Mesoscale Fracture Analysis of Multiphase Cementitious Composites Using Peridynamics

A comparison study on numerical analysis for concrete dynamic failure using intermediately homogenized peridynamic model and meso-scale peridynamic model

Concrete is a heterogeneous material exhibiting quasi-brittle behaviour. While homogenization of concrete is commonly accepted in general engineering applications, a detailed description of the material heterogeneity using a mesoscale model becomes desirable and even necessary for problems where drastic spatial and time variation of the stress and strain is involved, for example in the analysis of local damages under impact, shock or blast load. A mesoscale model can also assist in an investigation into the underlying mechanisms affecting the bulk material behaviour under various stress conditions. Extending from existing mesoscale model studies, where use is often made of specialized codes with limited capability in the material description and numerical solutions, this paper presents a mesoscale computational model developed under a general-purpose finite element environment. The aim is to facilitate the utilization of sophisticated material descriptions (e.g., pressure and rate dependency) and advanced numerical solvers to suit a broad range of applications, including high impulsive dynamic analysis. The whole procedure encompasses a module for the generation of concrete mesoscale structure; a process for the generation of the FE mesh, considering two alternative schemes for the interface transition zone (ITZ); and the nonlinear analysis of the mesoscale FE model with an explicit time integration approach. The development of the model and various associated computational considerations are discussed in this paper (Part 1). Further numerical studies using the mesoscale model for both quasistatic and dynamic loadings will be presented in the companion paper (Part 2).

Influences of multiple factors on the chloride diffusivity of the interfacial transition zone in concrete composites

Fractographic approach to metallurgical coke failure analysis. Part 1: Cokes of single coal origin

Mechanical properties of concrete, such as strength, stiffness and its damage characteristics, are found to depend significantly on the properties of constituent materials. However, this dependency is rarely taken into consideration in the prediction of material response to mechanical loads. Instead, the most generally sought alternative for prediction of material response involves conducting laboratory tests. A mesoscale model that incorporates the properties of the mesostructure and its influence on mechanical response is adopted. Mesoscale models of concrete contain coarse aggregates, cement mortar and, optionally, an interfacial transition zone. An aggregate shape idealisation scheme is determined numerically to generate a circular aggregate mesoscale model by carrying out numerical simulations under uniaxial compression and tensile conditions. The numerical procedure followed in the present mesoscale simulations is validated with the available experimental data. The circular aggregate model is generated by idealising the actual irregular aggregate to a circular one using: (a) an area-equivalence approach and (b) a circumference-equivalence approach. To assess the effective idealisation scheme under static loading conditions, aspects such as strength, stiffness and damage distribution are considered. Simulation results show that the circumference-based model provides higher compressive strength and stiffness and lower tensile strength than the area-based model.

Concrete might be subjected to impact or blast loading. To analyze the concrete behaviors under such loading cases, it is of interest to study the dynamic damage and failure behavior of concrete under high strain rate. In the present paper, a mesoscale model is developed to numerically analyze the dynamic damage process of concrete samples under high strain rate tension. In the mesoscale model, the concrete is regarded as a three-phase composite consisting of coarse aggregate, mortar matrix, and interfacial transition zone (ITZ) between the aggregate and the mortar matrix. Different coarse aggregate shapes, such as circular, oval, and polygon, are calculated and compared. It is found that the shapes of the coarse aggregates do affect the tensile strength and failure pattern.

Algorithms for generating and distributing random 3D sphere coarse aggregates were proposed. The 3D finite element mesoscale concrete model, which consists of mortar matrix and coarse aggregates, was established based on the theory of background element and material identification. The interfacial transition zone was simplified as a kind of contact between elements. Based on this model, continuous finite element code was used to simulate the process of rigid projectiles perforating concrete targets and the effect of 3 different coarse aggregate types on residual velocities was analyzed. This work indicates that the strength and density of coarse aggregates affects the residual velocity under lower and higher impact velocity respectively.

This paper reports the stab failure behaviors of coated and uncoated woven fabric in experimental and finite element analysis (FEA) approaches. In the experimental approach, the quasi-static stab behaviors of both the fabrics under the penetration of a rigid penetrator were tested to obtain the load–displacement curves. The stab failure morphologies were also observed and photographed to show the stab damage modes. In particular, the load–displacement curves were compared to find the difference between the coated and uncoated woven fabrics during stab penetration. In the FEA, microstructure geometrical models of both the fabrics were established to calculate the developments of stab damages. The influences of structure parameters of the fabrics on the stab resistance were discussed and the differences of the stab strengths between the two fabrics were also compared. From the FEA results, the development of stab damage could be visually displayed. With the visual results, it will be helpful to analyze the stress distribution under stab deformation, and to reveal the stab damage mechanism.

