Ceramic Matrix Composites: CMC II: Foreign Object Damage/NDE
Sponsored by: ACerS Engineering Ceramics Division
Program Organizers: Narottam Bansal, NASA Glenn Research Center; Sung Choi, Naval Air Systems Command; Jacques Lamon, CNRS
Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 16
Location: MS&T Virtual
Session Chair: Sung Choi, NAVAIR
2:00 PM Invited
In Situ Observation of Crack Formation in CMCs Using X-ray Computed Tomography up to 1200°C: Dong Liu1; Jon Ell2; Harold Barnard2; Stefan Reh3; Robert Ritchie2; 1University of Bristol; 2Lawrence Berkeley National Laboratory; 3DLR
A unique device permits in situ loading with real time X-ray computed tomography (XCT) imaging was used to study the deformation and fracture of a DLR WHIPOX CMC over a range of temperatures (RT, 900°C, 1050°C&1200°C). XCT scans were taken at multiple loading steps to capture the crack formation and propagation. The measured flexural strength was consistent with ex situ uniaxial tension and bending tests indicating the size of the samples used was adequate. The RT failure comprised of diffused fibre breakage accompanied by fibre/matrix delamination linking up existing pores. At 1050&1200°C, fibre/matrix delamination became the primary failure mechanism. Digital volume correlation (both local and global approaches) was used to derive the 3D displacement field and stress-strain behavior were extracted. Finally, residual stresses mapping in the fibre and matrix were conducted and the relaxation of these stresses was considered to have contributed to the high temperature delamination.
2:40 PM
Quantifying Damage Mechanisms by Observing Damage Evolution in SiC/SiC Composites using Micro-CT Techniques: Ashley Hilmas1; Kathleen Sevener2; John Halloran2; 1Air Force Research Lab; 2University of Michigan
In-situ mechanical testing of unidirectional and cross-ply SiC/SiC composites was performed at the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory. Composite samples were loaded at room temperature and imaged at incremental loads through fracture. The tomography images were used to observe the damage evolution throughout the volume of the specimens and quantify damage such as the onset of matrix cracking, subsequent matrix cracking and fiber fragmentation that occurred at each imaged stress increment. The damage was compared to well-known mechanical models and parameters such as debond length, onset of matrix cracking, and matrix crack spacing were evaluated. Comparisons were also made between the damage evolution observed in the unidirectional specimens and the cross-ply specimens.