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  • 1
    Online Resource
    Online Resource
    Numerical simulation of tensile behavior of corroded aluminum alloy 2024 T3
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 451-467
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 451-467
    Abstract: – The purpose of this paper is to develop a multi-scale modeling approach for simulating the tensile behavior of corroded aluminum alloy 2024 T3. Design/methodology/approach – The approach combines two FE models: a model of a three-dimensional representative unit cell representing a pit and a model of the tensile specimen. The models lie at the micro- and macro-scales, respectively. The local homogenized mechanical behavior of the corroded material is simulated for different pit configurations. Then, the behavior of the pits is introduced into different areas (elements) of the tensile specimen and final analyses are performed to simulate the mechanical behavior of the corroded material. The approach has been applied to six different exposure periods of the exfoliation corrosion test. Findings – The numerical results show that the presence of pits and exfoliated areas reduces the yield strength of the material. The comparison of predicted elongation to fracture with the experimental of each exposure period value allows for the indirect assessment of the effect of hydrogen embrittlement. Originality/value – Since the characteristics of corrosion damage evolution with exposure time are constant for the specific material, the model could be applied for the simulation of the mechanical behavior of any corroded structural part (e.g. a mechanically fastened panel) made from the aluminum 2024 T3 alloy.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-10-2014-0050
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 2
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    Micro/macro fatigue crack growth rate model for 2024-T3 aluminum panel
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 522-540
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 522-540
    Abstract: – Fatigue crack growth rate data for 2024-T3 aluminum are found using three parameters d *, σ * and μ * for short and long cracks for Regions I-III in conventional fatigue. Asymptotic solution of a line crack with a micro-tip is found to yield a singular stress behavior of order 0.75 in contrast to the 0.50 order known for the macrocrack. The difference is due to the micro-macro interaction effects. The three parameters account for the combined effects of load, material and geometry via the tip region. Data for short and long cracks lie on a straight with a slope of about 3.9-4.8 for R values of 0.286-0.565. The results were based on an initial crack a 1 mm where a is the half length for a central crack panel. The paper aims to discuss these issues. Design/methodology/approach – The belief that specimen fatigue data could assist the design of structural components was upended when FAA discovered that the NASGRO FCGD are not valid for short cracks that are tight and may even be closed. The regular Δ K vs da / dN model was limited to long cracks. The issue become critical for short cracks connecting the long ones of a few mm to cm or even m according to da/dN for the same crack history. The danger of short/long fatigue crack growth (SLFCG) prompted FAA to introduce an added test known as Limit of Validity (LOV), a way of setting empirical limits for structural components. The dual scale SLFCG data from Δ K micro/macro provide support for the LOV tests. Findings – Data for short and long cracks lie on a straight with a slope of about 3.9-4.8 for R values of 0.286-0.565. The single dual scale relation on Δ K micro/macro can switch from microscopic to macroscopic or vice and versa. The difference is fundamental. Order other than 0.75 can be obtained for simulating different microstructure effects as well as different materials and test conditions. Originality/value – Scale shifting from short to long fatigue cracks for 2024-T3 aluminum is new. The crack driving force is found to depend on the crack tightness. The sigmoidal curve based on the regular Δ K plot disappeared. The data from Δ K micro/macro for short cracks may supplement the FAA LOV tests for setting more reliable fatigue safe limits.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-05-2015-0014
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 3
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    Effect fracture resistance on retardation of crack growth
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 510-521
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 510-521
    Abstract: – The prediction of fatigue crack growth behaviour is an important part of damage tolerance analyses. Recently, the author’s work has focused on evaluating the FASTRAN retardation model. This model is implemented in the AFGROW code, which allows different retardation models to be compared. The primary advantage of the model is that all input parameters, including those for an initial plane-strain state and its transition to a plane-stress-state, are objectively measured using standard middle-crack-tension M(T) specimens. The purpose of this paper is to evaluate the ability of the FASTRAN model to predict correct retardation effects due to high loading peaks that occur during variable amplitude loading in sequences representative of an aircraft service. Design/methodology/approach – This paper addresses pre-setting of the fracture toughness K R (based on J -integral J Q according to ASTM1820) in the FASTRAN retardation model. A set of experiments were performed using specimens made from a 7475-T7351 aluminium alloy plate. Loading sequences with peaks ordered in ascending-descending blocks were used. The effect of truncating and clipping selected load levels on crack propagation behaviour was evaluated using both experimental data and numerical analyses. The findings were supported by the results of a fractographic analysis. Findings – Fatigue crack propagation data defined using M(T) specimens made from Al 7475-T7351 alloy indicate the difficulty of evaluating the following two events simultaneously: fatigue crack increments after application of loads with maximum amplitudes that exceeded J Q and subcritical crack increments caused by loads at high stress intensity factors. An effect of overloading peaks with a maximum that exceeds J Q should be assessed using a special analysis beyond the scope of the FASTRAN retardation model. Originality/value – Measurements of fatigue crack growth on specimens made from 7475 T7351 aluminium alloy were carried out. The results indicated that simultaneously evaluating fatigue crack increments after application of the load amplitude above J Q and subcritical increments caused by the loads at high stress intensity factors is difficult. Experiments demonstrated that if the fatigue crack reaches a specific length, the maximal amplitude load induces considerable crack growth retardation.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-10-2014-0053
