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Abstract: This paper deals with the formulation, calibration, and validation of the Lattice Discrete Particle Model (LDPM) suitable for the simulation of the failure behavior of concrete. LDPM simulates concrete at the meso-scale considered to be the length scale of coarse aggregate pieces. LDPM is formulated in the framework of discrete models for which the unknown displacement field is not continuous but only defined at a finite number of points representing the center of aggregate particles. Size and distribution of the particles are obtained according to the actual aggregate size distribution of concrete. Discrete compatibility and equilibrium equations are used to formulate the governing equations of the LDPM computational framework. Particle contact behavior represents the mechanical interaction among adjacent aggregate particles through the embedding mortar. Such interaction is governed by meso-scale constitutive equations simulating meso-scale tensile fracturing with strain-softening, cohesive and frictional shearing, and nonlinear compressive behavior with strain-hardening. The present, Part I, of this two-part study deals with model formulation leaving model calibration and validation to the subsequent Part II. [Copyright &y& Elsevier]

The application of explicit dynamics to simulate quasi-static events often becomes impractical in terms of computational cost. Different solutions have been investigated in the literature to decrease the simulation time and a family of interesting, increasingly adopted approaches are the ones based on the proper orthogonal decomposition (POD) as a model reduction technique. In this study, the algorithmic framework for the integration of the equation of motions through POD is proposed for discrete linear and nonlinear systems: a low dimensional approximation of the full order system is generated by the so-called proper orthogonal modes (POMs), computed with snapshots from the full order simulation. Aiming to a predictive tool, the POMs are updated in itinere alternating the integration in the complete system, for the snapshots collection, with the integration in the reduced system. The paper discusses details of the transition between the two systems and issues related to the application of essential and natural boundary conditions (BCs). Results show that, for one-dimensional (1D) cases, just few modes are capable of excellent approximation of the solution, even in the case of stress-strain softening behavior, allowing to conveniently increase the critical time-step of the simulation without significant loss in accuracy. For more general three-dimensional (3D) situations, the paper discusses the application of the developed algorithm to a discrete model called lattice discrete particle model (LDPM) formulated to simulate quasi-brittle materials characterized by a softening response. Efficiency and accuracy of the reduced order LDPM response are discussed with reference to both tensile and compressive loading conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the Lattice Discrete Particle Model for fiber reinforced concrete (LDPM-F) is calibrated and validated with reference to a new high-strength, ultra-high-performance concrete (UHPC) named CORTUF and applied to the simulation of projectile penetration. LDPM-F is a three-dimensional model that simulates concrete at the length scale of coarse aggregate pieces (meso-scale) through the adoption of a discrete modeling framework for both fiber reinforcement and embedding matrix heterogeneity. In this study, CORTUF parameter identification is performed using basic laboratory fiber pull-out experiments and experiments relevant to a CORTUF mix without fiber reinforcement. Extensive comparisons of the numerical predictions against experimental data that were not used during the calibration phase (relevant to both plain CORTUF and CORTUF with fiber reinforcement) are used to validate the calibrated model and to provide solid evidence of its predictive capabilities. Simulations are then carried out to investigate the behavior of protective CORTUF panels subjected to projectile penetration, and the numerical results are discussed with reference to available experimental data obtained at the Engineering Research and Development Center (ERDC). [Copyright &y& Elsevier]

The discrete element method (DEM) was used to model calcium-silicatehydrate (C-S-H) at the nanoscale. The C-S-H nanoparticles were modeled as spherical particles with diameters of approximately 5 nm. Interparticle forces included traditional mechanical contact forces, van der Waals forces and ionic correlation forces due to negatively charged C-S-H nanoparticles and ion species in the nanopores. Previous work by the authors demonstrated the DEM method was feasible in studying the properties of the C-S-H nanostructures. In this work, the simulations were performed to look into the effects of nanoparticle packing, nanoparticle morphology, interparticle forces and nanoparticle properties on the deformation mechanisms and mechanical properties of the C-S-H matrix. This work will provide insights into possible ways to improve the properties of the C-S-H matrix. [ABSTRACT FROM AUTHOR]

In Part I of this two-part study, a theory is provided for the extension of the lattice discrete particle model (LDPM) to include fiber reinforcing capability. The resulting model, LDPM-F, is calibrated and validated in the present paper by comparing numerical simulations with experimental data gathered from the literature. The analyzed experiments include direct tension, confined and unconfined compression, and notched three-point bending tests. [ABSTRACT FROM AUTHOR]

Abstract: The Lattice Discrete Particle Model (LDPM) formulated in the preceding Part I of this study is calibrated and validated in the present Part II. Calibration and validation is performed by comparing the results of numerical simulations with experimental data gathered from the literature. Simulated experiments include uniaxial and multiaxial compression, tensile fracture, shear strength, and cycling compression tests. [Copyright &y& Elsevier]