Experimental and numerical study of multi-scale tensile behaviors of Kevlar® 49 fabric

Kevlar (R) 49 fabrics have excellent performances such as high elastic modulus and high impact resistance, which are widely used in ballistic systems, aerospace, fabric reinforced composite materials and other fields. The present work studied the multi-scale mechanical behaviors of Kevlar (R) 49 in the forms of fiber, yarn and fabric subjected to uniaxial tension. The experimental results showed that the material mechanical properties are dependent on structural size scale and gage length of samples. The tensile strengths decrease with increasing gage length and structural size scale from fiber to yarn, and to fabric, and follow Weibull distribution by conducting statistical analysis, which is used to quantify the degree of variability in the tensile strengths of fiber and yarn with different gage lengths. At last, user-defined subroutines (UMAT) in ANSYS were implemented to simulate the tensile behaviors of single yarn and fabric by using the constitutive models of fiber and yarn, respectively, which considered their Weibull distribution in tensile strength. This probabilistic approach can simulate the multi-scale tensile behaviors of Kevlar (R) 49 accurately and reveal the mechanisms of deformation and failure process based on the various size scales. This approach is also applicable to study the multi-scale behaviors of other fabrics once their properties and Weibull parameters are determined.