MECHANICS OF QUASI-BRITTLE MATERIALS

Research Projects

G. Cusatis — Tue, 20 Jul 2010 03:34:06 +0000

20. High Strain Rate Behavior of Dam Concrete: Experiments and Multiscale Modeling. Sponsor: Department of Homeland Security. September 2009 – September 2011 . PI: G. Cusatis.

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19. Mesoscale Based Formulation of Microplane Model. Sponsor: U.S. Army Engineer Research and Development Center (ERDC). August 2009 – August 2010. PI: G. Cusatis. <\p>

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18. Man-made Hazard Mitigation of Reservoir Dams: Monte Carlo Simulation with Multiscale Modeling of Concrete and Accurate Fluid-Structure Interaction. Sponsor: National Science Foundation. July 2009 – July 2012. PI: G. Cusatis (60%), co-PI L. Zhang.

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17. A Multiscale Multiphysics Computational Framework for the Simulation of Blast Induced Pervasive Failure. Sponsor: Defense Threat Reduction Agency. April 2009 – April 2012. PI: G. Cusatis (50%), co-PIs: A. Oberai (Rensselaer), L. Zhang (Rensselaer), J. Bishop (Sandia).

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16. An Adaptive Multiscale Framework for the Simulation of Fiber-Reinforced High-Performance Concrete Subjected to High Speed Penetration. September 2008 – August 2009. Sponsor: U.S. Army Engineer Research and Development Center (ERDC) – subcontract through Software Systems Solutions, Inc. (ES3). PI : G. Cusatis.

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15. Microplane Modeling of Size-Effect in Composite Laminates. May 2008 – September 2008. Sponsor: Office of Naval Research – subcontract through Northwestern University. PI: G. Cusatis.

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14. Microplane Model for Stochastic Heterogeneous Quasi-Brittle Media. May 2008 – September 2008. Sponsor National Science Foundation – subcontract through Northwestern University. PI: G. Cusatis.

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13. Mesoscale and Macroscale Approaches for the Simulation of Quasi-Brittle Fracture. April 2008 – Aug. 2008. Sponsor: Sandia National Laboratory. PI: G. Cusatis.

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12. Constitutive Modeling and Numerical Algorithms for Concrete Behavior at High Strain Rate. Oct. 2005 – Aug. 2007. Sponsor: U. S. Army Engineer Research and Development Center (ERDC) – subcontract through Software Systems Solutions, Inc. (ES3). PI: G. Cusatis.

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11. Discontinuous Cell Method (DCM). Sponsor: Rensselaer Polytechnic Institute. Sep. 2007 – Dec. 2009.

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10. Spectral Particle Method (SPM). Sponsor: Rensselaer Polytechnic Institute. Jan. 2006 – Aug. 2007. PI: G. Cusatis.

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09. Lattice Discrete Particle Model (LDPM) for Concrete. Sponsor: Rensselaer Polytechnic Institute. Jan. 2006 – Aug. 2009. PI: G. Cusatis.

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08. Size Effect and Cohesive Crack Propagation in Quasi-Brittle Materials. Jan. 2006 – Aug. 2008. PI: G. Cusatis.

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07. Concrete Cracking Simulation at the Early-Ages. Aug. 2005 – Aug. 2006. PI: L. Cedolin (Politecnico di Milano University, Milan, Italy). Sponsor: CIS-E Consortium, Milan, Italy.

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06. Microplane Model for Composite Laminates. Jun. 2004 – Jun. 2005. PI: Z.P. Bažant (Northwestern University, Evanston, IL). Sponsor: Office of Naval Research.

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05. Theoretical and Experimental Study of the Behavior of Reinforced-Concrete Structures. Apr. 2002 – Jun. 2004. PI: P. Gambarova (Politecnico di Milano University, Milan, Italy). Sponsor: Italian Minister of University and Research, Rome, Italy.

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04. Adhesive Fastener Project (I-II-III). Nov. 2001 – Apr. 2003. PI: L. Cedolin (Politecnico di Milano University, Milan, Italy). Sponsor: Hilti Corporation, Schaan, Liechtenstein.

