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Mei, Hanfei, Asaad Migot, Mohammad Faisal Haider, Roshan Joseph, Md Yeasin Bhuiyan i Victor Giurgiutiu. "Vibration-Based In-Situ Detection and Quantification of Delamination in Composite Plates". Sensors 19, nr 7 (11.04.2019): 1734. http://dx.doi.org/10.3390/s19071734.
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This paper presents a new methodology for detecting and quantifying delamination in composite plates based on the high-frequency local vibration under the excitation of piezoelectric wafer active sensors. Finite-element-method-based numerical simulations and experimental measurements were performed to quantify the size, shape, and depth of the delaminations. Two composite plates with purpose-built delaminations of different sizes and depths were analyzed. In the experiments, ultrasonic C-scan was applied to visualize the simulated delaminations. In this methodology, piezoelectric wafer active sensors were used for the high-frequency excitation with a linear sine wave chirp from 1 to 500 kHz and a scanning laser Doppler vibrometer was used to measure the local vibration response of the composite plates. The local defect resonance frequencies of delaminations were determined from scanning laser Doppler vibrometer measurements and the corresponding operational vibration shapes were measured and utilized to quantify the delaminations. Harmonic analysis of local finite element model at the local defect resonance frequencies demonstrated that the strong vibrations only occurred in the delamination region. It is shown that the effect of delamination depth on the detectability of the delamination was more significant than the size of the delamination. The experimental and finite element modeling results demonstrate a good capability for the assessment of delamination with different sizes and depths in composite structures.
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Panda, Rabi S., Prabhu Rajagopal i Krishnan Balasubramaniam. "Characterization of delamination-type damages in composite laminates using guided wave visualization and air-coupled ultrasound". Structural Health Monitoring 16, nr 2 (24.09.2016): 142–52. http://dx.doi.org/10.1177/1475921716666411.
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This article reports on the characterization of delamination damages in composite laminates using wave visualization method. A combination of plate-guided ultrasound and air-coupled ultrasonics is used to locate and visualize delaminations. The study focuses on the physics of Lamb wave propagation and interaction with delaminations at various through-thickness locations and positions. Three-dimensional finite element simulations are used to study, in detail, the changes in wave features such as mode velocity, wavelength and wave refraction in the delamination region. These wave features provide information on the location, position and orientation of the delamination. These studies are validated by experimental measurements. The influence of position of source and delamination on wave refraction in the delamination region is examined. This method also correlates the results obtained from experiments and finite element simulations to theoretical dispersion curves in order to distinctly determine the delamination location.
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Ueda, Masahito, i Akira Todoroki. "Asymmetrical Dual Charge EPCM for Delamination Monitoring of CFRP Laminate". Key Engineering Materials 321-323 (październik 2006): 1309–15. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.1309.
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CFRP laminate is sensitive to impacts. Even a low impact creates delamination, bringing deterioration of the structural reliability. Monitoring for delamination is, therefore, indispensable to maintain the reliability of a CFRP structure. In this study, asymmetrical dual charge electric potential change method was introduced to estimate a delamination in the CFRP laminate. Delaminations were estimated using response surfaces as solver of the inverse problem. Learning data of response surfaces were calculated by FEM analyses. Actual delaminations in the CFRP laminate were successfully identified.
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Ellison, Andrew, i Hyonny Kim. "Shadowed delamination area estimation in ultrasonic C-scans of impacted composites validated by X-ray CT". Journal of Composite Materials 54, nr 4 (27.07.2019): 549–61. http://dx.doi.org/10.1177/0021998319865311.
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Although ultrasonic pulse-echo C-scanning is a mature non-destructive evaluation technique for imaging internal damage in composite structures, a major impediment of obtaining a full characterization of the internal damage state is delamination shadowing effects. Specifically, shadowing refers to regions of interest that are behind other delamination planes or discontinuities with respect to the scanning surface. The delamination planes block ultrasonic wave transmission and the regions of interest are thus hidden (i.e. shadowed) from the scan. A methodology has been developed to expand ultrasonic scan data of impacted composites by utilizing damage morphology information that is well established in the composite impact research community, such as matrix cracks bounding delaminations, to estimate shadowed delamination information and matrix cracking. First, impacted flat composite plates were C-scanned by pulse-echo ultrasonic and the results were segmented by depth of damage to establish interface-by-interface delamination information. These delaminations were then fit by bounding lines representing the fiber/matrix crack directions defined by the orientations of plies adjacent to each interface to estimate the shadowed portion of the delamination results. The area inside this boundary was added to the original ultrasonic delamination area to create an estimation of the full delamination state at each shadowed interface. Additionally, because this extension method is based on the interactions between delaminations and matrix cracking, this extension method provides an approximation of the matrix cracking of adjacent plies. Results were compared with X-ray computed tomography scans to assess the effectiveness of the extension method.
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Zhang, Zhi Fang, Krishna Shankar, Murat Tahtali i Evgeny V. Morozov. "Graphical Detection Method for Delaminations". Applied Mechanics and Materials 66-68 (lipiec 2011): 1410–15. http://dx.doi.org/10.4028/www.scientific.net/amm.66-68.1410.
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In this paper, a simple graphical method for the detection of delaminations in damaged composite laminates is introduced. By using this method, both delamination size and location can be predicted accurately. First, a frequency database for the damaged beams with a range of delamination sizes and locations is generated using a Finite Element (FE) model; then for each mode, a surface plot relating the delamination size, location and frequency shift is generated. The next step is to look up the actual frequency shift (either from numerical simulation or experiment) from surface plots relating to three or more modes to get the intersection curves, which show the possible combination of delamination size and location for each mode. Finally the intersection curves of different modes are plotted together and the intersection point of all the curves indicates the possible delamination size and location, where the frequency shifts for all the modes can be matched. We demonstrate that this method is able to predict both delamination size and location fairly accurately. This method can be expanded to detect the propagation of delaminations by only monitoring the shifts in natural frequencies. It has the potential to detect multiple delaminations through continuous monitoring, provided that they do not occur simultaneously. This method has promising applications in the Structure Health Monitoring (SHM) of composite structures.
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Hwang, Shun Fa, i Horng Ming Chen. "Compression Tests of Unidirectional Composite Laminates with Two Delaminations". Key Engineering Materials 306-308 (marzec 2006): 381–86. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.381.
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Compression tests are conducted on composite laminates consisting of 16 unidirectional carbon/epoxy layers with two through-width delaminations. Two types of delamination length and location are considered. One is that a short delamination is located at the middle surface along the thickness direction and a long delamination is positioned between the second layer and the third layer. The other is that a long delamination is located at the middle surface and the position of the short elamination is between the second layer and the third layer. The results indicate that if the long delamination is close to the surface of the laminate, the inner, short delamination has no effect on the critical buckling stresses. However, the presence of inner, short delamination may significantly change the critical delamination growth stresses. If the short delamination is above the long delamination that is located on the middle surface, the presence of the short delamination may significantly reduce the critical buckling stresses. But its effects on the critical delamination growth stresses are minor.
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Bhat, Sunil, i S. Narayanan. "Numerical investigations on delaminated Glare under uni-axial tension". International Journal of Structural Integrity 7, nr 4 (8.08.2016): 553–70. http://dx.doi.org/10.1108/ijsi-07-2015-0021.
