Mohsen Rezaee Hajidehi, Ph.D.

Department of Mechanics of Materials (ZMM)
Materials Modeling Group (ZeMM)
position: assistant
telephone: (+48) 22 826 12 81 ext.: 401
room: 236
e-mail: mrezaee

Doctoral thesis
2018-02-15Nonlinear analysis of reinforced concrete frames: safety evaluation and retrofitting techniques 
supervisor -- Prof. Giuseppe Giambanco, Ph.D., UDSDP
supervisor -- Prof. Stanisław Stupkiewicz, Ph.D., Dr. Habil., Eng., IPPT PAN
1371 
Recent publications
1.Rezaee-Hajidehi M., Tůma K., Stupkiewicz S., Gradient-enhanced thermomechanical 3D model for simulation of transformation patterns in pseudoelastic shape memory alloys, International Journal of Plasticity, ISSN: 0749-6419, DOI: 10.1016/j.ijplas.2019.08.014, pp.1-51, 2019
Abstract:

Stress-induced martensitic transformation in polycrystalline NiTi under tension often proceeds through formation and propagation of macroscopic phase transformation fronts, i.e., diffuse interfaces that separate the transformed and untransformed domains. A gradient-enhanced 3D finite-strain model of pseudoelasticity is developed in this work with the aim to describe the related phenomena. The underlying softening response is regularized by enhancing the Helmholtz free energy of a non-gradient model with a gradient term expressed in terms of the martensite volume fraction. To facilitate finite-element implementation, a micromorphic-type regularization is then introduced following the approach developed recently in the 1D small-strain context. The complete evolution problem is formulated within the incremental energy minimization framework, and the resulting non-smooth minimization problem is solved by employing the augmented Lagrangian technique. In order to account for the thermomechanical coupling effects, a general thermomechanical framework, which is consistent with the second law of thermodynamics and considers all related couplings, is also developed. Finite-element simulations of representative 3D problems show that the model is capable of representing the loading-rate effects in a NiTi dog-bone specimen and complex transformation patterns in a NiTi tube under tension. A parametric study is also carried out to investigate the effect of various parameters on the characteristics of the macroscopic transformation front.

Keywords:

Phase transformation, Softening, Strain localization, Micromorphic regularization, Finite-element method

Affiliations:
Rezaee-Hajidehi M.-IPPT PAN
Tůma K.-other affiliation
Stupkiewicz S.-IPPT PAN
2.Minafò G., Rezaee-Hajidehi M., Giambanco G., A Mechanical Approach for Evaluating the Distribution of Confinement Pressure in FRP-Wrapped Rectangular Columns, JOURNAL OF ENGINEERING MECHANICS-ASCE, ISSN: 0733-9399, DOI: 10.1061/(ASCE)EM.1943-7889.0001673, Vol.145, No.12, pp.04019092-1-9, 2019
Abstract:

In recent decades, fiber reinforced polymer (FRP) wrapping has become a common technique to retrofit reinforced concrete (RC) columns. Numerous research works have sought to verify analytically and experimentally its effectiveness in terms of enhancement of axial load bearing capacity and ductility. These studies highlighted that in the case of sharp-cornered sections, the maximum allowable confinement pressure is limited by premature failure at corners and, consequently, stress in the FRP, as well as the distribution of the confinement pressure, is not uniform. The prediction of this phenomenon is not straightforward, and existing theoretical studies propose complex numerical simulations, whereas technical codes provide simplified or empirical relationships for its assessment. This paper presents an analytical model for the evaluation of the effective distribution of confinement pressure in FRP confined concrete members with rounded corners. The model allows considering the interaction with the concrete core and different brittle failure modes, including FRP rupture and debonding. It leads to determining the distribution of the confinement pressure along the section. Results are compared with those achieved by finite-element (FE) analyses and with numerical and experimental data available in the literature. Good agreement is obtained in all cases, showing the reliability of the proposed model.

