• Progress in Superconductivity and Cryogenics
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• v.19 no.2
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• pp.25-28
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• 2017

In superconducting coil applications particularly in wet wound coils, coated conductor (CC) tapes are subjected to different type of stresses that could affect its electromechanical transport property. These include hoop stress acting along the length of the CC tape and the Lorentz force acting perpendicular to the CC tape's surface. Since the latter is commonly associated with the delamination problem of multi-layered REBCO CC tapes, more understanding and attention on the delamination phenomena induced in the case of coil applications are needed. Difference on the coefficient of thermal expansion (CTE) of each constituent layer of the CC tape, the bobbin, and the impregnating materials is the main causes of delamination in CC tapes when subjected to thermal and mechanical cycling. In the design of degradation-free superconducting coils, therefore, characterization of the delamination behaviors including mechanism and strength in the multi-layered REBCO CC tapes becomes a critical issue. Various trials to increase the delamination strength by improving interface characteristics at interlayers have been performed. In this study, in order to investigate the influences of laser cleaning and Ag annealing treated at the substrate side surface, transverse tensile tests were conducted under different sample configurations using $4.5mm{\times}8mm$ upper anvil. The mechanical delamination strength of differently processed CC samples was examined at room temperature (RT). As a result, the Sample 1 with the additional laser cleaning and Ag annealing processes and the Sample 2 with additional Ag annealing process only showed higher mechanical delamination strength as compared to the Sample 3 without such additional treatments. Sample 3 showed quite different behavior when the loading direction is to the substrate side where the delamination strength much lower as compared to other cases.

• Advances in aircraft and spacecraft science
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• v.3 no.1
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• pp.15-28
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• 2016

Although the aircraft industry was the first to use fibre composites, now they are increasingly used in a range of structural applications such as flooring, decking, platforms and roofs. Interlayer delamination is a major failure mode which threatens the reliability of composite structures. Delamination can grow in size under increasing loads with time and hence leads to severe loss of structural integrity and stiffness reduction. Delamination reduces the natural frequency and as a consequence may result in resonance. Hence, the study of the effects of delamination on the free vibration behaviour of multilayer composite structures is imperative. The focus of this paper is to develop a 3D FE model and investigate the free vibration behaviour of fibre composite multilayer sandwich panels with interlayer delaminations. A series of parametric studies are conducted to assess the influence of various parameters of concern, using a commercially available finite element package. Additionally, selected points in the delaminated region are connected appropriately to simulate bolting as a remedial measure to fasten the delamination region in the aim of reducing the effects of delamination. First order shear deformation theory based plate elements have been used to model each sandwich layer. The findings suggest that the delamination size and the end fixity of the plate are the most important factors responsible for stiffness reduction due to delamination damage in composite laminates. It is also revealed that bolting the delaminated region can significantly reduce the natural frequency variation due to delamination thereby improving the dynamic performance.

• Composites Research
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• v.34 no.3
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• pp.143-147
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• 2021

Full width half maximum (FWHM) analysis of superimposed terahertz (THz) signals in the glass fiber reinforced polymer (GFRP) was studied to detect fine delamination inside GFRP. The THz signals were measured for each fine delamination size inside the GFRP using the reflection mode of the terahertz time domain spectroscopy (THz-TDS) system. Then, the FWHM of the superimposed THz signal reflected at the fine delamination was extracted. Thereafter, the complex refractive index of the GFRP was measured using transmission mode of the THzTDS system. Based on this, the FWHM of the superimposed THz signal at the fine delamination were calculated and compared with respect to the fine delamination size. From the theoretically calculated superimposed signals, the relationship between the fine delamination size and the FWHM in the superimposed THz signal was derived. Consequently, the fine delamination size could be predicted through the analysis of the FWHM extracted from the THz signal at the fine delamination.

• Structural Engineering and Mechanics
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• v.87 no.1
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• pp.47-56
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• 2023

Any pre-existed delamination defect present during manufacturing or induce during service loading conditions in the wingskin adherend invariably shows a greater loss of structural integrity of the spar wingskin joint (SWJ). In the present study, inter-laminar delamination propagation at the critical location of the SWJ has been carried out using contact and multi-point constraint finite elements available with commercial FE software (ANSYS APDL). Strain energy release rates (SERR) based on virtual crack closure technique have been computed for evaluation of the opening (Mode-I), sliding (Mode-II) and cross sliding (Mode-III) modes of delamination by sequential release of multi point constraint elements. The variations of different modes of SERR are observed to be significant by considering varied delamination lengths, material properties of adherends and radius of curvature of the SWJ panel. The SERR rates are seen to be much different at the two pre-embedded delamination ends. This shows dissimilar delamination propagation rates. The maximum is seen to occur in the delamination front in the unstiffened region of the wingskin. The curvature geometry and material anisotropy of SWJ adherends significantly influences the SERR values. Increase in the SERR values are observed with decrease in the radius of curvature of wingskin panel, keeping its width unchanged. SWJs made with flat FRP composite adherends have superior resistance to delamination damage propagation than curved composite laminated SWJ panels. SWJ made with Boron/Epoxy (B/E) material shows greater resistance to the delamination propagation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.46-49
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• 2008

