On the relationship between shear angle and wrinkling of textile composite preforms

As a result of the increased use of composite materials in structural as well as non-structural applications, the need for a better understanding of the mechanics of fibre preforms during forming operations is imperative. During processes that involve automated moulding or forming of composite parts, wrinkling is one of the most common flaws, often leading to unexpected failures. A number of kinematic models have been developed to predict the conformability and wrinkling of fabrics. However, these have the shortcoming that they only deal with a single fabric layer, and in order to predict wrinkling they need to have the locking angle (determined experimentally) as an input. This paper presents the results of a study that investigated the relationship between the shear angle and wrinkling in a single fabric layer and a brief extension of the findings to multi-layer set-ups. A number of fabric parameters (friction, tow size and spacing) were related to the locking angle. A model to predict a lower bound for the locking angle (using pin-joint theory) is also presented, along with a discussion of factors that support the development of a combined mechanistic kinematic model.