Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Damage and failure of Orban’s gun during the bombardment of Constantinople walls in 1453
Get PDFIn this paper the bombardment of the Constantinople Theodosian Walls by the great cannon of Orban is numerically reproduced deploying Structural Mechanics. Overall gun dimensions were assessed based on historical reports, whereby, the gunpowder charge p was estimated at 177 kg, and the gun was placed at 500 m from the Inner Walls. Gun ballistics and effect on target have been evaluated analytically. The analysis has verified Orban’s gun muzzle velocity, cannonball trajectory and its effect on Constantinople Walls by successfully calculating the length of the breach in the wall, referred in historical reports, as well as the cannon ball penetration into soil. The evaluated sound pressure level inside Constantinople, produced by the bombard, confirmed the tremendous psychological effect of the cannon’s blast on the City’s population. A numerical effort was made to assess the combined effect of powder chamber internal pressure with associate temperature produced by powder ignition
Scaling Geological Fracture Network from a Micro to a Macro Scale
Get PDFCharacterizing fracture systems at various scales, modeling fracture distributions, and clarifying scale relations that correlate total fracture systems are of paramount importance in geology, mining, civil engineering, and petroleum engineering. In this paper, the conditions of fracture network geometry are investigated in a field scale (about 100 m) and a core sample scale (several centimeters). To achieve this purpose, field surveys and coring of rock outcrops were performed in the Asmari Formation of Iran. Fractures were manually sampled from rock outcrops on the field scale while micro-fractures were surveyed using CT-scan images of core samples on a small scale. To compare the fracture network geometry, two perspectives of fractal dimensions and orientation of fractures were used. The results showed that the fractal dimension has the same value in both field and core scales and the orientation of the fractures is similar in both scales. Therefore, it can be claimed that in the Asmari Formation of Iran the structure of the fracture network is similar in two studied scales
The FEA and experimental stress analysis in circular perforated plates loaded with concentrated force
No full textABSTRACT. The paper presents an analysis of an isotropic circular axisymmetric perforated plate loaded with concentrated force Pi applied in the geometric center of the plate using finite element software ANSYS. The test plate with diameter D = 300 mm has holes in ten circles. The plate has holes with diameter d1 = 3.5 mm on the first inner circle, and holes on the tenth outside circle have a diameter d10 = 20.5 mm. The plate of the above geometry was free supported and loaded with different values of concentrated force. By means of numerical calculations using the finite element method, the coordinates of concentration zones of reduced stress in the perforated plate were determined. These zones were located on the plate bridges between perforation holes. The most hazardous place in the analyzed perforated plate is associated with the tenth zone Z10 with the hole radius d1 = 3.5 mm at the circle radius R1 = 22.5 mm, where the highest stress concentration occurs. In this zone, the reduced stress is σred max = 416.90 MPa (point with the coordinates x, y, z [mm], i.e. P10 [-69.9; 72.5; 0.0]). The results of numerical calculations were verified with experimental results. The differences between the results of numerical calculations of the state of stress and those obtained experimentally did not exceed 36%
A biomechanical study of the role of sitagliptin on the bone characteristics of diabetic rats
Get PDFAn experimental protocol is described aiming to explore the influence of Type 2 Diabetes Mellitus on the biomechanical response of the bone tissue and, also, to quantify the potential beneficial role of a pharmaceutical treatment, based on sitagliptin, a diabetes drug that increases the levels of natural substances called incretins. Twenty eight male, 10-week old Wistar rats were used, divided into three groups, i.e., the control one, the group including the diabetic rats and, finally, the group including the diabetic rats which were treated using sitagliptin. The biomechanical study was based on a series of three-point bending tests of the femora of the sacrificed rats and the analysis of the experimental data was implemented in terms of the actual geometry of the fractured cross-section. It was concluded that diabetic bones undertake larger forces despite the fact that the “diameter” of their cross-section was somehow smaller. On the contrary, the slope of the load-deflection curve (corresponding to a measure of the stiffness) of diabetic bones is slightly lower compared to the control bones. Finally, it seems that treating diabetic animals with sitagliptin only partly reverses the effect of Type 2 Diabetes Mellitus on their bone tissue, at least concerning its strength and stiffness
Interlaminar shear strength study on CFRP/Al hybrid laminates with different properties
