Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Experimental analysis of aluminium/carbon epoxy hybrid laminates under flexural load
Get PDFIndustry needs new materials that present very high structural characteristic, such as high strength, low weight and high damage tolerance. To obtain these characteristics a new class of materials has been introduced: Fibre Metal Laminate (FML); they consist in metal sheets alternated to composite material layers: in such manner, the good characteristics of each constituent material confer the utmost properties to the FMLs. However, the mechanical properties depend, among other factors, on the thickness and the numerousness of the layers constituting the FML, as well as the interface between metal and composite. Therefore, in this paper, the influence of the abovementioned factors on the material answer to flexural load was investigated. In particular, different kinds of laminates were produced varying the layers adhesion and the layers thickness, but maintaining unaltered the metal/composite volume ratio and the total laminate thickness. Then their structural behaviour was investigated through three-point bending test, and it was found that the flexural behaviour was affected by both the investigated factors; in fact, the maximum flexural load diminished incrementing the number of layers and inserting an adhesive layer at the metal/composite interface
Retrofit assessment of masonry buildings through simplified structural analysis
Get PDFThe current seismic prevention strategy is based on a unitary approach aimed at a risk mitigation, also at territorial level. The Italian guidelines for the assessment and mitigation of seismic risk of cultural heritage provides indications for the seismic analysis of protected cultural heritage, with the aim of specifying a path of knowledge, assessing the level of safety and planning possible improvements. The Italian building heritage is very vast and heterogeneous and was devastated by earthquakes due to its high vulnerability; therefore, the seismic risk mitigation also requires the availability of simple and handy analysis tools. The aim of this paper is the illustration of an easy, although approximate, procedure for the evaluation of the seismic safety index and the optimization of strengthening interventions. The procedure is applied to buildings located in the province of Caserta. The analyses are performed with reference to two types of buildings that are particularly recurrent and representative of the building heritage of this area and placed in areas with different seismic hazard
The study of internal structure of woven glass and carbon fiber reinforced composite materials with embedded fiber-optic sensors
Get PDFIn this work, samples from composite materials with embedded optical fibers are investigated. It is known that for unidirectional layered composite materials, under certain conditions, a distortion of the internal structure and the formation of such technological defect as resin pocket in the region of the embedded optical fiber occur. So it is important to evaluate the change in the internal structure for other types of reinforcement, in particular, woven reinforcement. Analysis of the internal structure of the studied materials with 2´2 twill weave style was carried out using a digital microscope. In addition, the reflected optical signal from the Bragg gratings after being embedded into the composite material is analyzed
ANN Approach to Predict the Flow Stress of CMn (Nb-Ti-V) Micro Alloyed Steel
Get PDFThe hot behaviour of micro-alloy steel CMn (Nb-Ti-V) was studied using hot compression tests in a wide range of temperatures (700 to 1050 °C, step 50 °C), deformation rates (0.000794, 0.0029 and 0.01436 s-1) and true deformation rates of 0 to 0.8. Based on experimental stress-deformation data, artificial neuron network (ANN) methods were used to predict flow stress CMn (Nb-Ti-V). The optimal ANN model was developed using Levenberg-Marquardt algorithm, and vas formed with two hidden layers with ten neurons in the first and ten neurons in the second. This model has been shown to be more effective in predicting flow stress and results can also be used in the mathematical simulation of hot metal formation processes
Multi-level model describing phase transformations of polycrystalline materials under thermo-mechanical impacts
Get PDFThe problem of constructing the multilevel physical model of inelastic deformation in steels allowing to take into consideration diffusionless solid-state phase (martensitic) transitions is considered. The model structure includes three scale levels with the closed system of equations offered for them. Explicit internal variables reflecting the evolution of the material structure (both the defect structure and the grain one) are introduced at the lower scale levels of the model. The distinctive feature of the developed model is consideration of the lower scale level in such a way that a homogeneous element of this level completely turns into a new phase at a high speed (relative to the kinematic quasi-static loading), that is close to the speed of sound in the crystal medium. Based on the principles of classical thermodynamics the phase transformation criterion is written. According to this criterion, the choice of a transformational system under the martensitic transition is made. The algorithm of the model is developed and its realization features are described in connection with the high-rate restructuring of the face-centered cubic lattice to the body-centered tetragonal one. The result of this restructuring is a severe change in the physic-mechanical properties of the material
