Shear characterisation of viscous woven textile composites: a comparison between picture frame and bias extension experiments

An investigation of the testing methods employed in characterising the forming of woven composite materials has been performed. An energy argument is presented that shows that picture frame results should be normalised with respect to a characteristic length rather than area. A novel normalisation procedure for bias extension testing is proposed that allows direct comparison of bias extension and picture frame results. The investigation illustrates how bias extension and picture frame tests can be used together to perform reliable characterisation of a given material. Furthermore, a convenient method of determining a material’s locking angle using bias extension testing is outlined. Two different materials have been considered in the investigation, a 5-harness satin woven carbon/epoxy prepreg composite and a 2 × 2 twill woven glass/polypropylene thermoplastic composite. The suitability of the normalisation procedure with respect to each of these materials is discussed and the relative merits of each testing method are compared