My Hours: W 11-15am-12:15pm and R 3-4pm
AERO 214: Aerospace Continuum Mechanics
MEMA 641: Plasticity Theory
1989-1992: Classes Preparatoires, Physics, Lycee Massena, Nice, France
1995: Ingenieur Diploma ``B.Sc.'', Aerospace Engineering, Sup'Aero, Toulouse, France
1995: M.Sc., Mechanical Engineering, Universite Paul Sabatier, Toulouse, France
2000: Ph.D., Material Science & Engineering, Ecole des Mines de Paris, France
Thesis Advisor: Prof. Andre Pineau
Thesis Co-advisor: Dr. Jacques Besson
Areas of Interest
Professor Benzerga's research falls at the confluence of solid mechanics, material science and condensed matter physics, and concerns the deformation and failure of metals, polymers and their composites. Current thrusts are: macromolecular mechanics of polymers and composites; dislocation plasticity; and ductile fracture. These research thrusts share the following characteristics: (i) develop advanced material models with the ability to predict structure-property relationships; (ii) develop computational methods to enable analysis and simulation, from engineering materials to structural design; and (iii) experimental integration. Prof. Benzerga's contributions have received wide attention in the U.S. and abroad within the computational/solid mechanics, material science and structural integrity research communities. Current research interests concern materials under extreme environments, nano- and micro-scale engineering and advanced materials for energy applications.
Specific research areas include:
* Damage and Fracture of Ductile Metallic Materials
* Micro-scale Plastic Deformation and Dislocation Mechanics
* Computational Dislocation Dynamics / Crystal Plasticity
* Macromolecular Mechanics of Polymers and Their Composites
* Micromechanics of Defects in Solids
A more in-depth description of research thrusts is provided below:
1. Macromolecular Mechanics of Polymers and Their Composites:
Polymers and their composites are being sought in an increasing number of applications, including at high-rate deformation. The design and optimization of polymeric materials (thermoplastics or thermosets) and their composites for a specific application requires fundamental understanding of their deformation, fracture and, in some cases, their aging behavior. Much is known about the quasi-static behavior of polymers. Only recently has their dynamic response been a subject of thorough investigations. Although polymer matrix composites (PMCs) are technologically far more important today than metal or ceramic based composites, little has been done to develop a computational methodology to analyze damage and fracture in PMCs using physics-based polymer models, i.e., holding promises similar to those developed for MMCs. The challenges are even bigger for technologically advanced composites (e.g. microlaminates and nanocomposites): what is the effect of nano-particles on the macromolecular structure? If analysis is conducted at that scale, what is the proper structure of constitutive equations? One motivation for Prof. Benzerga's research in this area stems from (i) the need for a computational framework that incorporates physical mechanisms based constitutive description of polymer behavior and fracture to predict the dynamic response; (ii) the same for polymer composites, whether particulate (rubber-toughened, mineral particles etc..), structural (laminate, woven or braided) or nanostructured (e.g., nanotubes, nanoclays, nanoparticles); and (iii) model aging of polymers and PMCs, and this is best done when the modeling approach resolves the macromolecular scale (in a continuum sense).
Since his joining the faculty at Texas A&M, Prof. Benzerga's interactions with colleagues have led him to a new research activity focused on development of experimental and analytical methods for investigation of inelastic deformation and fracture in amorphous polymers and their composites. One contribution is a re-formulation of the macromolecular model for explicit finite-element code implementation with application to behavior under impact, dynamic shear banding and composite deformation. An other contribution is the development of a craze flow model that draws upon recent work and contrasts with current cohesive formulations. An enhanced version of the model is still under development. With respect to application to nanocomposites, nanoindentation has been used to interrogate the polymer response at reduced length scales with or without nanoscale constituents. In particular, an indentation size effect was noticed but remains difficult to ascertain in view of various challenging issues (surface preparation effect, stiction, creep, etc..), let alone the interpretation.
