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Durability of concrete with supplementary cementitious materials (SCMs) is crucial to the longevity of our built environment. Current research on the carbonation performance of concrete focuses on determining changes in microstructure induced by the chemical and physical interactions of CO2 with the cement phase in samples that do not undergo loading. Although this approach has enabled us to understand the chemical carbonation durability of concrete, the deterioration process is certainly not realistic considering the in-service conditions of structural concrete. Therefore, five different laboratories from RILEM TC 281-CCC WG4 conducted comparative testing of Portland cement concrete with/without SCMs under the combined action of carbonation and mechanical loading. The results indicated that the carbonation depth of concrete undergoing mechanical loading is lower in the case of a limited compressive load, and higher in the case of a high compressive load or tensile load, compared with unloaded specimens. The relative carbonation depth was decreased by 9–16% at 30% of the failure load in compression, independent of CO2 concentration and the presence of SCMs, while it was increased up to 13% at a 60% load level at most. Tension made the carbonation depth gradually increase, and up to 70% higher carbonation depth was reached at 60% of the tensile failure load. The combined effect of carbonation in concrete with SCMs and mechanical loading should therefore not be neglected in the service life prediction of concrete structures. [ABSTRACT FROM AUTHOR]

The paper presents an investigation study of the mechanical properties of metal foam. In this investigation, a numerical simulation by finite element method is used. For this purpose, the foam structure is modelled by a regular network of Kelvin cells. In these cells, the strands are modelled as a three-dimensional (3D) finite element beam. In particular, we consider four types of strands cross sections: (1) circular (2) square (3) triangular and (4) Plateau shape. Our numerical results are in agreement with the experimental results obtained on a real Nickel metallic foam. In addition, we perform a parametric analysis to study the effect of some geometrical characteristics on the elasticity of a metal foam. Among these geometrical characteristics, we consider the shape and dimensions of strands cross section as well as the inertia variation. [ABSTRACT FROM AUTHOR]

The objective of this research was to investigate the mechanical behavior of metal matrix composites (MMCs) 6061 aluminum, reinforced with silicon carbide particles, under unidirectional tensile loading by finite element analysis. The effects of particle's shape, size and content on the tensile properties of the composites were studied and compared with each other. In addition, stress and strain distributions and possible particle fracture or debonding were investigated. It was found that, among different shapes, a certain shape of reinforcement particle provided better tensile properties for MMCs and, within each shape category, composites with smaller particle size and higher particle content (20%) also showed better properties. It was also found that when the reinforcement content was 10%, the effects of shape and size of the particles were negligible. Not only interfacial length between the reinforcement and matrix materials, but also state of matrix material, due to the presence of the reinforcement particles, affected the stiffness of the MMCs. In almost all of the cases, except for MMCs with triangular particles, when the stress increased, with the increase in the applied positive displacement, the stress distributions remained unchanged. [ABSTRACT FROM AUTHOR]

An analytical approach is proposed for studying the elastic-plastic behavior of short-fiber-reinforced metal matrix composites under tensile loading. In the proposed research, a micromechanical approach is employed, considering an axisymmetric unit cell including one fiber and the surrounding matrix. First, the governing equations and the boundary conditions are derived and the elastic solution is obtained based on some shear-lag-type methods. Since under normal loading conditions and according to the fiber material characteristics, the metal matrix undergoes plastic deformation, while the fiber remains within the elastic region, a plastic deformation is considered for the matrix under each small tensile loading step. Then, applying the successive elastic solutions method, all the plastic strain terms are obtained for the matrix. Thereafter, the elastic-plastic stress transfer behavior of the composite is studied considering this plastic deformation. The results are finally compared with the numerical results obtained from the FE analysis of the considered micromechanical model. The proposed method is capable of predicting all plastic strain terms in the matrix and the stress terms, as well. [ABSTRACT FROM AUTHOR]

