Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Quantifying the out-of-plane response of unreinforced masonry walls subjected to relative support motion
Get PDFTThe supports of out-of-plane loaded unreinforced masonry walls in buildings are subjected to a motion that is filtered and amplified by the building structure and, in some cases, can be significantly different from the ground motion. Moreover, because these walls span one or several storeys, their top and bottom supports are subjected to motions that differ in phase and amplitude. In state-of-the-art assessment procedures for the out-of-plane stability of masonry walls any effect of a relative support motion is neglected. The objective of this paper is to study the effect of the relative support motion on the response of out-of-plane loaded vertically-spanning unreinforced masonry walls. The acceleration capacity of the walls is investigated by means of a discrete element model representative of different wall configurations. A set of ground motions covering a wide range of peak ground acceleration and peak ground displacement is used as input to the simulations. The relative motion between the wall supports is included in the model in a systematic way: firstly, through a motion that is non-synchronous but of equal amplitude; secondly, through a motion that is synchronous but of different amplitude. The effect of the relative support motion is studied on different wall configurations where the elastic modulus of masonry, the wall height-to-thickness ratio, the wall effective thickness and the overburden at the top wall are varied. The study shows that, because of the relative support motion, the acceleration capacity of the walls can drop by 20% and, in the cases where the overburden is high, by more than 50%
Web Rotational Stiffness of Continuous Steel-Concrete Composite Castellated Beams
Get PDFContinuous composite beams may suffer a global instability know as lateral distortional buckling (LDB). The design code EN 1994-1-1:2004 provides a procedure for the verification of this ultimate limit state, in which the resistant bending moment to LDB is calculated considering the behavior of the inverted “U-frame” mechanism. An essential parameter for the determination of this moment is the rotational stiffness of the composite beam, which depends on the web stiffness. The EN 1994-1-1:2004 procedure is restricted to composite beams with solid-web steel sections without openings. This paper presents several numerical analyses of the web rotational stiffness of castellated sections such as Anglo-saxon, Litzka and Peiner typology. Finally, based on numerical results obtained, a calculation procedure for determination of this stiffness was proposed
The Effects of Ply Orientation on Nonlinear Buckling of Aircraft composite Stiffened Panel
No full textIn this paper, gradual demand for curved, stiffened panels composite emerged from carbon fiber reinforced plastics (CFRP); these are structures that are frequently used in aerospace engineering. Up to 50% of the primary structure of the Boeing 787 is made up of woven graphite–epoxy. This research emphasizes the buckling analysis of stiffened composite panels using the nonlinear, finite element modeling. The stiffened panel is assumed to be subjected to a uniform axial compression load of . For the nonlinear buckling analysis, a stiffened composite panel is made of carbon fibre composite (CFC) in epoxy, Kevlar in epoxy and E-glass (EG) in epoxy. Due to the fact that there are numerous stiffened composite panels materials, this paper, therefore uses a numerical approach, to present the study and results of the nonlinear static buckling analysis of I-stiffened, on different composite panels. This research also presented the effect of the different ply orientations using Abaqus finite element analysis (FEA)
A metallurgical and thermal analysis of Inconel 625 electron-beam welded joints
Get PDFInconel 625 is a nickel-based superalloy that finds application in many industrial sectors thanks to its high strength, excellent fabricability, and outstanding corrosion resistance. It is characterized by a good weldability and often used in the as-welded conditions. In the following, a metallurgical and thermal analysis of Inconel 625 Electron-Beam welded joints is described. The thermal analysis was supported by a numerical model that uses a superimposition of a spherical and a conical shape heat source with Gaussian power density distribution in order to reproduce the nail-shape of the fusion zone. The heat source parameters were calibrated by using experimental data coming from metallurgical observations and temperature measurements. Numerical and experimental results were found in good agreement
Structural failure process of schistosity rock under microwave radiation at high temperatures
Get PDFThe effects of high temperature induced by microwave radiation on the schistosity structural rock were investigated. A 1.45 kW commercial microwave system was employed to irradiate specimens to a designed temperature (300–800 °C) for 15 minutes. Cracking and local melting initially appeared in the biotite enrichment area at 500 °C. Macro-cracks in the dark area were parallel to the schistosity trend, owing to the weak connection in a direction perpendicular to the schistosity plane. The composition of the rock did not significantly change before and after microwave radiation. The diffraction peak intensity of the biotite decreased with temperature increase, owing to melting. The average peak stress decreased significantly with increasing temperature. It is concluded that the high temperature induced by microwave radiation promotes hard rock breakage and the schistosity structure of rock significantly affects the cracking pattern
J integral computation and Limit load analysis of bonded composite repair in cracked pipes under pressure