Get PDFFML (Fibre Metal Laminate) is a hybrid material that presents outstanding structural properties, such as resistance to cyclic and dynamic loads, together with low specific weight. This material consists of metal sheets alternating to composite material layers. In the present work, the ILSS (Interlaminar Shear Strength) was evaluated for different types of carbon fibre/aluminium FML, produced varying the layer thickness and the bonding solution of layers. In fact, FMLs consisting of one or two metal sheets (a parameter strictly connected to the layer thickness, as the metal/composite volume fraction was kept at constant value) and bonded with structural adhesive or prepreg resin were considered for this study. The ILSS was determined according to the three-point bending method with short beam specimens. The experimental tests evidenced an effect of the adhesion methodology on the ILSS value, while the layer thickness did not influence the interlaminar strength. The mechanical behaviour after the maximum load point was investigated too, evaluating the trend of the shear stress as a function of the loading nose displacement
Evaluation of the dynamic response of structures using auxetic-type base isolation
Get PDFBase isolation is a widely-used method used to minimise the harmful effects of earthquakes on buildings. Unlike a fixed base building, a building with a base isolation system essentially decouples the superstructure from the substructure resting on the ground. Then, during earthquakes, the superstructure’s relative displacement is significantly reduced, minimising the structural damage. Auxetics, which are materials with a negative Poisson’s ratio, are known for possessing properties such as high energy absorption. Based on the energy absorbing capabilities of auxetic materials, it is proposed that incorporating them into base isolation structures would positively impact on the performance of the system. Therefore, the article aims to investigate the response of structures under seismic loading incorporating re-entrant hexagon layers into the base isolation system. This is assessed by defining and numerically testing the system using finite element analysis. The models developed for this study represent multi-storey structural steel frames combined with fixed base, conventional lead-rubber bearing and auxetic composite base isolation. Differences in the response obtained from the mentioned systems are highlighted. Results indicate that the auxetic base isolation may improve the dynamic response of structures, although a unique performance is not recorded
Numerical investigation of the effect of constrained groove pressing process on the mechanical properties of polyamide PA66
Get PDFThis research is a numerical study of the effect of the constrained groove pressing (CGP) process and its impact on a thermoplastic polymer (polyamide PA 66). A simulation is performed using a finite element tool. The effect of the process conditions and the tool geometry on the mechanical properties is noted. The results are significant, the equivalent strain and Von Moses stress have been progressed accordingly to the number of cycles and the tool geometry. Concluding remarks on the alteration of the microstructure have been proclaimed at the end of this paper
Numerical modeling based on moving mesh method to simulate fast crack propagation
Get PDFAn analysis to show the capability of moving mesh strategy to predict dynamic crack growth phenomena in 2D continuum media is proposed. The numerical method is implemented in the framework of the finite element method, which is coupled with moving mesh strategy to simulate the geometry variation produced by the crack tip motion. In particular, a computational procedure based on the combination of Fracture Mechanics concepts and Arbitrary Lagrangian-Eulerian approach (ALE) is developed. This represents a generalization of previous authors’ works in a dynamic framework to propose a unified approach for predicting crack propagation in both static and dynamic frameworks. The crack speed is explicitly evaluated at each time step by using a proper crack tip speed criterion, which can be expressed as a function of energy release rate or stress intensity factor. Experimental and numerical results are proposed to validate the proposed approach. Mesh dependence problem, computational efficiency and numerical complexity are verified by comparative result
A Numerical framework for fatigue lifetime prediction of complex welded structures
No full textAgeing infrastructure is of major concern for different industrial sectors across Europe. Fatigue cracking is one of the most important damage mechanisms that affect structural health of welded steel structures. Fatigue assessment of welded details in large, complex structures is a difficult and time consuming task. In this paper a numerical framework for fatigue assessment of welded details is presented. In view of industrial applications, automated hot spot stress algorithms for plate and tubular joints were developed and integrated in the framework. The framework provides practicing engineers with an effective tool for fatigue assessment of different components in conformity with leading design codes. Furthermore, apart from Miner’s rule the framework allows easy implementation of different non-linear damage accumulation models in order to account for load interaction and load sequence effects
Stress-strain assessment of plain dents in gas pipelines
Get PDFPaper presents the analytical solution of the stress-strain state for a dented pipeline, based on the method of equivalent loads. First off all solution for a harmonic imperfection is found, then using Fourier series expansion a semi-analytical procedure is proposed to assess single dent. Comparison between analytical and numerical results for the axial force and pressure load is given. Influence of the dent dimensions, shell radius to thickness ratio and initial loading to stress concentration factor are discussed