Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Reliability-Based Design of Reinforced Concrete Beams for Simultaneous Bending, Shear, and Torsion Loadings
Get PDFDesigning structural members is targeted in resisting against the loads such that the safety of considered structure is maintained regarding different conditions of loading. The method existing in ACI guideline is considered using load and resistance factors regardless of random nature of design parameters. Existing uncertainties in design parameters such as load and resistance have caused changes in safety of structure and the use of constant coefficients in different states of loading has often caused design unsafely. The present research has discussed the design of all the probabilities for reinforced concrete beams subjected to bending, shear and torsion stresses. For this, analytical relations of limit state have been developed to combine different stresses. Monte Carlo method is the method used to calculate safety measures, in which safety surface of American Concrete Institute (ACI) and different limit states have been calculated for three different sections (T-shape, rectangular shape and L-shape). The results of paper indicate that the safety index is considered in the range of 3 to 4 at different limit states. Load and resistance coefficients have been calculated in different safety indices and influence of load and resistance coefficients on American Concrete Institute (ACI) have been examined. Using the proposed method, designer enables to take an action for design by changing the conditions governing the problems such as dimensions, load and features of the section regarding the safety of structure. Further, under use of constant coefficients with sufficient information on composition of the considered loads, the designer enables to design and ratio of load and different limit states of the considered structure. Studying influence of changes of numbers in load and resistance coefficients on American Concrete Institute (ACI) has been mentioned as the major objective of the present research, indicating that resistance coefficient has more significantly influence on American Concrete Institute (ACI) in different loading compositions.  
Investigations in static response and free vibration of a functionally graded beam resting on elastic foundations
Get PDFIn this article, an analytical study was done to predict the behavior of the beam vis-à-vis bending, buckling, and dynamic responses of isotropic homogeneous beams based on an elastic foundation. The material properties of the FG-beams vary across the thickness using the power law. In this work, the sinusoidal shear deformation beams theory is used to investigate the static and dynamic behavior of FG beams. The present theory fulfills the condition of nullity of edge stresses and does not require the use of a shear correction factor. Hamilton's principle is used to deduce equations of motion, and analytical solutions for simply supported beams were obtained using the Navier resolution method. Nondimensional displacements, eigenfrequencies and critical-buckling loadcs of isotropic homogeneous beams were obtained for various values of the foundation parameters. The numerical results obtained by the present technique have been compared with the results of literature and are in excellent agreement with them. It can be concluded that the current HSDBT is simple and accurate in solving the bending, eigenfrequency and critical-buckling load problems for FGM beams
Analysis of Printed Circuit Boards strains using finite element analysis and digital image correlation
Get PDFThis paper investigates the use of digital image correlation (DIC) and finite element analysis for strain measurement on Printed Board Circuits (PCBs).
Circuit boards (PCBs) are designed to mechanically support and electrically connect an electronic component assembly. Due to screw assemblies, the surface level differences on which the PCB is placed, the process of assembling the electronic components induces a certain state of stress and deformation in the PCB. The main components affected are microprocessors due to the way they are glued to PCBs with BGA - Ball grid arrays (BGA).
Digital Image Correlation (DIC) is a full-field contactless optical method for measuring displacements and strain in experimental testing, based on the correlation of images taken during test. The experimental setup is realized with Dantec Q-400 system used for image capture and Istra 4D software for image correlations and data analyses. The maximum level of the obtained strain is compared with the allowable limit.
Finite element analysis (FEA) is a numerical method of analysis for stresses and strain in structures of any given geometry
Microstructural damage evaluation of ferritic-ausferritic spheroidal graphite cast iron
Get PDFThe goal of this work is to improve the understanding of the relation between the microstructural characteristics of Intercritical Austempered Ductile Cast Iron (IADI) and the damage micromechanisms observed during its tensile loading. The experimental methodology involves heat treatments to obtain IADI and the assessment of the damage mechanisms (sequence and occurrence) during step by step tensile testing. The damage evaluation was carried out by observing the surface of the tensile test specimen with optical and scanning electron microscopy.
The results show that small cracks start forming soon after the yield stress is surpassed. The crack initiation is preferentially located at matrix-nodule interface. As loading increases, cracks also develop at the ferritic grain boundaries and the ausferritic/ferritic interfaces. Consequently, at higher strain values, a competition between the plastic deformation on internodular zones and crack propagation along ausferritic phase is observed.
Finally, the final fracture is produced by the propagation of cracks across the internodular ligaments and through the ausferritic/ferritic interface that later coalesce into a single dominant crack leading to the material failure
Comparative experimental study of the mechanical and fracture properties of Portland limestone and Corsehill sandstone
Get PDFAn experimental investigation of the mechanical and fracture characteristics of Portland limestone and Corsehill sandstone is undertaken, aiming at enhancing understanding of the structural behaviour of these natural building stones commonly used in both new and restoration projects in Edinburgh, Scotland. A series of three-point bending and four-point bending tests on appropriately cut prismatic samples, in the presence of U-shape notches, were performed and results were interpreted following the concepts of crack mouth opening displacement and fracture energy. The critical crack opening displacement could be further investigated as a fracture criterion, independently of the method used for its determination. At a second stage, the effect of specimen shape and size on flexural strength, deflection at mid-span, crack mouth opening displacement and fracture energy was studied for Portland limestone. Despite the scattering of results, trends observed comprise (a) the negative correlation between the flexural strength of Portland limestone and the specimen span length and (b) the positive correlation between fracture energy and specimen size. Conclusions drawn are in good agreement with similar ones for other quasi-brittle materials and contribute to the assessment of the fracture behaviour of full size structural members that are often beyond the range of possible failure testing.  
