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The fatigue damage mechanisms of 3D woven composites are very complex. In this work the tension–compression (T-C) fatigue damage evolution of 3D woven composites is investigated using a multi-scale method. To avoid the buckling failure during the T-C fatigue tests, a novel anti-buckling device is designed. The authors combine the macro damage information (i.e., axial stiffness and surface temperature) and the meso-damage information (i.e., detection results by synchrotron radiation computed tomography (SRCT)) to investigate the fatigue damage evolution. The results show that the T-C fatigue process can be divided into two stages. The stiffness decreases slowly in a linear form in Stage I, and then decreases rapidly to final failure in Stage II. Most of the fatigue damage occurs in Stage II. The SRCT results can reveal the damage modes in either fatigue stage, in which the warp yarn breakage is the critical damage mode.

In this study, the laser repairing (LR) method is applied to 12Cr12Mo stainless steel, and the corresponding microstructural evolution, texture characteristic, and hardness variation are investigated. A 50/50 uniaxial tensile-test is conducted, and the mechanical failure mechanism is investigated using scanning electron microscope and transmission electron microscopy. The results show that the microstructure consists mainly of martensite and tiny M23C6 carbide particles in the deposited zone (DZ), while the substrate contains tempered martensite and coarse M23C6 carbide. The high laser-power generates a cubic texture in the DZ, while the substrate maintains a texture-free matrix. From the substrate to the DZ, the hardness increases sharply at the fusion line and then decreases gradually along the building direction. The tensile-test result indicates that the overall mechanical properties of LRed 12Cr12Mo stainless steel are comparable to wrought parts. Moreover, the microvoid-coalescence fracture indicates good plasticity of the LRed samples. Using this approach, we successfully repaired a 17th-stage stator cascade of a gas turbine, which indicates that LR can be used for the type of steel investigated in this study.

The foundation of AVIC Commercial Aircraft Engine Company (ACAE) in Shanghai triggers the hot upsurge of the civil aircraft engine development and study in China. Air worthiness requirements of the engine emission brings the new challenge to the combustor research and design. With the motivation of design high performance and clean combustor, CFD is utilized as the powerful design approach. In this paper, Reynolds averaged resolve of Navier-Stokes (RANS) equations of reaction two-phase flow in an experimental low emission combustor are performed. The numerical approach uses an implicit compressible gas solver together with a Lagrangian liquid-phase tracking method and the extended coherent flamelet model for turbulence-combustion interaction. The NOx formation is modeled by the concept of post-processing, which resolves the NOx transport equation with the assumption of frozen temperature distribution. Both turbulence-combustion interaction model and NOx formation model are firstly evaluated by the comparison of experimental data published in open literatures of a lean direct injection (LDI) combustor. The test rig studied in this paper is called Low Emission Stirred Swirl (LESS) combustor, which is a two stage model combustor, fueled with liquid RP-3 kerosene and designed by Beijing University of Aeronautics and Astronautics (BUAA). The main stage of LESS combustor employs the principle of lean prevaporized and premixed (LPP) concept to reduce pollutant, and the pilot stage depends on a diffusion flame for flame stabilization. Detailed numerical results including of species distribution, turbulence performance and burning performance are qualitatively and quantitatively evaluated. Numerical prediction of NOx emission shows a good agreement with test data both at idle condition and full power condition of LESS combustor. Preliminary results of the flame structure are shown in this paper. The flame stabilization mechanism and NOx reduction effort are also discussed with in-depth analysis.