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Purpose – Since failure of laminated composites by delaminations is common, the purpose of this paper is to present a numerical procedure to check the stability of delaminations in fiber metal laminate (Glare), with different possible damage configurations, under uni-axial tension. Deformation behavior of the laminate is also examined. Influence of the type and the extent of damage, represented by varying sizes and number of delaminations, on delamination driving force and laminate deformation is found. Design/methodology/approach – Delaminated Glare is modeled by finite element method. Interface cohesive elements are used to model the delaminations. Finite element results provide the deflection/deformation characteristics of the laminate. Driving forces of delaminations are estimated by J integrals that are numerically obtained over cyclic paths near delamination tips. Laminates with different types of delaminations are also fabricated and externally delaminated for measurement of their interlaminar fracture toughness. The delamination is considered to be stable if its driving force is less than corresponding interlaminar fracture toughness of the laminate. Findings – Delaminations are found to be stable in laminates with lower number of delaminations and unstable in laminates with higher number of delaminations. Increase in size of delaminations increases the deformations but reduces the delamination driving force whereas increase in number of delaminations increases both deformations and driving forces. The trends change in case of laminates with symmetrical damage. Shape of delamination is also found to influence the deformations and driving forces. The finite element model is validated. Research limitations/implications – There is scope for validating the numerical results reported in the paper by theoretical models. Practical implications – Checking the stability of delaminations and their effect on deformation behavior of the laminate helps is assessment of safety and remaining life of the laminate. If failure is predicted, preemptive action is taken by using repair patch ups at identified critical locations in order to avoid failures in service conditions. Originality/value – The paper offers the following benefits: use of cohesive zone method that is readily possible in finite element procedures and is relatively simple, fast and reasonably accurate is demonstrated; suitability of using J integrals over paths crossing non-homogeneous and property mismatched material layers is tested; and influence of the type and the extent of damage in the laminate on its deformation behavior and delamination driving forces is found. This type of work has not been reported so far.
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Kardomateas, G. A. "The Initial Post-buckling and Growth Behavior of Internal Delaminations in Composite Plates". Journal of Applied Mechanics 60, nr 4 (1.12.1993): 903–10. http://dx.doi.org/10.1115/1.2901000.
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The initial post-buckling and growth behavior of delaminations in plates is studied by a perturbation procedure. In this work, no restrictive assumptions regarding the delamination thickness and plate length are made, i.e., the usual thin film assumptions are relaxed. The perturbation procedure is based on an asymptotic expansion of the load and deformation quantities in terms of the distortion parameter of the delaminated layer, the latter being considered a compressive elastica. Closed-form solutions for the load and midpoint delamination deflection versus applied compressive displacement during the initial post-buckling phase are derived. Moreover, closed-form expressions for the energy release rate and the mixity ratio (i.e., Mode II versus Mode I) at the delamination tip are produced. A higher Mode I component is found to be present during the initial post-buckling phase for delaminations of increasing ratio of delamination thickness over plate thickness, h/T (i.e., delaminations further away from the surface). Moreover, the-energy release rate corresponding to the same applied strain is larger for a higher h/T ratio. The reduced growth resistance of these configurations is verified by experimental results on unidirectional composite specimens with internal delaminations.
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Xing, Shutao, Marvin W. Halling i Paul J. Barr. "Delamination Detection of Reinforced Concrete Decks Using Modal Identification". Journal of Sensors 2012 (2012): 1–17. http://dx.doi.org/10.1155/2012/156583.
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This study addressed delamination detection of concrete slabs by analyzing global dynamic responses of structures. Both numerical and experimental studies are presented. In the numerical examples, delaminations with different sizes and locations were introduced into a concrete slab; the effects of presence, sizes, and locations of delaminations on the modal frequencies and mode shapes of the concrete slab under various support conditions were studied. In the experimental study, four concrete deck specimens with different delamination sizes were constructed, and experimental tests were conducted. Traditional peak-picking, frequency domain decomposition, and stochastic subspace identification methods were applied to the modal identification from dynamic response measurements. The modal parameters identified by these three methods correlated well. The changes in modal frequencies, damping ratios, and mode shapes that were extracted from the dynamic measurements were investigated and correlated to the actual delaminations and can indicate presence and severity of delamination. Finite element (FE) models of reinforced concrete decks with different delamination sizes and locations were established. The modal parameters computed from the FE models were compared to those obtained from the laboratory specimens, and the FE models were validated. The delamination detection approach was proved to be effective for concrete decks on beams.
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Ding, Wenxiang, Maxime Bavencoffe i Marc Lethiecq. "Modeling and Experimental Characterization of Bonding Delaminations in Single-Element Ultrasonic Transducer". Materials 14, nr 9 (27.04.2021): 2269. http://dx.doi.org/10.3390/ma14092269.
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Ultrasonic transducers performance can be seriously deteriorated by loss of adhesion between some constitutive elements such as the active element, the backing, or the matching layer. In the present work, the influence of bonding delaminations on the performance of a single-element ultrasonic transducer, which is composed of a piezoelectric disk, a backing, and a matching layer, is studied numerically and experimentally. Based on the positions between layers, two cases, i.e., delaminations between ceramic and backing or between ceramic and matching layer, are considered. Each case involves three different types of delaminations, which are marked as delamination type (DT)-I, II, and III. DT-I, a circular shape delamination, starts from the center and expands towards the peripheric zone; DT-II, an annular shape delamination, starts from the peripheric zone and expands towards the center; DT-III is a sector shape delamination with a given angle. The numerical simulations are performed by the finite element method and the influence of delaminations on the electromechanical admittance (EMA) of the transducer is investigated. 3D printed backings and matching layers are mounted on a PZT sample to assemble delaminated single-element transducers. An impedance analyzer is used for experimental measurements. Comparison between numerical and experimental results shows a reasonable agreement making changes in EMA an interesting indicator to inform about the occurrence and severity of delaminations in a single-element ultrasonic transducer.
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Yang, Zheng, Chun Yong Huo i Wanlin Guo. "The Charpy Notch Impact Test of X70 Pipeline Steel with Delamination Cracks". Key Engineering Materials 297-300 (listopad 2005): 2391–96. http://dx.doi.org/10.4028/www.scientific.net/kem.297-300.2391.
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The effects of thickness, notch orientation and delamination cracks on the impact toughness of X70 pipeline steel are investigated experimentally by use of the instrumented Charpy impact tests at different temperatures. The couple effect of delamination cracks, thickness, notch orientation and temperature is discovered. The delamination cracks have certain direction, and their amount and size are related to the temperature and the specimen thickness. Though the delaminating orientations of T-S and T-L specimen are not same, the reasons for both T-S and T-L specimen delaminating are that the weak interfaces in the specimens are pulled apart by the stress perpendicular to them. The delamination cracks can improve the actual impact toughness of X70 pipeline steel both T-L and T-S specimens. The effect of delamination cracks on the actual impact toughness changes with the thickness and the temperature. The couple effect of wall thickness, defect orientation and working temperature of pipeline must be taken into account in safe assessment of pipeline.
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Toscano, Cinzia, Aniello Riccio, FrancescoPaolo Camerlingo i Carosena Meola. "On the use of lock-in thermography to monitor delamination growth in composite panels under compression". Science and Engineering of Composite Materials 21, nr 4 (1.09.2014): 485–92. http://dx.doi.org/10.1515/secm-2013-0156.
