Institute of Fundamental Technological Research
Polish Academy of Sciences


Prof. Masoud Tahani

Department of Information and Computational Science (ZIiNO)
Division of Computational Analysis of Advanced Structures (ZeKAZK)
telephone: (+48) 22 826 12 81 ext.: 183
room: 409

Recent publications
1.  Momeni-Khabisi H., Tahani M., Coupled thermal stability analysis of piezomagnetic nano-sensors and nano-actuators considering the flexomagnetic effect, EUROPEAN JOURNAL OF MECHANICS A-SOLIDS, ISSN: 0997-7538, DOI: 10.1016/j.euromechsol.2022.104773, Vol.97, pp.1-12, 2023

The current investigation deals with an analytical formulation and solution procedure for the thermal stability characteristics of piezomagnetic nano-sensors and nano-actuators considering the flexomagnetic effects and geometrical imperfection. Piezo-flexomagnetic nano-plate strips with the mid-plane initial rise are subjected to external uniform, linear, and nonlinear temperature rise loading across the thickness. The nonlinear size-dependent governing equations are derived within the framework of the first-order shear deformation plate theory, nonlocal strain gradient theory and considering the nonlinear von- Kármán strains. The proposed closed-form solutions and the obtained results are validated with the available data in the literature. The calculated buckling and post-buckling temperatures of piezo-flexomagnetic nano-plate strips are shown to be dependent on several factors including the scaling parameters, plate slenderness ratio, mid-plane initial rise, different temperature distributions, and scalar magnetic potential. The presented closed-form solutions and numerical results can serve as benchmarks for future analyses of piezo-flexomagnetic nano-sensors and nano-actuators.

Thermal buckling and post-buckling, Closed-form solution, Piezo-flexomagnetic plate strip, Size-dependent theories, Mid-plane initial rise

Momeni-Khabisi H. - other affiliation
Tahani M. - IPPT PAN
2.  Amin al-tojary G., Mohandes Y., Tahani M., A finite element study of a fractured tibia treated with a unilateral external fixator: The effects of the number of pins and cortical thickness, Injury, ISSN: 0020-1383, DOI: 10.1016/j.injury.2022.04.019, Vol.53, pp.1-9, 2022

Introduction: In the early stage of fracture fixation, the aim of a unilateral external fixator (UEF) to stimulate healing and maintain stability may be suppressed by using inadequate number of pins. Cortical thinning due to age or osteoporosis endangers a successful fracture fixation.
Materials and methods: This study evaluates the initial strength and stability of the fracture fixation and tissue differentiation under the influences of variable cortical thickness (5 mm to 1 mm) and variable number of pins (1 to 4 in each bone fragment). A finite element program was utilised to develop 20 three-dimensional models of simplified diaphyseal tibia with fracture callus fixed with UEF. A mechano-regulation code based on the deviatoric strain theory was written and applied to simulate tissue differentiation. The values of von Mises stress, interfragmentary strain (IFS), and fibrocartilage index (FCI) were evaluated.
Results: Cortical thinning from 5 mm to 1 mm increased IFS and FCI by an average of 30.3% and 18.7%, respectively, and resulted in higher stresses in the UEF and bone. Using 1 pin in each bone fragment produced excessive IFS in the models with 1 mm, 2 mm and 3 mm cortical thickness. Inserting the second pin into the bone fragment could considerably reduce the IFS and fibrocartilaginous tissue formation in the fracture site and improve load transmission to the fixator. Whereas inserting the fourth pin could minimally affect the mechano-biological environment of healing.
This study suggests that initial instability due to cortical thinning can be efficiently alleviated by adding the number of pins up to 3 in a UEF; additionally, it may improve the knowledge about applying UEFs adequately stable, whilst promoting inclination toward endochondral ossification, simultaneously.

