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The addition of dry ice as an admixture to cement pastes has many advantages such as improving the compressive strength and sequestration of CO2. However, its effect on the hydration mechanism of cement pastes is still unknown and will be investigated using electrochemical impedance spectroscopy in this paper. Based on the linear correlation of cumulative hydration heat from the isothermal calorimetry test and the logarithm of high-frequency resistivity, a modified Knudson equation is derived. Corresponding hydration kinetic parameters are calculated by applying the boundary nucleation and growth theory and kinetics model, including Avrami, geometrical contraction, and diffusion equations. The boundary area per unit volume (OvB) for the control specimen and specimens with 0.2% and 0.5% cement weight dry ice addition is 0.1171, 0.1250, and 0.1562, respectively, indicating that the dry ice addition increases the surface area of the nucleation process. In addition, the results show that the Avrami equation for monitoring the nucleation process is limited. Regarding the hydration curves, the transition from the nucleation and growth stage to the interaction of phase boundaries (I) stage is delayed by adding dry ice to the mixture. [ABSTRACT FROM AUTHOR]

Delamination is currently a difficult detectable form of damage in composite laminate materials. This paper presents a method to more easily detect delamination damage within composite materials using finite element analysis modeling, through the covariance of energy change. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data were then analyzed through the fast Fourier transform (FFT). Using the data from the FFT, the idea of covariance of energy change was suggested to correlate with defect characteristics. By comparing the covariance of energy change in beams with different delamination sizes, thicknesses, and depths, correlations between the covariance of energy loss and defect characteristics were able to be developed. With these correlations, the severity of these damages was able to be quantified.

Based on the simple Euler-Bernoulli beam theory, and the assumed elastic-brittle behavior of concrete, an innovative method is proposed to estimate the energy absorption capacity of un-cracked or cracked concrete elements through predicting its complete load-displacement curve. The predicted complete load-displacement curve with its softening tail is based on two common parameters of concrete--compressive and tensile strengths. Comparing to the four-parameter bilinear cohesive model in literature, the predicted load-displacement curve predicts experimental results very well and does not need to be used with a finite element (FEM) model. Effects of combined loads and loading rate on the energy absorption capacity of the concrete beam are also discussed, in which the compressive axial force will increase the concrete energy absorption capacity while the tensile axial force will reduce its corresponding energy absorption capacity. Finally, application of the model to capture the dynamic load-displacement history of an impact event is resorted and the predicted result is in reasonable agreement to the experimental results. Key words: energy absorption capacity, Euler-Bernoulli beam theory, elastic-brittle, loading rate. En se basant sur la theorie des poutres simples Euler-Bernoulli et le comportement elastique-cassant presume du beton, une methode novatrice est proposee pour estimer la capacite d'absorption d'energie d'elements en beton fissures ou non fissures en determinant leur courbe complete de contrainte-deformation. La courbe complete de contrainte- deformation prevue, avec le ramollissement en bout de courbe, est basee sur deux parametres communs du beton -- les resistances en compression et en tension. Comparee au modele cohesif bilineaire a quatre parametres trouve dans la litterature, la courbe contrainte-deformation prevue estime tres bien les resultats experimentaux et il n'est pas necessaire de l'utiliser avec un modele par elements finis. Les effets des charges combinees et du taux de chargement sur la capacite d'adsorption d'energie de la poutre en beton sont egalement abordes; la force de compression axiale augmentera la capacite d'adsorption d'energie alors que la force en tension axiale reduira cette capacite. Finalement, l'application du modele pour saisir l'historique de la contrainte-deformation dynamique d'un evenement ayant un impact est selectionnee et le resultat prevu est raisonnablement proche des resultats experimentaux. Mots-cles : capacite d'adsorption d'energie, theorie des poutres Euler-Bernoulli, elastique-cassant, taux de chargement. [Traduit par la Redaction], Introduction There has been a growing interest in the past few years among the engineering communities to understand and find a unified method to accurately evaluate energy absorption capacity of [...]

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures. CE Database subject headings: Impact; Energy absorption; Damage; Strain rate; Shock waves; Finite element method; Finite difference method; Nonlinear methods; Honeycomb structures; Sandwich structures; Composite materials; Blasting; Dynamics.

Both the crushing and indentation behaviors of sandwich materials are important aspects in failure analysis and energy absorption. In this paper, the core crushing strength of honeycomb materials from the experiment is briefly introduced, and the indentation of sandwich structures is studied in detail. Using the beam on elastic-plastic foundation models, theoretical formulations for predicting indentation behavior of sandwich materials are proposed, from which the mechanical response of elastic-plastic sandwich beams are obtained. Three stages of failure are clearly depicted by the global stiffness changes in the load versus displacement curve of elastic-plastic beams. The models are compared with the available experimental data and numerical simulation, and relatively close agreements are achieved. The compliance and compliance gradient derived form the indentation models are then incorporated with the equation of motion of the projectile to study impact response of elastic-plastic beams, and the impact energy dissipation due to the plasticity of elastic-plastic sandwich beam is uniquely recovered from the derived damping ratio. The beam on elastic-plastic foundation models proposed can be used to predict the indentation behavior of honeycomb sandwich materials, and the unique incorporation of the compliance and compliance gradient of the elastic-plastic sandwich beams in the standard mass-spring model can be utilized to characterize the effect of core compression and plasticity in the impact process. CE Database subject headings: Impact; Honeycomb structures; Sandwich structures; Aluminum; Simulation.