Drawing process of the high carbon steel wire with high speed is usually performed at room temperature using multi pass. Tn the multi pass drawing, temperature rise affects the mechanical properties of the final product. The excessive temperature rise during the deformation promotes the occurrence of delamination, and deteriorates the torsion property and durability of wire. This paper investigates the occurrence of delamination in the wire through the torsion test and the evaluation of wire temperature. The excessive wire temperature ieads to the occurrence of delamination. Based on the calculation of the wire temperature, a new pass schedule, that can prevent the delamination due to the excessive wire temperature rise, is designed through the isothermal pass schedule.

• Journal of the Korean Society of Safety
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• v.28 no.6
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• pp.36-41
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• 2013

Previous study showed that delamination region in concrete structures can be successfully visualized using mode shapes of delaminated concrete section. However, modal tests for this purpose to obtain mode shapes of the delaminated concrete section may not be applicable in practice since, to correctly obtain the mode shapes of the section, the location and the shape of the delamination region in a structure should be known in advance. Unfortunately those are normally unknown in a real structure. Therefore, a moving forward test method may be useful to obtain the mode shapes of the concrete section when the location and the shape of the delamination region are not known. In this study, impact-echo testing based mode shape estimation technique is proposed and experimentally validated for visualization of delamination region.

• Structural Engineering and Mechanics
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• v.67 no.5
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• pp.545-553
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• 2018

Mode II delamination propagation is an important damage mode in laminated composites and this paper aims to investigate the behavior of this damage in laminated composite materials using acoustic emission (AE) technique. Three different lay-ups of glass/epoxy composites were subjected to mode II delamination propagation and generated AE signals were recorded. In order to investigate the propagation of delamination behavior of these specimens, AE signals were analyzed using Wavelet Packet Transforms (WPT) and Fast Fourier Transform (FFT). In addition, conventional AE analyses were used to enhance understanding of the propagation of delamination damage. The results indicate that different fracture mechanisms were the main cause of the AE signals. The dominant mechanisms in all the specimens were matrix cracking, fiber/matrix debonding and fiber breakage, with varying percentage of the damage mechanisms for each lay-up. Scanning Electron Microscopy (SEM) observations were in accordance to the AE results.

• Journal of the Korean Society for Nondestructive Testing
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• v.13 no.1
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• pp.21-28
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• 1993

If the infinitesimal delamination exists and the two waves can hardly be distinguished from each other on account of being much closer, we cannot measure the thickness of delamination by the time difference method. On this study, we calculated the thickness of infinitesimal delamination model by means of measuring echo height due to the deflection of material particles and utilized Newton Ring for optical measurement as a delamination model. From the result of Newton Ring expressed in the delamination model, we can calculate the infinitesimal delamination thickness up to $0.2{\sim}0.3{\mu}m$ due to the difference of acoustic impedance by the ratio of the echo height to the total reflection.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.2
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• pp.140-146
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• 1982

The purpose of this study is to investigate the free edge delamination of the laminated composites under uniaxial strain. The laminate is modeled as a set of anisotropic layers with isotropic adhesive layers. Interlaminar stresses are calculated for laminate with various laminate parameters by using two dimensional finite difference method. The redistribution of interlaminar stresses after delamination and the relation between delamination any ply failure are obtained for [.+-.45.deg.]$_{s}$, [0.deg./.+-./.+-.45.deg./90.deg.]$_{s}$ and [0.deg./45.deg./90.deg/45.deg.]$_{s}$ laminates. It was found that delamination can not propagate the entire width of the laminate under the static loading condition.ition.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.05a
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• pp.800-804
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• 2005

In this paper, the radiated sound pressure induced by low velocity impact is obtained by solving the Rayleigh integral equation. For structurally radiated noise, the sound field is directly coupled to the structural motion. Therefore the impact response should be analyzed. It is well known that the presence of the delamination in a composite laminate introduces a local flexibility which changes the dynamic characteristic of the structure. The 2-D simplified delamination model is used to analyze the impact response. And the 3-D non-linear finite element model is developed using gap element to avoid the overlap and penetration between the upper and lower sub-laminates at delamination region. Predicted impact response using 2-D equivalent delamination model are compared with the numerical ones from the 3-D non-linear finite element model.