Carbon composites based on multiaxial multiply stitched preforms. Part 3: Biaxial tension, picture frame and compression tests of the preforms

Deformability of bi- and quadri-axial multi-axial multiply stitched preforms is studied in biaxial tension, shear (picture frame test) and compression. The results complement KES-F measurements in the low load range, reported in the Part 2 of the series (Compos A, 34, 2003, 359-70). The biaxial tension tests reveal a strong interrelation between the two directions of tension in the case of tension in bias direction (relative to the fibres) and independence of deformation in two directions for tension in fibre direction. Non-linearity of the initial part of the tensile diagram due to fibre misalignment is demonstrated. The picture frame test is combined with full-field optical measurements of the shear strain field, allowing true registration of the fabric shear angle (which differs from the shear angle of the frame). Difference between the shear behaviour in different directions relative to the stitching is shown. Thickness is measured for one of the sheared fabrics. Compression tests reveal a high compressibility of the preforms (up to 60%) and a limited nesting effect for compression of the laminates. The compression tests are done also on sheared fabrics.