Keywords:

Fiber reinforced polymer (FRP) wrapping, Corner radius, Confinement pressure, Brittle failure

Affiliations:
Minafò G.-University of Palermo (IT)
Rezaee-Hajidehi M.-IPPT PAN
Giambanco G.-University of Palermo (IT)
3.Rezaee-Hajidehi M., Stupkiewicz S., Phase-field modeling of multivariant martensitic microstructures and size effects in nano-indentation, MECHANICS OF MATERIALS, ISSN: 0167-6636, DOI: 10.1016/j.mechmat.2019.103267, pp.1-32, 2019
Abstract:

A finite-strain phase-field model is developed for the analysis of multivariant martensitic transformation during nano-indentation. Variational formulation of the complete evolution problem is developed within the incremental energy minimization framework. Computer implementation is performed based on the finite-element method which allows a natural treatment of the finite-strain formulation and of the contact interactions. A detailed computational study of nano-indentation reveals several interesting effects including the pop-in effect associated with nucleation of martensite and the energy-lowering breakdown of the symmetry of microstructure. The effect of the indenter radius is also examined revealing significant size effects governed by the interfacial energy. Keywords: phase-field method, microstructure, shape-memory alloys, nano-indentation, size effects

Affiliations:
Rezaee-Hajidehi M.-IPPT PAN
Stupkiewicz S.-IPPT PAN
4.Rezaee Hajidehi M., Stupkiewicz S., Gradient-enhanced model and its micromorphic regularization for simulation of Lüders-like bands in shape memory alloys, INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, ISSN: 0020-7683, DOI: 10.1016/j.ijsolstr.2017.11.021, Vol.135, pp.208-218, 2018
Abstract:

Shape memory alloys, notably NiTi, often exhibit softening pseudoelastic response that results in formation and propagation of Lüders-like bands upon loading, for instance, in uniaxial tension. A common approach to modelling softening and strain localization is to resort to gradient-enhanced formulations that are capable of restoring well-posedness of the boundary-value problem. This approach is also followed in the present paper by introducing a gradient-enhancement into a simple one-dimensional model of pseudoelasticity. In order to facilitate computational treatment, a micromorphic-type regularization of the gradient-enhanced model is subsequently performed. The formulation employs the incremental energy minimization framework that is combined with the augmented Lagrangian treatment of the resulting non-smooth minimization problem. A thermomechanically coupled model is also formulated and implemented in a finite-element code. The effect of the loading rate on the localization pattern in a NiTi wire under tension is studied, and the features predicted by the model show a good agreement with the experimental observations. Aditionally, an analytical solution is provided for a propagating interface (macroscopic transformation front) both for the gradient-enhanced model and for its micromorphic version

Keywords:

martensite, phase transformation, micromorphic model, strain localization, thermomechanical coupling

Affiliations:
Rezaee Hajidehi M.-other affiliation
Stupkiewicz S.-IPPT PAN
5.Ribolla E.M., Rezaee Hajidehi M., Rizzo P., Scimemi G.F., Spada A., Giambanco G., Ultrasonic inspection for the detection of debonding in CFRP-reinforced concrete, Structure and Infrastructure Engineering, ISSN: 1573-2479, DOI: 10.1080/15732479.2017.1384843, Vol.14, No.6, pp.807-816, 2018
Abstract:

Fibre-reinforced plastic (FRP) composites are extensively used to retrofit civil structures. However, the quality and the characteristics of the bond between the FRP and the structure are critical to ensure the efficacy of the retrofit. For this reason, effective non-destructive evaluation (NDE) methods are often necessary to assess the bonding conditions. This article presents an ultrasonic technique for detecting defects at the FRP-substrate interface. The technique uses the Akaike Information Criterion, to detect automatically the onset of the ultrasonic signals, and the novel Equivalent Time Lenght (ETL) parameter, to quantify the energy of the propagating ultrasonic signals along the interface between FRP and concrete. The uniqueness of the ETL is that it is not affected by the coupling conditions between the ultrasonic probes and the structure. The proposed NDE technique has been tested numerically by performing 2D Finite-Element analysis and experimentally on reinforced concrete samples. The results show that the method is robust and cost-effective.