Ongoing work focuses on development of multiscale modeling of inelastic deformation and damage of high-temperature composites for use in new designs of jet engine blade containment cases. With experiments conducted in collaboration with partners from NASA Glenn Research Center, pristine and aged polymer material is being characterized over a wide range of temperatures and strain rates for identification of both macromolecular model parameters and fracture locus. The research directions currently explored in Benzerga's group include: (i) development of improved computational formulations to address mesh-sensitivity issues in damage/fracture modeling and explore hyperelastic reformulation of current implementation to account for finite elastic stretches; (ii) development of improved network models valid at nanoscale and based on so-called "pseudo-particles" methods in collaboration with Prof. Cagin from TAMU/Chemical Engineering.
2. Micro-scale Plastic Deformation and Dislocation Mechanics:
There is an increasing amount of evidence that the mechanical behavior of crystalline materials changes at micro- and nano-scales in a way that is not necessarily captured by state-of-the-art plasticity models, i.e., based on the mechanics of generalized continua (gradient models; nonlocal models; field dislocation mechanics) or on statistical mechanics. Fundamental understanding of the critical length scales that control deformation and fracture will lead to achievement of higher strength materials with good toughness/ductility and thus can enable high-efficiency power generation systems and can translate into large energy savings for transportation vehicles due to weight reductions. In the emerging technologies, small dimensions are pervasive, e.g. in modern devices, from microelectronics to nano- and biotechnology. The design and optimization of devices often require knowledge of such fundamental properties as strength, toughness or fatigue life. The objective of this line of research is two-fold: develop novel semi-discrete models and computational methods that enable nano- and micro-scale engineering as manufacturing tools for future technologies; guide the development of improved physics-based continuum models of plasticity that will enable addressing the current technical bottlenecks facing materials under extreme environments with a focus on thermomechanical limits. An underpinning theme for responding to these scientific challenges ---whether relevant to micro/nano-devices and structures, or to the practical thermomechanical strength limits of material--- involves understanding the physics and mechanics of dislocation processes.
During the second part of his post-doctoral research at Brown University with Prof. Alan Needleman as mentor, Benzerga developed new discrete dislocation dynamics (DD) simulation techniques. The latter culminated in what has become to be known as the "2.5-D" DD paradigm, i.e., a computationally efficient, atomistically informed DD framework with the capability of reaching high dislocation densities (10^16/m2) and large strains (30% most recently, i.e., sufficiently large to discuss well-developed stage II hardening, transition to stage III and related phenomena) at moderate strain rates (less than 1000/s, i.e., much smaller than molecular dynamics). Recent applications of 2.5-D DD are in part technology-driven in that they aim at clarifying the origins of the size-dependence of mechanical response in micro- and nano-pillars. Most DD analyses of nanopillar mechanics conducted to date, including an earlier work by Benzerga, overemphasize the effect of isolated short-range dislocation interactions on nanopillar response. As part of his PhD dissertation work, Guruprasad used 2.5-D DD simulations to discover a new kind of plasticity size effect under nominally uniform deformation. Under the guidance of Prof. Benzerga, he developed a method to characterize the time evolution and spatial distribution of geometrically necessary dislocation densities directly from DD. The method is based on recent advances made in the characterization of GNDs and has led to development of a new crystal plasticity, size-dependent hardening model. It is gratifying to see that these predictions of size effects, published only in Jan. 2008, have already been confirmed experimentally by two independent groups in Germany (Prof. Arzt's former group at MPI Stuttgart) and Austria (Prof. Dehm's group). In addition to these studies, Prof. Benzerga has discussed behavior transitions at sub-micron scales from forest-hardening to exhaustion-hardening dominated regimes, obtaining again very good matching with published experimental data.
In 2008, Prof. Benzerga was the recipient of a CAREER award from NSF. One research objective developed there is to implement a multiscale modeling and simulation methodology in understanding the fundamentals of high-temperature deformation and creep with due account of both microstructural and dimensional constraints. The key enabling method is a high-temperature DD formulation based on rigorous coupling between elasticity and diffusion, the only possible atomic processes of displacement. In synergy with that effort, a DOE/LLNS project focuses on fundamental investigations of the ductile-brittle transition in single crystals and nanostructured metals using tessellation-based DD and the 3D DD code ParaDiS. Implementation of 2.5D DD involves using numerical methods for solving partial differential equations and dynamical systems. The (conventional) finite element method is currently used for the former and direct explicit algorithms are used for dislocation dynamics. Both are the subject of continuing research targeted at improving numerical efficiency and robustness. Many technological applications will be enabled as various computational challenges continue to be overcome. Developments that are nearly completed include the use of an adaptive multipole method in conjunction with 2.5D DD; and generalization to polycrystals using tools from computational geometry. Another ongoing effort consists of extending the framework to account for finite deformations.
