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A new type of modified concrete, termed metaconcrete, has been shown to exhibit trapping of wave energy and a reduction in mortar stress when subjected to dynamic loading. Metaconcrete replaces the standard stone and gravel aggregates of regular concrete with spherical inclusions consisting of a heavy core coated with a compliant outer layer. These new layered aggregates resonate at designed frequencies by allowing for relative motion between the heavy core and the mortar matrix, which causes the aggregate to absorb energy and therefore reduce stress within the mortar phase of the composite material. The transmission of wave energy through a metaconcrete slab can be used to visualize the effect of resonant behavior within the metaconcrete aggregates. To quantify this behavior we compute a transmission coefficient, which is a method of measuring the absorption of wave energy as an applied forcing of known frequency travels through the material. The transmission coefficient is plotted against forcing frequency for four different aggregate material and geometry configurations. A reduction in transmission ratio is observed at or near the computed natural modes of the aggregate, indicating the activation of resonance within the inclusions. This behavior is consistent with observations from studies on sonic metamaterials containing resonant inclusions with a similar layered structure. The frequency location and width of the dip in transmission coefficient will aid in the design of metaconcrete aggregates for specific forcing applications.

We derive and numerically verify scaling laws for the macroscopic fracture energy of polymers undergoing crazing from a micromechanical model of damage. The model posits a local energy density that generalizes the classical network theory of polymers so as to account for chain failure and a nonlocal regularization based on strain-gradient elasticity. We specifically consider periodic deformations of a slab subject to prescribed opening displacements on its surfaces. Based on the growth properties of the energy densities, scaling relations for the local and nonlocal energies and for the specific fracture energy are derived. We present finite-element calculations that bear out the heuristic scaling relations.

We study dynamic nanovoid growth in copper single crystals under prescribed volumetric strain rates ranging from moderate (∊=10^5 s^(-1)) to high (∊=10^(10)s^(-1)). We gain access to lower strain rates by accounting for thermal vibrations in an entropic sense within the framework of maximum-entropy non-equilibrium statistical mechanics. We additionally account for heat conduction by means of empirical atomic-level kinetic laws. The resulting mean trajectories of the atoms are smooth and can be integrated implicitly using large time steps, greatly in excess of those required by molecular dynamics. We also gain access to large computational cells by means of spatial coarse-graining using the quasicontinuum method. On this basis, we identify a transition, somewhere between 10^7 and 10^8 s^(−1), between two regimes: a quasistatic regime characterized by nearly isothermal behavior and low dislocation velocities; and a dynamic regime characterized by nearly adiabatic conditions and high dislocation velocities. We also elucidate the precise mechanisms underlying dislocation emission from the nanovoids during cavitation. We additionally investigate the sensitivity of the results of the analysis to the choice of interatomic potential by comparing two EAM-type potentials.

We present a validation assessment of the eigenerosion scheme applied in conjunction with the Optimal Transportation Meshfree (OTM) method. The assessment is based on the detonation-driven 304L steel spherical-cap fragmentation experiments of Campbell et al. (2007). Metrics used for purposes of validation include the velocity history of a witness point of the shell and the histogram of recovered fragment sizes. The results of the simulations are found to be in overall good agreement with the experimental measurements, especially when allowances are made for uncertainties in the characterization of the drive and material properties. The ability of the approach to predictively simulate exceedingly complex patterns of fracture and fragmentation under severe conditions of loading and material behavior is remarkable, especially in consideration of the simplicity of the fracture model and its implementation.

Plate impact experiments are presented for generating microcracks in ceramics under well-characterized loading conditions which also allow recovery of the specimen to examine the induced microcracking. A star-shaped aluminum flyer plate impacts a ceramic plate backed up by a steel plate. Compressive stress pulses and reflected tensile pulses propagate through these plates and eventually leave the aluminum and ceramic plates at rest while the steel plate carries away the momentum. The central region of the specimen is loaded by plane waves which are monitored by means of laser interferometry. The recorded velocity-time profiles provide an indication of the evolution of microcracking in the ceramic. Electron microscopy of the recovered specimens shows microcracks along grain boundaries in the ceramic. Their lengths can be measured easily and accurately with a transmission electron microscope. These experiments have proven to be successful in causing controlled microcracking in α-Al_2O_3 under well known stress conditions, while still allowing microstructural examination of the specimen. The information obtained from the experiments is used to evaluate a simple model for predicting the cracks resulting from the tensile interval of the stress history, showing that these tests can be used to develop a stress dependent theory of microcracking. Such a theory would contribute to a fundamental understanding of the phenomenon of microcracking in ceramics and thereby allow further progress towards toughening these highly brittle materials.

A theoretical framework for the analysis of localized failure in concrete is presented. The theory is predicated upon the assumption that discrete failure planes arise as a result of a process of localization of damage. The onset of localized modes is characterized as a bifurcation phenomenon whereby local neighborhoods of the material depart from near-uniform straining in favor of highly localized deformation patterns. Simple bifurcation techniques are discussed which suffice to detect when localization initiates and to determine the geometry of the localized deformation modes. Localization techniques are seen to provide a simple yet effective means of extending the range of applicability of traditional distributed damage models to situations of localized failure. Numerical calculations for biaxial stress paths exhibit a good overall agreement with experimental observations.

A general theory for the inelasticity of concrete is proposed, the main constituents being a new, rate independent model of distributed damage for mortar and the application of mixture theories to account for the composite nature of concrete. The proposed theory of damage is capable of accommodating fully anisotropic elastic degradation, both in tension and in compression, in a manner which is ideally suited for computation. Mixture theories, on the other hand, are found to provide a simple yet effective tool for characterizing the values of the phase stresses that act on mortar and aggregate and which drive damage and plastic flow. This uneven distribution of stresses between mortar and aggregate is seen to lie at the foundation of effects such as the characteristic splitting failure modes in uniaxial compression and the unloading hysteretic loops that arise during cyclic loading. Further to furnishing useful insights into the physical mechanisms underlying the inelastic behavior of concrete, the proposed model provides a simple means of quantifying such behavior in a way which can be readily implemented in any standard finite element code. Possible generalizations of the theory are suggested. In particular, it is noted how rate and rheological effects can be incorporated into the proposed framework by extending it into the viscoplastic range and through the use of Eyring's theory of thermal activation.