Fatigue crack growth in notched specimens: a numerical analysis: Fatigue crack growth in notched specimens
Get PDFFatigue crack growth (FCG) is linked to irreversible and non-linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-DK curves. The replacement of DK by non-linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range, dp. M(T) specimens with lateral notches of different radius (1, 2 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases dp and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation produces crack closure which compensates the effect of crack length and there is a stabilization of dp. The reduction of notch radius increases dp for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore dp is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of d
Fracture modelling of adhesively-bonded joints by an inverse method
Get PDFNowadays, any structure must have strength, robustness and lightness, which has increased the industrial interest and research efforts in adhesive joining, mainly in the improvement of strength and fracture properties of adhesives. Thus, in recent years, the use of adhesive joints in industrial applications has gradually grown, replacing some traditional bonding methods, since they have advantages such as reduced stress concentrations, reduced weight and cost, and ease of processing/manufacturing. In this work, the cohesive laws of three adhesives, Araldite® AV138, Araldite® 2015 and Sikaforce® 7752, were obtained by the application of an inverse adjustment method between the numerical and experimental load-displacement curves (P-d) of Double-Cantilever Beam (DCB) tests for tensile characterization and End-Notched Flexure (ENF) tests for shear characterization. Next, these laws were validated with experimental data of single-lap joints (SLJ) and double-lap joints (DLJ), using Abaqus®. For the Araldite® AV138 and Araldite® 2015, in tension and shear, the triangular law accurately predicted the behaviour of the SLJ and DLJ. For the Sikaforce® 7752, the triangular law did not suitably fit the experimental results. It was considered that, due to its ductility, the Sikaforce® 7752 is best modelled with a trapezoidal law
Microcrack interaction with circular inclusion and interfacial zone
Get PDFA geometrically simplified plane elasticity problem of a finite small crack emanating from a thin interfacial zone surrounding the circular inclusion situated in the finite bounded domain is investigated. The crack is arbitrarily oriented and modelled using the distribution dislocation technique. This model represents the inner solution of the studied problem. The corresponding fundamental solution is based on the application of Muskhelishvili complex potentials in the form of the Laurent series. The coefficients of the series are evaluated from the compatibility conditions along the interfaces of the inclusion, the interfacial zone and the enclosing matrix. The fundamental solution is also used in the solution of the boundary integral method approximating the stress and strain relations of the so-called outer solution. The asymptotic analysis at the point of the crack initiation combines the inner and the outer solution and results in the evaluation of the stress intensity factors of the crack tip, which lies in the matrix. The topological derivative is subsequently used to approximate the energy release rate field associated with the perturbing crack in the matrix. The extreme values of the energy release rate allow one to assess the crack path direction of the initiated microcrack
Cohesive fracture in composite systems: experimental setup and first results
Get PDFComposite systems are widely used in many engineering applications for new structures and strengthening of existing ones. Within the structural rehabilitation of civil constructions, the plating technique of beams with Fiber Reinforced Polymer (FRP) represents a quick and optimal intervention with respect to traditional ones. The failure of these composite systems usually occurs due to the FRP debonding, which corresponds to a mode II fracture of concrete specimens. In this paper, a new experimental setup for investigating the mode II fracture behavior of FRP-concrete composite structures is presented. The test equipment consists of both conventional equipment and a non-contact optical technique, Digital Image Correlation (DIC), and the test system was realized at the Design Machine Laboratory of the University of Salerno. A preliminary test was performed and the corresponding results are shown and discussed
Characterizations of TIG welded joints of Unalloyed Commercially Pure Titanium Gr-2 for Weld Process Parameters
Get PDFTitanium and Titanium Alloys can be welded by gas tungsten arc, gas metal arc, plasma arc and electron beam welding processes. Titanium material is a reactive metal and is sensitive to embrittlement by oxygen, nitrogen, and hydrogen gas, at elevated temperatures. Consequently, the metal must be protected from atmospheric contamination. This can be provided by shielding the metal with welding grade inert gas. The present work describes the application of TIG arc welding to titanium and investigated the effect of welding parameters like weld current, weld gap and gas flow rate on mechanical properties of welded joints of unalloyed commercially pure titanium Gr-2 materials. Taguchi optimization method has been used to find out optimal setting of parameters for weld joints characterization. The welded joints showed an ultimate tensile strength of about 429 MPa with 23.33% elongation. A significant grain coarsening is noticed in the fusion zone consisting of α-phase in different direction bounded by β-phase. The hardness value at fusion zone and base metal are typically observed to be 235 and 145HV