems and the structure in-between the cellulose fibers and the adhesives, the interfacial adhesion of such systems at multiscale would play a major role in determining their capability in load-bearing structural applications. In this research work, the interface between cellulose fiber and phenol-formaldehyde adhesive is chosen as a representative of the organic composite material system and molecular dynamics simulation is used for quantifying their mechanical properties and the corresponding interfacial adhesion. Here we demonstrate that cellulose fiber has a strong affinity to a phenol-formaldehyde adhesive with an adhesion energy of 151.3 mJ/m2. To the best of our knowledge, this is the first study that reports this material property for cellulose-adhesive system, which is three times larger than that between the gecko foot’s hair and the mineral surface. The mechanism of such strong adhesion is due to the possible hydrogen bonding between the cellulose and the adhesive.

Topology optimization is a systematic, computational approach to the design of structure, defined as the layout of materials (and pores) across a domain. Typically employed at the component-level scale, topology optimization is increasingly being used to design the architecture of high performance materials. The resulting design problem is posed as an optimization problem with governing unit cell and upscaling mechanics embedded in the formulation, and solved with formal mathematical programming. This paper will describe recent advances in topology optimization, including incorporation of manufacturing processes and objectives governed by nonlinear mechanics and multiple physics, and demonstrate their application to the design of cellular materials. Optimized material architectures are shown to (computationally) approach theoretical bounds when available, and can be used to generate estimations of bounds when such bounds are unknown.