Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Analysis of workability, mechanical strength and durability by the FT-IR method of concrete based on silica-limestone sand preserved in aggressive environments
Get PDFThe interest of using combined sand of equal percentage of silica and limestone becomes evident in the formulation of compacted concrete in several previous works around the world, due to the formidable percentage of fines that improves the compactness and increases various mechanical resistances, which produces a more durable construction against different probable aggressions.
This paper examines the effect of using this type of sand on workability, compressive strength, flexural strength, and splitting tensile strength. A durability test was consulted using infrared spectroscopy to assess diverse types of hydration products formed. Found results clearly show the advantages of using sand with silica and limestone grains (50/50)% in ordinary concrete infected by aggressive water. There is also an improvement in compactness, different mechanical resistances, and a reduction in the formation of harmful hydration products
Methodology of hydrogen embrittlement study of long-term operated natural gas distribution pipeline steels caused by hydrogen transport
Get PDFA methodology of experimental research on hydrogen embrittlement of pipe carbon steels due to the transportation of hydrogen or its mixture with natural gas by a long-term operated gas distribution network is presented. The importance of comparative assessments of the steel in the as-received and operated states basing on the properties that characterize plasticity, resistance to brittle fracture and hydrogen assisted cracking is accentuated. Two main methodological peculiarities are pointed out, (i) testing specimens should be cut out in the transverse direction relative to the pipe axis; (ii) strength and plasticity characteristics should be determined using flat tensile specimens with the smallest possible thickness of the working part. The determination of hydrogen concentration in metal, metallographic and fractographic analyses have been supplemented the study. The effectiveness of the proposed methodology has been illustrated by the example of the steel research after its 52-year operation
A probabilistic fatigue crack growth life approach to the definition of inspection intervals for railway axles
Get PDFDifferent options that rely on fracture mechanics are currently used in engineering during the design and assessment of components. One of the most important aspects is the time taken for a crack to extend to its critical size. If this time is long enough, a design concept based on inspection intervals can be applied, as is it the case of a railway axle component. To define inspection intervals that ensure the continuous and safe operation of a damage-tolerant railway axle, a reliable estimation of its fatigue crack growth life is required. Due to the uncertainties involved in the fatigue process, inspections must be devised not only considering the uncertainties in the performance of the inspection technique, but also based on a probabilistic lifespan prediction. From this premise, this paper presents a procedure for determination of inspection intervals that uses a conservative fatigue crack growth life estimation based on the lifespan probability distribution. A practical example to illustrate the reliability-based inspection planning methodology in a railway axle under random bending loading is given. The inspection intervals are further assessed in terms of overall probability of detecting cracks in successive inspections and in terms of probability of failure, considering the probability of detection curve of the non-destructive testing technique. The procedure developed provides recommendation for the definition of inspection intervals and associated inspection techniques
Inverse problems with the digital image correlation: approach and applications
Get PDFA viable approach to solve inverse problems in elasticity is proposed. It is based on regression algorithms to estimate materials and/or loading parameters by fitting the experimentally-evaluated displacement field to representative analytical solutions.
Displacements are measured by the digital image correlation (DIC) technique and they are used as input for numerical procedures able to minimize the estimation errors of the unknowns and to quantify the unavoidable rigid body motions of the samples/components. In addition, thanks to ad-hoc developed iterative algorithms, non-linear phenomena related to high and localized stress/strain states, can be captured successfully. This latter represents a relevant novelty of the methodology as it allows to investigate plasticity-induced mechanisms in solid mechanics which are impossible to analyze with more traditional DIC-based approaches.
Three different case studies are considered: 1) estimation of the stress intensity factor in fracture mechanics problems, 2) estimation of the elastic properties of a material by the Brazilian tests, 3) estimation of the contact pressure generated by thermally activated shape memory alloy (SMA) rings used for pipe coupling.
The reliability and the accuracy of the method is demonstrated through systematic comparisons of the results with conventional techniques in experimental mechanics
Asymptotic response of friction stir welded joint under cyclic loading
Get PDFFatigue takes a place more and more important in the design of structures, it remains a key point in the mechanical dimensioning of structures.
The Friction Stir Welding (FSW) process is regarded today as the most promising alternative to traditional joining methods. It ranks among the most recent assembly processes and is considered a new technique for the 21st century. Indeed, if the FSW welding process has several advantages, it introduces very strong microstructure heterogeneities in the welded joints.
This leads to heterogeneous mechanical behavior in each of the constituent zones. some important efforts have been deployed in industry as well as in research laboratories to understand the behavior of welded joints by the FSW process. There are many questions about the behavior of these areas.
This study led to the characterization and understanding of the fatigue behavior of a 2024T351 structure welded by the FSW process. It presente in a numerical work which aims to help determine the asymptotic response of each zone constituting the 2024T351 joint welded by FSW subjected to a cyclic loading and to fully understand the behavior of these zones.
