• Composites Research
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• v.18 no.2
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• pp.1-12
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• 2005

Fracture behaviors of single-edge-notched monolithic aluminum plates and glass fiber/aluminum laminates under tensile loadings have been studied using acoustic emission(AE) monitoring. AE signals from monolithic aluminum could beclassified into two different types. For glass fiber/aluminum laminates, AE signals with high amplitude and long duration were additionally confirmed on FFT frequency analysis, which corresponded to macrocrack propagation and/or delamination. AE source location determined by signal arrival time showed the zone of fracture. On the basis of the above AE analysis and fracture observation, characteristic features of fracture processes of single-edge-notched glass fiber/aluminum laminates were elucidated according to different fiber ply orientations and fiber/aluminum lay-up ratios.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.4
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• pp.274-286
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• 2005

Fracture behaviors and acoustic emission (AE) characteristics of single-edge-notched monolithic aluminum plates and glass fiber/aluminum hybrid laminate plates have been investigated under tensile loads. AE signals from monolithic aluminum could be classified into two different types: signals with low frequency band and high frequency band. High frequency signals were detected in the post stage of loading beyond displacement of 0.45mm. For glass fiber/aluminum laminates, AE signals with high amplitude and long duration were additionally confirmed on FFT frequency analysis, which corresponded to macro-crack propagation and/or delamination between A1 and fiber layers. On the basis of the above AE analysis and fracture observation with optical microscopy and ultrasonic T scan, characteristic features of AE associated with fracture processes of single-edge-notched glass fiber/aluminum laminates were elucidated according to different fiber ply orientations.

• Aerospace Engineering and Technology
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• v.13 no.1
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• pp.20-26
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• 2014

In this paper, yield stress, tangent modulus and failure strain were varied to ascertain the influence of impact response such as impact force histories and residual energy. And the buckling behavior of FML(Fiber Metal Laminates) were analyzed using numerical method. A number of analyses on FML and aluminum panel were conducted for shear and compression loading to compare the capability of stability. And to evaluate the static performance, static analysis has performed for box beam structure. Low-velocity impact analysis has performed on FML made of aluminum 2024 sheet and glass/epoxy prepreg layers. And the buckling and static performance of FML have been compared to aluminum using the analysis results. For the comparison of structural performance, similar analyses have been carried out on monolithic aluminum 2024 sheets of equivalent weight.

• Composites Research
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• v.14 no.6
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• pp.38-46
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• 2001

In this study, An optimization code that can design microwave absorbing composite laminates is developed, and 3-layered microwave absorbing composite laminates are developed by optimizing the thickness of each layer. The layers are 3 different composite laminates. Many variables including lay-up angles of electromagnetically orthotropic composite layer can be considered in this code. The developed laminate is composed of an impedance matching layer of glass/epoxy fabric laminate, a glass/epoxy fabric laminate layer containing aluminum filler and carbon/epoxy fabric laminate layer. Permittivities of the materials are obtained using a network analyzer and a coaxial air line.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.6 s.237
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• pp.876-888
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• 2005

Tensile properties and fracture toughness of monolithic aluminum, fiber reinforced plastics and glass fiber/aluminum hybrid laminates under tensile loads have been investigated using plain coupon and single-edge-notched specimens. Elastic modulus and ultimate tensile strength of GFMLs showed different characteristic behaviors according to the Al kind, fiber orientation and composition ratio. Fracture, toughness of A-GFML-UD which was determined by the evaluation of $K_{IC}$ and $G_{IC}$ based on critical load was similar to that of GFRP-UD and was much higher than monolithic Al. Therefore, A-GFML-UD presented superior fracture toughness as well as prominent damage tolerance in comparison to its constituent Al. By separating Al sheet from GFMLs after the test, optical microscope observation of fracture zone of GFRP layer in the vicinity of crack tip revealed that crack advance of GFMLs depended on the orientation of fiber layer as well as Al/fiber composition ratio.

• Composites Research
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• v.12 no.1
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• pp.47-58
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• 1999

This paper describes the results of experiments to analyze the free vibration of the laminated composite and hybrid composite plates with various shapes and boundary conditions. The materials of specimens were the carbon fiber reinforced plastic (CFRP), the glass fiber reinforced plastic (GFRP), the GFRP-Aluminum hybrid composite and the CFRP-CFRP hybrid composite. The natural frequencies and nodal patterns of plates with various shapes were experimentally obtained by impact exciting test using an impact hammer and an accelerometer. The experimental results were presented with normalized frequency parameters. The effects of composite material properties, fiber orientation angles, various geometrical shapes and boundary conditions on the vibration characteristics of composite plates were evaluated. To compare and verify these experimental results, the finite element analysis was carried out, and was well agreed with experimental results.

• Composites Research
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• v.22 no.6
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• pp.23-31
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• 2009

This paper investigated acoustic emission (AE) characteristics in association with various fracture processes of glass fiber reinforced plastic skin/ aluminum honeycomb core (GF-AH) hybrid composites under compressive and bending loads. Various failure modes such as skin layer fracture, skin/core interfacial fracture, and local plastic yield buckling and cell wall adhesive fracture occurring in the honeycomb cell wall were classified through the fracture identification in association with the AE frequency and amplitude analysis. The distribution of the event-rate in which it has a high amplitude showed a procedure of cell wall adhesive fracture, skin/core interfacial debonding and fiber breakage, whereas distribution of different peak frequencies indicated the plastic deformation of aluminum cell wall and the friction between honeycomb walls. Consequently, the fracture behaviors of GF-AH hybrid composites could be characterized through a nondestructive evaluation employing the AE technique.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1A
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• pp.11-18
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• 2012

This paper deals with the numerical determination of the stress intensity factors of cracked aluminum plates under the mixed mode of $K_I$ and $K_{II}$ in glass-epoxy fiber reinforced composites. For the stress intensity factors, two different models are reviewed such as VCCT and two-step extension method. The p-convergent partial layerwise model is adopted to determine the fracture parameters in terms of energy release rates and stress intensity factors. The p-convergent approach is based on the concept of subparametric element. In assumed displacement field, strain-displacement relations and 3-D constitutive equations of a layer are obtained by combination of 2-D and 1-D higher-order shape functions. In the elements, Lobatto shape functions and Gauss-Lobatto technique are employed to interpolate displacement fields and to implement numerical quadrature. Using the models and techniques considered, effects of composite laminate configuration according to inclined angles and adhesive properties on the performance of bonded composite patch are investigated. In addition to these, the out-of-plane bending effect has been investigated across the thickness of patch repaired laminate plates due to the change of neutral axis. The present model provides accuracy and simplicity in terms of stress intensity factors, stress distribution, number of degrees of freedom, and energy release rates as compared with previous works in literatures.