Innovative materials for post lithium-ion batteries

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Experimental characterization of elastic stiffness and delamination toughness in commercial thermal barrier coating systems

Layered thermal barrier coating (TBC) systems used in jet engines consist of a nickel-based superalloy substrate, intermetallic bond coat, thermally grown oxide (TGO) and a electron beam physical vapor deposition (EBPVD) 7% yttria-stabilized zirconia (7YSZ) top coat. Thermal protection is only provided when the TBC remains attached to the substrate, and mechanism-based lifetime assessment models rely on accurate knowledge of the experimentally measured interfacial fracture toughness and the topcoat modulus. We are employing conventional 4-point bend experiments and a newly developed compression edge-delamination (CED) methodology to make direct measurements of coating interfacial toughness as a function of mode mix. Of special interest are the CED specimens, which provide a direct measure of mode-II delamination toughness of the coating. In a parallel study, novel micro-bend techniques are being employed to measure the elastic modulus of both attached and freestanding EBPVD 7YSZ topcoats. Results for commercial TBC systems provided by industrial collaborators will be presented and used to characterize the effect of mode mix and various manifestations of thermal cycling on these material properties

DEVELOPMENT OF A MACHINE VISION SYSTEM FOR DAMAGE AND OBJECT DETECTION IN TUNNELS USING CONVOLUTIONAL NEURAL NETWORKS

Tunnel inspection, i.e. detection of damages and defects on concrete surfaces, is essential for monitoring structural reliability and health conditions of transport facilities, thus providing safe and sustainable urban transportation infrastructures. In this study, an innovative visual-based system is developed for damage and object detection tasks in roadway tunnels based on deep learning techniques. The main components of the developed Machine Vision System such as industrial cameras, flash-based light sources, controller, the synchronization unit and corresponding software programs are designed to collect high-resolution images with sufficient quality from dimly lit tunnel environments in normal traffic flows with an operating speed of 30–50 km/h. Unlike recent studies, the training data includes multiple types of damage such as cracks, spalling, rust, delamination and other surface changes. Furthermore, 10 classes of common tunnel objects including traffic signs, traffic cameras, traffic lights, ventilation ducts, various sensors and cables are labeled for object detection. As state-of-the-art Convolutional Neural Networks, DeepLab and U-Net are trained and evaluated using accuracy metrics for image segmentation. The results highlight the most important parameters of the discussed Machine Vision System as well as the performance of DeepLab and U-Net for object and damage detection

Region- and pixel-based image fusion for disaggregation of actual evapotranspiration

This paper compares a region-based and a pixel-based disaggregation method used to improve obtaining actual evapotranspiration (aET) data from MODIS images. Using these methods and the relationship between different vegetation indices form Landsat-5 and aET from MODIS, a 1 km resolution aET image was disaggregated to 250 and 30 m resolutions in two steps. Disaggregated aET images were compared with aET data obtained from a Landsat-5 TM image. A sensitivity analysis using synthetic data showed the impacts of land-cover homogeneity and registration error of the input images at the three scale levels. Accuracy assessment illustrated that the region-based disaggregation method using the Normalized Difference Vegetation Index (NDVI) has a good agreement with the Landsat-5 aET, having a mean absolute error equal to 0.93 mm. This method can be powerful for improving irrigation management, as it allows to increase the spatial resolution of aET derived from remote sensing images. The study concluded that a region-based method with NDVI data performs best to disaggregate MODIS aET data

Experimental measurements of thermal barrier coating interfacial fracture toughness as a function of mode-mix