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03. UE Anchor Project: Anchorages in Normal and High-Performance Concretes Subjected to Medium and High Strain Rates. Mar. 1999 – Mar. 2001. PI: L. Cedolin (Politecnico di Milano University, Milan, Italy). Sponsor: European Union.

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02. Confinement-Shear Lattice Model for Concrete. Sep. 1998 – Mar. 2002. PI: L. Cedolin (Politecnico di Milano University, Milan, Italy). Sponsor: Italian Minister of University and Research.

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01. Microprestress-Solidification Theory for Drying and Transitional Thermal Creep. Apr. 1997 – Jul. 1998. PI: L. Cedolin (Politecnico di Milano University, Milan, Italy). Sponsor: Politecnico di Milano.

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Protected: 1970-03-00

G. Cusatis — Fri, 16 Jul 2010 19:38:03 +0000

Gianluca Cusatis

G. Cusatis — Fri, 16 Jul 2010 19:05:28 +0000

I am a faculty member of the Civil and Environmental Engineering Department at Rensselaer Polytechnic Institute, where, since 2005, I have been teaching undergraduate and graduate courses of the civil engineering curriculum and performing research in the field of Mechanics of Quasi-Brittle Materials.

My alma mater is the Politecnico di Milano (Milan, Italy) where I worked in the research group of Prof. Luigi Cedolin. I obtained my “Laurea” degree in 1998, with a thesis on the viscoelastic behavior of concrete subjected to variable temperature and humidity, and my PhD degree in 2002, with a dissertation dealing with mesoscale modeling of concrete. Prior to joining Rensselaer, I worked, as post-doctoral research associate, in the research group of Prof. Zdeněk P. Bažant at Northwestern University. During that time I developed a microplane model for composite laminates with quasi-brittle matrix.

I am member of ASCE, ACI, and USACM and active in several technical committees. In the last ten years, I have been working in the field of computational and applied mechanics, with emphasis on heterogeneous and quasi-brittle materials, concrete and reinforced concrete modeling. In addition, my research interests include: micro- and meso-mechanics, linear and nonlinear fracture mechanics, nonlinear constitutive modeling, concrete creep, rate effect on material strength, moisture and heat transfer, and concrete-steel interface behavior. Currently, I am performing research aiming at the formulation and validation of computational technologies for the simulation of blast and impact effect on structures. My detailed Curriculum Vitae can be found here.

AFFILIATIONS
Department of Civil and Environmental Engineering & Multiscale Science and Engineering Center School of Engineering at Rensselaer Polytechnic Institute

CONTACT INFO
110 Eighth St,Troy, NY 12180-3590
Phone: (518) 276-3956; Fax: (518) 276-4833
E-mails: cusatg@rpi.edu; gianluca@cusatis.us

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Fragmentation video

G. Cusatis — Wed, 20 Jan 2010 03:47:44 +0000

This simulation consists of a metallic rod impacting a quasi-brittle brick at various velocities. The objective of this study is to demonstrate the ability of the Lattice Discrete Particle Model to simulate impact induced fragmentation. The image shows the failure patterns associated with four different velocities, ranging from 400 in/s to 1600 in/s. For the lowest velocity, the brick splits essentially in two fragments. At 800 in/s, there are four major fragments with some debris in between. At higher velocities the number of fragments increases up to the complete fragmentation of the brick.

To play the video in full-screen click on the full-screen icon on the left of “vimeo”.

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Tension tests on fiber reinforced concrete

G. Cusatis — Wed, 20 Jan 2010 03:25:04 +0000

This post discusses the numerical simulations of tension testes on fiber reinforced concrete specimens. Figure (a) below shows experimental and numerical stress versus displacement curves for four different fiber volume fractions (Vf ): 0% (plain concrete), 2%, 3%, and 6%. The lattice discrete particle model is able to predict the increased strength and ductility due to the effect of fibers. The behavior gradually transitions from softening for plain concrete and low Vf , to hardening for high Vf . The numerical results are further investigated in Fig. (b), where contours of the mesoscale crack opening at the end of the simulations are reported for three fiber volume fractions. For plain concrete, the crack pattern is characterized by one localized crack that propagates from one side of the specimen towards the other. As fracture propagates, material outsidethe crack unloads as the overall load applied tothe specimen tends to zero. For the 2% Vf , there is still one main crack propagation, but the entire specimen features diffuse cracking and no unloading occurs. Absence of unloading outside the main crack is due to the fact that even though the overall behavior is softening, the stress versus displacement curve shows a non-zero residual stress associated with the fiber crack bridging effect. Finally, for the 6% Vf , the crack pattern is characterized by several branched cracks whose propagation is arrested by the effect of the fibers. No unloading occurs outside the main cracks since the overall behavior is strain-hardening and, up to a displacement of 0.5 mm (average nominal strain of 0.5 mm / 120 mm 0.42%), no reduction of the load carrying capacity can be observed.

