Crack growth in planar elastic fiber materials

Particularly attention is here given to crack growth in opening mode in fiber networks. Low- and high-density cellulose fiber materials are used in synchrotron X-ray microtomography tensile experiments to illustrate phenomena arising during crack growth. To capture the observed fundamental mechanisms, significantly different from classical continua, a mechanical model based on a strong nonlocal theory is applied in which an intrinsic length reflects a characteristic length of the microstructure. Nonlocal stress and strain tensor fields are estimated by analytical solutions on closed form to a modified inhomogeneous Helmholtz equation using LEFM crack-tip fields as source terms. Justified by experimental observations, physical requirements of finite stresses and strains at infinity and at the tip are applied to remove singularities. The near-tip nonlocal hoop stress field is used to estimate crack growth directions and sizes of fracture process zones. Experimental observations are shown to be qualitatively well in accordance with numerical predictions, which justifies the adopted approach.