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Synchronous measurement of temperature and deformation at elevated temperatures is highly critical, yet challenging in evaluating mechanical properties of thermal protection systems. An ultraviolet (UV) imaging system is proposed to obtain noncontact, in situ, synchronous, and full-field temperature and deformation. The established system consists of a monochromatic UV illumination with a bandpass filter for radiation suppressing, a UV CCD camera for image capturing, and an infrared pyrometer for temperature recording. Additionally, an improved monochromatic radiation pyrometry method is proposed, while a deformation measuring method using the UV digital image correlation (UV-DIC) and natural textures-generated speckle is introduced. Furthermore, through camera calibration at room temperature and real-time exposure time adjusted at elevated temperatures, the influence of reflection on radiation pyrometry and unfiltered radiation on DIC analysis is eliminated. Synchronous temperature and deformation fields of C/SiC subjected to flame heating are experimentally measured with a temperature range of 500°C–1500°C, and results demonstrate the efficacy and potential of the proposed system and method. Finally, the importance of exposure time on balancing the light intensity of radiation and reflection is also discussed.

Optical method has been playing an important role in measuring temperature and deformation at elevated temperatures. Here we propose a simple and effective iterative algorithm to realize accurate and simultaneous measurement of the full-field temperature and deformation of specimens subjected to flame heating at temperatures up to 1000 °C. The algorithm separates the optical images of specimen surface into radiant and reflected parts. The radiant part is used to calculate the full-field temperature by an improved two-color method, and the reflected part is used to obtain the deformation of the specimen surface based on high-temperature digital image correlation method. Experimental validation shows that the proposed method can effectively eliminate the mutual interference between the radiation and reflected light, displaying great potential for synchronous measurement of temperature and deformation with sufficient accuracy by using one camera.

Over-expanded and under-expanded gas jets submerged in water have been studied through numerical simulation and experiments. Comparisons between numerical and experimental results are made to validate the conclusion that the ‘quasi-back-attack’ phenomenon in high-unexpanded conditions is caused by the obstruction of the shock waves acted on back-attacked gas. As a consequence, back-attacked gas cannot reach the wall of the motor. A detailed analysis of the results reveals the underlying mechanism of the structure of the gas jet under different operating conditions. Meanwhile, the characterization of the motor’s thrust indicates that the oscillation amplitude of thrust drops sharply after the occurrence of quasi-back-attack phenomenon, which is beneficial to the stability of the motor.

Synchronous measurement of temperature and deformation at elevated temperatures based on the noncontact optical method can be achieved through the allocation of channels R, G, and B for a color camera. Channels R and G are used for the radiation-based temperature measurement, while channel B is adopted for the deformation measurement. However, the existence of color crosstalk, which is mainly caused by the color camera's spectral response and the use of the narrow-band filtering technique, has a significant influence on the accuracy of temperature and deformation calculations. In this work, the color crosstalk effect in high-temperature optical imaging is analyzed, and a crosstalk correction algorithm based on grayscale calibration is performed on the different color channels (channels R, G, and B) of the color image. By solving the calibration equations, three corrected color channels are generated for a high-precision temperature and deformation calculation. A flame heating experiment of a C/SiC material up to 1100 °C is carried out to validate the applicability accuracy of the proposed method. The results show that the proposed method can effectively eliminate the color crosstalk between different channels and provide a non-contact, full-field, and synchronous measurement of temperature and deformation with higher accuracy than the existing methods.

Non-contact measurement method at elevated temperatures has been widely studied, which provides an efficient means for evaluating the properties of high-temperature materials. However, such high-temperature environment-induced challenges as strong light radiation and air disturbance may cause a huge quality decrease to the captured images based on the optical systems. As an important application of neural networks, Denoising Convolutional Neural Networks (DNCNN) has shown a considerable performance in conventional image denoising. In this work, an optimized DNCNN method based on the sub-region processing and transfer learning was proposed and applied in the high-temperature measurement. The thermal heating experiment of the SiC material was carried out to validate the applicability and accuracy of the method, while the synchronous measurement of temperature and deformation is realized. Simulation results based on the finite element method (FEM) agree well with the calculated data, indicating the proposed model can improve the measurement accuracy.

Synchronous measurement of full-field temperature and deformation at elevated temperature using non-contact optical methods attracts increasing attention in evaluating the high temperature properties of materials. The current optical methods all face one major challenge, which is the strong light reflection on the surface of the specimen. Such strong light reflection could greatly impair the measurement accuracy of the temperature field measured based on the radiation light information. Here, we develop an effective and simple testing system to overcome this difficulty. The measurement system consists of an image and temperature acquisition device, and a light source with the feature of high-frequency flashing and periodic flicking. High-frequency flashing of the light source is driven by a motor and controlled by a field programmable gate array controller. Our system can realize the synchronous control of light flashing, image capturing, and temperature acquisition. Images with light on are used to calculate the deformation field based on the digital image correlation method, and those with light off (without reflection) are used for the calculation of temperature. Based on the continuous change of temperature over time, the temperature field at the moment when light is on can be obtained by interpolating the temperature fields before and after the moment through the fitted curve. Experimental validation on the thermal heating of C/C fiber composites shows a satisfactory result for temperature and deformation measurement.

