Experimental and numerical study of high density filter textiles to determine permeability and retention properties under tensile stress

Weave and construction parameters of high density woven filter fabrics influence the pore morphology, which directly affects the functional properties such as permeability and retention. It is established that the morphology of multifilament woven filter fabrics comprises of meso and micro pores and, furthermore, their permeability can be tailored within suitable limits by adjusting the weaving machine, weave pattern and yarn type. It is known that the pore morphology will change due to mechanical loads, which occur during use, for instance. First, the change in morphology of the meso and micro structure is due to the transversal contraction of the yarns. Second, it changes since the overall textile structure deforms. This leads to a change of permeability and retention properties. In this work, we present a comparative experimental and numerical study to reveal the change of permeability and barrier properties of filter fabrics under tensile stress. Fabrics with different densities were used to gather data about how mechanical strain affects the pore morphology. The mechanical stresses occurring in the fabric during use and their effect on the change in pore morphology were tested and evaluated in the laboratory using a Zwick brand tensile testing machine. The analysis of pore morphology encompassed physical (flow porometer) and optical methods (microtome sections and image analysis). The pore size distribution was analyzed using a flow porometer PSM 165 (Topas GmbH, Germany) before uniaxial and biaxial, cyclic mechanical stress loads. The evaluated physical and geometrical parameters of the pore morphology serve as input for the numerical modeling and simulation of change of pore morphology under load, and for the modeling and simulation of multi-phase hydrodynamic properties (permeability and particle retention) of filter fabrics. We used the modules WeaveGeo, FeelMath and FilterDict of the simulation software GeoDict to perform the micro structure generation, the simulation of the tensile stress deformation and the computation of the filtration properties of undeformed and deformed filter media, respectively. The experimental and numerical results are compared in a qualitative and quantitative way giving a keen insight into the mechanisms at work.