A Review on Fatigue Life Prediction Methods for Metals

Metallic materials are extensively used in engineering structures and fatigue failure is one of the most common failure modes of metal structures. Fatigue phenomena occur when a material is subjected to fluctuating stresses and strains, which lead to failure due to damage accumulation. Different methods, including the Palmgren-Miner linear damage rule- (LDR-) based, multiaxial and variable amplitude loading, stochastic-based, energy-based, and continuum damage mechanics methods, forecast fatigue life. This paper reviews fatigue life prediction techniques for metallic materials. An ideal fatigue life prediction model should include the main features of those already established methods, and its implementation in simulation systems could help engineers and scientists in different applications. In conclusion, LDR-based, multiaxial and variable amplitude loading, stochastic-based, continuum damage mechanics, and energy-based methods are easy, realistic, microstructure dependent, well timed, and damage connected, respectively, for the ideal prediction model.This research was made possible by a NPRP award NPRP 5-423-2-167 from the Qatar National Research Fund (a member of the Qatar Foundation)

Study on start-up characteristics of H-Darrieus vertical axis wind turbines comprising NACA 4-digit series blade airfoils

Installation of H-type vertical axis wind turbines is in many cases limited by the inherent start-up issues associated with this type of turbine. This could be crucial in environments with low wind speed. The aim of this study is to provide an appropriate CFD modeling setup for investigation of the start-up behavior associated with this class of turbines. For this purpose, a series of transient CFD simulations were carried out using ANSYS Fluent. In contrast with the conventional approach, whereby a constant angular velocity is specified for the rotor, in the present work, the turbine was left free to accelerate based on the torque experienced over time. Careful considerations were made regarding turbulence modeling and grid generation, which are key to ensuring accuracy in this investigation. The result of this simulation, in the form of an accelerating time series, demonstrates good agreement with the published experimental data, and the method yields a high level of accuracy, proving its usefulness for similar problems. In another attempt, the validated CFD setup was utilized to evaluate the effects of several geometric attributes of the turbine rotor on the starting characteristics. Symmetric and cambered airfoils of different thicknesses with a wide range of pitch angles were examined. The optimum start-up characteristics were observed with the use of a medium-thickness cambered airfoil, NACA2418, put to use with an outward pitch angle of 1.5°; this configuration decreased the start-up time while retaining the turbine's peak performance

Estimation of Tsunami Bore Forces on a Coastal Bridge Using an Extreme Learning Machine

This paper proposes a procedure to estimate tsunami wave forces on coastal bridges through a novel method based on Extreme Learning Machine (ELM) and laboratory experiments. This research included three water depths, ten wave heights, and four bridge models with a variety of girders providing a total of 120 cases. The research was designed and adapted to estimate tsunami bore forces including horizontal force, vertical uplift and overturning moment on a coastal bridge. The experiments were carried out on 1:40 scaled concrete bridge models in a wave flume with dimensions of 24 m x 1.5 m x 2 m. Two six-axis load cells and four pressure sensors were installed to the base plate to measure forces. In the numerical procedure, estimation and prediction results of the ELM model were compared with Genetic Programming (GP) and Artificial Neural Networks (ANNs) models. The experimental results showed an improvement in predictive accuracy, and capability of generalization could be achieved by the ELM approach in comparison with GP and ANN. Moreover, results indicated that the ELM models developed could be used with confidence for further work on formulating novel model predictive strategy for tsunami bore forces on a coastal bridge. The experimental results indicated that the new algorithm could produce good generalization performance in most cases and could learn thousands of times faster than conventional popular learning algorithms. Therefore, it can be conclusively obtained that utilization of ELM is certainly developing as an alternative approach to estimate the tsunami bore forces on a coastal bridge.The study is made possible by the High Impact Research (HIR) Grant (UM.C/625/1/HIR/ 141), PPP Grant (PG017_2013B) and the research facilities of the Civil Engineering Department, University of Malaya

Tribo-Mechanical Properties and Corrosion Behavior Investigation of Anodized Ti–V Alloy

