Lei Li

Ni-based single-crystal superalloys (SX) turbine blades of aeroengines are inevitably damaged during using. Therefore, it is of great significance for commercial aeroengines with high economic requirements to repair SX turbine blades reasonably and continue to realize their value by Laser-Directed energy deposition (L-DED). The repairing of SX must maintain the epitaxial growth of single-crystal, so the microstructure adjustment and the inhibition of stray grains are important for the preparation of L-DED SX. In this work, the single channel monolayer and single channel five-layers SX have been prepared by L-DED. Based on the columnar transition to equiaxed theory (CET), the macroscopic temperature field simulations in the deposition processing and multiscale characterizations of deposition structure were used to analyze the formation and evolution mechanisms of unique precipitations and stray grains. Results shows that the element segregation results in the unique microstructure, include petal-shaped γ/γ′ eutectic and demarcation band with a thickness of single γ/γ′ eutectic. With the change of height at deposition region, dendritic orientation deviations affect the uniformity of element segregation in the CET region, and similar solid solution treatments under subsequent temperature cycling lead to the directional coarsening of the γ' phase and then produce γ/γ' eutectic bands, which manifest as grain boundaries at the mesoscale. At the same time, the formation of carbide and adjacent γ/γ′ eutectic leads to the misorientations between the dendrite core and the inter-dendrite zone, which also appears as stray grains at the mesoscopic scale. The revealed microstructure mechanism of stray grain formation contributes to the suppression of stray grains in the middle and bottom of the deposition region and promotes the application of L-DED technology in the repair of commercial aeroengine SX turbine blades.

Purpose: The purpose of this paper is to provide a comprehensive review of a non-contact full-field optical measurement technique known as digital image correlation (DIC).Design/methodology/approach: The approach of this review paper is to introduce the research pertaining to DIC. It comprehensively covers crucial facets including its principles, historical development, core challenges, current research status and practical applications. Additionally, it delves into unresolved issues and outlines future research objectives.Findings: The findings of this review encompass essential aspects of DIC, including core issues like the subpixel registration algorithm, camera calibration, measurement of surface deformation in 3D complex structures and applications in ultra-high-temperature settings. Additionally, the review presents the prevailing strategies for addressing these challenges, the most recent advancements in DIC applications across quasi-static, dynamic, ultra-high-temperature, large-scale and micro-scale engineering domains, along with key directions for future research endeavors.Originality/value: This review holds a substantial value as it furnishes a comprehensive and in-depth introduction to DIC, while also spotlighting its prospective applications.

Purpose: Sandwich structures with well-designed cellular cores exhibit superior shock resistance compared to monolithic structures of equal mass. This study aims to develop a comprehensive analytical model for predicting the dynamic response of cellular-core sandwich structures subjected to shock loading and investigate their application in protective design.Design/methodology/approach: First, an analytical model of a clamped sandwich beam for over-span shock loading was developed. In this model, the incident shock-wave reflection was considered, the clamped face sheets were simplified using two single-degree-of-freedom (SDOF) systems, the core was idealized using the rigid-perfectly-plastic-locking (RPPL) model in the thickness direction and simplified as an SDOF system in the span direction. The model was then evaluated using existing analytical models before being employed to design the sandwich-beam configurations for two typical engineering applications.Findings: The model effectively predicted the dynamic response of sandwich panels, especially when the shock-loading pulse shape was considered. The optimal compressive cellular-core strength increased with increasing peak pressure and shock-loading impulse. Neglecting the core tensile strength could result in an overestimation of the optimal compressive cellular-core strength.Originality/value: A new model was proposed and employed to optimally design clamped cellular-core sandwich-beam configurations subjected to shock loading.

This work presents an approach for sensitivity analysis of turbine cooling blade with surface thickness uncertainties, combining mesh deformation method, neural network model and multidisciplinary analysis. Normally, for even tiny shape changes, conventional geometry-based method failed easily during the auto-processing analysis. Therefore, mesh deformation method was utilized to capture the tiny size changes in the multidisciplinary analysis for both the fluid and the structure meshes. The neural network model is constructed by design of experiments to reduce the computational cost. Sensitivity analysis of the multidisciplinary system of blade is performed by numerical difference algorithm with the neural network model. Results showed that the proposed method was effective and practical in engineering.