Bondline Thickness Effects on Damage Tolerance of Adhesive Joints Subjected to Localized Impact Damages: Application to Leading Edge of Wind Turbine Blades

The leading edges of wind turbine blades are adhesively bonded composite sections that are susceptible to impact loads during offshore installation. The impact loads can cause localized damages at the leading edges that necessitate damage tolerance assessment. However, owing to the complex material combinations together with varying bondline thicknesses along the leading edges, damage tolerance investigation of blades at full scale is challenging and costly. In the current paper, we design a coupon scale test procedure for investigating bondline thickness effects on damage tolerance of joints after being subjected to localized impact damages. Joints with bondline thicknesses (0.6 mm, 1.6 mm, and 2.6 mm) are subjected to varying level of impact energies (5 J, 10 J, and 15 J), and the dominant failure modes are identified together with analysis of impact kinematics. The damaged joints are further tested under tensile lap shear and their failure loads are compared to the intact values. The results show that for a given impact energy, the largest damage area was obtained for the thickest joint. In addition, the joints with the thinnest bondline thicknesses displayed the highest failure loads post impact, and therefore the greatest damage tolerance. For some of the thin joints, mechanical interlocking effects at the bondline interface increased the failure load of the joints by 20%. All in all, the coupon scale tests indicate no significant reduction in failure loads due to impact, hence contributing to the question of acceptable localized damage, i.e., damage tolerance with respect to static strength of the whole blade.

In-situ leading-edge-induced damages of melting and cracking on W/Cu monoblocks as divertor target during long-term operations in EAST

Leading-edge-induced thermal loading effect due to assembly tolerance between neighboring castellated plasma facing components is a critical issue in fusion devices. Actively-cooled ITER-like W/Cu monoblocks were successfully installed for upper divertor target in EAST which significantly increases the ability of divertor power exhaust. The misalignment between neighboring monoblocks was formed inevitably during manufacturing and assembly processes, providing a possibility to demonstrate the leading-edge-induced thermal damages. Indeed, the leading-edge-induced melting phenomena of W/Cu monoblocks on upper divertor targets were observed during plasma discharges with a large number of droplets ejected from divertor target using CCD camera, which were also identified at the leading edges of W/Cu monoblocks. Not only that, but also many macro cracks with width of ~70 m and depth of < 5 mm along radial and toroidal directions were also found universally at the leading edges of W/Cu monoblocks by post-mortem inspection after plasma campaigns. Thermal-mechanical analysis by means of the finite element simulation demonstrated that the maximum temperature could reach W melting point under current projected heat load of ~3 MWm-2 on flat top surface with large misalignment up to 3 mm at the leading edges. Meanwhile, the high temperature also induced high thermal stress and strain concentration at the center of leading edges, at which the thermal fatigue cracking could be initially generated. Such kind of cracks at leading edges on W/Cu monoblocks may be unavoidable due to the long-term pulsed fatigue effects. However, the influence of these cracks seems to be acceptable thanks to the limited propagated distance by self-castellation effect, which still need long-term tracking. The in-situ leading-edge-induced damages of melting and cracking on W/Cu monoblocks of EAST upper divertor target provide significant reference to understand the leading-edge-induced thermal effect in ITER and future fusion devices.