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AbstractThe success of composites in automotive, aerospace, and naval applications is mainly related to their aptitude to be tailored to obtain a final product that perfectly fulfills the design requirements. However, during both manufacturing processes and maintenance, some flaws, like delaminations (which may escape simple visual inspection), may be induced in composite structures. The presence of delaminations is of major concern for the load-carrying capability of carbon fiber-reinforced polymer panels. Indeed, delaminations can strongly affect the structural strength and may grow under in-service loads, leading sometimes to catastrophic failures. The aim of this work is to explore the use of lock-in thermography for the monitoring of delamination propagation in composite structures when subjected to generic multiaxial loading conditions. A stiffened composite panel with an embedded skin delamination subjected to compressive loading was taken as a benchmark to assess experimentally the effectiveness of lock-in thermography for monitoring the delamination propagation in situ during the compressive mechanical test. The delamination size as a function of the applied load, observed by lock-in thermography during the execution of the compressive test, was used to validate the results of preliminary numerical computations.
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Hosseini-Toudeshky, Hossein, M. Saeed Goodarzi i Bijan Mohammadi. "Multiple Delaminations Growth in Composite Laminates under Compressive Cyclic Loading in Post-Buckling". Applied Mechanics and Materials 225 (listopad 2012): 195–200. http://dx.doi.org/10.4028/www.scientific.net/amm.225.195.
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Due to discontinuity of mechanical properties in composite laminates, failure occurs in different damage mechanisms. Delamination growth of adjacent layers is a major failure mechanism in laminates with various layup configurations. Pre existing delamination may initiate in composite laminate before use, due to impact in assembly and fabrication process. Cyclic compressive loading may cause delamination growth due to both post-bucking behavior and fatigue nature of loading. In this paper, a 3D mixed-mode interface element model has been developed to simulate the growth of multiple delaminations under compressive cyclic loading. For this purpose, the presented model should be able to handle the geometry nonlinearity of post-buckling and material nonlinearity of cohesive zone constitutive law under cyclic loading at interfaces. Because of mixed-mode condition of stress field at the delamination-front of post-buckled laminates, a mixed-mode bilinear constitutive law has been used as user material in this model. Paris Law has been used to relate the energy release rate to the fatigue crack growth in cohesive zone. A composite laminate with pre-existing delamination under buckling load, available from the literature has been reproduced with the present approach. Finally, laminates containing multiple delaminations in various interface layers have been analyzed under compressive fatigue loading. It is shown that the pre-existing delamination with more depth from the surface of laminate causes more initial static and fatigue delamination growth rate.
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Makeev, A., i E. Armanios. "A Geometrically Nonlinear Model for Laminated Composite Strips With Extension-Twist Coupling in the Presence of Delamination". Journal of Applied Mechanics 65, nr 3 (1.09.1998): 685–93. http://dx.doi.org/10.1115/1.2789112.
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A geometrically nonlinear analysis for the extension-twist coupling in pretwisted laminated composite strips in the presence of delamination is developed. Closed-form solutions for strips with internal and edge delaminations are obtained. A parametric study is performed to investigate the influence of delamination length, material system, and stacking sequence on the extension-twist coupling in a class of hygrothermally stable laminates. The model predictions are in good agreement with test data. The results indicate that internal delamination has a negligible influence on the extension-twist coupling behavior while free-edge delamination could result in a significant drop in coupling.
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Sreekanth, T. G., M. Senthilkumar i S. Manikanta Reddy. "Natural Frequency based delamination estimation in GFRP beams using RSM and ANN". Frattura ed Integrità Strutturale 16, nr 61 (19.06.2022): 487–95. http://dx.doi.org/10.3221/igf-esis.61.32.
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The importance of delamination detection can be understood from aircraft components like Vertical Stabilizer, which is subjected to heavy vibration during the flight movement and it may lead to delamination and finally even flight crash can happen because of that. Any solid structure's vibration behaviour discloses specific dynamic characteristics and property parameters of that structure. This research investigates the detection of delamination in composites using a method based on vibration signals. The composite material's flexural stiffness and strength are reduced as a result of delaminations, and vibration properties such as natural frequency responses are altered. In inverse problems involving vibration response, the response signals such as natural frequencies are utilized to find the location and magnitude of delaminations. For different delaminated beams with varying position and size, inverse approaches such as Response Surface Methodology (RSM) and Artificial Neural Network (ANN) are utilized to address the inverse problem, which aids in the prediction of delamination size and location.
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Chattopadhyay, Aditi, Changho Nam i Youdan Kim. "Damage Detection and Vibration Control of a Delaminated Smart Composite Plate". Advanced Composites Letters 9, nr 1 (styczeń 2000): 096369350000900. http://dx.doi.org/10.1177/096369350000900101.
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In this paper, the effects of delamination on the dynamic characteristics of a composite plate are investigated. The refined higher order theory is used to model the smart composite plate in the presence of delaminations. The theory accurately captures the transverse shear deformation through the thickness, which is important in anisotropic composites, particularly in the presence of discrete actuators and sensors and delaminations. Next, the detection of delamination is investigated using the Root Mean Square (RMS) values of the response of the composite plate subject to disturbances. An active control system is designed to minimise the effect of delamination. The pole placement technique is applied to design the closed loop system by utilising piezoelectric actuators. Numerical results show that the RMS information can be used to estimate the location of the delamination. The controller designed makes the delaminated plate behave like a healthy plate model. The controller also reduces the magnitudes of RMS responses due to disturbance.
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Huh, Jungwon, Quang Huy Tran, Jong-Han Lee, DongYeob Han, Jin-Hee Ahn i Solomon Yim. "Experimental Study on Detection of Deterioration in Concrete Using Infrared Thermography Technique". Advances in Materials Science and Engineering 2016 (2016): 1–12. http://dx.doi.org/10.1155/2016/1053856.
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Concrete is certainly prone to internal deteriorations or defects during the construction and operating periods. Compared with other nondestructive techniques, infrared thermography can easily detect the subsurface delamination in a very short period of time, but accurately identifying its size and depth in concrete is a very challenging task. In this study, experimental testing was carried out on a concrete specimen having internal delaminations of various sizes and at varying depths. Delaminations at 1 and 2 cm deep showed a good temperature contrast after only 5-minute heating, but delaminations at 3 cm practically identified the value of the temperature contrast from heating of 15 minutes. In addition, the size of the delamination at 3 cm deep could be estimated with a difference of 10% to 28% for 20 minutes of heating. The depth of the delamination was linearly correlated with the increase in its size.
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Yang, Zheng, Hyeon Gyu Beom, Chang Boo Kim i Chong Du Cho. "Different Delamination Cracks during Fracture and Their Influences on the Fracture of X70 Pipeline Steel". Advanced Materials Research 33-37 (marzec 2008): 91–96. http://dx.doi.org/10.4028/www.scientific.net/amr.33-37.91.
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Single or multiple of delaminations have been found frequently on the fracture surface of X70 pipeline steel. In this study, the delamination cracks and their influence on the fracture of pipeline are investigated by both experiment and three-dimensional fracture analyses. It is shown that the three-dimensional stress state is prerequisite for delamination crack and the strength distribution of material influences the form and direction of delamination crack. The delamination cracks are produced on the weak interfaces among the material by the tensile stress perpendicular to them before the fracture passes. The direction of delamination crack depends on the three-dimensional stress fields and strength distribution of material near the crack tip or notch root. The delamination cracks of the fracture through thickness of pipe wall make the effective thickness decrease and the delamination cracks of surface crack are perpendicular to the direction of fracture propagation direction. The delamination cracks reduce the stress triaxiality near crack tip and in turn, improve the fracture toughness of X70 pipeline steel.
