A new theory Is presented to predict the tensile behaviour of spun-bonded nonwoven fabrics from the knowledge of the stress-strain behaviour of its constituent fibers, their orientation angle distribution, the fabric's Poisson's ratio and their shear strains.

An experimental method based on video recording and image analysis is presented to characterize the lateral contraction of spunbonded nonwoven fabrics during uniaxial tensile deformation. A systematic study reports the effect of specimen dimensions on the nature of lateral contraction of a nonwoven fabric. Lateral contraction measure ments are made over the entire profile of the specimen, thus examining the validity of Saint Venant's principle to justify the assumption of homogeneous strain in the region of measurement. Some important observations are reported, which in future will influence the methodology of measuring transverse strains corresponding to applied longitudinal strains in a uniaxial test.

Deformation of a spunbonded nonwoven fabric specimen is extremely nonuniform during a uniaxial tensile test. Complex stress/strain fields are generated in the specimen due to the effect of the jaws, the nonlinear nature of deformation, and the low shear stiffness of the fabric, causing "necking" to take place in the unrestricted region. A finite element model is presented to model the nonuniform deformation of the fabric. Nonuniform stress/strain fields developing in the fabric during a uniaxial test are modeled for the first time. Data from representative tests are reported for comparison to the results. obtained with the model. The model correctly predicts the variation of Poisson's ratio with longitudinal strains. Unlike previous studies, correct boundary conditions and force equilibrium conditions are incorporated in the model. The important effects of fiber buckling and material nonlinearity are discussed.Uniaxial tensile testing is the most commonly used method for characterizing the tensile deformation of a nonwoven fabric. In current practice, a state of uniform stress and strain is assumed in the entire fabric in order to interpret the data from such experiments. For a linear isotropic material, the elffect of the end constraints is expected to vanish away from the jaws. However, in complex fibrous structures such as some nonwovens, unlike the linear elastic materials, deformation is extremely nonuniform. In such structures, for example, the lateral contraction of the specimen does not become constant at some distance away from the jaws, but increases gradually towards the center of the specimen, forming a &dquo;neck.&dquo; The nonlinear stress-strain behavior of the constituent fibers, the significant shear effects existing in a conventional uniaxial test, and the extremely low stiffness of the fabrics under compressive strains are some factors believed to be responsible for this behavior. In this paper, we take all these factors into account to correctly model nonuniform deformation of a fabric. We present analytical and experimental evidence to demonstrate that the stress and strain fields developing in a nonwoven. specimen are not uniform, and we formulate a finite element model to simulate the nonuniform development of stresses and strains in a fabric.

An analysis is presented to predict the biaxial tensile behavior of spun-bonded non woven fabrics using knowledge of the stress-strain behavior of their constituent fibers and their orientation angle distribution. Nonlinearity in fiber stress-strain behavior is considered in order to predict fabric stresses in the longitudinal and transverse direc tions under biaxial loading conditions. Only a special case of biaxial loading is con sidered in which the transverse strain is forced to be zero, i.e., strip biaxial loading conditions. Experimental results are obtained by evaluating four spunbonded fabrics on a Kawabata strip biaxial tester KES-G2 and are compared with the theoretical results.