3. Damage and Fracture of Ductile Metallic Materials:
Ductile fracture of structural materials and metal sheets is a fascinating and challenging subject which remains fundamentally important to the nation from a number of perspectives. New metallic materials that can perform at ever increasing thermomechanical extremes are required for future transportation vehicles, power generation facilities and associated infrastructure, and defense applications. In industrial manufacturing processes, mitigating fracture limits material waste and can lead to substantial cost savings and a positive impact on the environment. Structural materials constitute the backbone of the nation's infrastructure; protecting the structural integrity of the latter from malicious/hostile foreign objects and natural hazards, e.g., earthquakes, is a strategic need for which fundamental and applied fracture researches will be called for. So far, ductile fracture in structural metallic materials has most efficiently been understood using a top-down approach, whereby experimental calibration is conducted at the finest scale of relevance to the fracture process. Within such a framework, an attractive ductile fracture computational methodology was developed in the 1980s by Tvergaard and Needleman based on earlier work by Gurson and Rice, published in a paper that remains among the top ten cited papers ever in the fields of solid and computational mechanics combined (source iMechanica, accessed 2007). Outstanding issues chiefly concern experimental identification versus predictive capability; transferability of failure criteria from laboratory specimens to structural components; incorporation of material anisotropy; and pathological mesh-sensitivity that arises in the computational realization of the various formulations.
Prof. Benzerga's doctoral dissertation has addressed all but the last topic above. It has led to development of innovative experimental, mathematical and computational methods for analysis of ductile fracture in metal sheets and pressure vessels. One key contribution was the extension of Gurson's isotropic model to plastically anisotropic materials using nonlinear homogenization combined with limit analysis (a branch of functional analysis). An other important contribution was his micromechanical modeling of void coalescence in porous plastic media. With such contributions at hand, the core innovative concept of Prof. Benzerga's dissertation was a top-down approach to fracture realized through a new ductile fracture computational methodology with multiscale validation where experimental calibration is restricted to deformation related quantities. His approach thus possessed a truly predictive capability. Other findings include the discovery of "necklace" coalescence; the characterization of void rotation under superposed tensile and shear loading; a re-appraisal of the physical origins of slanted fracture and the interaction with shear bands; and the application to predictive simulation of crack propagation in pressure vessels using a semicoupled computational scheme for fluid--structure interactions.
Since his joining the faculty at Texas A&M University, Prof. Benzerga has initiated a DoD-funded activity in the area of ultra-high strength steel and an NSF-funded investigation of fracture in ultra-fine-grain steel processed by severe plastic deformation. In synergy with these efforts, theoretical focus is currently laid on a reconsideration of material anisotropy effects, material versus microstructural spin formulations with application to so-called shear failures, which have found renewed interest because of their relevance to a wide range of applications such as metal forming and ballistic penetration. From the computational standpoint, future efforts will concern the development of mathematically sound and physically based formulations that resolve the pathological mesh-dependence of numerical simulations of crack propagation.
Awards and Honors
2009 - Texas Engineering Experiment Station (TEES) Select Young Faculty Award
2008 - National Science Foundation CAREER Award Recipient
2000 - Highest Honors for Ph.D. Dissertation Work, Ecole des Mines de Paris, France
See More1992 - Ranked 2nd among foreign students (> 500), "Grandes Ecoles" National Entry Exam, Concours Mines-Ponts-SupAero, France
1989 - 6-year Government Scholarship, Classes Preparatoires & Engineering
Publications and Papers
2009 Benzerga, A. A., Poulain, X., Chowdhury, K. A., and Talreja, R. (2009), "A computational methodology for modeling fracture in fiber-reinforced polymer composites," Journal of Aerospace Engineering, In press.
2009 Benzerga, A. A. (2009), "Micro-Pillar Plasticity: 2.5D Mesoscopic Simulations" In review
2008 Keralavarma, S. M. and Benzerga, A. A. (2008), "An approximate yield criterion for anisotropic porous media," Comptes Rendus Mecanique, 336, 685-692
2008 Guruprasad, P. J. and Benzerga, A. A. (2008), "Size effects under homogeneous deformation of single crystals: A discrete dislocation analysis," Journal of the Mechanics and Physics of Solids, 56, 132-156.