Unilateral external fixator, Bone fracture healing, Osteoporosis, Interfragmentary strain, Mechanical stress, Endochondral ossification

Amin al-tojary G. - other affiliation
Mohandes Y. - other affiliation
Tahani M. - IPPT PAN
3.  Ghalami Y., Askari A.R., Awrejcewicz J., Tahani M., Strain gradient bistability of bimorph piezoelectric curved beam interacting with a curved electrode, Journal of the Brazilian Society of Mechanical Sciences and Engineering, ISSN: 1678-5878, DOI: 10.1007/s40430-022-03460-8, Vol.44, No.173, pp.1-17, 2022

In this study, the size-dependent bistable behavior of a micro-electro-mechanical curved beam under the piezoelectric actuation is investigated. The system is modeled as a clamped slightly curved Euler–Bernoulli beam sandwiched with two piezoelectric layers along its length and suspended over a curved fixed electrode. Employing the strain gradient theory, the nonlinear governing equilibrium equation is derived using the principle of minimum total potential energy. A multi-mode Galerkin’s weighted residual method with the linear undamped mode-shapes of the straight beam as the approximating functions is then utilized to solve the higher-order governing equilibrium equation. The instability thresholds of the system are then obtained by vanishing the determinant of the Jacobian of the reduced equations. It is found that the present solutions are completely converged when three eigenmodes are included in the reduced order model (ROM), while hiring a single mode solution predicts the position of the snap-through and pull-in points with errors of at most 13% and 1.4%, respectively. The accuracy of the converged results is also validated by the available experimental observations in the literature. Moreover, snapping criteria which provide the required combination of the system properties for prompting snap-through instability is introduced in this study. A detailed parametric study is finally conducted to investigate the combined effects of the fixed electrode curvature and the piezoelectric actuation on the size-dependent bistability of electrically actuated curved micro-beams. Results reveal that the position of the snapping zone in the limit points map can be controlled by the input piezoelectric voltage as well as the initial rise of the fixed electrode.

Bistability, Initially curved micro-beam, Curved fixed electrode, Piezoelectric actuation, Strain gradient theory

Ghalami Y. - other affiliation
Askari A.R. - other affiliation
Awrejcewicz J. - other affiliation
Tahani M. - IPPT PAN
4.  Jafari B., Katoozian H.R., Tahani M., Ashjaee N., A comparative study of bone remodeling around hydroxyapatite-coated and novel radial functionally graded dental implants using finite element simulation, Medical Engineering and Physics, ISSN: 1350-4533, DOI: 10.1016/j.medengphy.2022.103775, Vol.102, pp.1-12, 2022

This comparative study simulates bone remodeling outcome around titanium dental implants and compares the final bone configuration with the one around novel implants composed of radial functionally graded materials (FGMs) and the titanium implants with hydroxyapatite (HA) coating. A dental implant system embedded in 3D mandibular bone with masticatory loading was simulated by the finite element method. A bone remodeling algorithm was applied to cancellous and cortical bones. Young's modulus and von Mises stress were obtained to ensure bone homeostasis and evaluate the final bone configuration. Local stress distribution in the bone-implant interface was analyzed before and after bone remodeling. The average final Young's modulus of cancellous bone reached 2.68, 2.49, and 2.32 GPa for the FGM, HA-coated, and the titanium models, respectively. These values for cortical bone were 17.75, 16.86, and 17.20 GPa in the same order. Radial FGM implants generated the highest remodeling stimulus and bone density. Their superiority over the HA-coated models was confirmed by four implant surface stiffness values (10, 20, 30, and 40 GPa). Remodeling increased bone density around the implant, consistent with clinical data and reduced stress concentration in the cortical neck. The stress values were in the safe zone regarding overload-induced bone resorption. The findings of this study were substantiated by clinical images and bone density values from previous literature.

Dental implants, Bone remodeling, Finite element, Radial functionally graded material (FGM), Hydroxyapatite (HA) coating, Stress analysis

Jafari B. - other affiliation
Katoozian H.R. - other affiliation
Tahani M. - IPPT PAN
Ashjaee N. - other affiliation

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