Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Numerical simulation of creep notched bar of P91 steel
Get PDFNumerous components designed for use at elevated temperatures now exhibit multiaxial stress states as a result of geometric modification and material inhomogeneity. It is necessary to anticipate the creep rupture life of such components when subjected to multiaxial load. In this work finite element analysis has been performed to study the influence of different notches, namely blunt and medium notches on the stress distribution across the notch throat during the creep exposure. Within the FE model, a ductility exhaustion model based on the Cocks and Ashby model was utilized to forecast the creep rupture time of notched bar P91 material. The lower and upper bound of creep ductility are employed in the FE analysis. Different notch specimens have different stress and damage distribution. It is shown that for both types of notches, the von Mises stress is lower than the net stress, indicating the notch strengthening effect. The accumulation of creep damage in the minimum cross-section at each element across the notch throat increases over time. The point at which damage first occurs is closer to the notch root for the medium notch than for the blunt notch. The long-term rupture life predicted for blunt notch specimens appears to be comparable to that of uniaxial specimens. The upper bound creep ductility better predicts the rupture life for medium notches
Evaluation on fatigue behaviour of spot-welded joint under low blow impact treatment
Get PDFWelding is used widely in modern industries to combine parts needed complete a product. In this paper, we investigated the effect of post-weld impact treatment (PWIT) on spot-weld joints and evaluate the tensile and fatigue properties of the specimens. Currently, there is no simple failure criterion capable of predicting the strength of a spot weld under different loading conditions. The reliability of spot-welded structures treated with PWIT in terms of fatigue integrity could be understood more by the end of this research. The result showed that not only the tensile properties of PWIT specimens give an improvement, but there was also a significant increase in the fatigue life of the treated specimens
Experimental and numerical investigation of gap K-joints of rectangular hollow section trusses
Get PDFThis paper is concerned with investigating of the plastic behaviour on gap K-joints of truss girders, made from thin-walled rectangular hollow section members. An experimental study was carried out on a full-scale girder under a concentrated load on two central nodes. A numerical analysis was carried out using ABAQUS in order to clearly see the behaviour of this type of joint and to make a comparison with the experimentation. This study will make it possible to examine attentively and to define the analytical model for this type of joint. The results obtained in this paper have shown that the sections with very thin-walled present different behaviours compared to the thin or more or less thick sections. As a result, the tested truss made it possible to observe the failure mode of this type of section, follow-up of a comparative study on the determination of the joint capacity by Eurocode 3 and CIDECT
Estimation of the nonlinear dependence of the indications of a fiber Bragg grating on temperature and strain from experimental data
Get PDFThe readings of the Bragg grating are determined based on the optical radiation reflected from it. A quantitative characteristic of this radiation is the wavelength at which the maximum power of the optical signal is achieved. This characteristic is called the central wavelength of the grating. The central wavelength shift depends on temperature and strain. As a rule, a linear approximation of this dependence is used. However, from the available literature it is known that, the grating wavelength shift demonstrates a strong nonlinear dependence on temperature at 5<T<200K and a weak quadratic dependence close to room temperature. Thus far, the authors have not found studies that consider all terms in the quadratic expansion of the central wavelength of the Bragg grating as a function of temperature and strain at near-room temperatures. Our work is intended to fill this gap. The article describes an experiment in which an optical fiber with Bragg grating was subjected to loading using three different weights. A step-wise temperature change from 5 to 100 0С was realized for each weight. Based on these data, all terms of the quadratic expansion of the desired function are determined. The contribution of each term is estimated
Failure analysis of compressed earth block using numerical plastic damage model
Get PDFIn the last decade, several studies have been introduced to the development and use of compressed earth blocks in green building construction. Studying the evaluation of existing cracks in construction builders by these blocks is an important industrial and safety subject in recent research. This objective opens a new field in building construction where we describe the mechanical behavior of compressed earth solid blocks. In addition, we offer a solution to rupture damages presented by the propagation of masonry cracks. This paper aims to explore a numerical study in ABAQUS where we analyze the mechanical properties of this block. We started by investigating the elastic phase for this material and it has been generalized to a study in the plastic regime and rupture for the studied block. The different results of numerical simulation of the studied shape are presented, compared, and criticized
