RESUMEN
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.
RESUMEN
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.
RESUMEN
The high-temperature optical method has been widely used for evaluating structural materials subjected to high temperature. Obtaining high-quality images of a specimen surface in such a harsh environment is detrimental for the accurate measurement of temperature and strain field. However, the high-temperature environment poses many challenges on these measurements, e.g., the large luminance gradient on the sample surface would jeopardize the image quality when using the full-field optical method. In order to overcome this issue, we propose here a simple and effective algorithm to obtain image sequences with serial exposure times. This algorithm incorporates exponentially decreasing exposure times to successfully reduce the disturbance caused by large luminance gradient, as will be shown by the verification on samples tested both in arc wind tunnel and oxy-propane torch flame. In comparison to the images with single exposure time, further experiment carried out on C/SiC sample up to 1100°C shows that image sequences with different exposure times can be effectively obtained by the image fusion technique. The calculation of the deformation and temperature fields using the image sequence method gives more accurate and reasonable results.
RESUMEN
Peripheral neuromodulation has been widely used throughout clinical practices and basic neuroscience research. However, the mechanical and geometrical mismatches at current electrode-nerve interfaces and complicated surgical implantation often induce irreversible neural damage, such as axonal degradation. Here, compatible with traditional 2D planar processing, we propose a 3D twining electrode by integrating stretchable mesh serpentine wires onto a flexible shape memory substrate, which has permanent shape reconfigurability (from 2D to 3D), distinct elastic modulus controllability (from ~100 MPa to ~300 kPa), and shape memory recoverability at body temperature. Similar to the climbing process of twining plants, the temporarily flattened 2D stiff twining electrode can naturally self-climb onto nerves driven by 37°C normal saline and form 3D flexible neural interfaces with minimal constraint on the deforming nerves. In vivo animal experiments, including right vagus nerve stimulation for reducing the heart rate and action potential recording of the sciatic nerve, demonstrate the potential clinical utility.