Failure analysis and engineering mechanics modeling methods of a stitched ceramic sandwich structure

Stitched ceramic sandwich structures attract much attention in the aerospace field due to their advantage of heat insulation/load-bearing integration. In this study, the industrial camera and strain gauges were applied to perform out-of-plane tensile, compressive, interlaminar shear and 4-point bending tests of a stitched sandwich structure. Different specimens were fixed on the corresponding fixtures of a universal testing machine, and the loading rates referred to related standards. The images were captured at 1 Hz and analyzed by digital image correlation method. Based on macroscopic properties and microscopic damage mechanisms, progressive damage analysis was conducted to simulate mechanical behaviors of the structure. The representative volume element model was established for tensile, compressive and shear simulations, and several full models were proposed for bending simulations based on different degrees of simplification. The experimental results indicate that: The stitched sandwich structure shows approximately linear macroscopic mechanical behaviors under out-of-plane tensile and interlaminar shear loads, but exhibits bilinear behaviors under out-of-plane compression and 4-point bending loads. Core-related damage typically occurs first under external load, including interface debonding between the core and panel, shear delamination, collapse of holes, and densification of matrix; the sutures is the main load-bearing constituent. The precise model can describe nonlinear and bilinear behaviors, and characterize the damage evolution of the sandwich structure. The simplified model without considering the sutures is able to simulate 4-point bending behavior efficiently and accurately. The research demonstrates that, sutures can be ignored when simulating 4-point bending behavior, while they (especially out of plane) are necessary for vibration analysis. The mechanical effect of constituents during loading should be fully considered in the finite element model simplification.