Mechanism-based lifetime assessment models of thermal barrier coating (TBC) systems rely on accurate knowledge of the experimentally measured interfacial fracture toughness over a range of mode mix and especially at mode II. Previously, no reliable test method had been employed to evaluate these properties under pure mode II conditions, which are most representative of critical TBC spall delamination upon turbine engine cool down. We have used conventional 4-point bend experiments and a newly developed compression edge-delamination (CED) methodology to make direct measurements of coating interfacial toughness as a function of mode mix. The material system examined was provided by collaborators at GE and consists of an Electron-Beam Physical Vapor Deposited (EBPVD) 7% Yttria-Stabilized Zirconia (YSZ) top coat, which is deposited on a Pt-modified diffusion aluminide β-(Ni,Pt)Al bond coat on a single crystal René N5 substrate. CED tests showed that thermal cycling caused a 50% reduction in mode II interfacial toughness. Results for as-deposited samples tested using a modified 4-point bend technique match previously reported data, and a toughness function for the as-deposited interfacial toughness vs. mode mix has been developed using results from this study and from previously reported values. Crack face friction has also shown to play a profound role in calculation of the interfacial toughness, and details regarding the characterization and implementation into the finite element model used to extract the interfacial toughness will be examined. Finally, microstructural observations, including morphological and chemical changes, linked to the degradation of the coating interfaces due to thermal cycling will be analyzed. Please click Additional Files below to see the full abstract

Acculturation and Mental Health in Chinese Immigrant Youth

The dissertation investigated the relationship between acculturation, acculturative stress, locus of control, and perceived social support on the mental health of Chinese immigrant adolescents. Study participants included 81 first generation Chinese immigrant adolescents. Mental health was operationalized using the BASC emotional symptoms index and somatization score. As hypothesized, acculturative stress and perceived parental support were significant predictors of both emotional symptoms and somatization. Locus of control and perceived peer support were significant predictors of emotional symptoms only, while acculturation was not a significant predictor of either emotional symptoms or somatization. Furthermore, the results suggested that locus of control and social support had a direct impact on mental health outcomes, rather than an indirect, stress buffering role. Future research and study implications are discussed

EXPERIMENTAL CHARACTERIZATION OF ELASTIC STIFFNESS AND DELAMINATION TOUGHNESS IN THERMAL BARRIER COATING SYSTEMS

Reliable high-temperature propulsion materials are crucial to improved engine efficiency, reduced fuel costs and decreased life cycle costs. Multilayered thermal barrier coatings (TBC) are an effective way of extending the temperature capabilities of gas turbine engines, but accurate assessment and life prediction of these disparate material systems requires detailed knowledge of the constitutive behavior of each layer and the adhesion between layers. The focus of this study is to measure the properties relevant to thermal barrier coatings and elucidate how variations in the processing affect the mechanical response. Working closely with industrial suppliers at General Electric (GE) and Pratt & Whitney (P&W), novel Compression Edge Delamination (CED) tests were used to measure the Mode II interfacial toughness of two TBCs. GE’s standard diffusion aluminide bond coat/yttria stabilized zirconia (YSZ) topcoat TBC system was characterized at various stages of gradient thermal cycle life and compared to previous results for furnace cycled specimens with the same TBC. Both sets of samples exhibited comparable interfacial toughness and a decrease in interfacial strength with thermal cycling. The drop in interfacial strength was correlated with TGO and bond coat rumpling and found to be greater in the thermal gradient test, in part because these specimens experienced higher bond coat temperatures. CED testing was also performed on P&W’s low-pressure plasma sprayed NiCoCrAlY bond coat/YSZ topcoat TBC system at various stages of furnace cycle life. The delamination of this TBC resulted in the spallation of the topcoat in one large piece, facilitated by the absence of rumpling. The interfacial toughness of these specimens decreased with thermal cycling and was attributed to thickening of the thermally grown oxide (TGO), which in the absence of rumpling leads to increased stored strain energy that promotes delamination. A parallel investigation with P&W investigated the influence of off normal processing conditions on the intrinsic microstructure and mechanical properties of YSZ topcoats manufactured via electron-beam physical vapor deposition. Microstructural variations were subtle, but 3-point bend experiments on free-standing topcoats showed a strong tension/compression asymmetry and variations in modulus as a function of processing conditions