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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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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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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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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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Wei, Z., L. H. Yam i L. Cheng. "Delamination Assessment of Multilayer Composite Plates Using Model-based Neural Networks". Journal of Vibration and Control 11, nr 5 (maj 2005): 607–25. http://dx.doi.org/10.1177/1077546305052317.
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A procedure for damage detection in multilayer composites is described using model-based neural networks and vibration response measurement. The appropriate finite element model is established to generate the training data of neural networks. Internal delaminations with different sizes and locations are considered as the particular damage scenarios in multilayer composite plates. The damage-induced energy variation of response signal is investigated, and the mechanism of mode-dependent energy dissipation of composite plates due to delamination is revealed. In order to obtain the structural dynamic response of the samples, impulse forced vibration testing is conducted using a piezoelectric patch actuator and an accelerometer. To enhance the sensitivity of damage features in the vibrating plate, the damage-induced energy variation of the response signal decomposed by wavelet packets is used as the input data of backward propagation neural networks for the prediction of delamination size and location. The test results show that the proposed method is effective for the assessment of delamination status in composites.
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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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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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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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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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Azuan, S. A. Syed, J. M. Juraidi i Wan Mansor Wan Muhamad. "Evaluation of Delamination in Drilling Rice Husk Reinforced Polyester Composites". Applied Mechanics and Materials 232 (listopad 2012): 106–10. http://dx.doi.org/10.4028/www.scientific.net/amm.232.106.
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Delamination is recognized as one of the most critical defects that can result from the machining composites. Delamination has been a major form of failure in drilled composite materials due to the composites lack of strength in the drilling direction, which results in poor surface finish, reduction in bearing strength, reduction in structural integrity and ultimately poor performance of the composite. Currently, most of the major research reported delamination address specific of machining fiber glass, graphite fiber or carbon fiber reinforced polymer composites. It is not yet clear how different drilling parameters affect the machinability of natural fiber reinforced polymer composite materials and quality of drilled holes. This paper report the investigation in drilling holes on natural fibre reinforced polyester composites and evaluate its hole quality by measuring delamination. Three different type of drill: twist 118o drill, brad drill and end mill were used. Drilling process is carried out for three spindle speed (1500 rpm, 2000 rpm and 2500 rpm) and three feed rate (0.1 mm/rev, 0.15 mm/rev and 0.2 mm/rev). Brad drill experienced higher delamination values compared to twist and end mill. Increasing of feed rate and spindle speed also caused a relevant increase in the delamination values. It is found that Rice husk reinforced polyester composites delamination value is lower when compared to the glass fiber reinforced polymer.
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Ramadhan, Redha Akbar, Muhamad Giri Suada i Hendri Syamsudin. "A FINITE ELEMENT ANALYSIS OF CRITICAL BUCKLING LOAD OF COMPOSITE PLATE AFTER LOW VELOCITY IMPACT". Jurnal Teknologi Dirgantara 18, nr 2 (27.12.2020): 195. http://dx.doi.org/10.30536/j.jtd.2020.v18.a3328.
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Composite is a material formed from two or more materials that macroscopically alloyed into one material. Nowadays, composite has been generally applied as lightweight structure of aircraft. This is due to the fact that composites having high strength-to-weight ratio. It means the composites have the capability to take on various loads, despite their lightweight property.Laminate composite is one type of composite that has been generally used in aircraft industries. This type of composite is susceptible to low-velocity impact induced damage. This type of damage can be happening in manufacture, operation, or even in maintenance. Low-velocity impact could cause delamination. Delamination happens when the plies of laminated composites separated at the interface of the plies. This type of damage is categorized as barely visible damage, means that the damage couldn’t be detected with visual inspection. Special method and tool would be needed to detect the damage. Delamination will decrease the strength of the laminated composite.Delamination can be predicted with numerical simulation analysis. With increasing capability of computer, it is possible to predict the delamination and buckling of laminated composite plate. This research presents the comparisons of buckling analysis results on laminated plate composite and damaged laminated plate composite. By the result of LVI simulation, it is shown that low velocity impact of 19.3 Joule causing 6398 mm2 C-Scan delamination area inside the laminated composite. The delamination causing structural instability that will affect buckling resistance of the plate. The result of analysis shows that the existence of delamination inside laminate composite will lower its critical buckling load up to 90% of undamaged laminate’s critical buckling load.Keywords : composite, laminate, delamination, buckling.
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Hajikhani, Milad, Amir Refahi Oskouei, Mehdi Ahmadi Najaf Abadi, Amir Sharifi i Mohammad Heidari. "Progressive Fracture Evaluation in Composite Materials by Acoustic Emission Technique". Key Engineering Materials 465 (styczeń 2011): 535–38. http://dx.doi.org/10.4028/www.scientific.net/kem.465.535.
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Glass/polyester and glass/epoxy laminated composites widely used in structures and have very near properties. These composite laminates have poor inter-laminar fracture resistance and suffer extensive damage by delamination cracking when subjected to out of plane loading and hence are vulnerable to delamination. The presence of delamination in the composite material may reduce the overall stiffness. Structural design and nondestructive test techniques have evolved as increased emphasis has been placed on the durability and damage tolerance of these materials. There are several methods used to investigate damages of composite materials. Acoustic emission is one of these. In this work the effect of delamination propagation on acoustic emission (AE) events in glass/polyester and glass/epoxy composites is obtained also Fracture surface examinations were conducted using a scanning electron microscope (SEM) and results in these two common composites compared. Consequently, revealed that the AE technique is a practicable and effective tool for identifying and separating kinds of cracks in these composites.
