Nano-Indentation Measurement of Fracture Toughness of Dental Enamel

Effect of orthodontic bracket bonding-debonding on fracture toughness of human dental enamel was investigated by using nano-indentation test. For this purpose, some ceramic brackets were bonded by a dental adhesive on the buccal surface of sound human teeth enamel. All clinical requirements were considered for bracket bonding and sample preparation. After debonding of the brackets, the teeth were sectioned transverse to their longitudinal axes and from the middle of the bracket region to prepare the samples required for nano-indentation tests. The nanoindentation test was performed on both the enamel under bracket and the intact enamel. The values of fracture toughness of dental enamel in both regions were calculated from the analysis of nano-scale holes observed after the nano-indentation tests. A comparison between the results obtained from the two regions indicated that bracket bonding-debonding significantly decreased the fracture toughness of human dental enamel.     

Physical,mechanical and dry sliding wear properties of hybrid and non-hybrid Al–V nanocomposites produced by powder metallurgy

The present work aims to characterise the sliding wear behaviour of non-hybrid Al–Al₃V and hybrid Al–(Al₃V, Al₂O₃) nanocomposites. Wear rates were calculated from mass loss measurements. X-Ray diffraction (XRD) pattern was utilised to evaluate the microstructural changes during milling hot-pressed samples. It was found that the wear resistance of hybrid nanocomposites was enhanced by increasing Al₃V–Al₂O₃ percentage due to an increase in hardness. The mass loss measurement showed that not only was the wear rate of hybrid samples lower than that of Al–Al₃V, but also it had lower friction coefficients in comparison to the non-hybrid sample. The worn surface evaluation in hybrid samples indicated that the formed darker layer possesses the features of the mechanically mixed layer (MML), which inhibits mass loss intensification. Moreover, formation of MML as a lubricant layer promotes the friction characteristic of the hybrid nanocomposite.     

Candidate architectures for emerging IoV: a survey and comparative study

Intelligent Transportation System (ITS) is observing significant evolution in terms of technology and investment worldwide. This has given birth to the new concept of Internet of vehicles (IoV) as one of the leading applications of the Internet of Things. IoV aims to offer a better sharing of information and communication between vehicles, enabling higher cooperation for common interests. IoV is increasingly attracting the interest of a significant body of research. The e ort was mostly focused on solving various problems encountered in traditional VANETs, such as lack of coordination between vehicles, insufficient information, scalability, etc. Rapidly, IoV observed, particularly interesting advances taking advantage of exponential growth in communication and data analysis technologies. This includes cloud and/or fog computing, large data analytics, machine learning, and artificial intelligence. In this paper, we make a survey of the existing and recently proposed architecture solutions for IoV systems. Moreover, we define a list of criteria, features, and properties associated to the various architectures in order of making critical and insightful comparisons and assessments. Finally, we outline the key future research perspectives on the topic and define the key technical aspects that will help drive the future of IoV architectures.

     

Adjustment of Aging Temperature for Reaching Superelasticity in Highly Ni-Rich Ti-51.5Ni NiTi Shape Memory Alloy

In this research, the effects of aging temperature on the phase transformation, mechanical properties, and superelasticity of Ti–51.5 at.% Ni alloy were investigated. For this purpose, samples were solution annealed and then aged at different temperatures ranging from 300 to 700°C. The results showed that the change of aging temperature has a great influence on the behavior of the alloy. Aging at 300 and 400°C led to the occurrence of the austenite to R phase (A ? R) transformation. By aging at these temperatures, the ultimate tensile strength and elongation did not change significantly compared to the solution annealed sample. Aging at 500 and 600°C led to the appearance of B19′ phase during cooling cycle of differential scanning calorimetry tests. Samples aged at 500 and 600°C showed the best mechanical properties, in comparison with the other aging temperatures. Maximum tensile strength of 1250 MPa and the elongation of 25% were obtained by aging at 500 and 600°C, respectively. Solution-annealed sample showed no superelastic property. Complete superelasticity was observed by aging at 400 and 500°C. The sample aged at 700°C showed the transformation behavior and mechanical properties similar to the solution annealed sample.     

