http://users.auth.gr/~akonsta/2011_Gradient%20elasticity%20in%20statics%20and%20dynamics.pdf

Gradient elasticity in statics and dynamics: An overview of formulations, length scale identification procedures, finite element implementations and new results

In recent years, an emerging technology termed, “High-Performance Fiber-Reinforced Concrete (HPFRC)” has become popular in the construction industry. The materials used in HPFRC depend on the desired characteristics and the availability of suitable local economic alternative materials. Concrete is a common building material, generally weak in tension, often ridden with cracks due to plastic and drying shrinkage. The introduction of short discrete fibers into the concrete can be used to counteract and prevent the propagation of cracks. Despite an increase in interest to use HPFRC in concrete structures, some doubts still remain regarding the effect of fibers on the properties of concrete. This paper presents the most comprehensive review to date on the mechanical, physical, and durability-related features of concrete. Specifically, this literature review aims to provide a comprehensive review of the mechanism of crack formation and propagation, compressive strength, modulus of elasticity, stress–strain behavior, tensile strength (TS), flexural strength, drying shrinkage, creep, electrical resistance, and chloride migration resistance of HPFRC. In general, the addition of fibers in high-performance concrete has been proven to improve the mechanical properties of concrete, particularly the TS, flexural strength, and ductility performance. Furthermore, incorporation of fibers in concrete results in reductions in the shrinkage and creep deformations of concrete. However, it has been shown that fibers may also have negative effects on some properties of concrete, such as the workability, which get reduced with the addition of steel fibers. The addition of fibers, particularly steel fibers, due to their conductivity leads to a significant reduction in the electrical resistivity of the concrete, and it also results in some reduction in the chloride penetration resistance of the concrete.

High-performance fiber-reinforced concrete: a review

Recent progress in low-carbon binders

Use of macro plastic fibres in concrete: A review

Durability of ultra-high performance concrete – A review

Gradient elasticity theories can be used to simulate dispersive wave propagation as it occurs in heterogeneous materials. Compared to the second-order partial differential equations of classical elasticity, in its most general format gradient elasticity also contains fourth-order spatial, temporal as well as mixed spatial-temporal derivatives. The inclusion of the various higher-order terms has been motivated through arguments of causality and asymptotic accuracy, but for numerical implementations it is also important that standard discretization tools can be used for the interpolation in space and the integration in time. In this paper, we will formulate four different simplifications of the general gradient elasticity theory. We will study the dispersive properties of the models, their causality according to Einstein and their behavior in simple initial/boundary value problems.

/pdf/four-simplified-gradient-elasticity-models-for-the-40lrflzwtc.pdf

Four simplified gradient elasticity models for the simulation of dispersive wave propagation

Following the positive phase of a blast comes a period where the pressure falls below atmospheric pressure known as the negative phase. Whilst the positive phase of the blast is well understood, validation of the negative phase is rare in the literature, and as such it is often incorrectly treated or neglected altogether. Herein, existing methods of approximating the negative phase are summarised and recommendations of which form to use are made based on experimental validation. Also, through numerical simulations, the impact of incorrectly modelling the negative phase has been shown and its implications discussed.

/pdf/the-negative-phase-of-the-blast-load-30as1xamxp.pdf

The Negative Phase of the Blast Load

It is well known that when a blast wave strikes the face of a target, the duration of the loading, and hence the total impulse imparted to the target may be influenced by the propagation of a rarefaction, or “clearing” wave along the loaded face of the target adjacent to free edges. Simple methods of predicting the effect of clearing on reducing the blast loading impulse have been available for many years, but recent studies have questioned the accuracy and physical basis of these approaches. Consequently, several authors have used numerical modelling and/or experimental techniques to determine empirical predictive methods for the clearing effect. In fact, the problem had been addressed more than 50 years ago in a study which appears to have been since overlooked by the blast research fraternity. This article presents the results of that earlier study, and provides experimental validation. The analytical predictions are very simple to determine, and are shown to be in excellent agreement with experimental results.

Prediction of clearing effects in far-field blast loading of finite targets

In his article a special form of gradient elasticity is presented that can be used to describe wave dispersion. This new format of gradient elasticity is an appropriate dynamic extension of the earlier static counterpart of the gradient elasticity theory advocated in the early 1990s by Aifantis and co-workers. In order to capture dispersion of propagating waves, both higher-order inertia and higher-order stiffness contributions are included, a fact which implies (and is denoted as) dynamic consistency. The two higher-order terms are accompanied by two associated length scales. To facilitate finite element implementations, the model is rewritten such that 0-continuity of the interpolation is sufficient. An auxiliary displacement field is introduced which allows the original fourth-order equations to be split into two coupled sets of second-order equations. Positive-definiteness of the kinetic energy requires that the inertia length scale is larger than the stiffness length scale. The governing equations, boundary conditions and the discretized system of equations are presented. Finally, dispersive wave propagation in a one-dimensional bar is considered in a numerical example. Copyright © 2007 John Wiley & Sons, Ltd.

A new formulation and 0‐implementation of dynamically consistent gradient elasticity

The degradation of cementitious composite materials under chemical sulfuric acid attack has been widely investigated. The agglomeration of a global database of test results is complicated by the differing test methodologies employed in each study. As a result it is difficult to isolate the influence of individual test parameters and hence directly compare the relative performance of different cementitious material. In this study the existing accelerated test methodologies including: brushing, wetting and drying cycling, and increased concentration of sulfuric acid are investigated such that the influence of test methodology on degradation rate and microstructural performance can be identified. This approach is taken with the view of developing a common methodology for indicating the susceptibility of a given cementitious material in an aggressive environment. Rather than comparing the performance of individual materials this work aims to compare the influence of test methodology when applied to different materials.

Evaluation of accelerated degradation test methods for cementitious composites subject to sulfuric acid attack; application to conventional and alkali-activated concretes

Terry Bennett

Papers

Four simplified gradient elasticity models for the simulation of dispersive wave propagation

The Negative Phase of the Blast Load

Prediction of clearing effects in far-field blast loading of finite targets

A new formulation and 0‐implementation of dynamically consistent gradient elasticity

Evaluation of accelerated degradation test methods for cementitious composites subject to sulfuric acid attack; application to conventional and alkali-activated concretes