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Volume 7, Number 3, September 2018

This article studies the free and forced vibrations of the carbon nanotubes CNTs embedded in an elastic medium including thermal and dynamic load effects based on nonlocal Euler- Bernoulli beam. A Winkler type elastic foundation is employed to model the interaction of carbon nanotube and the surrounding elastic medium. Influence of all parameters such as nonlocal small-scale effects, high temperature change, Winkler modulus parameter, vibration mode and aspect ratio of short carbon nanotubes on the vibration frequency are analyzed and discussed. The non-local Euler-Bernoulli beam model predicts lower resonance frequencies. The research work reveals the significance of the small-scale coefficient, the vibrational mode number, the elastic medium and the temperature change on the non-dimensional natural frequency.

Key Words
Winkler\'s moduls; forced vibration; carbon nanotubes; non-local Euler beam theory

(1) Département de génie civil, Université Ibn Khaldoun Tiaret; BP 78 Zaaroura, Tiaret, Algérie;
(2) Laboratoire de Géomatique et Développement Durable, Université de Tiaret, Algérie.

The mechanism of biological materials structure is very complex and has optimal properties compared to engineering materials. Top Neck mollusks shells, as an example of biological materials, have hierarchical structure, which 95 percent of its structure is Aragonite and 5 percent organic materials. This article detected mechanical properties of the Top Neck mollusks shell as a Nano composite using Nano-indentation method in different situations. Research findings indicate that mechanical properties of the Top Neck mollusks shell including elastic modulus and hardness are higher than a fresh one preserved in -50 centigrade and also a Top Neck mollusks shell preserved in environmental conditions. Nano-indentation test results are so close in range, overall, that hardness degree is 3900 to 5200 MPa and elastic modulus is 70 to 85 GPa.

Key Words
nano indentation; top neck mollusks shell; mechanical properties; elastic modulus; hardness

(1) Abolfazl Darvizeh:
Department of Mechanical Engineering, University Campus 2, University of Guilan, Rasht, Iran;
(2) Asghar Zajkani:
Department of Mechanical Engineering, University of Guilan, Rasht, Iran;
(3) Amin Nouroozi Masir:
Department of Mechanical Engineering, Imam Khomeini International University, Qazvin, Iran.

High Strength low alloy steels containing various levels of C, Nb and Mn were used and for each of which, a simulated double thermal cycle was applied with the same first peak temperature and different second peak temperatures to produce HAZ microstructure corresponding to multi-pass weld. Effect of double cycle second temperature on the microstructure was observed and compared with single cycle results obtained from previous works, it was found that the percentage of martensite austenite constituent (MA) increases by Nb addition for all steels with the same Mn content and the increase in Mn content at the same Nb content shows an increase in MA area fraction as well. MA area fraction obtained for the double cycle is larger than that obtained for the single cycle for all steels used which imply that MA will have great role in the brittle fracture initiation for double cycle and the inter-pass temperature should be controlled for medium and high-carbon Mn steel to avoid large area fraction of MA. The beneficial effects of Niobium obtained in single pass weld were not observed for the double cycle or multi pass welds.

Key Words
HAZ; double cycle; multi pass weld; microstructure; carbon; manganese; niobium; MA

(1) Emad F. El-Kashif:
Department of Mechanical Design and Production Engineering, Cairo University, Egypt;
(2) Morsy A. Morsy:
Welding and NDT Laboratory, CMRDI, Cairo, Egypt.

This investigation is focused on the study of effect of hall current in transversely isotropic magneto thermoelastic homogeneous medium with fractional order heat transfer and rotation. As an application the bounding surface is subjected to normal force. The research becomes more interesting due to interaction of Hall current with the effect of rotation as it has found various applications. Laplace and Fourier transform is used for solving field equations. The analytical expressions of temperature, displacement components, stress components and current density components are computed in the transformed domain. The effects of hall current and fractional order parameter at different values are represented graphically.

Key Words
Laplace and Fourier Transform; thermoelastic; hall current; Transversely Isotropic; fractional order heat transfer

Department of Basic and Applied Sciences, Punjabi University, Patiala, Punjab, India.

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