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Mahjabin Momo, Mantaka, Nur Yazdani i Eyosias Beneberu. "Quantifying Shallow-Depth Concrete Delamination using Impact-Echo". Athens Journal of Τechnology & Engineering 10, nr 3 (25.08.2023): 147–60. http://dx.doi.org/10.30958/ajte.10-3-1.
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Corrosion-induced concrete deck delamination is quite common in bridges. Locating these embedded delaminations is important to assess the extent of the damage, the remaining member capacity and any necessary rehabilitation. The impact-echo (IE) is a simple and straightforward non-destructive testing (NDT) technique by which the depth and extent of concrete delamination may be estimated. It is effective in detecting the location and determining the depth of relatively deep delaminations in concrete. Delaminations that occur near the concrete surface can also be detected by the IE method. However, the exact depth cannot be quantified due to difficulties in analysing the flexural mode that dominates the vibration response over the corresponding delaminated region. This study developed an IE-based procedure to quantitatively estimate the depth of shallow depth delaminations in concrete slab members. Four slab specimens were prepared, each with three artificial delaminations with varying shapes and sizes at shallow depths. The frequency contour maps showed good agreement with the actual location of the delaminations. The perimeter-to-depth ratio of the delaminated region can be used to analyze the flexural mode vibration frequency. Two equations are proposed that relate the depth of arbitrarily shaped delaminations to the flexural mode vibration frequency measured over the shallow-depth delaminations. Keywords: impact echo, concrete delamination, concrete slabs, flexural mode vibration, non-destructive evaluation (NDE)
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Limanovskis, Valdemaras, Igor Iljin i Nikolaj Šešok. "INVESTIGATION INTO DELAMINATION". Mokslas - Lietuvos ateitis 2, nr 4 (31.08.2010): 10–12. http://dx.doi.org/10.3846/mla.2010.059.
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The paper investigates the process of delaminatinon. The carried out test included seven grades of paper and two types of lamination films (gloss and mat). Delamination was investigated at different ink coverage making from 400% to 90%. It was established that delamination was influenced by the properties of the paper, ink drying time, ink coverage, the type of a lamination film and folding direction. The optimal dependence of the lamination film on printing combination was established.
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Mahieddine, Ali, i Mohammed Ouali. "Analysis of Delaminated Composite Plates". Advanced Materials Research 686 (kwiecień 2013): 104–8. http://dx.doi.org/10.4028/www.scientific.net/amr.686.104.
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A mathematical model for plates with partially delaminated layers is presented to investigate their behavior. In this formulation account is taken of lateral strains. The principal advantage of the element is that it allows the modeling of delamination anywhere in the structure. The region without delamination is modeled to carry constant peel and shear stresses; while the region with delamination is modeled by assuming that there is no peel and shear stress transfer between the top and bottom layers. Numerical results of the present model are presented and its performance is evaluated for static problems. Laminated beams and plates are often used as primary load-carrying structures. However, the mechanical properties of composite materials may degrade severely in the presence of damage. One of the common types of damage modes in laminated composites is delamination. The presence of delamination is one of the most prevalent life-limiting failure modes in laminated composite structures. Many researchers had been studying the effect of delamination. Wee and Boay [1] developed an analytical model to predict the critical load of a delaminated composite laminated beam. Lee et al. [2] investigated the buckling behavior of the beam plate with multiple delaminations under compression. Kapania and Wolfe [3] examined the buckling behavior of a beam plate with two delaminations of equal length. Wang et al. [4] improved the analytical solution by including the coupling between the flexural and axial vibrations of the delaminated sub-laminates. Lee et al. [5] studied a composite beam with arbitrary lateral and longitudinal multiple delamination. Finite-element methods have been developed using the layerwise theory by Kim et al. [6]. Tan and Tong [7] developed a dynamic analytical model for the identification of delamination embedded in a laminated composite beam. To investigate the effects of delamination of a plate layers, a finite-element model is developed. Both displacement continuity and force equilibrium conditions are imposed between the regions with and without delamination. The accuracy of the approach is verified by comparing results with previously published data.
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Cai, Xiao Jiang, Sheng Qin, Qing Long An, Hong Zhou Zhang, Shu Han i Ming Chen. "Experimental Analysis on Delamination Damage by Acoustic Emission in High Speed Drilling of Carbon Fiber Reinforced Plastics". Key Engineering Materials 589-590 (październik 2013): 287–92. http://dx.doi.org/10.4028/www.scientific.net/kem.589-590.287.
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Carbon fiber reinforced plastics (CFRP) has increasing applications in aerospace and other fields, due to low density, high strength, high stiffness, great resistance to corrosion, etc. Although, delamination damages in drilling holes for assembly influence the final characteristics of CFRP components. This paper presents an experimental investigation to analyze delamination damage, in which acoustic emission and thrust force are monitored during drilling CFRP laminates to clarify the relationship between AE signals and delamination damages. The results show that delamination damage has close correlation with thrust force and acoustic emission energy. AE root mean square (rms) is recommended to be selected as AE signal parameter. Abrupt peak feature of AE rms can be used as a dependable trigger for delamination monitoring. The number of abrupt pulses of AE rms can be counted online to predict the degree of delamination damages, based on which delaminations can be monitored and controlled online.
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Gopal, P., L. R. Dharani i S.-C. Yen. "Measurement of Delamination Fracture Energy Using Stepped Laminates". Advanced Composites Letters 1, nr 4 (lipiec 1992): 096369359200100. http://dx.doi.org/10.1177/096369359200100402.
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Delamination is often the mode of failure in laminated composites. Therefore the quantification of delamination fracture energy is of vital importance. In this work, externally stepped graphite/epoxy (T300/934) laminates are tested in flexure, resulting in a series of delaminations at 0/90 interface. The delamination fracture energy is calculated based on the strain energy released and is found to be 535 J/m2. This value is in good agreement with the mode II strain energy release rate obtained by other workers.
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Brunner, Andreas J., René Alderliesten i John-Alan Pascoe. "In-Service Delaminations in FRP Structures under Operational Loading Conditions: Are Current Fracture Testing and Analysis on Coupons Sufficient for Capturing the Essential Effects for Reliable Predictions?" Materials 16, nr 1 (27.12.2022): 248. http://dx.doi.org/10.3390/ma16010248.
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Quasi-static or cyclic loading of an artificial starter crack in unidirectionally fibre-reinforced composite test coupons yields fracture mechanics data—the toughness or strain-energy release rate (labelled G)—for characterising delamination initiation and propagation. Thus far, the reproducibility of these tests is typically between 10 and 20%. However, differences in the size and possibly the shape, but also in the fibre lay-up, between test coupons and components or structures raise additional questions: Is G from a coupon test a suitable parameter for describing the behaviour of delaminations in composite structures? Can planar, two-dimensional, delamination propagation in composite plates or shells be properly predicted from essentially one-dimensional propagation in coupons? How does fibre bridging in unidirectionally reinforced test coupons relate to delamination propagation in multidirectional lay-ups of components and structures? How can multiple, localised delaminations—often created by impact in composite structures—and their interaction under service loads with constant or variable amplitudes be accounted for? Does planar delamination propagation depend on laminate thickness, thickness variation or the overall shape of the structure? How does exposure to different, variable service environments affect delamination initiation and propagation? Is the microscopic and mesoscopic morphology of FRP composite structures sufficiently understood for accurate predictive modelling and simulation of delamination behaviour? This contribution will examine selected issues and discuss the consequences for test development and analysis. The discussion indicates that current coupon testing and analysis are unlikely to provide the data for reliable long-term predictions of delamination behaviour in FRP composite structures. The attempts to make the building block design methodology for composite structures more efficient via combinations of experiments and related modelling look promising, but models require input data with low scatter and, even more importantly, insight into the physics of the microscopic damage processes yielding delamination initiation and propagation.