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Tian, Xinpeng, Dong Yao i Qun Li. "Thermal buckling response and fracture analysis for delaminated fiber reinforced composite plates under thermo-mechanical coupling". Journal of Composite Materials 52, nr 27 (2.05.2018): 3715–30. http://dx.doi.org/10.1177/0021998318769132.
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Fiber reinforced composites are often subjected to severe thermal-mechanical coupling loads. In order to predict the stiffness and strength of the designed composites, thermal buckling response of the delaminated fiber reinforced composite plates and fracture analysis along the delamination front under thermo-mechanical coupling are investigated based on the generalized layerwise plate theory. Delamination between individual layers is considered as discontinuities in the displacement field using Heaviside step functions in the finite element model of delaminated composite plates. Governing equations are derived using virtual work principle and fracture analysis is performed by calculation of the strain energy release rate along the delamination front by means of the virtual crack closure technique. The effect of laying angle, delamination size, and delamination position on the critical thermal buckling temperature of laminated composite plates are investigated. Numerical results reveal that the critical thermal buckling temperature is insensitive to the delamination size less than an ‘irrelevant size’ and then significantly decreases with the increase of delamination sizes. The inside delamination has a greater influence on the critical thermal buckling temperature than the outside delamination. The maximum values of strain energy release rate always occur in the ‘equivalent material direction’ when the delamination is located in the middle of composite plates, while it is determined by laying angle and delamination position together for non-middle plane delamination.
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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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Dilli Babu, G., K. Sivaji Babu i B. Uma Maheswar Gowd. "Determination of Delamination and Tensile Strength of Drilled Natural Fiber Reinforced Composites". Applied Mechanics and Materials 592-594 (lipiec 2014): 134–38. http://dx.doi.org/10.4028/www.scientific.net/amm.592-594.134.
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A study has been carried out to investigate the delamination and tensile properties of drilled composites made by reinforcing the natural fibers like hemp, jute, banana and vakka into a polyester resin matrix. The fibers extracted by retting and manual processes have been used to fabricate the composites. These composites are tested for delamination and tensile strength after drilling and compared with those of established composite like glass made under the same laboratory conditions. The Taguchi method with orthogonal array of L9 (34) was selected to realize the influence of the drilling parameters (cutting speed and feed rate) on delamination and tensile strength for various fiber reinforced composites. The results indicate that the delamination of the drilled natural fiber composites were in some cases better than those of glass fiber composites.
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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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Balasubramanian, M., i S. Madhu. "Evaluation of delamination damage in carbon epoxy composites under swirling abrasives made by modified internal threaded nozzle". Journal of Composite Materials 53, nr 6 (8.08.2018): 819–33. http://dx.doi.org/10.1177/0021998318791340.
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Carbon fibre-reinforced polymer composites are finding increased applications in the field of automotive manufacture and aircraft industries due to their appreciative combination of high strength and low weight. The machining of these composites with economically viable and high part qualities requires enhancement in machining strategies. Delamination and surface roughness are the undesirable geometrical defects inherent in abrasive jet machining of layered polymer composites. This investigation focuses on the mechanism of delamination and surface roughness in abrasive jet machining of carbon fibre-reinforced polymer composite. The paper endeavors at the exploration of the viability of imparting swirling motion to SiC abrasive particles by presenting internal threads in the newly designed nozzle. In this research, a novel threaded nozzle was introduced in the abrasive jet machine for making holes on the carbon fiber-reinforced polymer composites with the objective of reducing the delamination and surface roughness. This is a distinctive attempt of its kind and this has brought down the delamination factor considerably and, as a consequence, surface roughness obtained was minimum. Holes were made on carbon fiber-reinforced polymer composite by abrasive jet machining with a modified nozzle with and without an internal thread. The influence of abrasive jet parameters on the delamination factor (bottom and top) and surface roughness (Ra) was investigated. Maximum pressure and minimum SOD cause decrease in delamination and surface roughness in carbon fiber-reinforced polymer composite composites.
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Mouritz, Adrian P., Fabio Pegorin, Mohd Dali Isa i Khomkrit Pingkarawat. "Fatigue Properties of Aerospace Z-Pinned Composites". Applied Mechanics and Materials 828 (marzec 2016): 67–75. http://dx.doi.org/10.4028/www.scientific.net/amm.828.67.
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This paper presents an experimental study into the effect of through-thickness z-pin reinforcement on the in-plane and out-of-plane (delamination) fatigue properties of carbon-epoxy composites used in aerospace structures. The in-plane fatigue strength and fatigue life (load cycles-to-failure) of aerospace composite materials are reduced by z-pins. The in-plane compressive fatigue properties decrease when the volume content of z-pins is increased. Reductions to the in-plane fatigue properties are due to microstructural damage caused by the z-pins. However, the out-of-plane (delamination) fatigue properties of composites are increased greatly by z-pins. The mode I, mode II and mixed mode I/II delamination fatigue properties increase rapidly with increasing volume content of z-pins. The improvement is due to the z-pins forming a large-scale bridging zone along the delamination which resists fatigue crack growth. The work clearly reveals that a trade-off exists between the in-plane and out-of-plane fatigue properties of z-pinned composites. Improvements to the delamination fatigue properties come at the expense of lower in-plane fatigue performance, and this is a key consideration for the design of z-pinned aerospace composite structures.
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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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Kinawy, Moustafa, Richard Butler i Giles W. Hunt. "Bending strength of delaminated aerospace composites". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 370, nr 1965 (28.04.2012): 1780–97. http://dx.doi.org/10.1098/rsta.2011.0337.