In the work presented in this manuscript, a self-organized TiO2 nanotube array film was produced by electrochemical anodization of a Ti⁻V alloy in an electrolyte containing NH4F/H3PO4 and then annealed at different temperatures under different atmospheres. The effect of annealing temperature in different atmospheres on the morphology of the film was analyzed, and the tribo-mechanical property and corrosion behavior of TiO2 were investigated. The morphological features and phase compositions were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The results indicated that the TiO2 characteristic peaks did not appear after anodization because of the intrinsic amorphous feature. However, highly crystalline TiO2 (anatase and rutile) was produced after annealing from 200 to 600 °C. In addition, there was an improvement in the wear resistance of the Ti⁻V alloy due to the high hardness and low coefficient of friction of the TiO2 nanotubes’ coating. Moreover, the corrosion behaviors of TiO2 coated and uncoated substrates were evaluated in the synthetic medium, and it was confirmed that the corrosion resistance of the TiO2-coated Ti⁻V alloy, annealed at 200 °C in the atmosphere, was significantly higher when compared to the uncoated sample

Synthesis of Highly-Dispersed Graphene Oxide Nanoribbons–Functionalized Carbon Nanotubes–Graphene Oxide (GNFG) Complex and Its Application in Enhancing the Mechanical Properties of Cementitious Composites

In this study, a graphene oxide nanoribbons–functionalized carbon nanotubes–graphene oxide (GNFG) complex was hydrothermally synthesized as a nanomaterial for reinforcing cementitious composites, using a modified Hummers’ method. Three types of components existed in the GNFG: Type I, the functionalized carbon nanotubes–graphene oxide nanoribbons (FCNTs–GNR); and types II and III are graphene oxide (GO) and functionalized carbon nanotubes (FCNTs), respectively, which exist independently. The dispersivity of GNFG and its effects on the mechanical properties, hydration process, and microstructures of cement pastes were evaluated, and the results were compared with those using cement pastes incorporating other typical carbon nanomaterials. The results demonstrated that dispersion of GNFG in aqueous solutions was superior to that of the CNTs, FCNTs, and GO/FCNTs mixture. Furthermore, the highly-dispersed GNFG (0.05 wt.%) improved the mechanical properties of the cement paste after 28 days of hydration and promoted the hydration of cement compared to CNTs, GO, and GO/FCNTs mixture (0.05 wt.%). The results in this study validated the feasibility of using GNFG with enhanced dispersion as a new nano-reinforcing agent for various cementitious systems

An optimization technique on ultrasonic and cutting parameters for drilling and deep drilling of nickel-based high-strength Inconel 738LC superalloy with deeper and higher hole quality

In this research work, an ultrasonic assisted drilling system is employed to apply both rotation and vibration to drill bits. The transducer horn transfers power very efficiently and changes tools effortlessly. The setup used to conduct drilling tests is Inconel 738LC with depth-to-diameter ratios from 2 to 10 by conventional drilling (CD), ultrasonic assisted drilling (UAD), and electro discharge drilling (EDD). The effects of ultrasonic vibration amplitude, spindle speed, and number of steps to drill each hole on machining force and surface roughness in UAD are investigated. The results demonstrate not only a significant improvement in tool life (by applying ultrasonic vibration to the drilling process) but also a 40 % reduction in thrust force compared to CD. The UAD technique seems more appropriate than the EDD method due to the ability to reduce machining process time by up to 90 %, improve cylindricity by roughly 50 %, increase hole dimension accuracy by up to 80 %, and reduce surface roughness by 52 %.The authors would like to acknowledge Hanyang University for providing the necessary facilities and resources for this research. This research was funded by the Hanyang University?s research fund with number 201500000000438

Photocatalytic Performance Evaluation of Titanium Dioxide Nanotube-Reinforced Cement Paste

Considering the increase in research regarding environmental pollution reduction, the utilization of cementitious material, a commonly used construction material, in photocatalysts has become a desirable research field for the widespread application of photocatalytic degradation technology. Nano-reinforcement technology for cementitious materials has been extensively researched and developed. In this work, as a new and promising reinforcing agent for cementitious materials, the photocatalytic performance of titanium dioxide nanotube (TNT) was investigated. The degradation of methylene blue was used to evaluate the photocatalytic performance of the TNT-reinforced cement paste. In addition, cement paste containing micro-TiO2 (m-TiO2) and nano-TiO2 (n-TiO2) particles were used for comparison. Moreover, the effect of these TiO2-based photocatalytic materials on the cement hydration products was monitored via X-ray diffraction (XRD) and thermogravimetric analysis (TG). The results indicated that all the TiO2 based materials promoted the formation of hydration products. After 28 days of curing, the TNT-reinforced cement paste contained the maximum amount of hydration products (Ca(OH)2). Furthermore, the cement paste containing TNT exhibited better photocatalytic effects than that containing n-TiO2, but worse than that containing m-TiO2