THERMAL ABLATION MODELLING OF C/SIC FOR HYPERSONIC APPLICATIONS

Hypersonic vehicles are designed to operate at speeds above Mach 5. These vehicles are optimized to have low drag and have thin, slender bodies. The leading edges (nose and wings) are subjected to very high temperatures (above 3000 °C) due to the high heat fluxes. Carbon fiber reinforced Silicon Carbide matrix (C/SiC) composite is a ceramic matrix composite (CMC) that shows great potential for hypersonic applications as it has a low specific weight, high specific strength, and high specificity specific modulus, good thermal stability, and oxidation resistance. C/SiC can be used in leading edges, acreage, hot structures, and the propulsion system. The primary challenge of C/SiC is environmental durability caused by the oxidation and ablation of the material when subjected to extreme heat fluxes. Coatings must be added to the C/SiC substrate to withstand harsh environments at hypersonic speed. These coatings consist of an ultra- high temperature ceramic, an environmental barrier coating (EBC), and a bond coat (BC). This project aims to develop a computational model that will predict the thermal ablation of UHTC coatings when subjected to large heat fluxes. The finite element software used was ABAQUS 2020. Two different models in 2D were created, one for the ablation and one for the stress distribution through the coating. Ablative heat flux was applied at the surface on one side while the other side remains insulated. Preliminary results have shown that as the material is ablated, the temperature across the model started to rise due to the heat flux.

Gene Expression Meta-Analysis Reveals Interferon-Induced Genes Associated With SARS Infection in Lungs

BackgroundSevere Acute Respiratory Syndrome (SARS) corona virus (CoV) infections are a serious public health threat because of their pandemic-causing potential. This work is the first to analyze mRNA expression data from SARS infections through meta-analysis of gene signatures, possibly identifying therapeutic targets associated with major SARS infections.MethodsThis work defines 37 gene signatures representing SARS-CoV, Middle East Respiratory Syndrome (MERS)-CoV, and SARS-CoV2 infections in human lung cultures and/or mouse lung cultures or samples and compares them through Gene Set Enrichment Analysis (GSEA). To do this, positive and negative infectious clone SARS (icSARS) gene panels are defined from GSEA-identified leading-edge genes between two icSARS-CoV derived signatures, both from human cultures. GSEA then is used to assess enrichment and identify leading-edge icSARS panel genes between icSARS gene panels and 27 other SARS-CoV gene signatures. The meta-analysis is expanded to include five MERS-CoV and three SARS-CoV2 gene signatures. Genes associated with SARS infection are predicted by examining the intersecting membership of GSEA-identified leading-edges across gene signatures.ResultsSignificant enrichment (GSEA p&lt;0.001) is observed between two icSARS-CoV derived signatures, and those leading-edge genes defined the positive (233 genes) and negative (114 genes) icSARS panels. Non-random significant enrichment (null distribution p&lt;0.001) is observed between icSARS panels and all verification icSARSvsmock signatures derived from human cultures, from which 51 over- and 22 under-expressed genes are shared across leading-edges with 10 over-expressed genes already associated with icSARS infection. For the icSARSvsmock mouse signature, significant, non-random significant enrichment held for only the positive icSARS panel, from which nine genes are shared with icSARS infection in human cultures. Considering other SARS strains, significant, non-random enrichment (p&lt;0.05) is observed across signatures derived from other SARS strains for the positive icSARS panel. Five positive icSARS panel genes, CXCL10, OAS3, OASL, IFIT3, and XAF1, are found across mice and human signatures regardless of SARS strains.ConclusionThe GSEA-based meta-analysis approach used here identifies genes with and without reported associations with SARS-CoV infections, highlighting this approach’s predictability and usefulness in identifying genes that have potential as therapeutic targets to preclude or overcome SARS infections.

Review of variable leading-edge patents for aircraft wings and engine inlets and their relevance for variable pitot inlets in future supersonic transport

The motivation for designing variable pitot inlets for future supersonic transport (SST) is explained. A comprehensive overview of existing technological solutions for variable leading edges of aircraft wings and engine inlets is given. The advantages and limitations of over 80 solutions, as well as their relevance for application on variable pitot inlets for SST are described. The challenges of existing solution options concerning design methodologies, level of detail, and experience with a technology are identified.

