PARAMETRIC STUDY ONEFFECTIVE YOUNG'S MODULUS AND POISSON’S RATIOOF OPEN-CELL CARBON FOAM

摘要

The emerging ultralightweight material, carbon foam, was modeled with three-dimensionalmicrostructures to develop a basic understanding of the performance of open-cell foam materials.Because of the randomness and complexity of the microstructure of the carbon foam, representativecell ligaments were first characterized in detail at the microstructural level. In order to implement theinhomogeneous and anisotropic nature of material properties in the foam ligaments, we made the firstattempt to use a finite element method to achieve such variation along the ligaments as well as at anodal point where the ligaments meet.We observed that the effective elastic properties of the foams were dominated by the bending modeassociated with shear deformation. The effective Young’s modulus of the foam was stronglyinfluenced by the ligament moduli, but was hardly influenced by the ligament Poisson’s ratio. Theeffective Poisson’s ratio of the foam was practically independent of the ligament Young’s modulus,but dependent on the ligament Poisson’s ratio.We performed a parametric study varying the orthotropic properties in different directions in theligaments to assess how the microscopic properties in the ligaments affected the macroscopic bulkbehavior. The prediction indicated that the effective Young’s modulus of the carbon foam was moredependent on the transverse Young’s modulus and the shear moduli of the foam ligaments, than onthe ligament longitudinal Young’s modulus. The parametric study also indicated that the effectiveYoung’s modulus could be significantly improved by increasing the ligament modulus in its midlength,but nearly invariant with that at the nodal point where the ligaments join. Therefore, tooptimize bulk moduli of carbon foam, appropriate processing schemes toward improving modulus inthe middle section of the ligaments rather than at the nodal points are highly desirable.