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Buckling-driven delamination is considered among the most critical failure modes in composite laminates. This paper examines the propagation of delaminations in a beam under pure bending. A pre-developed analytical model to predict the critical buckling moment of a thin sub-laminate is extended to account for propagation prediction, using mixed-mode fracture analysis. Fractography analysis is performed to distinguish between mode I and mode II contributions to the final failure of specimens. Comparison between experimental results and analysis shows agreement to within 5 per cent in static propagation moment for two different materials. It is concluded that static fracture is almost entirely driven by mode II effects. This result was unexpected because it arises from a buckling mode that opens the delamination. For this reason, and because of the excellent repeatability of the experiments, the method of testing may be a promising means of establishing the critical value of mode II fracture toughness, G IIC , of the material. Fatigue testing on similar samples showed that buckled delamination resulted in a fatigue threshold that was over 80 per cent lower than the static propagation moment. Such an outcome highlights the significance of predicting snap-buckling moment and subsequent propagation for design purposes.
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Fan, Xue Ling, i Qin Sun. "Study on Mixed-Mode Interlaminar Fracture of Laminated Composites". Applied Mechanics and Materials 110-116 (październik 2011): 1345–52. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.1345.
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The superposition-finite element method is developed to analyze the mixed-mode delamination in laminated composites. Both a coarse global mesh and an overlaying fine local mesh are integrated into the finite element analysis model. The whole design domain is discretized by a uniform global mesh, while the high stress regions are discretized by fine local meshes. Local mesh is built independently from the global mesh, which greatly simplifies the model generation procedures. Strain energy release rate is calculated based on the modified virtual crack closure-integral method, which is used to describe the propagation of delamination in laminated composites. Mixed-mode bending tests are performed for unidirectional and cross-ply carbon fiber reinforced laminated composites to characterize the interlaminar fracture behavior under mixed-mode I/II loading conditions. The interlaminar fracture toughness is also given for different mixed-mode ratio. It is seen that fracture resistance for laminated composites exhibit R-curve behavior (increase as delamination propagation). However, once the delamination is sufficiently long, the interfacial fracture toughness changes slightly as the delamination extended and become almost independent of the delamination length. The results of finite element method are in good agreement with the experimental results and provides a basis for establishing failure criterion used in damage tolerance analysis of composite structures.
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Saravana Kumar, A., P. Maivizhi Selvi i L. Rajeshkumar. "Delamination in Drilling of Sisal/Banana Reinforced Composites Produced by Hand Lay-Up Process". Applied Mechanics and Materials 867 (lipiec 2017): 29–33. http://dx.doi.org/10.4028/www.scientific.net/amm.867.29.
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Natural fiber composites are presently replacing the synthetic fiber in many fields. The present research work study is an attempt to manufacture and test the sisal/banana fiber reinforced polymer composites. Composite have been manufactured using banana and sisal fiber along with epoxy resin as reinforcement. With these composites drilling has been carried out to study the factors and combination of factors that influence the delamination of drilled unidirectional sisal-banana fiber reinforced composites. Drilling experiments were performed based on the L9-Taguchi method. Delamination factor evaluated for the selected parameters spindle speed, feed and diameter of the drill tool with the help of signal to noise ratio, ANOVA analysis and to obtain the conditions for minimum delamination.
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Ovali, Ismail, i Ahmet Mavi. "Machinability Analysis in Drilling Glass/Epoxy Composites with Filled MWCNTS". Materials Science Forum 900 (lipiec 2017): 110–15. http://dx.doi.org/10.4028/www.scientific.net/msf.900.110.
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Drilling is the most used machining process in the assemble of Glass/epoxy composites. Material removing leads to damage and delamination in the drilling process. The present paper deals the effect of drill wt.% of multi walled carbon nanotubes (MWCNTs) on the drilling of glass/epoxy composites in term of torque and push-out delamination. Glass/epoxy composites manufactured by using pre-preg method. The filled rates were considered as 0.5, 1 and 2 wt.%. MWCNTs. Also, the unfilled composite samples were used for comparison. Various cutting speeds (40, 50 and 60 m/min) and feed rates (0.075, 0.1 and 0,125 mm/rev) for coated drills were used. The experimental result showed that the machinability properties of glass/epoxy composites samples can be improved with filling MWCNTs. Higher cutting speed and feed rate increase delamination. Push-out more severe than that of peel-up delamination.
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Dahlen, Christian, i George S. Springer. "Delamination Growth in Composites under Cyclic Loads". Journal of Composite Materials 28, nr 8 (maj 1994): 732–81. http://dx.doi.org/10.1177/002199839402800803.
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A semi-empirical model was developed for estimating the growth of delaminations inside fiber reinforced organic matrix composites subjected to cyclic loads. At any point on the circumference of the delamination mode I, mode II or mixed mode conditions may exist. The form of the proposed delamination growth model follows Elber's expression for the growth of a mode I crack in an aluminum sheet. By employing dimensional analysis, the parameters were established which are to be included in the model. The expression obtained depends on the material properties (transverse tensile ply strength, transverse tensile ply modulus, longitudinal ply shear strength, critical energy release rates) and on the energy release rate at the location under consideration. Tests were conducted with Fiberite T300/976 and IM7/977-2 graphite epoxy composites under mode I, mode II and mixed mode conditions using double cantilever beam, end notched cantilever beam, and mixed mode bending test coupons subjected to both static and cyclic loads. From these tests, first, the constants needed in the model were determined. Second, data were generated and compared to predictions of the model, and good agreement was found between the measured and predicted delamination growths. Results of the present model were also compared to data reported previously, and the model predictions agreed well with these previous data.
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Ji, Ai Hong, Min Lu, Meng Zha, Ben Zheng Dong, Li Hong Gao i Zhen Dong Dai. "Model I Interlaminar Fracture Toughness of Carbon Fiber Reinforced Polymer Matrix Composites". Advanced Materials Research 887-888 (luty 2014): 81–85. http://dx.doi.org/10.4028/www.scientific.net/amr.887-888.81.
