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This investigation presents the effect of different interlaminar hybridization and localized in-plane edge loads on the vibration and buckling characteristics of hybrid fiber metal laminates (HFMLs) by developing finite element formulation. A 9-noded heterosis plate element has been used to discretize the plate by taking into account the effect of shear deformation and rotary inertia. Since the stress distribution within the plate element is highly non-uniform in nature, the dynamic approach has been used to solve the buckling problems wherein two sets of boundary conditions are used, one for pre-buckling stresses and another for buckling load calculations. The present study consists of aluminum metal face sheets bound with four layered symmetric hybrid cross-ply and angle-ply laminate schemes. In each scheme, six different hybrid combinations have been considered. The performance of each hybrid combination is investigated under various loading combinations. Further, the effect of different parameters such as boundary condition, thickness of plate, width and position of localized edge loads, plate aspect ratio, and hybrid configurations are included in this work. The effect of each parameter is well investigated and explained by plotting mode shapes. It is revealed from the study that the hybrid configurations and localized edge loads significantly affect the vibration and buckling characteristics.

Fiber metal laminates based on aluminum–lithium alloy sheets are considered. The basic characteristics of such materials are considered as a function of their laminar structure. Tests show that laminar hybrids are preferable to traditional aluminum-alloy structures. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) based on carbon and glass fibers with aluminum as construction materials raise questions to the formation of corrosion. This article addresses the problem of the corrosion resistance of aluminum with glass and carbon fibers and with titanium layers. The laminates are exposed to the NaCl environment. Holes and half‐holes are made to identify the effect of carbon‐fiber layers to determine the corrosion behavior depending on the applied surface treatment. The dominant forms of corrosion occurring on the aluminum layer surface are pitting and intergranular corrosion. In addition to that, galvanic corrosion is treated in the laminates containing carbon fibers. [ABSTRACT FROM AUTHOR]

To enhance the interfacial and mechanical properties of magnesium alloy based fiber-metal laminates, a novel of AZ31B magnesium alloy-based hybrid fiber metal laminates (Mg-FMLs) bonded with Mg-Zn-Al eutectic alloy solder based on carbon fiber woven/polymer (epoxy resin) prepregs (CFRP) and AZ31B alloy sheets were prepared by using ultrasonic vibration assisted hot pressing technology. Interlaminar performance of the hybrid composite laminates was measured using double cantilever beam (DCB) and three-point end notched flexure (3ENF) tests. The interface morphologies and tensile behavior of the Mg-FMLs were evaluated. Results show that metallurgically-bonded interfaces have been formed in the Mg alloy-based hybrid FMLs. The present Mg-FMLs bonded with Mg alloy solder exhibit higher interlaminar and tensile performance than traditional Mg-FMLs bonded with epoxy resin. The enhanced tensile properties of the present Mg-FMLs can be attributed to the synergistic effect from the Mg alloy sheet and CFRP layer because of high interlaminar properties. For the same reason, the tensile fracture of the novel Mg-FMLs exhibits matrix and CFRP dominated mixed-mode failure.

In this paper, the influence of graphene-oxide nanoplatelets (GONPs) on the response of the glass laminate aluminum reinforced epoxy (GLARE) under high-velocity impact loading was investigated. Different weight percentages of nanofillers including 0.25, 0.50 and 1.00 wt % GONPs and a hybrid of 0.25 wt % GONPs and 0.25 wt % multiwalled carbon nanotubes (MWCNTs) were used for reinforcing GLAREs. Addition of 0.5 wt % GONPs reduced the residual impactor velocity by 33% and increased the energy absorption capability of GLARE by 22.9%. The SEM micrographs showed reinforced adhesion between the fibers and matrix and the optical microscope images showed improved cohesion in the matrix of the reinforced GLARE. This caused the secondary damage region in the composite layer to decrease considerably. However, GONPs imposed negative effect on the suppression of composite layer delamination and also interfacial strength between the composite and aluminum layers that provided more extensive plastic deformation of aluminum as an important energy absorption mechanism of GLAREs. Furthermore, the composite layers of the unreinforced and reinforced GLAREs were subjected to tensile test and the results showed improvements in the tensile stiffness, strength and toughness by 33.4, 45.0 and 25.6%, respectively, due to adding of 0.5 wt % GONPs to the matrix. [ABSTRACT FROM AUTHOR]

In recent years, studies on the development of new and advanced composite materials have been increasing. Among these new technological products, Fiber Metal Laminates (FML), and hybrid structures made of aluminium, carbon, glass or aramid fiber, are preferred especially in the aircraft industry due to their high performance. Therefore, free vibration analysis is necessary for the design process of such structures. In this study, the vibration characteristics of FML for clamped-free boundary conditions were investigated experimentally and numerically. Firstly, numerical results were obtained using Finite Element Method (FEM) and then these results were compared with the experimental results. It was seen that the numerical results were in good agreement with the experimental results. As the theoretical model was justified, the effects of various parameters such as number of layers, fiber orientations, and aluminium layer thickness on the in-plane vibration characteristics of the FML straight beam were analysed using FEM. Thus, most important parameters affecting the vibration characteristics of the hybrid structures were determined.

