37 Research Summary: Investigation of the Representative Volume Element in Fibrous Porous Systems

Faculty Mentor: Pania Newell (Mechanical Engineering, University of Utah)

Fibrous porous materials consist of networks of fibers that are intertwined through weaving, knitting, or bonding, creating a structure with interconnected pores that facilitate the transport of gases and liquids. The COVID-19 pandemic has caused a discussion of these materials to become highly relevant in the context of medical masks, since they are made of fibrous materials. Medical masks are subject to tensile loading throughout their use, which has a significant impact on their longevity and functionality. Being able to simulate fibers under such mechanical loading is integral to improving their design. Fibrous porous materials are highly random and anisotropic, however, which causes a numerical analysis of their properties to be very challenging. Simulations are most efficient when the sample cell is the minimum possible size while still possessing the macroscopic properties of the material– such a sample is called a representative volume element (RVE). We designed a computational framework for analyzing fibrous porous RVEs based on the finite element method. Using this framework, we conducted a parametric analysis in which we found the influence of fiber diameter, fiber cross sectional shape, and RVE size on the mechanical properties of various RVEs in an idealistic, but useful scenario consisting of polypropylene fibers that are orthogonally intersected within cubic boundaries. To help isolate the effect of each of the parameters of interest on the stiffness properties of the material, we created a set of RVEs with constant porosity. Once an appropriate RVE size was determined, we found that the stiffness of the samples increased as the cross-sectional shape progressed from a triangle to other regular polygons with an increasing number of sides largely due to the increases in intersection volume between fibers. We also found that increases in fiber diameter decreased the material stiffness due to the increased randomness created by the requirement of a constant porosity between RVEs. Ultimately, the project provides a valuable tool for designing and optimizing fibrous porous materials in various engineering applications.