To carry out an analysis and a simulation under cyclic loading, our choice fell on the use of the direct cyclic method. Numerical simulation of crack propagation was performed using the extended finite element method XFEM.
This research consists in the implementation of the X-FEM in fatigue in a multiscale model X-FEM / direct cyclic.
The numerical results consist in highlighting the heterogeneities in the mechanical behavior of the welded joint and in evaluating the impact of the FSW process on the failure of these FSW zones
Analysis of Above-Ground Steel Storage Tanks Resting Over Piles or Stone Columns
Get PDFStatic and dynamic behavior of above-ground steel storage oil tanks resting on end bearing piles or stone columns are studied and analyzed using ADINA (2019) program. The studied soil profile is an upper soft clay soil layer, followed by an extended dense sand layer. The main purpose of this research is to explore to what extent stone columns can be used as an effective alternative to concrete piles under steel storage tanks. Therefore, many three-dimensional numerical models are conducted to analyze and study the performance of such tanks in both static and dynamic cases. Ten of the studied cases are steel tanks resting over stone columns with different numbers and properties. On other hand, one model studied the behavior of steel tank resting on large diameter concrete piles. Results indicate that stone columns can be used instead of end bearing piles as long as the computed settlements are safe. In addition, stone columns are behaving better than concrete piles in decreasing of hoop stress in tank shell. It is also noticed that stone columns with high elastic modulus are effective in reducing the sloshing height of the oil surface during earthquakes
Damage severity for cracked simply supported beams
Get PDFThis paper investigated the static and dynamic behaviors of isotropic cracked simply supported beam using finite element analysis (FEA), ANSYS software. Modal and harmonic vibration analysis of intact and damaged beam were performed in order to extract mode shapes of bending vibration, natural frequencies and obtain frequency response diagram. Static finite element analysis of undamaged and damaged simply supported beam was carried out to determine zero frequency deflection, then stiffness of intact and cracked beam was computed using conventional formula. Crack damage severity of damaged beam was calculated and it is noticed that as crack position is increased from left hand support of beam up to central point and crack depth is increased, then crack damage severity increases. The effect of mode shape pattern is investigated and it is found that the amount of decreasing of natural frequency is proportional to the normalized mode shape at position of crack. The exhibited correlation between results for damaged beam revealed that crack damage severity is proportional to zero frequency deflection and inversely proportional to first mode frequency
Supervised Machine Learning Classification Algorithms for Detection of Fracture Location in Dissimilar Friction Stir Welded Joints
Get PDFMachine Learning focuses on the study of algorithms that are mathematical or statistical in nature in order to extract the required information pattern from the available data. Supervised Machine Learning algorithms are further sub-divided into two types i.e. regression algorithms and classification algorithms. In the present study, four supervised machine learning-based classification models i.e. Decision Trees algorithm, K- Nearest Neighbors (KNN) algorithm, Support Vector Machines (SVM) algorithm, and Ada Boost algorithm were subjected to the given dataset for the determination of fracture location in dissimilar Friction Stir Welded AA6061-T651 and AA7075-T651 alloy. In the given dataset, rotational speed (RPM), welding speed (mm/min), pin profile, and axial force (kN) were the input parameters while Fracture location is the output parameter. The obtained results showed that the Support Vector Machine (SVM) algorithm classified the fracture location with a good accuracy score of 0.889 in comparison to the other algorithms
Modelling of Low-velocity Impacts on Composite Beams in Large Displacement
Get PDFThe paper provides an evaluation of the nonlinear dynamic response of a cantilever beam made of composite material subjected to low-velocity impacts. The structure is assumed to respond in a quasi-static manner and modelled by a continuous beam in large displacement with a lumped mass attached. First, an analytical model was developed to study the free vibrations of a beam, taking into account the nonlinearities due to large displacements and inertia. Then, the analytical findings were compared with experimental test data. The vibration of a real composite beam has been acquired through high-speed imaging technique. The displacements of the beam were extracted by digital image analysis; then, the nonlinear parameters of the analytical model were determined by the Fitting Time History technique. The results obtained by the analytical model and the experimental test are compared with numerical analysis. The validated analytical model was adapted to study a low-velocity impact; the lumped mass was associated with a rigid projectile, whose initial speed represents the impact velocity
Sensitivity analysis of the GTN damage parameters at different temperature for dynamic fracture propagation in X70 pipeline steel using neural network
Get PDFIn this paper, the initial and maximum load was studied using the Finite Element Modeling (FEM) analysis during impact testing (CVN) of pipeline X70 steel. The Gurson-Tvergaard-Needleman (GTN) constitutive model has been used to simulate the growth of voids during deformation of pipeline steel at different temperatures. FEM simulations results used to study the sensitivity of the initial and maximum load with GTN parameters values proposed and the variation of temperatures.
Finally, the applied artificial neural network (ANN) is used to predict the initial and maximum load for a given set of damage parameters X70 steel at different temperatures, based on the results obtained, the neural network is able to provide a satisfactory approximation of the load initiation and load maximum in impact testing of X70 Steel.