A method for the approximation of non-uniform fiber misalignment in textile composites using picture frame test

Due to the complexity of woven structures, the assumption of perfectly aligned fibers for some textile composites is unrealistic. In more sophisticated material models, therefore, possible fiber misalignment is accounted for. On the other hand, non-uniformity of the misalignment distribution in a fabric may become a second but important problem. This paper presents an inverse methodology from which a reliable approximation of the non-uniform misalignment state in a woven fabric may be made. Basically, the approximation requires a representative constitutive model and a set of picture frame tests where fiber misalignment plays a key role. Uniaxial and bias-extension tests are also used to identify the constitutive model parameters independently. The detail procedure is shown for a typical 2 × 2 twill weave fabric as an illustrative example. Results are discussed and compared to other approaches to reveal the benefits and limitations of the proposed method.