Damage evolution in the AlMg6 alloy during high and very high cycle fatigue
Get PDFPaper presents the “in situ” method for determining of irreversible fatigue damage accumulation, based on the analysis of nonlinear manifestations of the feedback signal in a closed system of an ultrasonic fatigue system. During very high cycle (gigacycle) fatigue, the anomalies of the elastic properties of the material are appear, which leads to a nonlinearity effect in the amplitude of oscillations. This effect increases with the initiation and growth of fatigue cracks. The technology was applied to samples of AMG-6 alloy with preliminary dynamic deformation at various levels of average stress to determine the moment of initiation and growth of the fatigue crack in very high cycle fatigue regime. This method is applicable for the early detection of fatigue cracks both on the surface and inside the material under cyclic loading in the ultrasonic mode. On the basis of wide-range defining relations for a deformable solid body with mesoscopic defects, a mathematical model has been proposed that can adequately describe behavior of the material during fatigue failure. The results of mathematical modeling are in good agreement with the experimental dat
Numerical analysis of the state of stress and strain in the Yenisei Ridge based on the regional tectonic state in the Asian continent
Get PDFThe paper presents the calculation of modern tectonic flow fields in the Yenisei Ridge located on the stable Siberian Craton. At the first stage, we solve the problem of calculating the average field of tectonic flows due to collisional processes at the southern and northeastern margins of the Eurasian Plate with Indian and Arabian and with North American plates, respectively. These calculations clarify the state of stress and the structure of tectonic flows on the territory of the Siberian Craton. The subtraction of the average displacements of the Siberian Craton as a whole in the northeast direction reveals the detailed structure of tectonic flows. Structural models are built along the Batolit-1982 and Shpat geological profiles crossing the Yenisei Ridge. At the second stage, we numerically study the state of stress and strain along these profiles determined by the global tectonics of Central and Southeast Asia, as well as their structural organization and interaction with the neighboring crustal elements.
 
Fracture properties of green mortars with recycled sand
Get PDFUrbanisation is consuming huge amounts of sand, being the basic element of concrete and glass, two of the most popular construction materials. Unfortunately, sand mining is causing environmental damage and drastically reducing the amount of raw resources. The main topic of this research is to investigate the use of Construction and Demolition waste finer fraction - namely recycled sand - to totally replace the standard one into traditional mortars. From the analysis of the mechanical characterization of specimens, it is possible to state that recycled sand could represent a new resource for green and sustainable mortars
Using XFEM Techniques to Predict the Damage of aluminum 2024T3 notched under tensile load
Get PDFThe objective of this work is to analyze some geometrical effect to predict the damage of aluminum 2024T3 structure after validate numerical model by experimental test. The mechanical of damage behaviour under tensile tests of several plates with notches of various forms are investigated using an XFEM technique. The finite element analysis is performed to determine the failure load of these plates. Four different form of notched plates in another part of this work are reinforced by a thickness augmentation with different shapes around the notch. The results of the tensile analysis show that the reinforcements gives the best increase in failure load of each plates
Predicting the crack path in a wedge under a concentrated tensile force by means of variational principle
Get PDFVariational principle of brittle fracture mechanics is employed to predict the crack path in an infinite wedge under a concentrated tensile force. The weight function in basic equation of variational problem is assumed to be proportional to the maximum strain in the uncracked wedge. Obtained equation for solving the variational problem allowed predicting the crack path in general. The predicted crack path is in agreement with experimental results obtained in the case of the truncated wedge