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Carbon fiber reinforced polymer matrix composites have been widely used in many fields. It is necessary to test the performance of interlaminar fracture toughness of composites and provide useful information for product development and material selection. In this paper polymer matrix films embedding with carbon fiber reinforced composite laminates curing at high temperature were used to study the performance of model I inter-laminar fracture toughness. Mode I interlaminar fracture toughness of composites reinforced by carbon fiber was measured according to ASTM D5528 standard. Three groups of samples cut into double cantilever beam (DCB) specimens were measured to compare their performance. The results showed that there was no fiber-bridging in multidirectional composite laminations. The delamination for all specimens extended slowly and stably. All of three groups of carbon fiber composites had strong model I interlaminar fracture toughness and high delamination tolerances. The sensitive to delamination is different because of different composition of these three carbon fiber reinforced composites.
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Sellitto, Andrea, Aniello Riccio, A. Russo, Antonio Garofano i Mauro Zarrelli. "Nanofillers’ Effects on Fracture Energy in Composite Aerospace Structures". Key Engineering Materials 827 (grudzień 2019): 43–48. http://dx.doi.org/10.4028/www.scientific.net/kem.827.43.
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Composite materials damage behaviour is, nowadays, extensively investigated in the frame of aerospace research programmes. Among the several failure mechanisms which can affect composites, delamination can be considered as the most critical one, especially when combined to compressive loading conditions. In this context, nanofillers can represent an effective way to increase the composites fracture toughness with a consequent reduction of the delamination onset and evolution. Hence, in this paper, the toughening effect of the nanofillers on the delamination growth in composite material panels, subject to compressive load, has been numerically studied. A validated robust numerical procedure for the prediction of the delamination growth in composite materials panel, named SMXB and based on the VCCT-Fail release approach, has been used to perform numerical analyses by considering two different types of nanofillers. Reference material, without nanofillers insertion, has been used as benchmark in order to assess the capability of nanofillers to enhance the fracture toughness in composite laminates.
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Saadati, Yousef, Jean-Francois Chatelain, Gilbert Lebrun, Yves Beauchamp, Philippe Bocher i Nicolas Vanderesse. "A Study of the Interlaminar Fracture Toughness of Unidirectional Flax/Epoxy Composites". Journal of Composites Science 4, nr 2 (5.06.2020): 66. http://dx.doi.org/10.3390/jcs4020066.
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Having environmental and economic advantages, flax fibers have been recognized as a potential replacement for glass fibers as reinforcement in epoxy composites for various applications. Its widening applications require employing failure criteria and analysis methods for engineering design, analysis, and optimization of this material. Among different failure modes, delamination is known as one of the earliest ones in laminated composites and needs to be studied in detail. However, the delamination characteristics of unidirectional (UD) flax/epoxy composites in pure Mode I has rarely been addressed, while Mode II and Mixed-mode I/II have never been addressed before. This work studies and evaluates the interlaminar fracture toughness and delamination behavior of UD flax/epoxy composite under Mode I, Mode II, and Mixed-mode I/II loading. The composites were tested following corresponding ASTM standards and fulfilled all the requirements. The interlaminar fracture toughness of the composite were determined and validated based on the specific characteristics of natural fibers. Considering the variation in the composite structure configuration and its effects, the results of interlaminar fracture toughness fit in the range of those reported for similar composites in the literature and provide a basis for the material properties of this composite.
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Jain, S., i D. C. H. Yang. "Effects of Feedrate and Chisel Edge on Delamination in Composites Drilling". Journal of Engineering for Industry 115, nr 4 (1.11.1993): 398–405. http://dx.doi.org/10.1115/1.2901782.
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Delamination accompanied with the drilling of composite laminates has been recognized as a major problem. An analytical model is established to predict critical thrust force and critical feedrate at which the delamination crack begins to propagate. For unidirectional composites, the delamination zone is modeled as an elliptical plate, with clamped edges and subjected to a central load. Based on fracture mechanics, laminated plate theory and cutting mechanics, expressions are developed for critical thrusts and critical feedrates at which delamination is initiated at different ply locations. This model has been verified by experiments. A variable feedrate strategy is formulated based on this model, which avoids delamination while drilling in a time-optimal fashion. In addition, the need to modify tool geometry to avoid delamination is highlighted. Chisel edge width has been identified as an important factor contributing to the thrust force and hence delamination.
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Deniz, Mehmet Emin, i Nevra Oral. "Buckling behavior of laminated composites with embedded delaminations". Materials Testing 64, nr 5 (1.05.2022): 736–45. http://dx.doi.org/10.1515/mt-2021-2089.
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Abstract The aim of this study is to determine the structural effects of different delamination types on buckling behavior of the E-glass/epoxy with [0]8, [90]8, [±45]4 orientation angles and aramid/epoxy with [±45]4 orientation angle of the composite plates. The buckling behaviors of the layered composites with three different artificial delamination geometries namely, RECDel (rectangular delamination), SQRDel (square delamination), and CIRDel (circle delamination) as well as with different delamination locations (at depth ratios of t/h = 0.25 and t/h = 0.5) were investigated under compression load experimentally. The boundary conditions were clamped for loaded ends while they were freed for the other edges. The dimensions of rectangular composite plates were selected as 150 mm (L) × 25 mm (b) × 2.32 mm (h). Five specimens for each parameter of delaminated composite plates were tested to get the average buckling load. The test results showed that load values of the aramid/epoxy load values were higher than load values of the glass/epoxy load values regardless of the similarity of the buckling loads for t/h = 0.25 and t/h = 0.5 depth ratios. Furthermore, it is possible to conclude that the performance of both the glass/epoxy and the aramid/epoxy buckling are strongly influenced by the layered orientation configurations.
