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CONTENTS
Volume 13, Number 4, October 2022
 

Abstract
The microstructure and mechanical properties of Cr-Ni steel and Cr-Ni steel-matrix nanocomposites reinforced with nano-ZrO2 particles were investigated in this study. Cr-Ni steel and Cr-Ni/ZrO2 nanocomposites were produced using a combination of high-energy ball milling, pressing, and sintering processes. The microstructures of the specimens were analyzed using EDX and XRD. Compression and hardness tests were performed to determine the mechanical properties of the specimens. Nano-ZrO2 particles were effective in preventing chrome carbide precipitate at the grain boundaries. While t‒ZrO2 was detected in Cr-Ni/ZrO2 nanocomposites, m‒ZrO2 could not be found. Few α'‒martensite and deformation bands were formed in the microstructures of Cr-Ni/ZrO2 nanocomposites. Although nano-ZrO2 particles had a negligible impact on the strength improvement provided by deformation-induced plasticity mechanisms in Cr-Ni/ZrO2 nanocomposites, the mechanical properties of Cr-Ni steel were significantly improved by using nano-ZrO2 particles. The hardness and compressive strength of Cr-Ni/ZrO2 nanocomposite were higher than those of Cr-Ni steel and enhanced as the weight fraction of nano-ZrO2 particles increased. Cr-Ni/ZrO2 nanocomposite with 5wt.% nano-ZrO2 particles had almost twofold the hardness and compressive strength of Cr-Ni steel. The nano-ZrO2 particles were considerably more effective on particle-strengthening mechanisms than deformation-induced strengthening mechanisms in Cr-Ni/ZrO2 nanocomposites.

Key Words
Cr-Ni steel; deformation-induced strengthening mechanisms; nanocomposite; nano-ZrO2

Address
Özlem Sevinç: Interdisciplinary Division of Materials Science and Engineering, Ege University, 35040, Izmir, Turkey

Ege A. Diler: Department of Mechanical Engineering, Ege University, 35040, Izmir, Turkey

Abstract
Endophytes ascertain a symbiotic relationship with plants as promoters of growth, defense mechanism etc. This study is a first report to screen the endophytic population in Waltheria indica, a tropical medicinal plant. 5 bacterial and 3 fungal strains in leaves, 3 bacterial and 1 yeast species in stems were differentiated morphologically and identified by biochemical and molecular methods. The phylogenetic tree of the isolated endophytes was constructed using MEGA X. Silver nanoparticles were biosynthesized from a rare endophytic bacterium Cupriavidus metallidurans isolated from the leaf of W. indica. The formation of silver nanoparticles was confirmed by UV-Visible spectrophotometer that evidenced a strong absorption band at 408.5 nm of UV-Visible range with crystalline nature and average particle size of 16.4 nm by Particle size analyzer. The Fourier Transform Infra-Red spectrum displayed the presence of various functional groups that stabilized the nanoparticles. X-ray diffraction peaks were conferred to face centered cubic structure. Transmission Electron Microscope and Scanning Electron Microscope revealed the spherical-shaped, polycrystalline nature with the presence of elemental silver analyzed by Energy Dispersive of X-Ray spectrum. Selected area electron diffraction also confirmed the orientation of AgNPs at 111, 200, 220, 311 planes similar to X-ray diffraction analysis. The synthesized nanoparticles are evaluated for antimicrobial activity against 7 bacterial and 3 fungal pathogens. A good zone of inhibition was observed against pathogenic bacteria than fungal pathogens. Thus the study could hold a key aspect in drug discovery research and other pharmacological conducts of human clinical conditions.

Key Words
antimicrobial activity; Cupriavidus metallidurans; endophytes; silver nanoparticles; Waltheria indica

Address
C.Nirmala and M.Sridevi: Department of Biotechnology, Vinayaka Mission's Kirupananda Variyar Engineering College, Vinayaka Mission's Research Foundation (Deemed to be University), Salem, Tamilnadu, India


Abstract
The continuous elements method, also known as the dynamic stiffness method, is effective for solving structural dynamics problems, especially over a large frequency range. Before applying this method to fluid-structure interactions, it is advisable to check its validity for pure acoustics, without considering the different coupling parameters. This paper describes a procedure for taking wave propagation into account in the formulation of a Dynamic Stiffness Matrix. The procedure is presented in the context of the harmonic response of acoustic pressure. This development was validated by comparing the harmonic response calculations performed using the continuous element model with the analytical solution. In addition, this paper illustrates the application of this method to a simple compressible flow problem, since it has been applied solely to structural problems to date.

