Complexity of crack front geometry enhances toughness of brittle solids.

Brittle solids typically fail by growth and propagation of a crack from a surface flaw. This process is modelled using linear elastic fracture mechanics, which parameterizes the toughness of a material by the critical stress intensity factor, or the prefactor of the singular stress field. This widely used theory applies for cracks that are planar, but cracks typically are not planar, and instead are geometrically complex, violating core tenets of linear elastic fracture mechanics. Here we characterize the crack tip kinematics of complex crack fronts in three dimensions using optical microscopy of several transparent, brittle materials, including hydrogels of four different chemistries and an elastomer. We find that the critical strain energy required to drive the crack is directly proportional to the geodesic length of the crack, which makes the sample effectively tougher. The connection between crack front geometry and toughness has repercussions for the theoretical modelling of three-dimensional cracks, from engineering testing of materials to ab-initio development of novel materials, and highlights an important gap in the current theory for three-dimensional cracks.

Lumbar Cistern Drainage and Gentamicin Intrathecal Injection in the Treatment of Carbapenem-Resistant Klebsiella Pneumoniae Intracranial Infection After Intracerebral Hemorrhage craniotomy: A Case Report.

Background: Intracranial infection is a common complication caused by craniotomy. In particular, patients in Intensive Care Units (ICU) are prone to intracranial infection with multiple drug-resistant bacteria. Due to the lack of sensitive antibiotics for the treatment of multiple drug-resistant bacteria, there are few literatures focusing on the treatment of intracranial infection, and patients often fail to receive unified and standardized treatment. Consequently, patients with Carbapenem-resistant bacteria intracranial infection report poor prognosis and high mortality. It is very important to discuss how to treat patients with intracranial infection caused by multidrug resistant bacteria. Case Presentation: We reported a case of intracranial infection of Carbapenem-resistant Klebsiella pneumoniae(CRKp) due to high flap tension, poor wound healing and CSF leakage caused by subcutaneous fluid accumulation after intracerebral hemorrhage craniotomy. Since the patient was exposed to intracranial infection resulted from subcutaneous fluid accumulation, we adopted the method of continuous drainage with subcutaneous tube. When subcutaneous effusion disappeared, the subcutaneous drainage tube was pull out, while patients exhibited high fever again, the waist big pool drainage catheter and continuous drainage were carried out. According to the result of Subcutaneous effusion and CSF culture indicated multiple drug resistant Klebsiella pneumoniae intracranial infection and drug susceptibility, The treatment of gentamicin intrathecal injection, intravenous use amikacin and oral Paediatric Compound Sulfamethoxazole Tablets was adopted, the condition of intracranial infection was eventually controlled, with the consciousness restored. This patient was characterized by intracranial infection with Carbapenem-resistant Klebsiella pneumoniae(CRKp). Conclusions: Subcutaneous effusion is a high-risk factor for poor wound healing and interventions are required to be conducted to promote healing as early as possible to contribute to decreasing the menace of CSF leakage. In this case, Continuous drainage and intrathecal injection of sensitive antibiotics serve as critical process to determine the best strategy for clinical treatment of intracranial infection.

Heatwave distortion correction using an improved reference sample compensation method and multispectral digital image correlation.

Heatwave distortions, caused by unevenly distributed temperature and refractive index in the optical path, unavoidably occur in high-temperature digital image correlation (DIC) measurement. To eliminate these distortions, a multispectral DIC-aided reference sample compensation method is proposed. The proposed method first adheres a correcting transparent glass (decorated with fluorescent speckle patterns) onto the test specimen (sprayed with red speckle patterns). Then, by illuminating the specimen with ultraviolet- and red-light sources, the blue light excited from the correcting glass and the red light reflected from the specimen surface can be captured by a 3CCD camera, forming a color image. After separating the recorded color images into red and blue subimages, the original and the correcting displacement fields can be calculated from these two sets of subimages using the subset-based local 2D-DIC algorithm. By point-to-point subtracting the correcting displacement fields from the original ones, the heatwave distortions can be eliminated, and the corrected real displacement fields can be obtained. For validation, static heatwave experiments show the feasibility and accuracy of the proposed method in correcting heatwave distortions. A uniaxial tensile test of an aluminum specimen with a central hole was also performed, further confirming the practicality of the proposed method in correcting heatwave distortions and revealing heatwave-hidden deformation.

Enhanced Digital Gradient Sensing Using Backlight Digital Speckle Target.

Digital gradient sensing (DGS) is a non-contact and full-field optical measurement technique, which assesses mechanical behaviors of transparent materials or specular structures by measuring angular deflections of light rays. However, owing to the poor light-gathering capability of its imaging system, the dynamic performance of DGS is heavily restricted. Here, a method of enhancing the dynamic performance of DGS by improving its speckle target is proposed. The method employs the technique of backlight illumination, which significantly increases the utilization efficiency of light, shortens the exposure time, and enhances the dynamic performance of DGS. Additionally, it also uses the optimized digital speckle pattern to improve the measurement precision and accuracy. For validation, a comparison experiment was conducted, proving that the proposed method can improve the utilization efficiency of light by about 80 times and improve the quality of the speckle images by about 40%. Real tests, including a uniaxial tension test using transmission-mode DGS (t-DGS) and a three-point bending test using reflection-mode DGS (r-DGS), were also carried out, showing the efficacy and high compatibility of the proposed backlight digital speckle target. In summary, this simple method greatly improves the performance of DGS, which can be used as a standard method in both t-DGS and r-DGS.

High-throughput measurement of coefficient of thermal expansion using a high-resolution digital single-lens reflex camera and digital image correlation.

High-throughput measurement of thermal deformation and determination of coefficient of thermal expansion (CTE) using a high-resolution digital single lens reflex (DSLR) camera and digital image correlation (DIC) is described. To mitigate the mosaic effect caused by the Bayer filter of DSLR cameras, a color image pre-processing method, which adjusts the brightness and equalizes the color channels of the raw image, is carried out. In addition, a Gaussian pre-filtering step is adopted for denoising the images captured with DSLR cameras to enhance the subpixel registration accuracy. Then, by processing the recorded images using the state-of-the-art DIC algorithm, full-field displacements and strains can be determined. Compared with conventional industrial cameras, a DSLR camera offers not only portability, compactness, and economy but also much higher resolution of recorded images, allowing CTE characterization with higher throughput. Real experiments, including a verification experiment of the color image pre-processing technique, a benchmark CTE determination of Al alloy, and a high-throughput CTE determination of 15 samples of three different metals, validated the feasibility and accuracy of the proposed technique. The proposed method is cost-effective and time-saving, showing great potential in the high-throughput CTE measurement and other high-throughput strain measurement scenarios.

Ultrasensitive video extensometer using single-camera dual field-of-view telecentric imaging system.

Video extensometer assesses mechanical properties of materials by measuring their length changes under different loadings with combined use of video recording and image processing. In this Letter, an ultrasensitive video extensometer implemented on a single-camera dual field-of-view (dual FOV) telecentric imaging system is proposed. The method integrates the idea of FOV separation and telecentric imaging, which can increase the strain resolution with an order of magnitude and enhance the strain accuracy significantly. Validation experiments indicate that the root mean square error of a video extensometer was effectively decreased from 25.2 to 4.4 microstrains after employing the proposed method. Time-varying thermal strains of Al alloy and alumina ceramic samples were also precisely measured by the established ultrasensitive video extensometer, confirming its accuracy and practicality.