Supervision  of PhD theses

Zied Ktari, Experimental and numerical study of modified Ring Hoop Tensile Test for mechanical characterization of anisotropic tubular materials.,

Concluded and defended in January 22, 2022.

Supervisor: Dr. Ali Khalfallah.

The main objective of this thesis is to develop experimental systems for mechanical material characterization to enrich to experimental data which is used in parameter identification (direct and/or inverse identification methods) to accurately simulate tube metal forming processes (tube hydroforming, tube rolling, etc.). In this work, FEM, DoE and RSM along with ANN were used to optimize shape samples and to identify tubular material parameters in the orthotropic directions. In this PhD subject, innovation results have been obtained and disseminated to scientific community throughout the publication of 2 (two) articles in prestigious specialized journals. A patent (N° 26527 has been published on 08/03/2021.

Nasra Hannachi, Numerical Simulation of Friction Stir Welding Process: analysis of the influence of base materials plastic properties on weldability (date of first enrollment: 2016-2017) (Cotutelle-agreement signed between the University of Sousse -Tunisia and the University of Coimbra- Portugal).

Orientators: Dr. Ali Khalfallah and Dr. Dulce Rodrigues (UC).,

Concluded thesis and defended on 28 June 2022.

The main objective of this research is to focus on the numerical simulation of the friction stir welding process (FSW). The proposed working plan envisages providing a better understanding on the influence of base materials plastic behavior, at high temperatures and strain rates on weldability in friction stir welding, using numerical analysis. 3D thermo-mechanical model will be developed to run extensive parametric analysis in order to achieve thermal analysis not previously contemplated.

Mariem Nouira, Calibration of Ductile Fracture Models used in the numerical simulation of sheet metal forming processes (date of first enrollment: 2017- 2018) (Cotutelle-agreement signed between the University of Sousse -Tunisia and the University of Coimbra- Portugal).   Concluded and defended in January 28, 2023

Orientators: Dr. Ali Khalfallah and Dr. Marta Oliveira (UC).

The objective of this thesis is to propose new strategies for the calibration of ductile fracture models in order to possess relevant behavior models enable to predict fracture in metal forming processes.

Temim Zribi, Experimental and Numerical study of Tube Hydroforming process (Concluded and defended on 14/05/2014 at University of Monastir- Tunisia).

Orientator: Dr. Ali Khalfallah & Dr. BelhadjSalah Hedi

This thesis deals with the development of an inverse approach strategy to determine the constitutive parameters of tubular materials made of low carbon steel S235 and aluminum alloy AA6063-O. For this purpose, a new self-designed bulge forming machine is manufactured to perform tubular bulge tests. The proposed inverse identification method based on FEMU technique is developed to identify accurately the flow stress parameters considering material anisotropy effects. This method is made up of an optimization algorithm that connects experimental free bulge test results and finite element analysis. In this thesis, it was shown that this identification strategy provides appropriate flow stress relationship which can be used to predict accurate plastic deformation behavior during the tube hydroforming process.