Key Words
acoustic; continuous element; dynamic stiffness; flow; wave propagation

Address
Mohamed A. Khadimallah: Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia/ Laboratory of Systems and Applied Mechanics, Polytechnic School of Tunisia, University of Carthage, Tunis, Tunisia

Imene Harbaoui: Laboratory of Applied Mechanics and Engineering LR-MAI, University Tunis El Manar- -ENIT BP37- Le belvédère, 1002, Tunisia

Jean B. Casimir: Institut Supérieur de Mécanique de Paris, Quartz (EA 7393), 3 rue Fernand Hainaut, Saint-Ouen 93407, France

Lamjed H. Taieb: Department of Civil Engineering, College of Engineering in Al-Kharj, Prince Sattam Bin Abdulaziz University, Al-Kharj, 11942, Saudi Arabia/ Research Laboratory of applied fluid mechanics, process engineering and environment, National Engineering School of Sfax, Sfax University, Tunisia

Muzamal Hussain: Department of Mathematics, Govt. College University Faisalabad, 38040, Faisalabad, Pakistan

Abdelouahed Tounsi: YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea/ Department of Civil and Environmental Engineering, King Fahd University of Petroleum and Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia

Abstract
Recently, promising structural technologies like multi-function, ultra-load bearing capacity and tailored structures have been put up for discussions. Finite Element (FE) modelling is probably the best-known option capable of treating these superior properties and multi-domain behavior structures. However, advanced materials such as Functionally Graded Material (FGM) and nanocomposites suffer from problems resulting from variable material properties, reinforcement aggregation and mesh generation. Motivated by these factors, this research proposes a unified shape function for FGM, nanocomposites, graded nanocomposites, in addition to traditional isotropic and orthotropic structural materials. It depends not only on element length but also on the beam's material properties and geometric characteristics. The systematic mathematical theory and FE formulations are based on the Timoshenko beam theory for beam structure. Furthermore, the introduced element achieves C1 degree of continuity. The model is proved to be convergent and free-off shear locking. Moreover, numerical results for static and free vibration analysis support the model accuracy and capabilities by validation with different references. The proposed technique overcomes the issue of continuous properties modelling of these promising materials without discarding older ones. Therefore, introduced benchmark improvements on the FE old concept could be extended to help the development of new software features to confront the rapid progress of structural materials.

Key Words
finite element modeling; functionally graded material; functionally graded nanocomposites beams; isotropic; nanocomposites; orthotropic; timoshenko beam element

Address
A. M. El-Ashmawy: Department of Aircraft Mechanics, Military Technical College, Cairo, Egypt

Yuanming Xu: School of Aeronautic Science and Engineering, Beihang University, Beijing, 100191, China/ Beijing Advanced Discipline Center for Unmanned Aircraft System, Beijing, China

Abstract
Dynamic study of concrete plates under impact load is presented in this article. The main objective of this work is presenting a mathematical model for the concrete plates under the impact load. The concrete plate is reinforced by carbon nanoparticles which the effective material proprieties are obtained by mixture's rule. Impacts are assumed to occur normally over the top layer of the plate and the interaction between the impactor and the structure is simulated using a new equivalent three-degree-of-freedom (TDOF) spring–mass–damper (SMD) model. The structure is assumed viscoelastic based on Kelvin-Voigt model. Based on the classical plate theory (CPT), energy method and Hamilton's principle, the motion equations are derived. Applying DQM, the dynamic deflection and contact force of the structure are calculated numerically so that the effects of mass, velocity and height of the impactor, volume percent of nanoparticles, structural damping and geometrical parameters of structure are shown on the dynamic deflection and contact force. Results show that considering structural damping leads to lower dynamic deflection and contact force. In addition, increasing the volume percent of nanoparticles yields to decreases in the deflection.

