Full-field characterisation of oxide-oxide ceramic-matrix composites using X-ray computed micro-tomography and digital volume correlation under load at high temperatures

In situ synchrotron X-ray computed micro-tomography and digital volume correlation (DVC) were utilised to understand the failure mechanisms at room temperature and 1050 degrees C of two Nextel (TM) 720/alumina oxide-oxide ceramic-matrix composites (CMCs), termed materials A and B, sintered respectively at 1200 degrees C and similar to 1250 degrees C. At both test temperatures, three-point-bending strengths were similar to 55-58 MPa for material A and similar to 94-100 MPa for material B. Damage was associated with three primary types of cracking modes: interfacial delamination, inclined cracks within fibre tows, opening of existing matrix shrinkage cracks. Material A exhibited higher shrinkage cracking, whereas material B displayed more pronounced diagonal matrix microcracking. At 1050 degrees C, both systems showed less microcracking but more pronounced delamination. Such damage characteristics were rationalised in terms of the corresponding 3D DVC displacement/strain fields. Specifically, global DVC was utilised and maximum principal strain locations prior to failure, which varied from 0.005 to 0.01, correlated well to the fracture initiation sites. Further, abrupt positive to negative transitions of shear strain components were observed and were attributed to the different bonding strengths between 0 degrees/90 degrees fibres and the matrix. The current study demonstrates that in situ high-temperature tomography/DVC is a powerful method for studying the deformation and fracture of oxide-oxide CMCs. (C) 2021 The Authors. Published by Elsevier Ltd.