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 4
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    Numerical stability analysis of imperfect single-walled carbon nanotubes under axial compressive loads
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 423-438
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 423-438
    Abstract: – A computational structural mechanics approach, based on the exclusive use of standard bar elements is utilized in order to investigate the elastic stability of single-walled carbon nanotubes (SWCNTs) with atom vacancy defects under axial compressive loads. The paper aims to discuss this issue. Design/methodology/approach – The proposed model uses three dimensional, two nodded, linear truss finite elements of three degrees of freedom per node to represent the force field appearing between carbon atoms due to the basic interatomic interactions. Findings – Numerical results concerning the critical forces which cause instability of pristine nanotubes are compared with corresponding data given in the open literature in the effort to demonstrate the good accuracy of the method. Then, it is assumed that SWCNTs present-specific structural defects defined by their length, width, orientation and longitudinal position. The influence of these four geometric parameters of the imperfections considered on the stability of SWCNTs is investigated in detail and essential conclusions are revealed. Originality/value – To the authors’ best knowledge, is the first time that the specific method is introduced for the prediction of buckling behavior of defective SWCNTs. The structural defect here is considered as atoms vacancy that forms a like-crack defect having a specific length, width, orientation and position along the nanotube length.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-10-2014-0056
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 5
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    On the damages detection in aluminium beam using Hilbert-Huang transformation
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 493-509
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 493-509
    Abstract: – Continuous on-line monitoring of structural integrity are in priority in many engineering fields such as aerospace, automotive, civilian structures, and industrial applications. Of all these possible applications, the aerospace industry has one of the highest payoffs. Possible damage can lead to catastrophic failures and costly inspections. On the other hand, processing a signal consists of important feature from sensors measurements to reach the considered target. Typically, the sensors translate a physical phenomenon from one or many sources in temporal variations or in spatial variations. The purpose of this paper is to investigate damages, in terms of suddenly screw removal or in a small cut, detection in vibrating (clamped-free) aluminum beam structures using the empirical mode decomposition (EMD) method along with the Hilbert-Huang transformation (HHT). The perspective is to identify very small defects in real aircraft structures. Design/methodology/approach – The proposed method deals with a new time-frequency signal processing analysis tool, for damages detection in a vibrating plate. An experimental test ring is used in order to excite a clamped-free aluminum plate. Two types of excitations are used. The first one is a harmonic excitation and the second one is a random excitation provided by an impact hammer. A hole and its filled by a screw with mass of 0.2 g, and a small cut is created, simulating a cut creation, are produced afterword, and the HHT is used in order to arise the developed oscillations, and to reveal hidden reflections in the data and to provide a high-resolution energy-time frequency spectrum. Findings – The major finding was the clear amplitude increment either for screw removal or for cut creation, using the EMD process with the HHT, giving the possibility to detect them. Originality/value – The use of the HHT to detect, using an experimental procedure, two different defects: a suddenly screw removal and a cut creation, in a clamped-free beam, excited by non-stationary and non-linear signals.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-09-2014-0042
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 6
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    Online Resource
    Homogenization of selective laser melting cellular material for impact performance simulation
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 439-450
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 439-450
    Abstract: – The purpose of this paper is to present, the global behaviour of sandwich structures comprising cellular cores is predicted by finite element (FE) analysis. Two modelling approaches are investigated, providing different levels of accuracy; in both approaches, the sandwich structure is idealised as a layered stack with the skin modelled using shell elements; while the core is either modelled with fine detail using beam micro-elements representing the cell struts, or is modelled by three-dimensional solid elements after an appropriate core homogenisation. Design/methodology/approach – The applied homogenisation methodology, as well as the all important modelling issues are presented in detail. Experimental tests performed using a mass-drop testing machine are used for the successful validation of the simulation models. Findings – It was concluded that the core microscale models having detailed FE modelling of the core unit cells geometry with fine scale beam elements are suitable for the analysis of the core failure modes and the prediction of the basic core stiffness and strength properties. It was demonstrated that the homogenised core model provides significant advantages with respect to computing time and cost, although they require additional calculations in order to define the homogenised stress-strain curves. Research