Cascade With Sinusoidal Leading Edges: Identification And Quantification of Deflection With Unsupervised Machine Learning

One of the key issues in turbomachinery design is the identification of loss mechanisms and their quantification, both during preliminary design and in all subsequent optimization loops. Over the years, many correlations have been proposed, accounting for different dissipative mechanisms that occur in blade-to-blade passages, such as the development of boundary layers, turbulent wake mixing, shockwaves, and secondary flows or off-design incidence. In recent years, the fan industry started the production of more complex rotor geometries, characterized by sinusoidal leading and trailing edges, mostly to extend stall margin and to reduce noise emissions. Literature still lacks a quantification of the losses introduced by the secondary motions released by serrated leading-edges. In this paper we investigate a design of experiments that entails 76 cases of a 3D flow cascade with NACA 4digit profiles with sinusoidal leading edges to measure losses according to the Lieblein’s approach. The flow field simulated with RANS strategy was investigated using an unsupervised machine learning strategy to classify and isolate the turbulent wake downstream of the cascade with a combination of Principal Component Analysis and Gaussian Mixture clustering. Then a gradient boosting regressor was used to derive the correlation between input parameters and cascade deflection.

Contractility, focal adhesion orientation, and stress fiber orientation drive cancer cell polarity and migration along wavy ECM substrates

Contact guidance is a powerful topographical cue that induces persistent directional cell migration. Healthy tissue stroma is characterized by a meshwork of wavy extracellular matrix (ECM) fiber bundles, whereas metastasis-prone stroma exhibit less wavy, more linear fibers. The latter topography correlates with poor prognosis, whereas more wavy bundles correlate with benign tumors. We designed nanotopographic ECM-coated substrates that mimic collagen fibril waveforms seen in tumors and healthy tissues to determine how these nanotopographies may regulate cancer cell polarization and migration machineries. Cell polarization and directional migration were inhibited by fibril-like wave substrates above a threshold amplitude. Although polarity signals and actin nucleation factors were required for polarization and migration on low-amplitude wave substrates, they did not localize to cell leading edges. Instead, these factors localized to wave peaks, creating multiple “cryptic leading edges” within cells. On high-amplitude wave substrates, retrograde flow from large cryptic leading edges depolarized stress fibers and focal adhesions and inhibited cell migration. On low-amplitude wave substrates, actomyosin contractility overrode the small cryptic leading edges and drove stress fiber and focal adhesion orientation along the wave axis to mediate directional migration. Cancer cells of different intrinsic contractility depolarized at different wave amplitudes, and cell polarization response to wavy substrates could be tuned by manipulating contractility. We propose that ECM fibril waveforms with sufficiently high amplitude around tumors may serve as “cell polarization barriers,” decreasing directional migration of tumor cells, which could be overcome by up-regulation of tumor cell contractility.

Transient Analysis of Flow Unsteadiness and Noise Characteristics in a Centrifugal Compressor with a Novel Vaned Diffuser

The demands to apply transonic centrifugal compressor have increased in the advanced gas turbine engines. Various techniques are used to increase the aerodynamic performance of the centrifugal compressor. The effects of the inclined leading edges in diffuser vanes of a transonic centrifugal compressor on the flow-field unsteadiness and noise generation are investigated by solving the compressible, three-dimensional, transient Navier–Stokes equations. Diffuser vanes with various inclination angles of the leading edge from shroud-to-hub and hub-to-shroud are numerically modeled. The results show that the hub-to-shroud inclined leading edge improves the compressor performance (2.6%), and the proper inclination angle is effective to increase the stall margin (3.88%). In addition, in this study, the transient pressure variations and radiated noise prediction at the design operating point of the compressor are emphasized. The influences of the inclined leading edges on the pressure waves were captured in time/space domain with different convective velocities. The pressure fluctuation spectra are calculated to investigate the tonal blade passing frequency (BPF) noise, and it is shown that the applied inclination angles in the diffuser blades are effective, not only to improve the aerodynamic performance and stall margin, but also to reduce the BPF noise (7.6 dB sound pressure level reduction). Moreover, it is found that the diffuser vanes with inclination angles could suppress the separation regions and eddy structures inside the passages of the diffuser, which results in reduction of the overall sound pressure level and the broadband noise radiated from the compressor.