A flexible wearable self-supporting hybrid supercapacitor device based on hierarchical nickel cobalt sulfide@C electrode

Abstract A flexible wearable electrode consisting of nickel–cobalt sulfide (NCS) nanowires was fabricated in this study. Self-supporting NCS was grown in situ on porous carbon nanofibers without a binder as a novel material for supercapacitor electrodes. The NCS nanowires were grown using cyclic voltammetry electrodeposition, which proved to be a fast and environmentally friendly method with good controllability of the material structure. One-dimensional carbon nanofibers (C) have high surface-area-to-volume ratios, short ion transmission distances, excellent mechanical strengths, and remarkable flexibilities. Moreover, the NCS@C flexible electrode exhibited a synergetic effect with the active compounds, and the dense active sites were uniformly distributed across the entire surface of the carbon fibers, enabling rapid electron transport and enhancing the electrochemical properties of the NCS@C nanowires. The NCS@C achieved specific capacitances of 334.7 and 242.0 mAh g−1 at a current density of 2 A g−1 and high current densities (up to 40 A g−1), respectively, corresponding to a 72.3% retention rate. An NCS@C-nanofilm-based cathode and an activated-carbon-based anode were used to fabricate a flexible asymmetric supercapacitor. The device exhibited high energy and power densities of 12.91 Wh kg−1 and 358 W kg−1, respectively

Review on medical implantable antenna technology and imminent research challenges

Implantable antennas are mandatory to transfer data from implants to the external world wirelessly. Smart implants can be used to monitor and diagnose the medical conditions of the patient. The dispersion of the dielectric constant of the tissues and variability of organ structures of the human body absorb most of the antenna radiation. Consequently, implanting an antenna inside the human body is a very challenging task. The design of the antenna is required to fulfill several conditions, such as miniaturization of the antenna dimension, biocompatibility, the satisfaction of the Specific Absorption Rate (SAR), and efficient radiation characteristics. The asymmetric hostile human body environment makes implant antenna technology even more challenging. This paper aims to summarize the recent implantable antenna technologies for medical applications and highlight the major research challenges. Also, it highlights the required technology and the frequency band, and the factors that can affect the radio frequency propagation through human body tissue. It includes a demonstration of a parametric literature investigation of the implantable antennas developed. Furthermore, fabrication and implantation methods of the antenna inside the human body are summarized elaborately. This extensive summary of the medical implantable antenna technology will help in understanding the prospects and challenges of this technology. 2021 by the authors. Licensee MDPI, Basel, Switzerland.Funding: This research was funded by Qatar National Research Fund, a member of Qatar Foundation, Doha, Qatar, grant number NPRP11S-0102-180178 and the APC was funded by grant number NPRP11S-0102-180178. The statements made herein are solely the responsibility of the authors.Scopu

Electrodeposited nickel aluminum-layered double hydroxide on Co3O4 as binder-free electrode for supercapacitor

Here, we report a heterostructured core–shell electrode consists of cobalt oxide (Co3O4 ) nanowire core and nickel aluminum (NiAl)-layered double hydroxide (NiAl-LDH; herein Co3O4@LDH) nanosheet shell grown on nickel foam as advanced electrode for supercapacitor. Benefiting from the core–shell configuration and smart hybridization, the optimized Co3O4@LDH core–shell electrode exhibits a high capacitance of 2011 Fg−1 at 2Ag−1 and remains 1455 Fg−1 at 40 Ag−1 , which outperforms the electrochemical performance of individual component of Co3O4 (720 Fg−1 at 2 Ag−1). A hybrid supercapacitor using Co3O4@LDH as positive electrode and carbon nanotube as negative electrode delivers an energy density of 18.1 Whkg−1 at a power density of 375 kWkg−1 at a current density of 0.5 Ag−1 . Smart hybridization of core–shell electrode shows great promise as advanced electrode materials for supercapacitor with high electrochemical performance