Keywords:

CFRP, fibre-reinforced materials, concrete, bonding, non-destructive testing, ultrasonic methods, equivalent time length

Affiliations:
Ribolla E.M.-University of Palermo (IT)
Rezaee Hajidehi M.-other affiliation
Rizzo P.-University of Pittsburgh (US)
Scimemi G.F.-University of Palermo (IT)
Spada A.-University of Palermo (IT)
Giambanco G.-University of Palermo (IT)
6.Rezaee Hajidehi M., Spada A., Giambanco G., The multiple slope discontinuity beam element for nonlinear analysis of RC framed structures, MECCANICA, ISSN: 0025-6455, DOI: 10.1007/s11012-018-0817-3, Vol.53, No.6, pp.1469-1490, 2018
Abstract:

The seismic nonlinear response of reinforced concrete structures permits to identify critical zones of an existing structure and to better plan its rehabilitation process. It is obtained by performing finite element analysis using numerical models classifiable into two categories: lumped plasticity models and distributed plasticity models. The present work is devoted to the implementation, in a finite element environment, of an elastoplastic Euler–Bernoulli beam element showing possible slope discontinuities at any position along the beam span, in the framework of a modified lumped plasticity. The differential equation of an Euler–Bernoulli beam element under static loads in presence of multiple discontinuities in the slope function was already solved by Biondi and Caddemi (Int J Solids Struct 42(9):3027–3044, 2005, Eur J Mech A Solids 26(5):789–809, 2007), who also found solutions in closed form. These solutions are now implemented in the new beam element respecting a thermodynamical approach, from which the state equations and flow rules are derived. State equations and flow rules are rewritten in a discrete manner to match up with the Newton–Raphson iterative solutions of the discretized loading process. A classic elastic predictor phase is followed by a plastic corrector phase in the case of activation of the inelastic phenomenon. The corrector phase is based on the evaluation of return bending moments by employing the closest point projection method under the hypothesis of associated plasticity in the bending moment planes of a Bresler’s type activation domain. Shape functions and stiffness matrix for the new element are derived. Numerical examples are furnished to validate the proposed beam element.

Keywords:

Slope discontinuity, Nonlinear pushover analysis, Lumped plasticity, Plastic hinge

Affiliations:
Rezaee Hajidehi M.-other affiliation
Spada A.-University of Palermo (IT)
Giambanco G.-University of Palermo (IT)
7.Spada A., Rezaee Hajidehi M., Giambanco G., A BEAM ELEMENT ALLOWING MULTIPLE SLOPE DISCONTINUITIES FOR RC STRUCTURES: AN APPLICATION, JOURNAL OF EARTHQUAKE ENGINEERING, ISSN: 1363-2469, Vol.XXXV, No.1, pp.131-150, 2018
Abstract:

A beam/column element allowing the formation of multiple plastic hinges in columns or beams of a reinforced concrete (RC) framed structure is used in this work to show, through an application, its advantages with respect to conventional lumped plasticity models. Slope discontinuities can be located at any position of an Euler-Bernoulli beam span and not at the two extremes only. The model is in fact written in the framework of a modified lumped plasticity theory, and respectful of a thermodynamic approach. Flow rules and state equations are derived invoking the Theorem of maximum dissipation and using a Bresler’s type activation domain. The beam element has already been implemented in a researchoriented code to run nonlinear analyses on 2-D frames. The discretized loading process is separated, at each step, in two phases: a predictor and a corrector phase. Numerical examples highlight how the new finite element permits to run nonlinear analyses avoiding a mesh refinement.

Keywords:

beam element, plastic hinge, lumped plasticity, slope discontinuity, nonlinear FEM analysis

Affiliations:
Spada A.-University of Palermo (IT)
Rezaee Hajidehi M.-other affiliation
Giambanco G.-University of Palermo (IT)