Variation of PEEK matrix crystallinity in APC-2 composite subjected to large shearing deformations

This paper presents an experimental investigation of matrix cracking and mi crostructure variations in order to evaluate their relative contributions t o the shear stiffness loss of AS4/PEEK composite material subjected to larg e shear deformations. Specimen observations by X-radiography allow us to ch aracterize the matrix cracking, and measurements of the matrix crystallinit y at different levels of loading give information on the microstructure alt eration of the PEEK matrix. These measurements have been performed by using three different methods that have been compared: wide-angle X-ray scatteri ng (WAXS), conventional differential scanning calorimetry (DSC) and modulat ed differential scanning calorimetry (MDSC). The relationship between the m atrix cracking development, the change in the PEEK crystallinity and the se cant shear stiffness variation is discussed. This study shows that, neither the presence of inter- or intra-ply cracks nor the decrease of the PEEK ma trix crystallinity degree, are sufficient to induce the significant loss of the ply shear stiffness measured in [+/- 45](2s) APC-2 laminates tested in tension. (C) 2000 Elsevier Science Ltd. All rights reserved.