Evaluation of the behaviour of reinforced concrete beams repaired with glass fibre reinforced polymer (GFRP) using a damage variable
Get PDFThe use of fibre reinforced polymers (FRP) for increasing the strength of RC structures became a usual method. FRP presents easy application and demands low space and provide significant strength increase. Usually, the decision for FRP use is made in terms of applied loads and deflections. However, such quantities can vary significantly depending on the characteristics of the structural element e.g. span, effective depth and concrete resistance. Therefore, this paper aims to present an alternative control variable to analyse the behaviour of RC beams repaired with glass fibre reinforced polymer (GFRP), called damage. Such damage variable accounts for concrete cracking and it was experimentally measured before and after the application of GFRP. Note that the application of GFRP increased the ultimate load for all repaired beams. The damage values of such beams also increased when collapse was reached. Furthermore, it was observed that the collapse mechanism shifted to shear and did not occurred the failure of the GFRP
Enhancement of Blast Resistance of R.C Beams Using Micro/Nano Silica in Presence of Steel Fibers
Get PDFAn analytical investigation using ABAQUS/Explicit dynamic analysis was carried out to investigate the effect of using Micro/Nano silica in the presence of steel fibers on improving the dynamic response of reinforced concrete beams. According to the results of Magnusson and Hallgren's experimental investigation, the FE model has been well verified and calibrated. The finite element test program was extended further to study the effect of tensile reinforcement ratio by (0.5%, 0.78%, and 1.13%) comparing with the enhancement of concrete’s material on the behavior of tested R.C beams under blast loading. The results where compared in terms of changes in the max deflection at mid-span and flexural toughness values. The results showed that the combination between the compressive and flexural characteristic of concrete is necessary in case of high steel reinforcement ratio to reduce the brittle behavior of the R.C structure element, especially when the R.C elements exposed to a high strain rate loading due to the addition value of (DIF) for steel reinforcement properties which make the element stiffer than usual, compared with quasi-static loading condition.
 
Mixed Finite Element Computation of Energy Release Rate in Anisotropic Materials Based on Virtual Crack Closure-Integral Method
Get PDFThe material with anisotropic properties are becoming widely essential due to the ease to manipulate their mechanical properties in order to obtain a particular quality, insure safety or a specific behavior. Those kind of materials are considered anisotropic because their characteristics and behavior are dependent to every direction of the material’s orientation.
In this work, the virtual crack closure-integral technique is implemented to a mixed finite element, in addition with the stiffness derivative procedure, to evaluate the energy release rate of crack extension in anisotropic materials. A simulation of a cracked edge rectangular plat with anisotropic characteristics is taken for example.
The results obtained are in good agreement with the analytical results, making the proposed technique a good model for fracture investigation and allow it to study more complicated cases in future works
Effect of the Stress State on the Adhesive Strength of an Epoxy-Bonded Assembly
Get PDFThe paper studies the adhesive strength of aluminum alloy specimens bonded with the use of an epoxy adhesive, under the tensile-shear stress state, depending on the testing temperature. Tension of modified Arcan specimens with load angles of 0, 22.5, 45, 67.5, and 90° with respect to the plane of adhesion is chosen as the experimental method. Experiments were performed at temperatures of −50, +23, and +50 °С. The analysis of the obtained results yields a linear fracture criterion and a fracture locus for the adhesive failure strain energy density, which takes into account the ratio of the elastic properties of the adhesive to those of the substrate. The region bounded by the fracture loci of adhesive strength and ultimate strain energy density determines the conditions for the safe loading of the bonded assembly in terms of the energy and force criteria of adhesive failure. The proposed fracture loci can be used, preferably simultaneously, to estimate the in-service strength and reliability of adhesively bonded assemblies
The effect of using polypropylene fibers on the durability and fire resistance of concrete
Get PDFIn order to study the effect of polypropylene fibers on the durability of cementitious composites, several experimental tests have been carried out in the laboratory. The composite was tested with different volume fractions of polypropylene fibers (0.05%, 0.10%, 0.30% and 0.50%). All the results relating to the indicators (porosity accessible to water εb, to the oxygen permeability Kapp.gas and diffusivity Dns) indicate that the addition of polypropylene fibers in a cement matrix represents only a small effect on durability. This panel of general sustainability indicators can be supplemented by indicators more specific to each degradation process identified or envisaged depending on the environmental conditions of the structure. However, the addition of the volume fraction of polypropylene fibers (0.50%) in a cementitious composite, increases fire resistance. Such behavior gives fiber composites interesting properties which favor their use in structures exposed to fire risks