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Probabilistic fatigue life estimation of plate with multiple stress concentration zones}.
No full textFatigue is a complex phenomenon which causes sudden failure of a component subjected to cyclic loading in the elastic region. Fatigue lives of nominally identical specimens subjected to the same nominal cyclic stress display scatter. This phenomenon reflects the stochastic nature of a fatigue damage process. Probabilistic and statistical methods are appropriate for managing the large uncertainties that exist in the fatigue process and provide reliability as a measure of structural performance. In this work, MATLAB was used as a platform to evaluate probabilistic fatigue life of the plate with multiple stress concentration zones using Latin Hypercube sampling. Fatigue reliability was computed by accounting for the scatter present in material properties in terms of random design variables and verified. Among the random design variables, fatigue strength exponent was having higher influence on fatigue life. Fatigue reliability was found to be decreasing with increase in input variation
The tensile fatigue behaviour of aligned MWNT/epoxy nanocomposites.
No full textThe emergence of carbon nanotubes (CNTs) has created new opportunities for the fabrication of polymer composites that possess strong potential for a wide spectrum of applications. The one-dimensional structure of carbon nanotubes has a very high anisotropic nature and unusual mechanical properties, which made them as promising nanofiller for the composite structures. But the particle-level exceptional properties are not completely utilised when they are used as reinforcement in composites due to inadequate and immature processing techniques. In the present work, we have made an attempt to utilise the strong anisotropic nature of multi-walled carbon nanotubes (MWNTs) for improving the fatigue life of nanocomposites, especially for very low weight percentages. The MWNTs anisotropy was imparted to the nanocomposites by aligning them in the epoxy matrix with DC electric field during curing. Nanocomposites were made for 0.1 wt% MWNT loading. Totally, three categories of nanocomposites were prepared: nanocomposites with aligned CNT (with electric field), nanocomposites without CNT alignment (without electric field), and neat epoxy for the comparison purpose. The tensile fatigue behaviour was investigated under stress control mode by applying cyclic sinusoidal load with the frequency range of 1–3 Hz and stress ratio of R = 0.1. The specimens were tested for the fatigue load until the failure or 1E+05 cycles. The fractured surfaces were examined through scanning electron microscope to analyse the fatigue fracture behaviour
EM performance analysis of radomes.
No full textThe study of antenna-radome interaction is performed by using 3D ray-tracing procedure based on geometrical optics along withaperture integration method (Kozakoff 2010; Nair et al. in CMC Comput Mater Continua 40(2):131–143, 2014)
Processing and characterization of lead-free ceramics on the base of sodium-potassium niobat.
Get PDFLead-free sodium–potassium niobate-based piezoelectric materials are most intensively studied in order to replace the widely used Pb-based ones. In this work, the effects of modification of compositions by donor and acceptor dopants in the A- and B-sites of perovskite lattice on structure, dielectric, ferroelectric, and piezoelectric properties of ceramics from Morphotropic Phase Boundary in the (1−x)(K0.5Na0.5)NbO3–xBaTiO3 system and in compositions with x=0.05 and 0.06 additionally doped by Ni3+ cations have been studied
Effect of inhomogeneous mesoporosity and defects on the luminescent properties of slanted silicon nanowires prepared by facile metal-assisted chemical etching
No full textSlanted silicon nanowires show an improved optical absorption and better electrical contact than the vertical silicon nanowires. High aspect ratio mesoporous slanted silicon nanowires oriented along the ⟨100⟩ direction are fabricated by a facile two-step metal-assisted chemical etching process. Inhomogeneous porosity with a pore diameter of 2–10 nm is identified by the analysis of transmission electron microscopy, angle dependent Raman spectroscopy, and Brunauer-Emmett-Teller measurements. Slanted silicon nanowires possess a core/shell structure, and the porosity varies from top to bottom of the slanted silicon nanowires. The presence of neutral oxygen defects, self-trapped excitons, and surface defects is identified by photoluminescence spectroscopy, and the results are correlated with Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy data. In addition to mesoporosity, defects such as self-trapped excitons, oxygen vacancies, and surface defects on Si/SiOx interface contribute to the luminescence of slanted silicon nanowires. Red shift in the photoluminescence with increasing etching time is explained using quantum confinement luminescent center model. Understanding the role of defects and porosity in slanted silicon nanowires is highly desirable to increase the efficiency of silicon nanowires based optoelectronic devices
Electrolyte bi-layering strategy to improve the performance of an intermediate temperature solid oxide fuel cell: A review
No full textLowering of operation temperature has become one of the primary goals of solid oxide fuel (SOFC) research as reduced temperature improves the prospects for widespread commercialization of this energy system. Reduced operational temperature also mitigates the issues associated with high temperature SOFCs and paves way not only for the large scale stationary power generation but also makes SOFCs viable for portable and transport applications. However, there are issues with electrolyte and cathode materials at low temperatures, individually as well as in association with other components, which makes the performance of the SOFCs less satisfactory than expected at lowered temperatures. Bi-layering of electrolytes and impregnation of cathodes have emerged as two important strategies to overcome these issues and achieve higher performance at low temperatures. This review article provides the perspective on the strategy of bi-layering of electrolyte to achieve the desired high performance from SOFC at low to intermediate temperatures
