《Article Title》: Dynamic quantitative deformation mapping of slip activities in NBSC superalloy using sampling moiré method

《Journal》: Chinese Journal of Aeronautics

《Client Institution》: Beihang University

《Product Used》: Ultra-high temperature tensile stage

This paper proposes an advanced grating-based method for discontinuous displacement field measurement, which deeply integrates the sampling moiré method (SMM) with a novel adaptive weighted least squares (AW-LS) phase unwrapping algorithm, solving the long-standing issue of error propagation in the measurement of discontinuous deformation fields such as cracks. The core innovation of the AW-LS algorithm lies in its ability to automatically construct a continuously data-driven weight matrix based on the variance of local phase gradients, adaptively identifying and isolating phase discontinuities in crack regions without manual intervention, while fully preserving high-quality deformation information from surrounding areas. Numerical simulations based on analytical solutions from linear elastic fracture mechanics validate the sub-pixel measurement accuracy of the method, with relative errors within 5% of the grating pitch. In the in-situ tensile experiment of nickel-based single crystal (NBSC) superalloy, the method quantitatively captured, for the first time, the full-field displacement evolution process from microcrack initiation at 853 MPa to final fracture at 978 MPa, with experimental errors below 10% of the grating pitch, providing a reliable optical metrology framework for fracture mechanics experimental research.

The realization of the above experiments was made possible by the critical support of the in-situ tensile testing stage from GoGo Instruments Technology (Shanghai). This device, used in conjunction with a digital optical microscope, forms a complete in-situ observation system capable of continuous real-time imaging of the specimen notch region without interrupting the loading process. Its synchronous symmetrical stretching mechanism ensures stable observation field of view throughout the loading process, while the built-in force-displacement sensor simultaneously records the engineering stress–strain curve, providing a reliable guarantee for accurate correspondence between displacement field evolution and loading state. Relying on the device’s ability to continuously capture the entire process from microcrack initiation to final fracture, the research team obtained a complete sequence of full-field displacement evolution, achieving the first quantitative characterization of discontinuous deformation fields in NBSC superalloy.

《Article Title》: Advanced grid method for discontinuous displacement field measurement

《Journal》: International Journal of Mechanical Sciences

《Client Institution》: Beihang University

《Product Used》: Ultra-high temperature tensile stage

For the first time, this paper employs the sampling moiré method (SMM) to perform dynamic quantitative deformation field measurement of slip activities during in-situ uniaxial tensile experiments on nickel-based single crystal (NBSC) superalloys. Microscale orthogonal gratings with a pitch of 6 μm were fabricated on the specimen surface, and grating images were continuously captured using a digital optical microscope, obtaining full-field strain and displacement data with high spatial and temporal resolution in the notch region. The results show that SMM achieves nanoscale displacement resolution (displacement field color scale range: ±1 μm). Before the appearance of slip traces, the method successfully predicted their precise initiation locations through local strain and displacement concentration regions. Subsequently, it quantitatively tracked the entire evolution process of slip bands from initiation at 637 MPa to continuous development up to 776 MPa, with peak strain accumulating to 12.39%. This approach overcomes the longstanding challenge in traditional HR-DIC methods of balancing high spatial resolution with high temporal resolution, providing a new experimental tool for studying microscopic plastic damage mechanisms in crystalline metals.

The dynamic continuous characterization capability of this study relies critically on the experimental conditions provided by the in-situ tensile testing stage from GoGo Instruments Technology (Shanghai). This device adopts a continuous uninterrupted loading mode combined with optical microscopy, eliminating the need to pause the experiment for SEM scanning imaging. This fundamentally avoids the interference of load holding on material deformation mechanisms, which is inherent in traditional interruptive experiments. It allows the optical microscope to acquire grating images in real time at a high frame rate under continuous loading, fully recording every stage of slip trace initiation and slip band evolution. A vibration isolation table further ensures the stability of image acquisition, laying the hardware foundation for high-precision phase extraction in SMM.

Model: FH5000-1000V

Heating/Cooling Method: Resistive heating

Temperature Range: RT ~ 1000°C

Temperature Stability: ±0.1°C

Temperature Control Rate: Maximum heating rate: 150°C/min; cooling rate controllable

Specimen Stage: Ceramic; φ7 mm

Top Window Size: φ85 mm × 1 mm

Force Range: 5000 N; Force Accuracy: 0.5% F.S.

Displacement Range: 20 mm

Tensile Speed: 0.1 ~ 5 mm/min

Mechanical Modes: Tension, Compression, Shear, Bending

Chamber: Vacuum