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Bazardehi, Sayyed Roohollah Kazemi, i Mohammad Ali Kouchakzadeh. "Detection of delamination in composite laminated plates using filtered mode shapes". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, nr 12 (21.03.2012): 2902–11. http://dx.doi.org/10.1177/0954406212442052.
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Filtered mode shapes are used to detect the presence, location, size and shape of the delaminations in composite laminated plates with various boundary conditions. This method is the extension of a previous study by the authors on the delamination detection in the beams using irregularities of the mode shapes. The mode shapes are filtered to separate the smooth and irregular parts. Presence and situation of delamination affects these separated parts, and these effects are used to detect the delamination. Here, two new indicators, named ‘slope of smooth part’ and ‘irregularities in the slope of smooth part’, are introduced to increase the clarity of detected damage and reduce the noisy effects. The former one is obtained by differentiating the smooth part of the mode shape and the latter by applying the filter on the slope of smooth part for another time. Using this method and the mentioned indicators, delaminations may be detected in the plates using the data of just the damaged structure. This is considered as an important advantage of the method as we do not need the intact structure data. The method is validated utilizing the numerical data for a delaminated plate model. This method lacks the ability to locate the position of delamination through the thickness and the delamination should not be too close to the edges of the plate.
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Yeh, Meng Kao, i In Shung Lee. "Delamination Growth in Ball Grid Array Electronic Package". Key Engineering Materials 306-308 (marzec 2006): 363–68. http://dx.doi.org/10.4028/www.scientific.net/kem.306-308.363.
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The delamination problem in plastic ball grid array electronic package was investigated analytically and experimentally. The ANSYS code was used in the analysis to find the deformation and the stress distribution in electronic package due to the thermal mismatch between different materials at reflow temperature with saturated moisture pressure at the delaminated region. The stress intensity factor and the strain energy release rate at the tip of interfacial delamination were calculated using the fracture mechanics approach. The results show that the delaminaton occurs at the corner of the die pad and at the middle region of the die attach/die pad interface. The delaminaton grew from the middle region of the die attach/die pad interface, along the epoxy molding compoend/die pad interface, the epoxy molding compound/substrate interface to the exterior surface. Possible growth directions of the interfacial delamination in plastic ball grid array electronic package were identified and observed in the experimental results. In addition, the reflow temperature affected the stress distribution and the strain energy release rate at the tip of interfacial delaminaton.
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Chang, Fu-Kuo, i Zafer Kutlu. "Delamination Effects on Composite Shells". Journal of Engineering Materials and Technology 112, nr 3 (1.07.1990): 336–40. http://dx.doi.org/10.1115/1.2903334.
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An analytical investigation was performed to study the effect of delamination on the response of cylindrical composite shells subjected to external loadings. It was of particular interest to determine the buckling load and the post-buckling behavior of externally pressurized cylindrical composite shells containing delaminations. An analytical model was developed that consists of a structural analysis for calculating the global deformations of the structures and a fracture analysis for determining the delamination growth in the structures. A nonlinear finite element code based on the updated Lagrangian formulation was developed for the model. Based on the results of calculations, it was found that delamination can significantly affect the buckling load and response of cylindrical composite shells subjected to externally pressurized loadings, depending upon the initial length and location of the delamination, ply orientation and laminate curvature. The calculated strain energy release rate at the crack tips indicates that delamination growth occurs in the wake of buckling due to Mode II shear fracture.
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Fuoss, E., P. V. Straznicky i C. Poon. "Prediction of Impact-Induced Delamination in Composite Plates". Advanced Composites Letters 3, nr 6 (listopad 1994): 096369359400300. http://dx.doi.org/10.1177/096369359400300602.
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The bending stiffness mismatch method is examined for its ability to predict delaminations within multi-ply composite plates. Bending stiffness is found to be insufficient to predict delamination size through thickness. A combination of several parameters may be required to model delaminations resulting from an impact response.
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Erives, R., B. F. Sørensen, S. S. Samareh-Mousavi, A. Bangaru, X. Chen, X. Y. Miao i M. McGugan. "Design of an element test specimen for fatigue delamination growth of a thick laminate". IOP Conference Series: Materials Science and Engineering 1293, nr 1 (1.11.2023): 012017. http://dx.doi.org/10.1088/1757-899x/1293/1/012017.
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Abstract Following the observation of multiple delaminations growing from a tunnelling crack in the spar cap of a wind turbine rotor blade subjected to cyclic loading, an element test specimen is proposed. Design of the element test specimen to study fatigue delamination of a thick laminate is presented. Complexities inherent to a full structure e.g., curvatures, ply drops, manufacturing defects, etc. are removed to study the fatigue delamination damage mechanism. The element test specimen is made of unidirectional layers with two embedded artificial delamination cracks connected by a tunnelling crack. In this paper, analytical and numerical (2D) models are used to design the element test specimen.
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Sellitto, Andrea, R. Borrelli, Francesco Caputo, Aniello Riccio i Francesco Scaramuzzino. "Application of the Mesh Superposition Technique to the Study of Delaminations in Composites Thin Plates". Key Engineering Materials 525-526 (listopad 2012): 533–36. http://dx.doi.org/10.4028/www.scientific.net/kem.525-526.533.
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Laminated composite structures are increasingly finding more applications in various fields thanks to their lower weight if compared with other materials of the same strength. Nevertheless, composites thin plates show a critical behavior in terms of damage propagation mechanisms when subjected to (low velocity) impact. Indeed they tend to produce delaminations which can be hardly detected by optical inspections and can affect the global load carrying capability, leading to a premature structural collapse. The aim of this paper is to assess the capabilities of the Davies-Zhang approach (introduced in 1994 and aimed to the estimation of both the delamination initiation impact load and the size of the impact induced delaminations) by using a multiscale FE model based on the mesh superposition technique. Indeed the impact area has been modeled layer-wise with an element per layer while the rest of the structure has been modeled at laminate level by layered elements by means of a homogenization approach for the determination of the equivalent laminate material properties. The impact induced delamination area has been determined by adopting stress-based criteria. The results (in terms of delamination initiation impact force and delamination size) have been compared to the ones obtained by adopting the Davies-Zhang approach.
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Heberger, L., S. Nissle, M. Gurka, B. Kirsch i J. C. Aurich. "Qualitätssteigerung von Bohrungen in Faserkunststoffverbunden*/Increased quality of bores in fiber reinforced polymers". wt Werkstattstechnik online 105, nr 07-08 (2015): 501–7. http://dx.doi.org/10.37544/1436-4980-2015-07-08-59.