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Kopparthi, Phaneendra Kumar, Srikar Gemaraju, Bhaskara Rao Pathakokila i Suresh Gamini. "Failure analysis of delaminated carbon/epoxy composite under pure bending: validation with numerical analysis". Multidiscipline Modeling in Materials and Structures 17, nr 5 (6.07.2021): 974–89. http://dx.doi.org/10.1108/mmms-01-2021-0015.
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PurposeDelamination is a common and crucial damage mode which occurs during manufacturing of layered composites or their service life. Its existence leads to degradation in mechanical properties or even structural failure of composites. Hence, the purpose of this article is to study the effect of induced delamination on flexural performance of CFRP composites.Design/methodology/approachIn this article, the flexural behaviors of intact and delaminated carbon/epoxy laminates were investigated under pure bending. A circular PTFE film was introduced during fabrication to create artificial delamination. Moreover, finite element models were developed for intact and delaminated composites using ANSYS. The created models were discretized using 3D structural eight node solid elements.FindingsThe delamination influenced considerably flexural properties of composite. The composite exhibited a linear elastic nature prior to the damage of top ply on the compression side. The flexural strength and stiffness of the composite reduced to 44.5% and 18.2% respectively due to the existence of artificial delamination. The results of four point bending experiments and finite element analysis agreed for both intact and delaminated composites within acceptable error. Finally for same composites, first ply failure analysis was carried out using Tsai-Hill, Tsai-Wu and Hashin failure criteria.Originality/valueIn pure bending, beam section of the middle portion is free from shear. It is not so in case of three-point bending. Hence, the effect of embedded artificial defect on bending performance of CFRP composite due to pure bending has been investigated.
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Liu, Peng-fei, Jun Yang i Xiong-qi Peng. "Delamination analysis of carbon fiber composites under hygrothermal environment using acoustic emission". Journal of Composite Materials 51, nr 11 (10.08.2016): 1557–71. http://dx.doi.org/10.1177/0021998316661043.
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Non-destructive test technique for monitoring delamination failure under complex load and environments is still not mature until now. The purpose of this paper is to study mixed-mode delamination failure properties of carbon fiber/epoxy composite laminates under hygrothermal environment using acoustic emission. Different water-saturated composite specimens with initial intralaminar and interlaminar defects are tested. Two loading modes including single-leg and over-leg three-point bending are applied under hygrothermal environment. By analyzing the responses of acoustic emission parameters including amplitude and energy, the effects of the hygrothermal environment, layup pattern and initial defect on the delamination behaviors of composite specimens are studied. Besides, different failure modes are observed through scanning electron microscope. Quantitative acoustic emission results show hygrothermal environment and load mode affect the delamination properties of composites remarkably.
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Kim, Heung Soo, Jae Hwan Kim i Seung Bok Choi. "Characterization of Delamination in Laminated Composites Based on Damage Indices". Key Engineering Materials 321-323 (październik 2006): 925–29. http://dx.doi.org/10.4028/www.scientific.net/kem.321-323.925.
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A modal strain based damage index is proposed to investigate the damage effects of discrete delaminations in a laminated composite structure. The Fermi-Dirac distribution function is incorporated with an improved layerwise laminate theory to model smooth transition of the displacement and the strain fields at the delaminated interfaces. Modal analysis is conducted to investigate dynamic effects of delamination in a laminated structure and to obtain modal strains. The damage index is calculated based on fundamental modal strains of laminated structures. The damage effects of laminated structures are investigated using arbitrary size, number, location and boundary conditions of discrete delaminations.
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Gillespie, J. W., i L. A. Carlsson. "Buckling and Growth of Delamination in Thermoset and Thermoplastic Composites". Journal of Engineering Materials and Technology 113, nr 1 (1.01.1991): 93–98. http://dx.doi.org/10.1115/1.2903387.
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Compression instability growth of through-width delaminations in composite laminates is investigated. A previously developed beam model that incorporates effects of elastic restraint at the ends of the delamination is combined with a finite element superposition model that yields the Mode I (GI) and Mode II (GII) components of the strain energy release rate. Experimental data were generated for near surface delaminations over a wide range of crack lengths in unidirectional graphite/epoxy and graphite/PEEK laminates. Good agreement between experimentally observed critical loads for crack propagation and analytical predictions was observed using a linear mixed-mode crack growth criterion.
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Cornie, James A., Ali S. Argon i Vijay Gupta. "Designing Interfaces in Inorganic Matrix Composites". MRS Bulletin 16, nr 4 (kwiecień 1991): 32–38. http://dx.doi.org/10.1557/s0883769400057080.
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The key to controlling and predicting the properties of metal matrix composites lies in understanding and controlling the interface. When properly designed, the interface between reinforcing fibers and the matrix or protective coating can act as a mechanical fuse through a controlled delamination mechanism.Controlled delamination, in effect, results in the decoupling of fibers from early damage due to stress concentrations in the vicinity. The delamination event must precede the crack bridging and frictional pull-out mechanisms that have been so effectively demonstrated in ceramic matrix composites. The delamination event, therefore, is the necessary precondition, and so analysis of composite toughening must start with a definition of the conditions for interface debonding.This decoupling can be expressed in terms of cohesive strength of the interface, shear strength of the interface, and fiber fracture stress. In a related but alternative manner, debonding can be expressed in terms of the intrinsic work of fracture of the interface as compared to the transverse work of fracture of the fiber.