Stress versus strain curves and fracture patterns for fiber reinforced concrete specimens

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Fracture of fiber reinforced concrete

G. Cusatis — Wed, 20 Jan 2010 02:46:22 +0000

This post deals the results of three-point bending test simulations on notched specimens. Only the central part of the specimen is simulated through the accurate lattice discrete particle model while the two lateral parts are modeled used elastic finite elements. This is reasonable because the presence of the notch ensures that damage localizes ahead of the notch tip. The figures below the meso-scale crack openings (blue=0.0005 mm, red=0.66 mm and above) for plain concrete (top) and fiber reinforced concrete (bottom) with a 0.45% volume fraction. As one can see for the fiber reinforced case fracture are less localized compared to the plain concrete case.

Meso scale racture distribution for plain concrete (top) and fiber reinforced concrete (bottom).

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Biaxial tests on concrete

G. Cusatis — Wed, 20 Jan 2010 02:11:30 +0000

In this figure the results of biaxial quasi-static tests on plain concrete panels are reported. In the center of the picture one can see the comparison between the numerical (solid curves) and experimental (circles) failure domains normalized with the compressive strength. The top left of the figure shows classical shear band failure characterizing uniaxial unconfined compression tests. The top right shows the failure mode under uniaxial tension. The bottom left is relevant to equi-biaxial tension characterized by a 45 deg fracture. The bottom right reports the failure mode obtained while applying compression in the vertical direction and transverse tension.

Simulation of biaxial loading of concrete panels

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Blast induced fragmentation

G. Cusatis — Wed, 20 Jan 2010 02:05:28 +0000

The simulation of damage induced by a blast on a reinforced concrete wall is reported in this figure. The top of the figure shows the geometry of the wall as well as the position of the charge. The bottom of the figures reports the damage evolution at three time instants during the simulation. At the beginning the wall shows a failure that resembles the effect of a concentrate load with several radial cracks emanating for the center of the wall. Later damage concentrates at the bottom (where the wall is clamped) and the final failure mode is characterized by the complete shearing of the wall base.

Simulation of blast effects on a reinforced concrete wall

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Fragmentation

G. Cusatis — Wed, 20 Jan 2010 01:56:09 +0000

This simulation consists of a metallic rod impacting a quasi-brittle brick at various velocities. The objective of this study is to demonstrate the ability of the Lattice Discrete Particle Model to simulate impact induced fragmentation. The image shows the failure patterns associated with four different velocities, ranging from 400 in/s to 1600 in/s. For the lowest velocity (top left), the brick splits essentially in two fragments. At 800 in/s (top right), there are four major fragments with some debris in between. At higher velocities (bottom left and right) the number of fragments increases up to the complete fragmentation of the brick.

Simulation of fragmentation caused by a steel rod impacting a brick of quasi-brittle material

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Penetration

G. Cusatis — Wed, 20 Jan 2010 01:28:23 +0000

This figure shows the simulation of a steel projectile penetration through a reinforced concrete slab. Concrete, rebars, and projectile are modeled by LDPM, elasto-platic beam elements, and elasto-plastic brick elements, respectively (top left and top right). The striking velocity is 1060 m/s. The the projectile velocity history during the penetration is reported in the bottom left of the figure. Initially, the projectile velocity decreases linearly with time. About 0.18 ms after the impact the front face scabbing initiates and the projectile deceleration is greatly reduced. After 0.35 ms the projectile achieved complete penetration with an exit velocity of about 960 m/s. The damage distribution after the penetration event is shown in the bottom right of the figure.

Simulation of a steel projectile penetration into a reinforced concrete slab.

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