limitations/implications – Special microscale material tests are required for the determination of appropriate materials parameters of the core models, as steel selective laser melting (SLM) microstrut properties differ from the constitutive steel material ones, due to the core manufacturing SLM technique. Stress interactions were not taken into account in the homogenisation, as the applied core material model supports the introduction of independent stress-strain curves; however, the predicted load deflection results appeared to be very close to those obtained from the detailed core micromodels. Originality/value – The paper is original. The dynamic behaviour of conventional sandwich structures comprising conventional honeycomb type cores has been extensively studied, using simple mass-spring models, energy based models, as well as FE models. However, the response of sandwich panels with innovative SLM cellular cores has been limited. In the present paper, novel modelling approaches for the simulation of the structural response of sandwich panels having innovative open lattice cellular cores produced by SLM are investigated.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-10-2014-0059
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 7
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    Three-dimensional cracked discs under anti-plane loading and effects of the boundary conditions : A review of recent developments
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 541-564
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 541-564
    Abstract: – Accordingly to the recent multi-scale model proposed by Sih and Tang, different orders of stress singularities are related to different material dependent boundary conditions associated with the interaction between the V-notch tip and the material under the remotely applied loading conditions. This induces complex three-dimensional stress and displacement fields in the proximity of the notch tip, which are worthy of investigation. The paper aims to discuss these issues. Design/methodology/approach – Starting from Sih and Tang’s model, in the present contribution the authors propose some analytical expressions for the calculation of the strain energy density (SED) averaged over a control volume embracing the V-notch tip. The expressions vary as a function of the different boundary conditions. Dealing with the specific crack case, the results from the analytical frame are compared with those determined numerically under linear-elastic hypotheses, by applying different constraints to the through-the-thickness crack edges in three-dimensional discs subjected to Mode III loading. Free-free and free-clamped cases are considered. Findings – Due to three-dimensional effects, the application of a nominal Mode III loading condition automatically provokes coupled Modes (I and II). Not only the intensity of the induced modes but also their degree of singularity depend on the applied conditions on the crack flanks. The variability of local SED through the thickness of the disc is analysed by numerical analyses and compared with the theoretical trend. Originality/value – The capability of the SED to capture the combined three-dimensional effects is discussed in detail showing that this parameter is particularly useful when the definition of the stress intensity factors (SIFs) is ambiguous or the direct comparison between SIFs with odd dimensionalities is not possible.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-02-2015-0007
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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  • 8
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    Design evaluation of the fractured main landing gear of a BAE Jetstream SX-SKY aircraft
    Emerald ; 2015
    In:  International Journal of Structural Integrity Vol. 6, No. 4 ( 2015-8-10), p. 468-492
    Details
    In: International Journal of Structural Integrity, Emerald, Vol. 6, No. 4 ( 2015-8-10), p. 468-492
    Abstract: – The purpose of this paper is to study the main landing gear (MLG) mechanism configuration. Design/methodology/approach – Mechanism kinematics and dynamics, stress analysis and sizing of the MLG structural members, and fatigue issues related with the mechanism operation. Spreadsheet solutions were incorporated to this survey to analyze the most conceivable loading situations, and important factors of the mechanism design for an initial evaluation of safety implications. Findings – MLG design approach along with conservative fatigue design factors lies in the area of accepted limits in commercial aircraft industry. Research limitations/implications – MLG loading associated with landing as well as those associated with ground maneuvers (steering, braking and taxiing) contribute significantly to fatigue damage, along with the stresses induced by manufacturing processes and assembly. The application of FEA methods for the design of the landing gear does not always guarantee a successful approach to the problem solution, if precise analytical solutions are not available in advance. Practical implications – From the investigation of this incident of fractured struts of the MLG it is confirmed that the reduction in Pintle Housing diameter on the upper part has contributed to the avoidance of damaging the fuel tank above the MLG that would lead to a catastrophic event. On the other hand, the airframe of the SKY-Jet was proved efficient for a belly landing with minor damages to the passengers and heavier damages for the aircraft. Social implications – On-line vibration monitoring sensors hooked up to the landing gear strut and Pintle House would greatly enhance safety, without relying in optical surveys in hard to access and inspect areas of the landing gears mechanisms housings. Originality/value – Analytic methods were adopted and spreadsheet solutions were developed for the MLG main loading situations, along with design issues concerning mechanism kinematics and dynamics, stress analysis and sizing of the MLG structural members, as well as fatigue issues related with the mechanism operation. Spreadsheet solutions were incorporated to this survey to analyze the most conceivable loading situations, and important factors of the mechanism design for an initial evaluation of safety implications.
    Type of Medium: Online Resource
    ISSN: 1757-9864
    URL: Article
    DOI: 10.1108/IJSI-08-2014-0039
    Language: English
    Publisher: Emerald
    Publication Date: 2015
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