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Mitra, Nilanjan, Alak K. Patra, Satya P. Singh, Shyamal Mondal, Prasanta K. Datta i Shailendra K. Varshney. "Interfacial delamination in glass-fiber/polymer-foam-core sandwich composites using singlemode–multimode–singlemode optical fiber sensors: Identification based on experimental investigation". Journal of Sandwich Structures & Materials 22, nr 1 (29.09.2017): 40–54. http://dx.doi.org/10.1177/1099636217733983.
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Identification of interfacial delamination in the glass fiber/polymer-foam-core sandwich composites is difficult if the delamination does not propagate to the side surface of the specimen. However, these damages may eventually lead to compromising the sandwich composite structural component. A cost-effective novel embedded fiber optic sensor is being proposed in this manuscript, which works on the principle of multimode interference, to perform distributed sensing of interfacial delamination within the sandwich composites while in service. Even though this easy to use methodology has been used to identify interfacial delamination, this methodology can also be used for different other types of interfacial/interlaminar distributed strain sensing of samples under mechanical as well as thermal loads.
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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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Tan, Chye Lih, Azwan Iskandar Azmi i Noorhafiza Muhammad. "Critical Thrust Force for On-Set Delamination of Hybrid FRP Composite during Drilling Process". Key Engineering Materials 740 (czerwiec 2017): 111–17. http://dx.doi.org/10.4028/www.scientific.net/kem.740.111.
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Hole quality is one of the important criteria for hybrid composite components when assessing drilling behaviour because it influences the strength of composite parts post assembly. Nonetheless, some unique characteristics of hybrid Fibre-Reinforced Polymer (FRP) composites make them difficult to obtain the required quality and strict final dimensional accuracy. Based on previous studies, delamination has been recognized as one of the critical failure mechanisms in the drilling operation of FRP composites. It can often be the limiting factor for the final composite materials applications. Thus, in order to achieve a delamination-free in the drilling of hybrid FRP composites, an analytical model and a series of thrust force experiments are endeavoured in this study. The main purpose of the model is to compute the critical thrust force at the on-set of delamination during the drilling process. Results of this analytical study indicated that the delamination damage can be alleviated if the applied thrust force is lower than the critical thrust force value. Importantly, a good agreement was evident between the estimated critical thrust force and the measured thrust force in this particular study.
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Tsao, Chung Chen, i You Qian Lin. "Taguchi Optimization of Machining Quality in Step Drilling of Composites Based on Membership Function". Applied Mechanics and Materials 284-287 (styczeń 2013): 533–37. http://dx.doi.org/10.4028/www.scientific.net/amm.284-287.533.
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Delamination-free hole is expected for composite parts using optimized drilling parameters due to an increase in composite structures production and in the need for higher quality machining. The influence of the various machining parameters (step angle, stage ratio, feed rate and spindle speed) on thrust force and equivalent delamination factor in step drilling composites was investigated in this study. The use of membership function based on Taguchi method to obtain the optimization of the process parameters by considering multiple performance characteristics has been reported. Finds based on the membership function show that the lowest thrust force of step drilling composites to be about 25.6 N and equivalent delamination factor about 1.005 pixel/pixel.
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Garcia, Cristobal, Irina Trendafilova, Andrea Zucchelli i Justin Contreras. "The effect of nylon nanofibers on the dynamic behaviour and the delamination resistance of GFRP composites". MATEC Web of Conferences 148 (2018): 14001. http://dx.doi.org/10.1051/matecconf/201814814001.
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Vibrations are responsible for a considerable number of accidents in aircrafts, bridges and other civil engineering structures. Therefore, there is a need to reduce the vibrations on structures made of composite materials. Delamination is a particularly dangerous failure mode for composite materials because delaminated composites can lose up to 60% of their strength and stiffness and still remain unchanged. One of the methods to suppress vibrations and preventing delamination is to incorporate nanofibers into the composite laminates. The aim of the present work is to investigate how nylon nanofibers affect the dynamic behaviour and delamination resistance of glass fibre reinforced polymer (GFRP) composites. Experiments and numerical simulations using finite element modelling (FEM) analysis are used to estimate the natural frequencies, the damping ratio and inter-laminar strength in GFRP composites with and without nylon nanofibers. It is found that the natural frequencies of the nylon nano-modified composites do not change significantly as compared to the traditional composites. However, nano-modified composites demonstrated a considerable increase in damping ratio and inter-laminar shear strength due to the incorporation of nylon nanofibers. This work contributes to the knowledge about the mechanical and dynamic properties of glass fibre reinforced polymer (GFRP) composites with nylon nanofibers.
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Mohsin, Muhammad Ameerul Atrash, Lorenzo Iannucci i Emile S. Greenhalgh. "Delamination of Novel Carbon Fibre-Based Non-Crimp Fabric-Reinforced Thermoplastic Composites in Mode I: Experimental and Fractographic Analysis". Polymers 15, nr 7 (23.03.2023): 1611. http://dx.doi.org/10.3390/polym15071611.
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Delamination, a form of composite failure, is a significant concern in laminated composites. The increasing use of out-of-autoclave manufacturing techniques for automotive applications, such as compression moulding and thermoforming, has led to increased interest in understanding the delamination resistance of carbon-fibre-reinforced thermoplastic (CFRTP) composites compared to traditional carbon-fibre-reinforced thermosetting (CFRTS) composites. This study evaluated the mode I (opening) interlaminar fracture toughness of two non-crimp fabric (NCF) biaxial (0/90°) carbon/thermoplastic composite systems: T700/polyamide 6.6 and T700/polyphenylene sulphide. The mode I delamination resistance was determined using the double cantilever beam (DCB) specimen. The results were analysed and the Mode I interlaminar fracture toughness was compared. Additionally, the fractographic analysis (microstructure characterisation) was conducted using a scanning electron microscope (SEM) to examine the failure surface of the specimens.