With the utilisation of recycled aggregate concrete (RAC) in building construction, the durability of this material requires particular attention, especially in terms of chloride penetration. This paper presents a numerical study on the chloride diffusion mechanism within RAC. Considering the random distribution of recycled coarse aggregates (RCA), a five-phase RAC model – including new mortar, adherent old mortar, new interfacial transition zone (ITZ), old ITZ and original natural coarse aggregates – is proposed to predict the effective diffusion coefficient of chlorides in RAC. The parametric studies, based on a series of critical factors (i.e. volume fraction of RCA, adhesive ratio of old mortar, chloride diffusivity of adherent old mortar, thicknesses of old and new ITZs and chloride diffusivity of old and new ITZs), reveal the properties of each phase and their individual impact on the effective diffusion coefficient of chlorides in RAC. The results obtained indicate that, interestingly, the effective diffusion coefficient tends to vary in terms of its relationships with high-quality adherent old mortar, lower adhesive ratio of old mortar, smaller thickness of ITZs and relatively superior chloride penetration resistance of ITZs, which cannot be found from existing models and experiments.

A three-dimensional meso-scale model based on the finite-element method was developed to simulate the creep response of steel-fibre-reinforced concrete (SFRC), which was treated as a composite of mortar, coarse aggregates and fibres. The SFRC meso-structures were randomly generated. The fibres were explicitly modelled using line elements, while the other two phases were modelled using solid elements. By attributing the creep response to the mortar phase while assuming the aggregates and fibres to be elastic, the proposed meso-scale model was able to simulate the compressive creep response of SFRC cylinders with different fibre contents. The model’s prediction of the compressive creep response was in good agreement with experimental studies in the literature. The model proposed was used to examine the effect of fibres on cracked SFRC specimens. Cracking was attributed to the mortar and the interfacial transition zone on the meso-scale, which were modelled using a continuum damage model and a cohesive zone model, respectively. Numerical simulations were carried out on notched SFRC beams subjected to sustained three-point bending to demonstrate the capability of the model in simulating the creep of cracked SFRC and capturing the crack-bridging effect of steel fibres.

In this paper, concrete was analyzed as a composite consisting of coarse aggregate, mortar matrix and interfacial transition zone (ITZ). Because permeability of each phase are not the same, ITZ will affect the concrete permeability. Effect of ITZ on the concrete permeability was studied by laboratory test and numerical analysis.The diffusion coefficient of ITZ, mortar,and concrete can be caculated by laboratory test. The results indicate that the diffusion coefficient of ITZ is far greater than mortar，which is about 40 times of mortar. The chloride ions diffusion ignoring ITZ and considering ITZ were simulated, the results show that the diffusion coefficient of concrete was bigger when the ITZ was considered, which was closer to the experimental results.

Nano/microcharacterization and image analysis on bonding behaviour of ITZs in recycled concrete enhanced with waste glass powder

Mesoscale numerical simulation of fracture of cement treated base material during semi circular bending test with discrete element model

Four simply supported reinforced concrete (RC) beams were test experimentaly and analyzed using the extended finite element method (XFEM). This method is used to treat the discontinuities resulting from the fracture process and crack propagation in that occur in concrete. The Meso-Scale Approach (MSA) used to model concrete as a heterogenous material consists of a three-phasic material (coarse aggregate, mortar, and air voids in the cement paste). The coarse aggregate that was used in the casting of these beams rounded and crashed aggregate shape with maximum size of 20 mm. The compressive strength used in these beams is equal to 17 MPa and 34 MPa, respectively. These RC beams are designed to fail due to flexure when subjected to load as a two-point loading. To model the coarse aggregate realistically, the aggregate must distributed randomly according to the gradient and amount actually used in the mix design. This property is not found in the ABAQUS program that resulted in the use of an alternate program to represent the aggregate randomly. Next, the random representation of the aggregate were transfered to the ABAQUS program by using commands and instructions that the program can understand, to draw as a sketch. The comparison between experimental and numerical results showed that the XFEM is a good method used to simulate the non-smooth behavior in RC beams such as discontinuitiy and singularity. While a mesoscale model can be simulated the non-homogeneity in the concrete.

Finite element analyses on transverse impact behaviors of 3-D circular braided composite tubes with different braiding angles