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Volume 12, Number 1, March 2023

The combination of cobalt ferrite and natural rubber has a potential to enhance the functional properties of rubber ferrite composites available on the market. In this study, cobalt ferrite was synthesized by the sol-gel method with tapioca starch as a cheating agent and then incorporated into natural rubber using an internal mixer. The curing characteristics, magnetic hysteresis, complex permeability, and permittivity of the rubber ferrite composites were studied as a function of the loading from 0 to 25 phr. The cure time and scorch time tended to reduce with the addition of non-reinforced cobalt ferrite fillers. The remanent and saturation magnetizations were linearly proportional to the cobalt ferrite loading, consistent with the rule of mixture. On the other hand, the increase in cobalt ferrite loading from 5 to 25 phr slightly affected the coercive field and the complex permeability. Using the maximum loading of 25 phr, both real and imaginary parts of the permittivity were significantly raised and reduced with the frequency in the 10-300 MHz range.

Key Words
cobalt ferrite; curing; magnetic hysteresis; natural rubber; rubber ferrite composite

Anuchit Hunyek: Program of General Education-Science (Physics), Faculty of Liberal Arts, Rajamangala University of Technology Rattanakosin, Wangklaikangwon Campus, Prachuap Khiri Khan, Thailand
Chitnarong Sirisathitkul: Division of Physics, School of Science, Walailak University, Nakhon Si Thammarat, Thailand; Functional Materials and Nanotechnology Center of Excellence, Walailak University, Nakhon Si Thammarat, Thailand

In this paper, fracture analysis of a continuously inhomogeneous arch structure with two longitudinal cracks is developed in terms of the time-dependent strain energy release rate. The arch under consideration exhibits non-linear creep behavior. The cross-section of the arch is a rectangle. The material is continuously inhomogeneous along the thickness of the cross-section. The arch is loaded by two bending moments applied at its end sections. The mechanical behavior of the material is described by using a non-linear stress-strain-time relationship. The two longitudinal cracks are located symmetrically with respect to the mid-span of the arch. Due to the symmetry, only half of the arch is considered. Time-dependent solutions to strain energy release rate are obtained by analyzing the balance of the energy. For verification, time-dependent solutions to the strain energy release rate are derived also by considering the time-dependent complementary strain energy. The evolution of the strain energy release rate with the time is analyzed. The effects of material inhomogeneity, locations of the two cracks along the thickness of the arch and the magnitude of the external loading on the time-dependent strain energy release rate are evaluated.

Key Words
analytical investigation; inhomogeneous arch; longitudinal crack; non-linear creep behavior; time-dependent solution

Victor I. Rizov: Department of Technical Mechanics, University of Architecture, Civil Engineering and Geodesy, Chr. Smirnensky Blvd., 1046-Sofia, Bulgaria
Holm Altenbach: Lehrstuhl für Technische Mechanik, Fakultät für Maschinenbau, Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Deutschland

In the present article, the effects of three thermal relaxation times in living tissue under the three-phaselag (TPL) bioheat model are introduced. Using the Laplace transforms, the analytical solution of the temperature and the resulting thermal damages in living tissues are obtained. The experimental data are used to validate the analytical solutions. By the formulations of Arrhenius, the thermal damage of tissue is estimated. Numerical outcomes for the temperature and the resulting of thermal damages are presented graphically. The effects of parameters, such as thermal relaxation times, blood perfusion rate on tissue temperature are also discussed in detail.

Key Words
bio-heat transfer; laplace transforms; living tissues; three-phase lag model

Ibrahim A. Abbas, Aboelnour Abdalla, Fathi Anwar and Hussien Sapoor: Department of Mathematics, Faculty of Science, Sohag University, Sohag, Egypt

Free vibration analysis of power law and sigmoidal sandwich plates made up of functionally graded materials (FGMs) has been carried out using finite element based higher-order zigzag theory. The present model satisfies all-important conditions such as transverse shear stress-free conditions at the plate's top and bottom surface along with continuity condition for transverse stresses at the interface. A Nine-noded C0 finite element having eleven degrees of freedom per node is used during the study. The present model is free from the requirement of any penalty function or post-processing technique and hence is computationally efficient. The present model's effectiveness is demonstrated by comparing the present results with available results in the literature. Several new results have been proposed in the present work, which will serve as a benchmark for future works. It has been observed that the material variation law, power-law exponent, skew angle, and boundary condition of the plate widely determines the free vibration behavior of sandwich functionally graded (FG) plate.

Key Words
free vibration; higher-order zigzag theory; power-law; sandwich FG plate; sigmoidal law

Aman Garg: Department of Civil and Environmental Engineering, The NorthCap University, Gurugram, Haryana, 122017, India
Simmi Gupta: Department of Civil Engineering, National Institute of Technology Kurukshetra, Haryana, 136119, India
Hanuman D. Chalak: Department of Civil Engineering, National Institute of Technology Kurukshetra, Haryana, 136119, India
Mohamed-Ouejdi Belarbi: Laboratoire de Recherche en Génie Civil, LRGC. Université de Biskra, B.P. 145, R.P. 07000, Biskra, Algeria
Abdelouahed Tounsi: YFL (Yonsei Frontier Lab), Yonsei University, Seoul, Korea; Department of Civil and Environmental Engineering, King Fahd University of Petroleum &Minerals, 31261 Dhahran, Eastern Province, Saudi Arabia
6Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algeria
Li Li: State Key Laboratory of Digital Manufacturing Equipment and Technology, School of Mechanical Science and
Engineering, Huazhong University of Science and Technology, Wuhan 430074, China
A.M. Zenkour: Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia; Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafrelsheikh, Egypt

Basalt and poly-ester fibers along with epoxy resin were used to produce inter-ply, intra-ply and functionally gradient hybrid composites. In all of the composites, the relative content of basalt fiber to poly-ester fiber was equal to 50 percent. The flexural and charpy impact properties of the hybrid composites are presented with particular regard to the effects of the hybrid types, stacking sequence of the plies, loading direction and loading speed. The results show that with properly choosing the composition and the stacking sequence of the plies; the inter-ply hybrid composites can achieve better flexural strength and impact absorption energy compared to the intra-ply and functionally gradient composites. The flexural strength and impact absorption energy of the functionally gradient hybrid composites is comparable to, or higher than the intra-ply sample. Also, by increasing the loading speed, the flexural strength increases while the flexural modulus does not have any special trend.

Key Words
basalt fiber; FGM; flexural properties; hybrid composites; impact properties

Ehsan Fadayee Fard, Hassan Sharifi: Department of Materials Science, Faculty of Engineering, Shahrekord University, Shahrekord, Iran
Majid Tehrani: Department of Art, Shahrekord University, Shahrekord 56811-88617, Iran
Ehsan Akbari: Department of Materials Science, Faculty of Engineering, Shahrekord University, Shahrekord, Iran

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