2008 Benzerga, A. A. (2008), "An analysis of exhaustion hardening in micron-scale plasticity," International Journal of Plasticity, 24, 1128-1157
2008 Guruprasad, P. J. and Benzerga, A. A. (2008), "A phenomenological model of size-dependent hardening in crystal plasticity," The Philosophical Magazine, 88, 3585-3601.
2008 Guruprasad, P. J., Carter, J. W., and Benzerga, A. A. (2008), "A mechanism-based discrete dislocation analysis of the Bauschinger effect in micro-crystals," Acta Materialia, 56, 5477-5491
2008 Chowdhury, K. A., Benzerga, A. A., and Talreja, R. (2008), "A computational framework for analyzing the dynamic response of glassy polymers," Computer Methods in Applied Mechanics and Engineering, 197, 4485-4502.
2008 Chowdhury, K. A., Benzerga, A. A., and Talreja, R. (2008), "An analysis of impact-induced deformation and fracture modes in amorphous glassy polymers," Engineering Fracture Mechanics, 75, 3328-3342.
2008 Chowdhury, K. A., Talreja, R., and Benzerga, A. A. (2008), "Effects of manufacturing-induced voids on local failure in polymer-based composites," Journal of Engineering Materials and Technology, 130, Art. No. 021010.
2007 Keralavarma, S. M. and Benzerga, A. A. (2007), "A discrete dislocation analysis of strengthening in bilayer thin films," Modelling and Simulation in Materials Science and Engineering, 15, S239-S254.
2006 Benzerga, A. A. and Shaver, N. F. (2006), "Scale dependence of mechanical properties of single crystals under uniform deformation," Scripta Materialia, 54, 1937-1941
2005 Benzerga, A. A., Brechet, Y., Needleman, A., and Van der Giessen, E. (2005), "The stored energy of cold work: predictions from discrete dislocation plasticity," Acta Materialia, 53, 4765-4779.
2004 Benzerga, A. A., Brechet, Y., Needleman, A., and Van der Giessen, E. (2004), "Incorporating three-dimensional mechanisms into two-dimensional dislocation dynamics," Modelling and Simulation in Materials Science and Engineering, 12, 159-196
2004 DeSandre, D. A., Benzerga, A. A., Tvergaard, V., and Needleman, A. (2004), "Material inertia and size effects in the Charpy V-notch test," European Journal of Mechanics, 23A, 373-386
2004 Benzerga, A. A., Besson, J., and Pineau, A. (2004), "Anisotropic ductile fracture. Part I: Experiments," Acta Materialia, 52, 4623-4638.
2004 Benzerga, A. A., Besson, J., and Pineau, A. (2004), "Anisotropic ductile fracture. Part II: Theory," Acta Materialia, 52, 4639-4650.
2002 Benzerga, A. A., Besson, J., Batisse, R., and Pineau, A. (2002), "Synergistic effects of plastic anisotropy and void coalescence on fracture mode in plane strain," Modelling and Simulation in Materials Science and Engineering, 10, 73-102
2002 Benzerga, A. A. (2002), "Micromechanics of Coalescence in Ductile Fracture," Journal of the Mechanics and Physics of Solids, 50, 1331-1362
2002 Benzerga, A. A., Tvergaard, V., and Needleman, A. (2002), "Size effects in the Charpy V-notch test," International Journal of Fracture, 116, 275-296
2001 Benzerga, A. A. and Besson, J. (2001), "Plastic potentials for anisotropic porous solids," European Journal of Mechanics, 20A, 397-434
2001 Benzerga, A. A., Hong, S. S., Kim, K.-S., Needleman, A., and Van der Giessen, E. (2001), "Smaller is Softer: A Discrete Dislocation Analysis of an Inverse Size Effect in a Cast Aluminum Alloy," Acta Materialia, 49, 3071-3083
1999 Benzerga, A. A., Besson, J., and Pineau, A. (1999), "Coalescence-Controlled Anisotropic Ductile Fracture," Journal of Engineering Materials and Technology, 121, 221-229