J integral and local strain energy density approach to characterize the cracks in anisotropic hyperelastic skin type composite materials

It has been proposed that the response of soft tissues and skin type materials critically depends on the orientation and re-orientation of reinforcing fiber. Here, we quantify the effect of fiber orientation on the mechanical and fracture properties of anisotropic hyperelastic glass fiber (GF)/polydimethylsiloxane (PDMS) composites through a unified experimental and computational analysis. Experimental results show that the tensile strength and fracture toughness of skin type materials depends on the initial orientation of fiber families and is maximum for 0-90 fiber orientation. The re-orientation of fibers under tensile loading is experimentally demonstrated. The experimental findings are well complimented by the finite element (FE) simulations performed using bilinear strain stiffening fiber and matrix (BLFM) material model for soft tissues. The material model parameters are obtained by fitting the experimental data for a meaningful comparison. It is observed that fiber rotation along the loading direction indeed enhances the resistance to crack growth in skin type materials. The size of process zone (R-C) ahead of the crack tip and relative contribution of anisotropic energy is characterized using J integral and average strain energy density (ASED) criteria. The R-C and anisotropic energy contribution (phi(aniso-avg)/phi(avg)) depends on the fiber orientation with higher values for 0-90 fiber orientation. The larger process zone enhances the fracture toughness for 0-90 orientation in comparison to other orientations. Moreover, R-C and phi(aniso-avg)/phi(avg) are found to be independent of initial crack length and therefore, they can be considered as material parameters for a given fiber orientation. The findings of the present investigations may be used to explore GF/PDMS composite as a possible candidate for soft actuator and bio-medical applications with enhanced toughness.