Get PDFIn this paper, an additional criterion was introduced to evaluate the composite repair systems using the limit load analysis. The plastic collapse pressure of API 5L X65 PSL2 steel pressure vessel structure with crack defect is numerically investigated after the structure was been repaired by composite overwrap. The objective of this study was the analysis of the efficiency of composite repair systems using this additional criterion to gain more confidence on it taking into account, the cracks and the overwrap geometries. The material of the pipe is elastic perfectly plastic for the plastic collapse pressure criterion and elastic-plastic using the Romberg Osgood model for fracture mechanic criterion. The additional criterion allows us to compare the uncracked and cracked pipe to estimate the repair efficiency. Moreover, the composite overwrap could restore 90% of the plastic collapse pressure for cracked pipes
Restoring stone monuments: Enlightening critical details by the combined use of innovative sensing techniques
Get PDFThe experience gathered during the implementation of long series of laboratory experimental protocols, aiming to study the mechanical response of restored structural elements, is summarized. Conclusions are drawn concerning the proper exploitation of the laboratory results in field applications in the frame of on-going restoration projects of ancient stone monuments. The need of continuous bidirectional interaction between the scientific personnel working in the site and the scientists working in the laboratory is emphasized. The role of the Digital Image Correlation technique in quantifying parasitic effects influencing the laboratory data is proven decisive. The need to use modern sensing techniques, providing data from the interior of loaded restored complexes (simulating restored structural elements), like the Pressure Stimulated Currents and the Acoustic Emissions ones, according to a combined manner is highlighted. The capability of these two techniques to monitor the damage evolution within the mass of the elements tested and to provide clear pre-failure indicators renders them flexible tools in the hands of engineers designing the restoration projects
Damage evolution in marble under uniaxial compression monitored by Pressure Stimulated Currents and Acoustic Emissions
Get PDFThe spatiotemporal evolution of damage in marble specimens under uniaxial compression is monitored using Pressure Stimulated Currents (PSCs) and Acoustic Emissions (AEs). The novelty of the study is the use of an integrated grid of sensors (instead of a single pair of electrodes) to detect the weak electrical signals, emitted during loading. The use of such a grid of sensors does indeed enhance the capabilities of the PSC technique providing valuable information about the initiation and propagation of micro-fracturing at the interior of the specimens. The experimental results indicate that both the improved b-value of the AE hits and the energy of the PSCs offer information about the proximity of the applied stress to that causing fracture. It is thus concluded that both quantities could be considered as pre-failure indicators
Verification of the ΔKeff hypothesis along the fatigue crack path in thin and thick Al specimens
Get PDFElber assumed that the actual driving force for fatigue crack growth (FCG) is the effective stress intensity factor ΔKeff. To verify this hypothesis, both DC(T) and C(T) specimens are cut from a 6351-T6 Al alloy circular bar with two different thicknesses, 2 and 30mm, tested under fixed ΔK and Kmax to simulated plane stress and plane strain FCG conditions. A strain-gage bonded on the back face of the specimens is used to measure the crack length and a custom-made Labview program is used to control the applied load, maintaining ΔK and Kmax constant along the crack path. Moreover, the crack opening load is redundantly measured during the FCG tests, using far field strains from the back face gage and near field strains from a series of gages bonded along the crack path, as well as an independent digital image correlation system to measure displacement/strain fields on the face of the specimens. These tests show that the Al specimens reproduce the behavior previously observed in similar tests in 1020 steel: a significant decrease of the opening load as the cracks grow along the specimens, while maintaining a FCG rate essentially constant under the fixed {ΔK, Kmax} loading, a behavior that cannot be explained by the ΔKeff hypothesis
Intermetallic phase kinetic formation and thermal crack development in galvanized DCI
Get PDFA new class of material characterized by mechanical properties close to the traditional low and medium carbon steel is the Ductile Cast Irons (DCIs). High castability and low production costs allow them to be used in many fields, ranging from automotive to piping. In this class of iron-based alloy the content of carbon is mainly localized in the graphite nodules, which are dispersed in a metallic matrix characterized by different phases: ferrite, austenite, pearlite, martensite or their mix, depending on the chemical composition and the heat treatment. Metallic matrix is subjected to the corrosion phenomenon, and, for this reason, the study and the development of traditional and innovative protection techniques are important, mainly in critical applications. Hot dip galvanizing is one of the investigated protections because the zinc is able to protect the iron-based alloys thanks to the reduction potential that is lower than the iron one.
In this work, a ferritic-pearlitic DCI (GS500) is galvanized by using a pure Zn bath at 440°C in order to generate a zinc coating at different dipping time. The presence of thermal cracks is observed by means of a Scanning Electron Microscope (SEM)