In service, reinforced concrete structures undergo various stresses inducing cracks. These cracks provide a preferential path for water and aggressive agents penetration into concrete, which compromises the structural durability by accelerating concrete and steel reinforcement deterioration. In this context, durability of cracked concrete has become an important research topic and can be studied through the permeability of concrete. This research project focuses on the influence of the fiber content and steel reinforcement ratio on the water permeability of reinforced concrete. Water permeability tests were carried out simultaneously with a uniaxial tensile loading applied on reinforced concrete prisms made of high performance concrete (HPC), high performance fiber reinforced concrete (HPFRC) and ultra high performance fiber reinforced concrete (UHPFRC). In service conditions, permeability is reduced by 31, 92 and 99 % for fiber contents of 0.75 % (HPFRC), 1.5 % (HPFRC) and 2 % (UHPFRC) respectively compared with conventional HPC. The increase of steel reinforcement ratio from 1.23 to 2.47 % reduced the permeability by 70 % at service loading. [ABSTRACT FROM AUTHOR]

Enhancing quality of food products and reducing volume of waste during mechanical operations of food industry requires a comprehensive knowledge of material response under loadings. While research has focused on mechanical response of food material, the volume of waste after harvesting and during processing stages is still considerably high in both developing and developed countries. This research aims to develop and evaluate a constitutive model of mechanical response of tough skinned vegetables under postharvest and processing operations. The model focuses on both tensile and compressive properties of pumpkin flesh and peel tissues where the behaviours of these tissues vary depending on various factors such as rheological response and cellular structure. Both elastic and plastic response of tissue were considered in the modelling process and finite elasticity combined with pseudo elasticity theory was applied to generate the model. The outcomes were then validated using the published results of experimental work on pumpkin flesh and peel under uniaxial tensile and compression. The constitutive coefficients for peel under tensile test was α = 25.66 and β = −18.48 Mpa and for flesh α = −5.29 and β = 5.27 Mpa. under compression the constitutive coefficients were α = 4.74 and β = −1.71 Mpa for peel and α = 0.76 and β = −1.86 Mpa for flesh samples. Constitutive curves predicted the values of force precisely and close to the experimental values. The curves were fit for whole stress versus strain curve as well as a section of curve up to bio yield point. The modelling outputs had presented good agreement with the empirical values and the constructive curves exhibited a very similar pattern to the experimental curves. The presented constitutive model can be applied next to other agricultural materials under loading in future. [ABSTRACT FROM AUTHOR]

In this study, the central cracked aluminum plates repaired with two sided composite patches are investigated numerically for their response to static tensile and transient dynamic loadings. Contour integral method is used to define and evaluate the stress intensity factors at the crack tips. The reinforcement for the composite patches is carbon fibers. The effect of adhesive thickness and patch thickness and configuration in tensile loading case and pre-tension, pre-compression and crack length effect on the evolution of the mode I stress intensity factor (SIF) (K) of the repaired structure under transient dynamic loading case are examined. The results indicated that K of the central cracked plate is reduced by 1/10 to 1/2 as a result of the bonded composite patch repair in tensile loading case. The crack length and the pre-loads are more effective in repaired structure in transient dynamic loading case in which, the 100 N pre-compression reduces the maximum K for about 40 %, and the 100 N pre-tension reduces the maximum K after loading period, by about 196 %. [ABSTRACT FROM AUTHOR]

A variety of methods have been used to study the tensile properties of cells or the influence of tensile loading on cellular function. Such methods are frequently limited either by cellular detachment or by an inability to image cells at high temporal or spatial resolution. Previously, we preserved cellular adhesion during loading and imaging by using a flexible silicone membrane inverted over a glass coverslip. This enabled high magnification real-time imaging of subcellular structures but chemical and physical access to the cells was limited due to geometric constraints. In this study, we present a method to integrate thin films made from poly(dimethylsiloxane) (PDMS) into a novel device. The optically clear PDMS thin films allow simultaneous tensile loading and high magnification microscopy without the need to invert the cells, maintaining physical access during experiments. To characterize the utility of this technology, we evaluated fabrication conditions for optimizing the geometry, durability, and uniformity of these films. Additionally, we demonstrate the suitability of this device for use in high-magnification, live-cell fluorescence microscopy by examining the response of the cytoskeletal protein actin, expressed in cultured primary sensory neurons, to a tensile load. This technology offers considerable potential for extending our understanding of mechanical influences on cellular function at a variety of spatial and temporal scales. [ABSTRACT FROM AUTHOR]