Mixed mode cohesive zone modelling and analysis of adhesively bonded composite T-joint under pull-out load
No full textThe failure behaviour of three different configurations of adhesively bonded carbon fibre composite T-joints subjected to pull-out load is investigated. Finite element analysis is carried out on the carbon fibre composite T-joint models. A non-linear, contact target-based cohesive zone model with appropriate traction separation law is selected to simulate the pull-out test condition in FE package ANSYS®. The FE analysis results are in close agreement with available experimental results
Surface and Electrochemical Characteristics of Novel Chromate-Free Mn-V Oxyanion Sealed Tartaric–Sulfuric Acid Anodized Coating
No full textIn the present investigation, a novel chromate-free Mn and V oxyanions sealed tartaric–sulfuric acid anodic oxide coating (TSA) was developed on airframe grade aluminum alloy (AA2024). The results obtained from field emission scanning electron microscopy and energy-dispersive x-ray analysis showed effective surface modification of TSA after Mn-V oxyanions sealing (TSAMnVO). Potentiodynamic polarization results showed no significant difference in corrosion current density value (0.01 µA/cm2) after 1 h and 336 h of immersion in 3.5% NaCl solution. EIS result exhibited barrier layer resistance (Rb) value of TSAMnVO > 106 kΩ cm2 even after 336 h of immersion in NaCl solution. The 3D profile and Raman analysis showed no significant difference in the topography and composition, respectively, on the surface of TSAMnVO even after 1000 h of salt spray test. TSAMnVO also showed excellent adhesion with aircraft grade epoxy primer as per the ASTM 3359. Tensile and constant amplitude fatigue test results of TSAMnVO exhibited ultimate tensile strength and number of cycles to failure comparable with chromic acid anodization (CAA) process. Hence, the developed novel TSAMnVO coating system eliminates the usage of chromate ions completely in anodization process since it provides comparable corrosion resistance and mechanical properties with CAA
Probabilistic strength based matrix crack evolution model in multi directional composite laminates under fatigue loading
No full textA model to predict the matrix crack evolution in multi-directional (MD) polymer matrix composite laminates under in-plane fatigue loading is presented in the current work. Unlike matrix crack evolution under static loading, the matrix cracks in off-axis plies do not form tunneling cracks under fatigue loading; rather, they initiate and grow with increasing load cycles. A probabilistic strength based criterion for matrix crack initiation in off-axis plies based on a Weibull distribution for in situ ply strength variation has been used. An oblique co-ordinate based shear lag analysis has been used to estimate the stresses in the cracked laminate. Smith Watson Topper (SWT) parameter has been used to model the number of cycles to initiate the first matrix crack, and log-normal probability distribution has been used to handle the scatter in crack initiation life. The matrix crack growth rate has been modeled using Paris law based on mixed mode effective stress intensity factor. Using the crack initiation curve and strength degradation based on Palmgren-Miner damage rule, new crack initiation has been simulated. Few parameters needed for the threshold stress intensity and saturation crack spacing have been identified from a reference stress data of cross-ply laminate. The crack density evolution has been simulated for cross-ply and MD-laminates under various constant amplitude in-plane fatigue stress levels. The matrix crack density evolution and its stiffness degradation predictions with the number of cycles have been compared with existing experimental values. A good correlation is found to exist between the experimental data and predictions for both cross-ply and MD-laminates
An Investigation on the Wear and Corrosion Behavior of HVOF-Sprayed WC-12Co-Al2O3 Cermet Coating
No full textThe aim of the present study is to develop thermally sprayable WC-12Co and WC-12Co-xAl2O3 (x = 10
and 15 wt.%) cermet coatings on steel substrate (SS 304) by high-velocity oxy fuel (HVOF) method.
Influence of Al2O3 addition on the wear and corrosion behavior of WC-12Co coating has been studied. The
microstructure and chemical composition of the coatings were analyzed using field emission scanning
electron microscope (FESEM), and phase identification was carried out using x-ray diffraction (XRD)
studies. The morphology of the coating appears as coarse granular structure. The XRD studies revealed the
presence of hexagonal WC phase along with g-Co6W6C phase. It has been observed from the microhardness
measurements, that the values gradually increase from 950 to 1300 HK with the addition of Al2O3
from 0 to 15 wt.%. The wear rate of WC-12Co-15Al2O3 (3.1931026 mm3/Nm) and WC-12Co-10Al2O3
(5.2631026 mm3/Nm) coatings was seen to be one order of magnitude lower than that of WC-12Co
(2.931025 mm3/Nm) coating. The polarization studies revealed that WC-12Co-15Al2O3 cermet coating
showed superior corrosion protection than that of WC-12Co-10Al2O3 and WC-12Co coatings. This has
been attributed to the gradual decrease in the porosity levels with an increase in Al2O3 content which is
supported by morphology studies. The microhardness and wear behavior of WC-12Co-Al2O3 coatings are
equivalent to those of hard chrome suggesting the possibility of its replacement