Finite-element modeling of rate dependent mechanical properties in nanocrystalline materials

A generalized self-consistent polycrystal model is used to study the mechanical properties of polycrystalline metals as the grain size decreases from the ultra-fine size to the nanometer scale. The model takes each oriented grain and its immediate grain boundary to form a pair. Then by making use of a composite model, the nonlinear behavior of the nanocrystalline polycrystal is determined. The finite-element method is employed in conjunction with the unit cell of the composite to investigate the rate-dependent tensile behavior of the system. A dislocation density based constitutive equation is used to describe the plastic flow behavior of the grain interior. The boundary phase is assumed to have the mechanical properties of quasi-amorphous material. The constitutive equations for both grain interior and boundary phase are implemented into a finite-element program and the results of the calculations are compared with previously published experimental data. For some cases, an optimization procedure was used to tune some parameters of the model in order to decrease the distance between the calculated and experimental stress–strain curves. The agreement between results indicates the suitability of the updated model for nanocrystalline materials.     

Effect of frequency and duty cycle on corrosion and wear resistance of functionally graded Zn–Ni nanocomposite coating

In this study, functionally graded Zn–Ni nanocomposite coatings with a nanoparticle mix of 80?wt-% alumina, 5?wt-% yttria and 15?wt-% graphene were electrodeposited on a mild steel substrate by the pulsed current method. The effects of pulse parameters such as frequency and duty cycle on chemical composition, microstructure, corrosion resistance and tribological properties of coated specimens were evaluated. The coatings were formed through changing the duty cycle from 10% to 90% in five steps during the coating process and different frequencies of 500, 1000, 3000 and 5000?Hz. A continuous decrease in the duty cycle led to an increase of the nanoparticles embedded in the coating structure from the interface to the surface, so that most increments corresponded to the sample with a 500?Hz frequency and was 1.41?wt-%. By increasing the frequency, Ni and nanoparticle content in the coating surfaces increased up to 3.6?wt-% and 1.82?vol.-%, respectively. In particular, by increasing the frequency and nanoparticle content in the coatings, corrosion and wear resistance of coatings improved.     

Thermodynamic analysis of NiTi formation by mechanical alloying

Disordered B2-NiTi intermetallic phase was produced from a mixture of Ni and Ti powders by mechanical alloying (MA). X-ray technique was used for phase analysis. The results indicated that Ni(Ti) solid solution can be formed earlier and changed to disordered B2-NiTi intermetallic phase after 60 h of MA. A thermodynamic analysis of the process was then carried out using Miedema model. The results showed that there is a thermodynamic driving force in Ni–Ti binary to form solid solution at all compositions and amorphous phase in the composition range X_Ni: 0.05–0.95 where X_Ni is mole fraction of Ni. However, the stable phase which has the minimal Gibbs free energy is solid solution compared to amorphous phase at all compositions. The results of MA were compared with thermodynamic analysis and it was indicated that the product of MA is the most stable phase in Ni–Ti binary system.     

Synthesis of mesoporous ZSM-5 from rice husk ash with ultrasound assisted alkali-treatment method used in catalytic cracking of light naphtha

A series of mesoporous ZSM-5 zeolite was synthesized with ultrasonic assisted alkali-treatment technique and their catalytic activity was investigated in catalytic cracking of light naphtha. ZSM-5 zeolite was synthesized from rice husk ash without using any organic template. Effect of alkali-treatment conditions on physicochemical properties of synthesized zeolite was investigated with XRD, FESEM, TEM, N2 adsorption-desorption isotherm, NH3-TPD and TGA technique. It was found that ultrasound energy facilitates the creation of hierarchical structure of ZSM-5 during alkali-treatment. According to XRD analysis, zeolite structure was preserved after 20 min ultrasonic assisted alkaline treatment. However, prolonged dessilication time led to the destruction of MFI zeolite structure. The synthesized ZSM-5 represented highly ordered hexagonal-shape morphology. With increasing alkali-treatment time, the plough land roughness appeared on the surface of zeolite. Comparison of the textural properties samples revealed that the mesopore surface area of alkali-treated samples increased considerably with the increase of ultrasonic assisted alkali-treatment time. Results from catalytic activity tests showed that ultrasound energy has great influence on the activity of ZSM-5. The sample had the highest activity after alkali-treated for 20 min in presence of ultrasound energy which was due to their appropriate hierarchical structure.