• Composites Research
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• v.23 no.1
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• pp.8-16
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• 2010

The Fiber/Metal Laminates (FMLs) have been developed as a new composite material for aerospace application to reduce weight and improve damage tolerance. In this study, firstly FMLs were manufactured and the tensile test was performed to investigate the mechanical properties of FMLs. Furthermore, impact behavior of the low velocity on FMLs which consisted of different types of aluminum or fiber/epoxy layers was tested by the drop weight impact tester based on the different impact energy conditions. The load-time and energy-time curves were employed to evaluate the impact performance of different specimens. Moreover, finite element analysis (FEA) was also performed to simulate the tensile test and impact behavior of FMLs under the same conditions with the tests and good agreements have been obtained between the FEA predictions and experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.960-968
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• 2002

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, Al laminate was etched using FPL methods. The static indentation test were conducted by using UTM under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber breakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. The Angle ply FML has a critical cross-angle which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

• Composites Research
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• v.29 no.2
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• pp.45-52
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• 2016

An understanding of the failure mechanisms of the adhesive layer is decisive in interpreting the performance of a particular adhesive joint because the delamination is one of the most common failure modes of the laminated composites such as the fiber metal laminates. The interface between different materials, which is the case between the metal and the composite layers in this study, can be loaded through a combination of fracture modes. All loads can be decomposed into peel stresses, perpendicular to the interface, and two in-plane shear stresses, leading to three basic fracture mode I, II and III. To determine the load causing the delamination growth, the energy release rate should be identified in corresponding criterion involving the critical energy release rate ($G_C$) of the material. The critical energy release rate based on these three modes will be $G_{IC}$, $G_{IIC}$ and $G_{IIIC}$. In this study, to evaluate the fracture behaviors in the fracture mode I and II of the adhesive layer in fiber metal laminates, the double cantilever beam and the end-notched flexure tests were performed using the reference adhesive joints. Furthermore, it is confirmed that the experimental results of the adhesive fracture toughness can be applied by the comparison with the finite element analysis using cohesive zone model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.2 s.233
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• pp.220-227
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• 2005

In this study, stress-displacement analytic solutions are obtained by a shear lag modeling method constructed for the spliced joint area with a splicing gap in the fiber metal laminate (FML). This gap can be empty or be filled with an adhesive material of elastic modulus $E_a$. Two splicing types are considered for spliced shear models, one for spliced in the center metal layer, the other for spliced in the outer metal layer. It is shown that from the viewpoint of the load transfer efficiency and the avoidability of disbond generation due to the shear and axial stresses at the interface between metal layer and composite layer of the gap-front in the spliced area, the center spliced type (k=2) is much preferable to the outer spliced type (k=1).

• Transactions of Materials Processing
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• v.24 no.1
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• pp.52-61
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• 2015

Evaluation of the elevated temperature flow stress for thermoplastic fiber metal laminates(TFMLs) sheet, comprised of two aluminum sheets in the exterior layers and a self-reinforced polypropylene(SRPP) in the interior layer, was conducted. The flow stress as a function of temperature should be evaluated prior to the actual forming of these materials. The flow stress can be obtained experimentally by uniaxial tensile tests or analytically by deriving a flow stress model. However, the flow stress curve of TFMLs cannot be predicted properly by existing flow stress models because the deformation with temperature of these types of materials is different from that of a generic pure metallic material. Therefore, the flow stress model, which includes the effect of the temperature, should be carefully identified. In the current study, the flow stress of TFMLs were first predicted by using existing flow stress models such as Hollomon, Ludwik, and Johnson-Cook models. It is noted that these existing models could not effectively predict the flow stress. Flow stress models such as the modified Hollomon and modified Ludwik model were proposed with respect to temperatures of $23^{\circ}C$, $60^{\circ}C$, $90^{\circ}C$, $120^{\circ}C$. Then the stress-strain curves, which were predicted using the proposed flow stress models, were compared to the stress-strain curves obtained from experiments. It is confirmed that the proposed flow stress models can predict properly the temperature dependent flow stress of TFMLs.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.37-43
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• 2015

The purpose of the current study is to improve the clinching joint strength of aluminum and fiber metal laminates (FMLs) comprised of three layers. The joining of FML and Al 5052 by a conventional clinching joint has some disadvantages such as necking of the upper sheet, lack of interlocking, defects caused by the vertical load, and especially loss of strength of the composite material due to the low ductility. In the current study, a tapered-hole clinching method is proposed as an alternative for the joining of Al 5052 and FMLs. A hole with a tapered shape is formed before the joining process. The design parameters were evaluated using the Taguchi method for the geometry of the tapered hole in order to determine the maximum separation load. The diameter of the punch corner, clearance, punch stroke and the tapered length were used as the main variables in the Taguchi method. In conclusion, the contribution ratio for each of the fours variable examined was 35.07%, 22.44%, 21.32% and 14.11%, respectively. In addition, the appropriate combination of the design parameters can make a 5% improvement in the vertical direction joint strength.