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Beim Bohren von kohlefaserverstärktem Kunststoff treten verstärkt Schädigungen wie Delaminationen und Faserüberstände auf. Mit dem Ziel die Bohrlochqualität zu verbessern, wurde der Einfluss der Werkstückeinspannung hinsichtlich Einspanngeometrie, -kraft und -material untersucht. Zusätzlich zur konventionellen optischen Delaminationsmessung wurde die äußere und die innere Delamination mittels Mikrocomputertomografie analysiert. Durch eine Optimierung der Einspannung konnte die Bohrlochqualität gesteigert werden. When drilling carbon fiber reinforced polymers damages like delamination and fiber protrusion appear. Aiming to improve the drill hole quality, the influence of the fastening device with respect to fastening geometry, force and material is analyzed. In addition to the conventional optical delamination measurement, the outer and inner delamination is investigated by micro computer tomography. The optimization of the fastening device leads to a higher drill hole quality.
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Subba Rao, V. V., Godavarthi Yeswanth Kiran Kumar i Sansanka Pentapalli. "Reduction of AWJ Induced Delaminations by Impregnated Nanoclay GFRP Composites". Materials Science Forum 969 (sierpień 2019): 284–90. http://dx.doi.org/10.4028/www.scientific.net/msf.969.284.
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Composite materials are extensively used in various applications like space, aircraft, and automobile sector because of superior physical and mechanical properties even though they are costly. In recent technological innovations, using Montmorillonite (Nanoclay) to reinforce polymer-based composites has raised attention to academic and industrial sectors since small addition could enhance Mechanical properties thereby decreasing failures like delaminations. In present research work, the effect of AWJ machining parameters on delaminations of glass fibre reinforced epoxy composite is investigated. The Main objective is determining delamination factor and reduce delaminations which is major failure in laminates. This paper investigates on effects of impregnated Nanoclay epoxy in Bi-directional GFRP where previous research has been made only in changing the parameters for reduction of delaminations. The samples were machined using AWJ, delamination factors are measured using image-J software and SEM analysis for comparing micrographs. Finally with increase in nano clay weight fraction, delaminations are checked.
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Kay, R. W., i S. Mahlburg Kay. "Delamination and delamination magmatism". Tectonophysics 219, nr 1-3 (marzec 1993): 177–89. http://dx.doi.org/10.1016/0040-1951(93)90295-u.
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Papanaboina, Mastan Raja, Elena Jasiuniene, Vykintas Samaitis, Liudas Mažeika i Paulius Griškevičius. "Delamination Localization in Multilayered CFRP Panel Based on Reconstruction of Guided Wave Modes". Applied Sciences 13, nr 17 (27.08.2023): 9687. http://dx.doi.org/10.3390/app13179687.
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Multi-layered composite materials are being used in various engineering fields, such as aerospace, automobile, and wind energy, because of their superior material properties. Due to various impact loads during the service life of composite structures, different types of defects can occur, such as matrix cracking, fiber breakage, delaminations, etc. In this research, a novel SHM technique for delamination detection and localization using a minimum number of sensors is proposed. The analytical, numerical, and experimental analysis of GW was performed to increase the probability of detection and localization of delaminations in CFRP material. A new analytical model was developed, which enables identifying converted and transmitted modes in the presence of multiple GW modes. A 2D FFT-based spatial filtering was used to filter the GW modes. The dominant A0 mode was separated to inspect the delamination. Phase velocity is one of the important features in GW inspection to localize the delamination. A phase spectrum approach was developed to reconstruct the phase velocity dispersion of the GW modes in case material properties are unknown.
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Gillespie, David I., Andrew W. Hamilton, Robert C. Atkinson, Xavier Bellekens, Craig Michie, Ivan Andonovic i Christos Tachtatzis. "Composite Laminate Delamination Detection Using Transient Thermal Conduction Profiles and Machine Learning Based Data Analysis". Sensors 20, nr 24 (17.12.2020): 7227. http://dx.doi.org/10.3390/s20247227.
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Delaminations within aerospace composites are of particular concern, presenting within composite laminate structures without visible surface indications. Transmission based thermography techniques using contact temperature sensors and surface mounted heat sources are able to detect reductions in thermal conductivity and in turn impact damage and large disbonds can be detected. However delaminations between Carbon Fibre Reinforced Polymer (CFRP) plies are not immediately discoverable using the technique. The use of transient thermal conduction profiles induced from zonal heating of a CFRP laminate to ascertain inter-laminate differences has been demonstrated and the paper builds on this method further by investigating the impact of inter laminate inclusions, in the form of delaminations, to the transient thermal conduction profile of multi-ply bi-axial CFRP laminates. Results demonstrate that as the distance between centre of the heat source and delamination increase, whilst maintaining the delamination within the heated area, the resultant transient thermal conduction profile is measurably different to that of a homogeneous region at the same distance. The method utilises a supervised Support Vector Classification (SVC) algorithm to detect delaminations using temperature data from either the edge of the defect or the centre during a 140 s ramped heating period to 80 °C. An F1 score in the classification of delaminations or no delamination at an overall accuracy of over 99% in both training and with test data separate from the training process has been achieved using data points effected by transient thermal conduction due to structural dissipation at 56.25 mm.
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Karim, M. R., T. Kundu i C. S. Desai. "Detection of Delamination Cracks in Layered Fiber-Reinforced Composite Plates". Journal of Pressure Vessel Technology 111, nr 2 (1.05.1989): 165–71. http://dx.doi.org/10.1115/1.3265653.
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In this paper, the dynamic response of delamination cracks in a layered fiber-reinforced composite plate is analytically studied. The plate is subjected to an antiplane loading and its surface response is computed in absence as well as in presence of delaminatioin cracks. To what extent the surface response is influenced by the presence of internal delamination cracks is investigated here. This study is important for nondestructive evaluation of internal damage in composites due to delamination. The problem is formulated in terms of integral equations in frequency domain. These equations are then solved by expanding the unknown crack opening displacement in a complete set of Chebychev’s polynomials, whose coefficients are solved by satisfying the traction-free condition at the crack surface. The time histories are obtained numerically by inverting the spectra via Fast Fourier Transform (FFT) routine. The results show significant influence of delamination crack geometries on the surface response of the plate.
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Erdelyi, Nicholas H., i Seyed M. Hashemi. "On the Finite Element Free Vibration Analysis of Delaminated Layered Beams: A New Assembly Technique". Shock and Vibration 2016 (2016): 1–14. http://dx.doi.org/10.1155/2016/3707658.
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The dynamic analysis of flexible delaminated layered beams is revisited. Exploiting Boolean vectors, a novel assembly scheme is developed which can be used to enforce the continuity requirements at the edges of delamination region, leading to a delamination stiffness term. The proposed assembly technique can be used to form various beam configurations with through-width delaminations, irrespective of the formulation used to model each beam segment. The proposed assembly system and the Galerkin Finite Element Method (FEM) formulation are subsequently used to investigate the natural frequencies and modes of 2- and 3-layer beam configurations. Using the Euler-Bernoulli bending beam theory and free mode delamination, the governing differential equations are exploited and two beam finite elements are developed. The free bending vibration of three illustrative example problems, characterized by delamination zones of variable length, is investigated. The intact and defective beam natural frequencies and modes obtained from the proposed assembly/FEM beam formulations are presented along with the analytical results and those available in the literature.
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Giannakopoulos, A. E., K. F. Nilsson i G. Tsamasphyros. "The Contact Problem at Delamination". Journal of Applied Mechanics 62, nr 4 (1.12.1995): 989–96. http://dx.doi.org/10.1115/1.2896034.
