סמינר המחלקה להנדסה ביו רפואית -הרצאת אורח של פרופ' ראמי חג'-עלי

Nonlinear and Large Deformation Formulations of the Parametric HFGMC Micromechanics for Soft and Hard Tissues
Rami Haj-Ali
The Nathan Cummings Chair in Mechanics
Faculty of Engineering, Tel-Aviv University, Israel, rami98@tau.ac.il

The parametric high fidelity generalized method of cells (HFGMC) micromechanical framework is presented for the three-dimensional (3D) modeling of multi-phase heterogeneous materials.   Nonlinear and strain-softening constitutive modeling along with large deformation formulations will be discussed and shown to be effective in simulating both damage in aerospace composites and mechanical behavior of soft or hard tissues.  In the framework of HFGMC, the multi-phase heterogeneous composite (e.g. tissue) is assumed to possess a periodic microstructure.  The detailed interactions between the constituents are explicitly accounted for. For the case of multiphase soft tissue, the constituents are considered to be hyperelastic, and the overall behavior of the composite tissue is established along with the field distributions within the constituents. For hard bone tissue, the HFGMC-based multiscale micromechanical model is employed for predicting the overall effective and damage mechanical behavior of vertebral trabecular bones (VTBs). Thus, the hierarchical VTB micromodeling is composed of three-levels: two 3D-HFGMC analyses as well as the 3D-sublaminate-model.  At the nano-scale level, the 3D-HFGMC method is applied to obtain the effective properties representing the mineral collagen fibrils composite. Next, at the sub-micron scale level, the 3D sublaminate-model is used to generate the effective properties of a repeated stack of multi-layered lamellae demonstrating the nature of the trabeculae (bone-wall). Thirdly, at the micron-scale level, the 3D-HFGMC method is used again on a representative unit-cell of the highly porous VTB microstructure. The soft HFGMC tissue model is calibrated using available experimental data of artery layers.  The results from this model are also compared to the well-known anisotropic constitutive model proposed by Holzapfel and coworkers.  Similarly, the hard-tissue HFGMC model is applied for VTB microstructures taken from micro-computed tomography (μCT) scans. The predicted overall anisotropic properties for native VTBs are examined and compared with reported values of moduli found in the literature.  In conclusion, the HFGMC is shown to be an effective and viable micromechanical modeling approach for a wide range of soft and hard tissues.

Bio-Sketch

Rami Haj-Ali is the Nathan Cummings Professor of Mechanics at Tel-Aviv University.  He received his BSc-ME from the Technion, MSc from Tel-Aviv University (TAU), and Ph.D. from the University of Illinois at Urbana-Champaign (UIUC) in 1996.  He was an Assistant, Associate and Full Professor at Georgia Institute of Technology (Georgia Tech) from 1997-2010 and from 2008-current as a Full Professor in Mechanical Engineering at Tel-Aviv University.  Dr. Haj-Ali has published over 150 research papers and technical reports, and over 75 refereed archival publications. His research interests include: Nonlinear and damage modeling of composite materials and structures, Micromechanics, Computational Mechanics, Bio-materials, and Biomechanics of Aortic Valves (AVs). His research attracted support from several competitive and industrial sponsors, including the US National Science Foundation (NSF), Israel Ministry of Science (MOST), German-Israel Foundation (GIF), European Union (EU-FP7), NASA, Lockheed Martin, Rafael, IMI, Edwards Lifesciences Co., among others. He has won numerous awards, including the Chester P. Siess Award for outstanding PhD and research, University of Illinois at Urbana-Champaign (1997), the National Science Foundation (NSF-USA) CAREER award (1999), the Maof Fellow from PBC-Kahanoff Foundation (2008) and the Marie Curie Fellow from the EU-IRG-FP7 (2009), and the Nathan Cummings Endowed Chair of Mechanics at TAU (2016).

ההרצאה תתקיים ביום ראשון 31.12.17, בשעה 14:00
בחדר 315, הבניין הרב תחומי, אוניברסיטת תל אביב