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Aravindh, S., i K. Umanath. "Delamination in Drilling of Natural Fibre Reinforced Polymer Composites Produced by Compression Moulding". Applied Mechanics and Materials 766-767 (czerwiec 2015): 796–800. http://dx.doi.org/10.4028/www.scientific.net/amm.766-767.796.
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Natural fibre composites today are replacing synthetic fibre composites due to superior properties of natural fibres such as low density, high specific strength and modulus, relative no abrasiveness, ease of fibre surface modification, and wide availability .Drilling is often required to facilitate the assembly of the parts to get the final product. however, drilling composite materials present a number of problems such as delamination associated with the characteristics of the material and with the used cutting parameters .The present investigation is an attempt to study the factors and combination of factors that influence the delamination of drilled unidirectional jute fibre reinforced composites using taguchi, signal to noise ratio, Anova analysis and to achieve the conditions for minimum delamination.
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Williams, J. G. "Fracture Mechanics of Composites Failure". Proceedings of the Institution of Mechanical Engineers, Part C: Mechanical Engineering Science 204, nr 4 (lipiec 1990): 209–18. http://dx.doi.org/10.1243/pime_proc_1990_204_099_02.
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A review of how fracture mechanics can be applied to the various fracture modes observed in composites is given. It is shown that rather conventional methods may be used for short-fibre composites but that oriented laminates undergo delamination, often parallel to the applied loads, and energy release rate methods must be used to analyse these failures. The importance of delamination toughness in determining composite behaviour is emphasized and details of the various test methods and analysis techniques are given. Finally, some discussion of the more complex failures seen in cross-ply laminates is presented.
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Balaji, N. S., S. Jayabal, S. Kalyana Sundaram, S. Rajamuneeswaran i P. Suresh. "Delamination Analysis in Drilling of Coir-Polyester Composites Using Design of Experiments". Advanced Materials Research 984-985 (lipiec 2014): 185–93. http://dx.doi.org/10.4028/www.scientific.net/amr.984-985.185.
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Drilling of fiber reinforced composite materials presents a plethora of questions to the engineers and scientists. A number of research endeavors have been made in the recent years to fully characterize the drilling process of fiber reinforced composite materials. The efforts have been made in the direction of optimization of the operating variables and conditions for minimizing the drilling induced damages. This paper presented the delamination analysis of drilled holes in coir fiber-reinforced polyester composites. The results indicated that the delamination factor in coir fiber-reinforced composites is lower comparing with glass fiber reinforced composites.
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Korlos, Apostolos, Dimitrios Tzetzis i Gabriel Mansour. "Investigation of the Electro-Discharge Open-Hole Machining on the Structural Behavior of Carbon Fiber Reinforced Polymers". Applied Mechanics and Materials 657 (październik 2014): 321–25. http://dx.doi.org/10.4028/www.scientific.net/amm.657.321.
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The current work investigates the electro-discharge machining (EDM) of plain woven carbon reinforced polymer composites with pulse durations of 100 μs, 200 μs, 300 μs, currents 1 A, 3 A and 5 A, and a voltage of 100 V. An x-ray computed tomography (CT) is employed to examine the delaminations, while a delamination factor model utilizing the equivalent delamination diameter provides the measuring quantity for assessment. Finite element simulations compute the stress concentrations around the holes by taking into account the delamination equivalent diameters of the open-holes, as monitored from the x-ray CT. The Whitney-Nuismer point stress criterion is utilised in order to predict the failure strength of the machined open-hole laminates and it is compared with the experimentally derived mechanical strength values. The results reveal that EDM is a feasible method for open-hole machining of composites, however proper selection of the operational parameters is needed. By accurately measuring the peripheral delamination areas of the machined holes, it is shown that the analysis of the mechanical behaviour of the plain woven laminates by the means of finite element method and the Whitney-Nuismer criterion can accurately predict the response of such composites when subjected to tensile loads.
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Tabatabaeian, Ali, Mohammad Baraheni, Saeid Amini i Ahmad R. Ghasemi. "Environmental, mechanical and materialistic effects on delamination damage of glass fiber composites: Analysis and optimization". Journal of Composite Materials 53, nr 26-27 (23.04.2019): 3671–80. http://dx.doi.org/10.1177/0021998319844811.
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Machining process of glass fiber composites usually induces delamination damage. The presence of delamination may cause changes in the mechanical characteristics of the composite structures. In this research, a comprehensive experimental study is performed to analyze the influence of different parameters such as thermal fatigue, lay-up arrangement, resin type, feed rate and cutting velocity on the delamination of glass fiber composites under different drilling processes. Besides, influence of ultrasonic vibration exerting on the tool as a new and high-tech process is investigated. To follow this aim, different composite specimens with various resin types and lay-up arrangements are fabricated and a thermal fatigue condition is provided. Additionally, the Taguchi method is employed to obtain the optimized damage reduction condition in terms of mentioned parameters. The results indicated that thermal fatigue and unsymmetrical lay-up arrangement result in more delamination damage. It was also established that the influence of mentioned parameters is more considerable in higher cutting velocities. Moreover, ultrasonic vibration application is suggested to have the least delamination damage.
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Gao, Tianfang, Yishou Wang i Xinlin Qing. "A New Laser Ultrasonic Inspection Method for the Detection of Multiple Delamination Defects". Materials 14, nr 9 (6.05.2021): 2424. http://dx.doi.org/10.3390/ma14092424.