Measuring temperature and deformation at elevated temperature has recently been a major concern for the engineering tests and the quality improvement of captured images is critical to it. Here, we propose a simple, high-precision and easy-to-implement technique combing the image capturing and processing methods to obtain the high-resolution images as well as the corresponding temperature and deformation fields. The super-resolution convolutional neural network (SRCNN) algorithm is used for the super-resolution reconstruction, while the deformation field is calculated by the DIC method and the temperature field is synchronous obtained by the improved two-color method. Flame heating experiment of the SiC material validated the applicability and the improvement of the proposed method, showing the improvement in image quality (with PSNR increased 16.7 %) and calculation accuracy of temperature and deformation (with error decreased 3.57 %). Meanwhile, the phenomenon of "feature point drift" is pointed out and the error of deformation measurement for high-resolution and low-resolution is analyzed. Furthermore, the sub-pixel edge detection can be achieved by the combination of the proposed method and the edge detection method, which shows a potential value in detecting of surface defects or cracks.

Synchronous measurement of temperature and the deformation field can be achieved through reasonable assignment of R, G, and B channels of a CCD camera in a high-temperature environment. The R and G channels are used for colorimetric temperature measurement, and the B channel is adopted for deformation measurement. However, the external blue compensation light source may cause crosstalk of the R and G channels, leading to inaccurate measurement. To eliminate such an interference phenomenon, we first use the function relationship between the illumination of the object surface and the exposure time to calibrate the camera parameters at room temperature, thus removing the initial gray level of the R and G channels in the high-temperature image. This contributes to improving the low-temperature measurement accuracy for the temperature field, with a calculation error of

The chemo-mechanical coupling effect has been widely investigated due to its important impact on many areas, such as Li-ion batteries, biomechanical engineering, hydrogen embrittlement, etc. Meanwhile, the chemo-mechanical coupling effect on the high temperature oxidation process is drawing increasing attention. During oxidation, stress can be induced in the oxide film and will in turn influence the diffusion process and oxidation kinetics. Understanding the coupling effect between stress and oxidation helps to illuminate the mechanism of material degradation and failure. In this work, a concise physical model is developed for oxidation kinetics at elevated temperatures considering the diffusion-stress coupling effect, where both the inward and outward diffusion are considered. The model prediction shows an excellent agreement with the experimental observation. Based on this physical model, we also proposed a parameter to characterize the effects of cation/anion diffusion as well as a phase diagram to describe the universal diffusion–oxidation growth process.

Synchronous measurement of the temperature and deformation fields of large-scale flat specimens is challenging in engineering experiments, especially for high-temperature environment where the non-contact optical method is attempted. To overcome this difficulty of large-scale flat specimens tested at high temperature in the open arc wind tunnel environment, measurement principles and experiments of large-scale flat specimens based on a multi-camera system are proposed using digital image stitching as well as the improved two-color method for temperature measurement. First, the digital image mosaic method is used to process and evaluate the mosaic effect of multi-camera images, the optimal mosaic parameters are selected, and the calculation results are given. Second, a set of images for large-scale flat specimens are deduced based on an improved two-color method of temperature measurement and digital image mosaic algorithms. A stitching algorithm for full-field temperature measurement and calculation results are given. Finally, full-field displacement of the stitched images is calculated by the digital image correlation method. Synchronous measurement of temperature and deformation established in this paper provides guidance for measurement of large-scale flat specimens with high spatial resolution in engineering tests.

In this paper, the recent progress of ferroelectric topologies is briefly reviewed with the emphasis on the important role of state-of-the-art aberration-corrected transmission electron microscopy in revealing the topological features in nanoscale ferroelectric materials. By identifying the ion displacement at a sub-angström level, the corresponding polarization distribution can be determined which uncovers the characteristics of topological structures. The formation mechanisms of ferroelectric topological structures and their evolutions under external fields are summarized from the perspective of strain, screening, and external fields for two prototypical ferroelectric materials, PbTiO3 and BiFeO3. For the PbTiO3, its topological structures such as flux-closures, vortices, bubbles, skyrmions, and merons can be well demonstrated in a thickness-strain-screening phase diagram, which could be a guideline for better understanding the topological structures and also for the future exploration. For BiFeO3, its topological structures reported are classified as two categories: one is the unscreened topological structure such as vortices and the other is the screened topological structure (center-type domains). Finally, we present the prospects for the future development of the ferroelectric topologies.

In this work, we develop an optoelectronic system for in situ observation and measurement in hypervelocity flows. The system has the advantages of strong radiation resistance and self-adaptive exposure time of the cameras. Thermal ablation test using flat plate thermal protection system material was carried out in an arc jet. Real-time ablation images were captured and analyzed to understand the thermal ablation mechanism. Through the modified algorithms of particle image velocity (PIV) and image feature detection, the surface recession rate and the velocity distribution of the melted droplets flowing on the sample surface were obtained. The experimental results demonstrate vast potential for using this in situ measuring technique in various engineering applications. Finally, the formation and merging of the melted droplets was analyzed based on energy theory, and the numerical simulation results showed good agreement with the actual experimental results.