ABSTRACTLightweight porous metallic materials are generally created through specialized processing techniques. Their unique structure gives these materials interesting properties which allow them to be used in diverse structural and insulation applications. In particular, highly porous Al structures (Al foams) have been used in aircraft components and sound insulation; however due to the difficulty in processing and random nature of the foams, they are not well understood and thus they have not yet been utilized to their full potential. The objective of this project was to determine whether a relationship exists between the relative density (porous density/bulk density) and the mechanical properties of porous Al structures. For this purpose, a combination of computer simulations and experiments was pursued to better understand possible relationships. A Finite Element Method (FEM)-based software, COMSOL Multiphysics 4.3, was used to model the structure and to simulate the mechanical behavior of porous Al structures under compressive loads ranging from 1-100 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 performed using the Instron Universal Testing Machine (IUTM) on porous Al specimens created via a computernumerically-controlled (CNC) mill. CES EduPack software, a materials design program, was also used to estimate the mechanical properties of porous Al and 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 solid Al samples tested. The main results from experiments were that the Young’s moduli (E) for porous Al samples (55.8% relative density) were 15.9-16.6 GPa depending on pore diameter, which is in good agreement with the CES EduPack predictions; while the compressive strengths (σc) were 155-185 MPa, higher than those predicted by CES EduPack. The results from the FEM simulations using 3D models (55.8% relative density) revealed the onset of yielding at 13.5-14.0 MPa, which correlates well with CES EduPack data. Overall results indicated that a combination of experiments and FEM simulations can be used to calculate structure-property relationships and to predict yielding and failure, which may help in the pursuit of simulation-based design of metallic foams. In the future, more robust modeling and simulation techniques will be explored, as well as investigating closed cell Al foams and different porous geometries (nm to micron). This study can help to improve the current methods of characterizing porous materials and enhance knowledge about their properties for alternative energy applications, while promoting their design through integrated approaches.
An interface-enriched generalized finite element method for level set-based topology optimization