Key Words
concrete plate; CPT; low velocity impact; nanoparticles; numerical method

Address
Jijun Luo: Shaanxi Engineering Research Center of Controllable Neutron Source, Xijing University of School of Electronic Information, Xijing University, Xi'an 710123, Shaanxi, China


Meng Lv: China Construction Seventh Engineering Division Corp., LTD., Zhengzhou 450000, Henan, China

Suxia Hou: Shaanxi Engineering Research Center of Controllable Neutron Source, Xijing University of School of Electronic Information, Xijing University, Xi'an 710123, Shaanxi, China

Mohsen Nasihatgozar: Department of mechanical engineering, Kashan Branch, Islamic Azad University, Kashan, Iran

Amir Behshad: Faculty of Technology and Mining, Yasouj University, Choram 75761-59836, Iran

Abstract
One factor that can heighten the risk of the rapture intracranial aneurysm (IA) is bifurcations, which can cause the IA to evaluate. This study presents the effect of geometric of intracranial vascular on the bifurcation analysis of the aneurysm occurrence. The aneurysm mechanism is mathematically modeled based on the nano pipe structures under the thermal stresses, and the impact of the aneurysm geometric on the stability and bifurcation points is analyzed. Because of the dimension of these structures, the classical theories could not predict their behavior perfectly, so the nonclassical and nonlocal theories are required for the mechanical modeling of the aneurysm. The presented results show that the bifurcation point of the aneurysm mechanism is dependent on the environment temperature, and the temperature change plays an essential role in the stability of these structures.

Key Words
aneurysm mechanism; bifurcation; buckling behavior; dynamic characteristics; mechanical analysis

Address
Jun Liu: The Second Affiliated Hospital, Wannan Medical College, Wuhu 241001, Anhui, China/ Vascular Diseases Research Center, Wannan Medical College, Wuhu 241001, Anhui, China

Qingyun Zhang: Ma An Shan General Hospital of Ranger-Duree Healthcare, Maanshan 243000, Anhui, China

Hua Chen: The First Affiliated Hospital, Nanjing Medical University, Nanjing 210029, Jiangsu, China

Abstract
In the present article, functionally graded small-scaled plates based on modified strain gradient theory (MSGT) are studied for analyzing the nonlinear bending and post-buckling responses. Von-Karman's assumptions are applied to incorporate geometric nonlinearity and the first-order shear deformation theory is used to model the plates. Modified strain gradient theory includes three length scale parameters and is reduced to the modified couple stress theory (MCST) and the classical theory (CT) if two or all three length scale parameters become zero, respectively. The Ritz method with Legendre polynomials are used to approximate the unknown displacement fields. The solution is found by the minimization of the total potential energy and the well-known Newton-Raphson technique is used to solve the nonlinear system of equations. In addition, numerical results for the functionally graded small-scaled plates are obtained and the effects of different boundary conditions, material gradient index, thickness to length scale parameter and length to thickness ratio of the plates on nonlinear bending and post-buckling responses are investigated and discussed.

Key Words
FG small-scaled plates; length scale; modified couple stress theory; modified strain gradient theory; nonlinear bending; post-buckling behavior

Address
S. Amir M. Ghannadpour and Selma Khajeh: Faculty of New Technologies Engineering, Shahid Beheshti University, Tehran, Iran

Abstract
In this study, the gravitating mechanical stir casting method was used to fabricating the Nb2O5/AZ31 magnesium matrix nanocomposites. Niobium pentoxide (Nb2O5) used as reinforcement with two different weight percentages (3 wt % and 6 wt %). The influence of Nb2O5 on microstructure and mechanical properties has been investigated. The microstructure analysis showed that the composites are mainly composed of the primary α-magnesium phase and phase β-Mg17Al12 secondary phase. The secondary phase was dispersed evenly along the grain boundary of the Mg phase. The Nb2O5/AZ31 nanocomposites revealed that the grain size and its lamellar shape (β-Mg17Al12) were gradually refined. Different strengthening mechanisms were assessed in terms of their contributions. Results showed that composite material properties of hardness, yield strength, and fracture study were directly related to Nb2O5 as a reinforcement. The maximum values of the mechanical properties were achieved with the addition of 3 wt% Nb2O5 on the AZ31 alloy.

Key Words
casting; mechanical properties; mechanical testing; metal-matrix composites (MMCs); microstructural analysis; nanocomposites

Address
Song-Jeng Huang, Sathiyalingam Kannaiyan and Murugan Subramani: Department of Mechanical Engineering, National Taiwan University of Science and Technology, Taipei, 10607, Taiwan, (ROC)

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