Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Effect of different parameters controlling the flexural behavior of RC beams strengthened with NSM using nonlinear finite element analysis
Get PDFNear surface mounted technique become the most attractive technique for strengthening RC structures. Several researches had been conducted to study experimentally the flexural behavior of RC members strengthened with NSM technique unlike the numerical researches. In this paper a numerical investigation utilizes the non-linear finite element (FE) modeling using ANSYS was performed. The developed FE model considers the behavior of the epoxy-concrete interface using a particular continuum damage approach, called cohesive zone model (CZM) which is capable of predicting the failure mode of the strengthened beams. The modified model study the effect of different parameters such as NSM bar number, NSM bar length, end inclination angle and end inclination leg length on the flexural behavior of strengthened beams. The results showed that, The developed FE model able to predict the expected modes of failure in NSM technique, the NSM bar length was effective till 0.5 of beam span, beams strengthened with end inclined angle 45º NSM bar gives the highest improvement in load carrying capacity, this improvement was very close in case of using end inclined angle of 60º and 90º
Stress intensity factors for mixed-mode crack growth in imitation models under biaxial loading
Get PDFIn this study a procedure to stress intensity factors calculation for imitation models made of titanium alloy is described. In service fatigue cracks are detected in a disk and blade “dovetail type” attachment. On the base of this attachment dimensions and with taking into account the biaxial loading conditions of rotating compressor disk the two geometries of imitation model of gas turbine engine compressor disk are developed. To accurate verification of biaxial loading conditions, the first imitation model of constant thickness is used. In order to fully reproduce the geometry of the compressor disk and conditions of mixed mode crack growth, the second imitation model with reduced cross section is proposed. The fatigue crack growth experiments of imitation models were carried out at room temperature on a biaxial testing machine. Two different stress ratio values are applied several times to each imitation model in order to fix the experimental crack front positions. The elastic and plastic stress intensity factors used for the representation of the experimental results are computed by using full-size 3D Finite Element analysis of the imitation models with surface quarter elliptical and through-thickness cracks
Finite element analysis of the thermomechanical behavior of metal matrix composites (MMC)
Get PDFIn this work the finite element method (FEM) was used to analyze the mechanical behavior of the composite materials subjected to the mechanical loading. This behavior is studied in terms of stress intensity factor variation as a function of the applied stress intensity. The residual stresses induced in the composites, during the elaboration of these composites are taken into consideration in this study. The superimposition of these types of stresses (residuals and commissioning) is simulated here by thermomechanical stresses. The results obtained show that in the vicinity very close to the fiber-matrix interface and under the effect of this loading type, the matrix cracks propagate in modes I, II and III, and far from the interface, in mode I. The propagation kinetics is slowed down by the interface-crack interaction.
The effects of the crack size, the orientation and propagation of the crack, commissioning stresses, the elaboration temperature, fiber physical properties, matrix stiffness and thermomechanical stresses have been highlighted in this work
Finite element analysis of the interface defect in ceramic-metal assemblies: Alumina-Silver
Get PDFThe realization of a connection between a ceramic and a metal is always accompanied by the creation of a multi-axial stress field. Different physical and mechanical origins explain the genesis of stresses at the bonding interface in the ceramic and metal at the bond formation of ceramic-metal. In this study, a finite element model is developed to analyze numerically the effect of the sites of alumina grains snatches on the distribution and stresses level of the interface with the silver. The analysis has been extended to the effect of alumina grains-alumina grains interaction, alumina grains size and form
Monitoring and analysis of reinforced concrete plate-column structure under room temperature and fire based on acoustic emission
Get PDFThis paper attempts to disclose the damage mechanism of reinforced concrete plate-column structure under room temperature and fire. Several tests were carried out to record the law of crack development on the plate surface under room temperature. The infrared detection technology was adopted to observe how cracks develop under fire. The acoustic emission (AE) signals at different positions of the specimen were monitored by the AE techniques. Coupled with the macroscopic test phenomena, several characteristic parameters collected by the AE system, namely, cumulative number of events, event rate, energy rate and b-value, were analyzed in details. The results show that: the cumulative number of events was active in the loading, heating and cooling stages; the crack density and the change of internal forces could be derived from the trend of event rate; the local energy changes of the specimen could be deciphered from the curves of energy rate and b-value, making it possible to judge if a component has reached the failure state; the specimen suffered the most severe damages, when the AE parameters suddenly changed; AE monitoring enables the early warning of fire to reinforced concrete plate-column structure; infrared detection technology is suitable for real-time monitoring of crack development under high temperature.