The presence of cracks in reinforced concrete structures is recognized to increase the penetration of water and aggressive agents into concrete and thus accelerate its deterioration. In order to gain knowledge on the influence of cracking on concrete durability and assess admissible loads to ensure long-term performance of structures, an innovative water permeability device was developed to estimate water flow in plain and cracked reinforced concrete. Permeability measurements were taken simultaneously with the application of a uniaxial tensile load on the testing specimen. The device permitted the estimation of the average stress in the reinforcing bar and the maximum crack opening in the concrete specimen. The experimental program comprised studies on result repeatability and the influence of testing parameters, such as pressure gradient, pressure regulation, loading rate and loading control mode. Test results showed that the modification of the testing parameters had a negligible impact on water permeability. Moreover, correlations were established between the water permeability, the average stress in the steel reinforcement, and the crack opening width in the reinforced concrete. Analysis of the results demonstrated the potential of the research results to improve the design criteria of reinforced concrete at serviceability limit states. [ABSTRACT FROM AUTHOR]

Chromium (Cr) films are widely used as interlayers to promote the adhesion of copper or gold to substrates. However, the Cr interlayer usually fractures at lower strains than the ductile metal films. In this paper, the cracking and buckling behavior of Cr films on polyethylene terephthalate (PET) substrates were studied in situ under tensile loading with the Atomic Force Microscope (AFM) and optical microscope imaging. Cr films with three nominal thicknesses of 15, 70 and 140 nm were studied. The depth and width of the cracks, as well as the height and width of the buckles, were measured from AFM images acquired at incremental loading steps. The buckle shapes at different strain levels were carefully examined using AFM line profile. It was found that at large strain levels the measured buckle shapes usually deviated from the elastic buckling mode shapes. Further in situ AFM imaging of the buckles at a smaller scan area revealed that in some cases the buckles were cracked at the apex. These in situ nanoscale measurements provided experimental observations and data for further model development and more accurate measurement of the interfacial fracture energy at the Cr-PET interface. [ABSTRACT FROM AUTHOR]

The purpose of this study is to describe the interfacial interactions in terms of stress distributions on short fibers in fiber-matrix unit-cell models. The fiber and matrix are subjected to tensile loading. The study consists of three main parts. First, fiber-matrix cell segments are modeled using a 3D finite-element analysis (FEA) with ANSYS. Three different finite-element geometrical unit-cell models are generated in order to simulate the Cox analytical model: a fiber-matrix combination, a single fiber, and a single matrix element. The second part contains the results of 3D FE analyses, which are applied to the Cox formulations by using a computer program developed. In the last part, the analytical solutions for distributions of normal and shear stresses are investigated. Cox 2D linear elasticity solutions, together with finite-element ones, are presented in detail in graphs. The interfacial interactions between the fibers and matrix are also discussed considering the relative changes in the distributions of normal and shear stresses. [ABSTRACT FROM AUTHOR]

The flexural behavior of unidirectional composites at 90° to the axis was investigated. The experimental data and finite element method results indicate that beam specimens undergo large deformations. An analytical model was developed to calculate the correct maximum stress level obtained during the flexural tests. Models have been developed to describe the time-dependent viscoelastic-viscoplastic stress-strain relationship of unidirectional fibre reinforced thermoset matrix composites. A procedure that extends the classical lamination theory to include time related response of composite materials for membrane and flexural loading resulted in a FORTRAN program, LAMFLU. For Fibredux 920C-TS-5-42 graphite-epoxy composite the constants in the stress-strain relationships were determined from data obtained in four-point bending tests. The model characteristics for tensile loading have been determined by Qin [1] and were adapted to the LAMFLU procedure. The maximum strain history calculated with both models was compared with experimental results from two different flexural loading programs. [ABSTRACT FROM AUTHOR]

Relaxation of residual stresses in metallic materials is caused by diffusion of inhomogeneously distributed solved alloying elements and by microstructural mechanisms like rearrangements of dislocation structure and precipitation processes, respectively. Both processes are often linked with each other. Therefore, the description and the modelling of stress relaxation on a microstructural basis is very complicated. The aim of this study was to demonstrate some models for stress relaxation in metallic materials. The paper presents the relaxation of tensile loading stresses in Ni-based and Co-based superalloys at high temperatures. In stress relaxation tests the microstructure development was connected with a rearrangement of the dislocation structures and by a decreasing dislocation density. The stress relaxation in carbide strengthened superalloys is a typical case of dislocation relaxation in the presence of precipitations. By including the determined microstructure parameters, the effective stress model and also a constitutive model yields to qualitatively correct predictions of the tensile and relaxation behaviour. [ABSTRACT FROM AUTHOR]