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Delamination is one of the most common types of defects for carbon fiber reinforced plastic (CFRP) composites. The application of laser techniques to detect delamination faces difficulties with ultrasonic wave excitation because of its low thermal conductivity. Much of the research that can be found in the literature has only focused on the detection of a single delamination. In this study, aluminum foil was pasted onto the surface of the composite so that it was vulnerable to ablation and could acquire a usable signal. Using a fully noncontact system with laser excitation at a fixed point and a scanning laser sensor, the effects of different aluminum foil sizes and shapes on the wavefield were studied for the composites; we decided to use a rectangle with 3 mm length and 5 mm width for laser excitation experiments. Wavefield characteristics of the composite plates were analyzed with single- and multi-layered Teflon inserts. Taking the time window for standard ultrasonic testing as a reference, the algorithms for localized wave energy with appropriate time windows are presented for the detection of single and multiple defects. The appropriate time window is meaningful for identifying each delamination defect. The algorithm performs well in delamination detection of the composites with one or multiple Teflon inserts.
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Žmindák, Milan, Vladimir Dekýš i Pavol Novák. "Fracture Mechanics Approach for Analysis of Delamination in Composite Plates". Advanced Materials Research 969 (czerwiec 2014): 176–81. http://dx.doi.org/10.4028/www.scientific.net/amr.969.176.
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Delamination can be a substantial problem in designing composite structures. Modelling of delamination by finite element (FE) codes is limited. Previous efforts to model delamination and debonding failure modes using FE codes have typically relied on ad hoc failure criteria and quasi-static fracture data. Improvements to these modelling procedures can be made by using an approach based on fracture mechanics. A study of modelling delamination using the FE code ANSYS was conducted. This investigation demonstrates the modelling of composites through improved delamination modelling. Further developments to this approach may be improved.
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Marino, Salvatore Giacomo, Florian Mayer, Alexander Bismarck i Gergely Czél. "Effect of Plasma-Treatment of Interleaved Thermoplastic Films on Delamination in Interlayer Fibre Hybrid Composite Laminates". Polymers 12, nr 12 (28.11.2020): 2834. http://dx.doi.org/10.3390/polym12122834.
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Safe, light, and high-performance engineering structures may be generated by adopting composite materials with stable damage process (i.e., without catastrophic delamination). Interlayer hybrid composites may fail stably by suppressing catastrophic interlayer delamination. This paper provides a detailed analysis of delamination occurring in poly(acrylonitrile-butadiene-styrene) (ABS) or polystyrene (PS) film interleaved carbon-glass/epoxy hybrid composites. The ABS films toughened the interfaces of the hybrid laminates, generating materials with higher mode II interlaminar fracture toughness (GIIC), delamination stress (σdel), and eliminating the stress drops observed in the reference baseline material, i.e., without interleaf films, during tensile tests. Furthermore, stable behaviour was achieved by treating the ABS films in oxygen plasma. The mechanical performance (GIIC and σdel) of hybrid composites containing PS films, were initially reduced but increased after oxygen plasma treatment. The plasma treatment introduced O-C=O and O-C-O-O functional groups on the PS surfaces, enabling better epoxy/PS interactions. Microscopy analysis provided evidence of the toughening mechanisms, i.e., crack deflection, leading plasma-treated PS to stabilise delamination.
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Grasso, Marzio, i Yigeng Xu. "Threshold Identification and Damage Characterization of Woven GF/CF Composites under Low-Velocity Impact". Journal of Composites Science 6, nr 10 (11.10.2022): 305. http://dx.doi.org/10.3390/jcs6100305.
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The Delamination Threshold Load (DTL) is a key parameter representing damage resistance of a laminate and is normally identified by locating a sudden drop in the impact force-time history for the laminate made of unidirectional layers. For the woven composite, however, their failure mechanisms appear different and the current literature is not providing any clear procedure regarding the identification of the delamination initiation, as well as the evolution of the failure mechanisms associated with it. In this paper, experimental data have been collected using woven glass and carbon fiber composites. The results are analyzed in terms of force-time and force-displacement curves. While delamination and other damages were clearly observed using ultrasonic scans, the analysis of the results does not reveal any trend changes of the curves that can be associated with the incipient nucleation of delamination. A preliminary discussion regarding the nature of the mechanisms through which the delamination propagates in woven composite and a justification for the absence of a sudden change of the stiffness have been presented. It raises a question on the existence of DTL for woven composites under low velocity impact.
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Bilisik, Kadir, Nesrin S. Karaduman i Erdal Sapanci. "Flexural characterization of 3D prepreg/stitched carbon/epoxy/multiwalled carbon nanotube preforms and composites". Journal of Composite Materials 53, nr 5 (13.07.2018): 563–77. http://dx.doi.org/10.1177/0021998318787861.
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The effect of through-the-thickness stitching and incorporation of multiwalled carbon nanotubes (MWCNTs) on the flexural properties of three-dimensional (3D) carbon/epoxy composites was studied. The flexural strength of the carbon twill fabric composites was improved by stitching due largely to delamination suppression, whereas stitching negatively influenced the flexural strength of the carbon satin fabric composites due to stitch-induced irregularities and fiber breakages. The failure mode of the unstitched base (without MWCNTs) and unstitched nano-added structures involved fiber breakage, matrix cracking, and delamination, while the stitched base and stitched nano-added samples exhibited lateral matrix cracking, multiple warp, and stitch yarn breakages with less delamination compared with unstitched structures. The results showed that both stitching and the incorporation of MWCNTs improved the out-of-plane failure properties due largely to restricted delamination. Therefore, stitching and MWCNTs can effectively be used to increase the damage tolerance of carbon fiber/epoxy composite laminates.