 
Risk based analysis of RHPP penstock structural integrity
Get PDFRisk based analysis of reverse hydro power plant penstock structural integrity is performed using fracture mechanics parameters. To assess its structural integrity, extensive testing of the full-scale prototype had been performed, including hydrostatic over-pressurizing, during the design phase. More recently, the Failure Assessment Diagramme has been used to evaluate probability, whereas phenomenological analysis has been used to estimate consequence, in the scope of common risk estimation. It is shown that over-pressuring has potential detrimental effect on pipeline safety, i.e. structural integrity
Numerical analysis of reinforced concrete beams pre cracked reinforced by composite materials
Get PDFThis work constitutes a contribution to the analysis of the behavior of beams reinforced by composite materials. The analysis was made by a study on concrete elements, and in pre-cracked reinforced concrete then reinforced with carbon fiber fabric bonded in tusi using an epoxy resin. In order to study the influence of the initial state of cracking, one of the beams was reinforced without it being pre-cracked and was compared to a pre-cracked and reinforced beam then to another loaded until rupture without being pre-cracked or reinforced and neither reinforced. the beams were pre-cracked and reinforced in their stretched part and on the lateral part with bands of different dimensions in order to avoid delamination on the one hand and to study the recovery of the composite under the effect of shearing and detachment on the other hand. However, the arrival of these structures brings new scientific problems and in particular the mode of rupture.
The aim of this work is to increase the bearing capacity, reduce the deflection and limit the opening of cracks by ensuring better behavior of this element. The results obtained showed that the bonding of composite materials on reinforced concrete structures gave an increase in the ultimate breaking load and a reduction in deformations in concrete and steels.
The results of this method coincide perfectly with those from the literature.
The reinforcement allowed a significant increase in the breaking load and a reduction in the deflection at break up to 80%. The theoretical model based on the theory of modified reinforced concrete made it possible to predict with good precision the behavior in bending until the ultimate and it would be possible to use the fabric and the epoxy resin for the reinforcement in bending in building site, beams
Numerical analysis of circular and square section concrete filled aluminum tubes under axial compression
No full textIn this paper, the finite element (FE) method was used to investigate the axial compressive behaviors of circular and square concrete filled aluminum tubes (CFAT). Firstly, the simulational results were compared with the experimental results and the accuracy of the proposed FE model was verified. On this basis, the FE model was further applied to compare the mechanical properties of both circular and square CFATs under axial compression. It was found that the circular CFATs have a better effect on restraining the core concrete than square CFATs. The parametric analysis was also conducted based on the proposed FE model. It was noticed that the mechanical differences of the two kinds of CFATs gradually decreased with the increase of the aluminum ratio, aluminum strength and concrete strength
Numerical analysis of the influence of maximum residual thermal stresses on the intensity factor between the matrix and particle interfaces in metal matrix composite
Get PDFA critical problem in the application of metal matrix composites is the presence of high residual thermal stresses induced during the development process. These thermally induced stresses are generally detrimental to the service life of this type of composite. This article discusses the influence of maximum residual stresses on the intensity factor. The results interpreted in terms of damage, allowed us to identify the risk zones; characterized by a significant level of maximum residual stresses (S11Max, S22Max, S33Max), namely the particle/Matrix interface.
The results also show that the loading conditions and the inter-distance between matrix and particle with two interfacial cracks have an important effect on max residual stresses and stress intensity factors.
 
Analysis of strengthened short deficient rubberized concrete-filled steel tubular columns
Get PDFConcrete-filled steel tubular (CFST) columns are broadly used in many structural systems for their well-known merits. This paper presents a finite element investigation on the structural behaviour of short circular deficient steel tubes filled with rubberized concrete (RuC), under axial compressive load. To accomplish this study, a validation of the proposed three-dimensional nonlinear finite element model; using ANSYS software; was carried out showing good accurateness. The analysis involved two different concrete mixes with 5% and 15% replacement of fine aggregate volume with crumb rubber particles. Columns strength reduction due to horizontal or vertical deficiencies was handled by increasing the thickness of the steel tube or wrapping the columns with two different types of FRP sheets. Five strengthening arrangements were studied using GFRP sheets and CFRP sheets. The results indicated that the ultimate bearing capacity of the RuCFST columns was increased with increasing the steel tube thickness. application of FRP sheets for strengthening the deficient RuCFST columns efficiently managed to retrieve the strength-lost due to either horizontal or vertical deficiency. Moreover, an enhancement in the columns’ ductility was observed especially when using GFRP sheet