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The important phenomenon of delamination buckling is examined subjected to the condition of frictionless contact. Buckled delamination is examined in particular, because in-plane compressive loading is typical and detrimental. Two types of contact can be distinguished, local and global. The latter may occur everywhere in the plate while the local contact is limited to the crack front (negative KI stress intensity factors). Both local and global contact conditions were considered using a finite element scheme which employed nonlinear plate theory. The global contact problem is formulated as it appears in post-buckling of delamination. The case of simultaneous buckling and contact is also addressed in this paper. Two particularly interesting examples of thin film delaminations are presented. In the first, the contact at buckling is due to the material anisotropy. In this case the bucking load and the post-bucking analysis were very well supported by experiments. In the second example, contact at buckling arises because of a pin that holds down the delaminated layer at its center. The treated cases indicated that contact may significantly affect the fracture parameters along the delamination front, and is, therefore, important for delamination arrest.
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Tay, TE. "Characterization and analysis of delamination fracture in composites: An overview of developments from 1990 to 2001". Applied Mechanics Reviews 56, nr 1 (1.01.2003): 1–32. http://dx.doi.org/10.1115/1.1504848.
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Delamination is a major failure mode in laminated composites and has received much research attention. A huge amount of literature has been published on this subject, resulting in considerable improvement in our understanding of delamination behavior. A rather comprehensive review paper was published by Garg in 1988. That paper contains 136 references from 1971 to 1988, a period spanning roughly two decades. A more recent survey by Pagano and Schoeppner contains critical reviews of many selected papers, especially the pioneering works on delamination research. An overview of Russian and Soviet literature on this subject is also given by Bolotin. The present paper aims to review major developments in the analysis and characterization of buckling driven delamination from 1990 to the present. Its abridged version was presented in a plenary lecture at the 13th International Conference on Composite Materials, Beijing. Particular emphasis is placed on the application of fracture mechanics methods in the analysis of delamination. The question of the extent of fracture mechanics’ success in characterizing delamination, both in laboratory-based specimens and in more realistic structural composite components, is discussed. Some recent numerical formulations for efficient computational modeling and analysis of delaminations are also reviewed. This review lists 270 major works covering a period of about a decade, indicating that there is still considerable research interest and activity in this field.
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Craven, R., L. Iannucci i R. Olsson. "Delamination buckling: A finite element study with realistic delamination shapes, multiple delaminations and fibre fracture cracks". Composites Part A: Applied Science and Manufacturing 41, nr 5 (maj 2010): 684–92. http://dx.doi.org/10.1016/j.compositesa.2010.01.019.
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Pascoe, J. A., C. D. Rans i R. Benedictus. "Characterizing fatigue delamination growth behaviour using specimens with multiple delaminations: The effect of unequal delamination lengths". Engineering Fracture Mechanics 109 (wrzesień 2013): 150–60. http://dx.doi.org/10.1016/j.engfracmech.2013.05.015.
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Shu, Dong Wei. "Vibration of Beams with a Single Delamination under Axial Loading". Materials Science Forum 675-677 (luty 2011): 477–80. http://dx.doi.org/10.4028/www.scientific.net/msf.675-677.477.
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In this work analytical solutions are developed to study the free vibration of composite beams under axial loading. The beam with a single delamination is modeled as four interconnected Euler-Bernoulli beams using the delamination as their boundary. The continuity and the equilibrium conditions are satisfied between the adjoining beams. The studies show that the sizes and the locations of the delaminations significantly influence the natural frequencies and mode shapes of the beam. A monotonic relation between the natural frequency and the axial load is predicted.
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He, Yu Ting, Hong Peng Li, Rong Hong Cui i Chao Hua Fan. "Influence of Delamination of Epoxy/Dielectric Interfaces on Pattern Shift and Passivation Cracking under Aeronautical Conditions". Materials Science Forum 575-578 (kwiecień 2008): 919–23. http://dx.doi.org/10.4028/www.scientific.net/msf.575-578.919.
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Interfacial delamination is a recognized failure mode in Integrated circuits (ICs). A major cause for this failure is the mismatch of Thermal Expansion Coefficients, Young’s modulus, and Poisson’s ratios of the package materials. Here, the influence of delamination between epoxy and dielectric layers on pattern shift and passivation cracking in IC package under aeronautical conditions, mainly temperature and load cycles, is studied by maximum plastic strain and maximum principal stresses theory using a certain 2D FEM model with different delamination length “L_c.right”. Delaminations are easy to introduce more dangerous impact to the package, because the IC microstructures endure serious thermo-mechanical loading under aeronautical working conditions. The method can be used to find the dangerous designed structure schedules and will provide a basis for selecting passivation materials of aeronautical IC packages.
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Wu, D., i S. S. Law. "Delamination Detection-Oriented Finite Element Model for a Fiber Reinforced Polymer Bonded Concrete Plate and Its Application With Vibration Measurements". Journal of Applied Mechanics 74, nr 2 (3.02.2006): 240–48. http://dx.doi.org/10.1115/1.2190228.
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Delamination is a common type of damage in laminated fiber-reinforced polymer (FRP) composites. As FRP composites are becoming popular in upgrading and strengthening of civil concrete structures, the specific delamination damage, i.e., the FRP-concrete debonding, is considered more critical than inter-laminar delamination occurring in the FRP composites. A finite element formulation on the FRP-bonded concrete plate with this type of delamination fault is developed in the context of non-destructive evaluation from vibration measurements and compared with a two-layer solid element model. An adhesive interface where possible debonding could occur is introduced between the FRP and the concrete plates. A scalar damage parameter characterizing the delamination is incorporated into the formulation of a finite element model that is compatible with the vibration-based damage identification procedure. The formulated model is then applied to the prediction of FRP-concrete delaminations from modal test results based on the sensitivity analysis of uniform load surface curvature, which has been previously proposed by the authors. The validity of the methodology is demonstrated in two numerical examples. The first one is used to check the model accuracy, while the second one assesses the efficiency of the model-based identification method.
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Xu, Changhang, Jing Xie, Changwei Wu, Lemei Gao, Guoming Chen i Gangbing Song. "Enhancing the Visibility of Delamination during Pulsed Thermography of Carbon Fiber-Reinforced Plates Using a Stacked Autoencoder". Sensors 18, nr 9 (25.08.2018): 2809. http://dx.doi.org/10.3390/s18092809.
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The effectiveness of pulsed thermography (PT) for detecting delamination in carbon fiber-reinforced polymer (CFRP) plates has been widely verified. However, delaminations are usually characterized by weak visibility due to the influences of inspection factors and the delaminations with weak visibility are easily missed in real inspections. In this study, by introducing a deep learning algorithm—stacked autoencoder (SAE)—to PT, we propose a novel approach (SAE-PT) to enhance the visibility of delaminations. Based on the ability of SAE to learn unsupervised features from data, the thermal features of delaminations are extracted from the raw thermograms. The extracted features are then employed to construct SAE images, in which the visibility of delaminations is expected to be enhanced. To test the performance of SAE-PT, we inspected CFRP plates with prefabricated delaminations. By implementing SAE-PT on the raw inspection data, the delaminations were more clearly indicated in the constructed SAE images. We also compare SAE-PT to the widely used principal component thermography (PCT) method to further verify the validity of the proposed approach. The results reveal that compared to PCT, SAE-PT can show delaminations in CFRP with higher contrast. By effectively enhancing the delamination visibility, SAE-PT thus has potential for improving the inspection accuracy of PT for non-destructive testing (NDT) of CFRP.
