Characterization and modeling of the mechanical properties of wound oxide ceramic composites

Kurzfassung

In the present work, an oxide/oxide Ceramic Matrix Composite WHIPOXTM (Wound Highly Porous Oxide Ceramic) that was manufactured via the filament winding technique was investigated. The aim of the work was the characterization and modeling of the mechanical properties of wound oxide ceramic composites with varied fiber orientations. For this purpose, the characteristics of a virtual equivalent unidirectional layer (UD-layer) were calculated and applied through the Inverse Laminate Theory and modified Tsai-Wu failure criterion. All modeling approaches developed in this study are dependent on experimental determination and microstructure analysis. The mechanical properties of the investigated material in different wound orientations, including initial stiffness, strength, strain, elastic and inelastic behavior, were completely evaluated with in-plane experimental tests at room temperature. Based on the microstructural analysis through Micro Computed Tomography, the modeling of the properties of WHIPOXTM was divided into two classes: WHIPOXTM with matrix cracks (WC) and WHIPOXTM without matrix cracks (NC). Due to the lack of the required matrix and fiber properties within the composite and by the unavailable representative characteristics of CMC UD-materials, the traditional modeling methods and classic failure criterion cannot be directly adapted to describe the material behavior of wound CMCs. Therefore, advanced modeling approaches with virtual equivalent UD-layer properties are created for the evaluation and prediction of the material properties of the investigated material WHIPOXTM. As the core component of the modeling chain, complete material properties of the equivalent UD-layer were calculated and evaluated: elastic properties through the Inverse Laminate Theory; strength properties by fitting different test results to modified Tsai-Wu criterion; failure strain using the inelastic deformation behavior factor Δ. All the values are discussed and calculated with consideration given to different microstructures with or without matrix cracks. Through the stacking of these equivalent UD-layers with any desired fiber orientation, e.g. non-orthogonal, orthogonal and asymmetrical (off-axis), an equivalent layered composite is created and its material constants can be predicted by using the modified stiffness matrix. In order to predict the mechanical properties with more accuracy, particular features of the investigated materials have to be taken into consideration. For the investigated composite WHIPOXTM, four distinctive features are implemented in the modeling approaches: identification of inhomogeneity of the investigated plate; interaction between failure strength and strain through inelastic deformation; division of material modeling groups based on the analysis of microstructure; update of analytical model of different batches with inhomogeneities created due to the manufacturing process. Based on the good correlation between the experiments and the modeling results, it can be shown that modeling approaches factoring in the above mentioned particular material features allow a very accurate prediction of the in-plane mechanical properties for CMC laminates. The present work has identified a general modus operandi going from experimental determination and microstructure analysis to the prediction of the mechanical behavior of wound CMCs with varied fiber orientations. The results of this work are of great value for the future design and development of this class of composites. In this way the application of CMC-components in new fields like aerospace and civil engineering may be enhanced.