• Structural Engineering and Mechanics
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• v.57 no.1
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• pp.45-63
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• 2016

Fiber metal laminates (FMLs) represent a high-performance family of hybrid materials which consist of thin metal sheets bonded together with alternating unidirectional fiber layers. In this study, the buckling behavior of a FML circular cylindrical shell under axial compression is investigated via both analytical and finite element approaches. The governing equations are derived based on the first-order shear deformation theory and solved by the Navier solution method. Also, the buckling load of a FML cylindrical shell is calculated using linear eigenvalue analysis in commercial finite element software, ABAQUS. Due to lack of experimental and analytical data for buckling behavior of FML cylindrical shells in the literature, the proposed model is simplified to the full-composite and full-metal cylindrical shells and buckling loads are compared with the available results. Afterwards, the effects of FML parameters such as metal volume fraction (MVF), composite fiber orientation, stacking sequence of layers and geometric parameters are studied on the buckling loads. Results show that the FML layup has the significant effect on the buckling loads of FML cylindrical shells in comparison to the full-composite and full-metal shells. Results of this paper hopefully provide a useful guideline for engineers to design an efficient and economical structure.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.204-209
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• 2001

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, Al laminate was etched using FPL methods. The static indentation test were conducted by using UTM(5ton, Shimadzu) under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber breakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. The Angle ply FML has a critical cross-angle which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.4
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• pp.592-601
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• 2001

Fiber reinforced metal laminates(FRMLs) are new types of hybrid materials. FRMLs consists of high strength metal(Al 5052-H34) and laminated fiber with structural adhesive bond. The mixture ratio effect of epoxy resin$.$curing agent$.$accelerator on the fatigue behavior of FRMLs was investigated in this study. The epoxy, diglycidylether of bisphenol A(DGEBA), was cured by methylene dianiline(MDA) with or without an accelerator(K-54). Eight different kinds of resin mixture ratios were selected for the test ; five kinds of FRMLs(1) and three others of FRMLs(2). The relationship between da/dN and ΔK with variation of resin mixture ratio was studied. FRMLs(1) and FRMLs(2) indicated approximately 2 times and 2.2 times more improved maximum bending strengths in comparison with those of Al 5052-H34. The resin mixture ratio <1:1> in case of FRMLs(1) indicated the maximum fatigue life, while the resin mixture ratio <1:1:0.2> in case of FRMLs(2) indicated the maximum fatigue life. As results, FRMLs(2) turned out to have more effective characteristics on the fatigue properties and the bending strength than those of FRMLs(1).

• Transactions of Materials Processing
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• v.23 no.5
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• pp.289-296
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• 2014

Uniaxial tensile tests were conducted to accurately evaluate the in-plane mechanical properties of fiber metal laminates (FMLs). The FMLs in the current study are comprised of a layer of self-reinforced polypropylene (SRPP) sandwiched between two layers of aluminum alloy 5052-H34. The nonlinear tensile behavior of the FMLs under in-plane loading conditions was investigated using both numerical simulations and a theoretical analysis. The numerical simulation was based on finite element modeling using the ABAQUS/Explicit code and the theoretical constitutive model was based on the volume fraction approach using the rule of mixture and a modification of the classical lamination theory, which incorporates the elastic-plastic behavior of the aluminum alloy and the SRPP. The simulations and the model are used to predict the inplane mechanical properties such as stress-strain response and deformation behavior of the FMLs. In addition, a post-stretching process is used to reduce the thermal residual stresses before uniaxial tensile testing of the FMLs. Through comparison of both the numerical simulations and the theoretical analysis with the experimental results, it is concluded that the numerical simulation model and the theoretical approach can describe with sufficient accuracy the actual tensile stress-strain behavior of the FMLs.