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Matalgah, Khaled, Pruthul Kokkada Ravindranath, Daniel Pulipati i Trevor J. Fleck. "Automated Quantification of Interlaminar Delaminations in Carbon-Fiber-Reinforced Polymers via High-Resolution Ultrasonic Testing". Polymers 15, nr 24 (13.12.2023): 4691. http://dx.doi.org/10.3390/polym15244691.
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This article presents a method of ultrasonic testing (UT) that detects and quantifies interlaminar delaminations in CFRP composites with high resolution in terms of both spatial resolution in the planar dimension and depth into the laminate. Unidirectional and woven CFRP laminates were fabricated for this study, with a PTFE film inserted at various depths throughout the laminate to act as intentional crack initiation sites. All samples were mechanically tested via a three-point, end-notched flexure (ENF) test, followed by a quantification of the extent of the induced interlaminar delaminations using UT and X-ray computed tomography (CT). UT analysis for unidirectional CFRP samples was able to show a clear contrast between the delaminated area and the non-delaminated area. UT analysis of the woven CFRP samples yielded comparable results but required finer tuning of analysis parameters due to the interlocking woven fabric. CT results revealed a significant contrast between the crack and composite; thus, fine geometrical features of the crack front could be observed. UT and CT measurements were then compared, revealing an average difference of 1.09% in the delamination area, with UT overestimating as compared to CT. A UT depth study was also performed to automatically locate the interlaminar delamination at different depths throughout the components, with the delamination being predicted within one lamina interface for all samples. These results demonstrate UT’s ability to accurately detect and quantify the extent and location of interlaminar delaminations due to bending.
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Nanda, Namita. "Spectral finite element method for wave propagation analysis in smart composite beams containing delamination". Aircraft Engineering and Aerospace Technology 92, nr 3 (29.01.2020): 440–51. http://dx.doi.org/10.1108/aeat-02-2019-0026.
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Purpose The purpose of the study is to present a frequency domain spectral finite element model (SFEM) based on fast Fourier transform (FFT) for wave propagation analysis of smart laminated composite beams with embedded delamination. For generating and sensing high-frequency elastic waves in composite beams, piezoelectric materials such as lead zirconate titanate (PZT) are used because they can act as both actuators and sensors. The present model is used to investigate the effects of parametric variation of delamination configuration on the propagation of fundamental anti-symmetric wave mode in piezoelectric composite beams. Design/methodology/approach The spectral element is derived from the exact solution of the governing equation of motion in frequency domain, obtained through fast Fourier transformation of the time domain equation. The beam is divided into two sublaminates (delamination region) and two base laminates (integral regions). The delamination region is modeled by assuming constant and continuous cross-sectional rotation at the interfaces between the base laminate and sublaminates. The governing differential equation of motion for delaminated composite beam with piezoelectric lamina is obtained using Hamilton’s principle by introducing an electrical potential function. Findings A detailed study of the wave response at the sensor shows that the A0 mode can be used for delamination detection in a wide region and is more suitable for detecting small delamination. It is observed that the amplitude and time of arrival of the reflected A0 wave from a delamination are strongly dependent on the size, position of the delamination and the stacking sequence. The degraded material properties because of the loss of stiffness and density in damaged area differently alter the S0 and A0 wave response and the group speed. The present method provides a potential technique for researchers to accurately model delaminations in piezoelectric composite beam structures. The delamination position can be identified if the time of flight of a reflected wave from delamination and the wave propagation speed of A0 (or S0) mode is known. Originality/value Spectral finite element modeling of delaminated composite beams with piezoelectric layers has not been reported in the literature yet. The spectral element developed is validated by comparing the present results with those available in the literature. The spectral element developed is then used to investigate the wave propagation characteristics and interaction with delamination in the piezoelectric composite beam.
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Zulkarnain, Zulkarnain, Ismet Hari Mulyadi, Jupri Jupri i Siswandi B. "PENGARUH SUDUT PAHAT PADA PENGGURDIAN KOMPOSIT SERAT DAUN NANAS / TERMOPLASTIK PADA PEMBENTUKAN DELAMINASI". INOVTEK POLBENG 13, nr 1 (1.06.2023): 97. http://dx.doi.org/10.35314/ip.v13i1.3325.
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This study aims to determine the effect of the Gurdi tool angle on delamination in composite laminates in the formation of delaminations. The spacing of the selected reinforcing fibers was 2.4 and 6 mm in a composite laminate of ethylene vinyl acetate (EVA) polymer matrix with reinforcing fibers from pineapple leaves. The method used in composite fabrication is hand lay-up, namely by direct casting on three layers of fiber that has been woven and tied to the sides of the mold. For cutting speed, Vf 72 mm / min, using a chisel with a diameter of 8 mm with a tool angle of 70o and 118o. Delamination was determined using the Feda method. The delamination sections were observed using a digital microscope and then processed using AutoCAD to measure Dmax and Ad. The delamination ratio in the top hole for the tool diameter of 8mm with a 70° angle at the variation of the distance of 2 mm, 4 mm and 6 mm were 1.268, 1.224 and 1.192 for the bottom hole were 1.078, 1.042 and 1.029, respectively. Meanwhile, the ratio of delamination in the upper hole for a tool diameter of 8mm with an angle of 118° at a distance variation of 2mm, 4mm and 6mm were 1.194, 1.194, 1.158 for the bottom hole, respectively, 1.046, 1.042 and 1.038.
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Devivier, C., Daniel Thompson, Fabrice Pierron i M. R. Wisnom. "Correlation between Full-Field Measurements and Numerical Simulation Results for Multiple Delamination Composite Specimens in Bending". Applied Mechanics and Materials 24-25 (czerwiec 2010): 109–14. http://dx.doi.org/10.4028/www.scientific.net/amm.24-25.109.
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This paper studies the effect of delaminations on strain maps for a simple cantilever beam. The aim is to build an experimental set-up which allows detecting very slight modifications in the strain maps. The case studied is a single delamination on the mid-plane. The measurement method is the deflectometry technique which enables direct slope measurements on a reflective specimen. The comparison with finite element models clearly indicated that the surface strains bear the information of the extent of the delamination. The second step is to use these surface strains to identify a stiffness reduction map for real impact damages.
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Sellitto, Andrea, Salvatore Saputo, Michele Damiano, Angela Russo i Aniello Riccio. "Mixed-Mode Delamination Growth Prediction in Stiffened CFRP Panels by Means of a Novel Fast Procedure". Applied Sciences 9, nr 22 (7.11.2019): 4761. http://dx.doi.org/10.3390/app9224761.
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Carbon fiber reinforced plastic (CFRP) structures are highly sensitive to delaminations, resulting from low energy impacts or manufacturing defects. Non-linear numerical algorithms are mandatory to investigate the complex mechanisms governing the delamination growth phenomena. Although the high computational costs associated to the non-linear algorithms are acceptable in a detail verification design stage, less expensive procedures are desired in a preliminary design stage or during optimization procedure. In this work, a fast numerical procedure, able to determine the delamination growth initiation in composite structures in the framework of a damage tolerant design approach when mixed mode I and II growth is expected, is introduced. The state of the art of the fast delamination growth procedures is critically discussed and improvements to the existing approaches are proposed to extend their applicability and to increase their accuracy. Comparisons with the standard non-linear delamination growth approaches are presented to assess the effectiveness of the proposed novel Fast approach. The results of the proposed fast approach are comparable with the ones obtained by means of standard numerical non-linear technique, allowing up to 95% computational cost saving.