The main objective of this study is to reduce weight and to improve the mechanical properties of aircraft wing by using Hybrid materials known as fiber metal laminates (FMLs). They are new age of engineering materials, which consist of metal layers reinforced with fibers emerged by matrix phase. In this study, seven layers were used to produce the FMLs, which are consist of aluminum alloy2024-T3 reinforced by carbon and glass fibers bonded with using blend of graphite-polyester as adhesion. The Carbon Glass Reinforced Aluminum Laminates (CAGRALLs) is used as FMLs. The results show that the CAGRALLs give better in mechanical properties because of increasing in tensile strength, yield strength, , elastic modulus, elongation at fracture, flexural modulus and impact toughness except flexural strength by comparing with FMLs by using commercial epoxy as adhesion for other researchers. The increasing in layers is led to weaken adhesion force between layers of FMLs that led to decrease almost mechanical properties. The FMLs has good mechanial properties by using carbon and glass fiber by comparing with carbon and jute fibers. The CAGRALLs have the higher numbers of cycles at failure under cyclic loadings than Aramid Reinforced Aluminum Laminates (ARALLs). The CAGRALLs have the lower density by comparing with aluminum alloy 2024-T3 and steel that used in manufacturing of aircraft wing.

This paper presents the novel concept of structuring a planar coil antenna structured into the outermost stainless-steel layer of a fiber metal laminate (FML) and investigating its performance. Furthermore, the antenna is modified to sufficiently work on inhomogeneous conductive substrates such as carbon-fiber-reinforced polymers (CFRP) independent from their application-dependent layer configuration, since the influence on antenna performance was expected to be configuration-dependent. The effects of different stack-ups on antenna characteristics and strategies to cope with these influences are investigated. The purpose was to create a wireless self-sustained sensor node for an embedded structural health monitoring (SHM) system inside the monitored material itself. The requirements of such a system are investigated, and measurements on the amount of wireless power that can be harvested are conducted. Mechanical investigations are performed to identify the antenna shape that produces the least wound to the material, and electrical investigations are executed to prove the on-conductor optimization concept. Furthermore, a suitable process to fabricate such antennas is introduced. First measurements fulfilled the expectations: the measured antenna structure prototype could provide up to 11 mW to a sensor node inside the FML component.

The increasing demand for high performance and lightweight materials has stimulated the development of alternative materials, namely fiber metal laminates (FMLs). FML is a sandwich structure which is formed by bonding the metallic layers with composite as core constituent using an adhesive agent. In this study, the mechanical behavior of FMLs with the core constituents of environmental friendly kenaf bast fiber reinforced polypropylene composites bonded with aluminum skin layers was investigated. The effects of fiber compositions (50, 60, and 70 wt.%), fiber lengths (30, 60, 90 mm), and alkali treatment on the mechanical responses of FML were investigated. The overall results revealed that the increase of fiber composition and fiber length reduces the mechanical strength of FML owing to the agglomeration of natural fibers when the fiber length exceeds the critical limit. However, the chemical treated kenaf bast fiber reinforced FML showed a significant enhancement of the mechanical properties in comparison to the non-treated fiber reinforced FML owing to the improved fiber-matrix adhesion level. [ABSTRACT FROM AUTHOR]

Tensile and flexural properties of aluminum/self-reinforced polypropylene fiber metal laminates (Al/SRPP FMLs) based on 2/1 and 3/2 configurations are investigated in this paper. The Al/SRPP FMLs based on 2/1 configuration exhibit better performance than the Al/SRPP FMLs based on 3/2 configuration in terms of tensile and flexural properties. The metal volume fraction plays an important role in the tensile strength and flexural strength in both Al/SRPP-2/1 FMLs and Al/SRPP-3/2 FMLs. The tensile stress–strain curves of Al/SRPP-2/1FMLs and Al/SRPP-3/2FMLs decline while the ductility of both FMLs enhances as the temperature increases. The elevated temperature intensifies the delamination of the Al/SRPP FMLs, especially for Al/SRPP-3/2FMLs because of possible more manufacture defects. The outer metal cracking and inter-laminar delamination are the main tensile failure mechanisms. However, delamination at the metal/composite interface and breakage of the constituent materials does not occur after the flexural tests. [ABSTRACT FROM AUTHOR]

In this study, the effect of the arrangement of Kevlar and basalt fibers as the reinforcements on the Charpy impact behavior of hybrid epoxy composites was investigated. Also, the effect of adding metal plates (aluminum 2024-T3 and stainless steel 316L) into the basalt/ Kevlar fibers reinforced epoxy composites to fabricate fiber metal laminates under Charpy impact loads was studied. The fabricated fiber metal laminates in this research consisted of three metal plates and two groups of composite layers placed between them and were fabricated by the hand lay-up technique. Results indicated that the stacking sequence of fibers due to the hybridization effect caused a considerable improvement in the energy absorption value (99%) of hybrid composites, compared to specimens with one kind of fibers. Moreover, the effect of adding aluminum plates for the fabrication of fiber metal laminate was greater than adding steel plates. Considering the weight of composites, fiber metal laminates with aluminum and steel sheets, it was found that the average specific energy absorption value of aluminum fiber metal laminates was about 2.5 times higher than those of steel fiber metal laminates and composites. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are a special type of composite structure consisting of metal sheets bonded to composite laminas. The current study investigated the effect of the replacement of cross-ply (0/90°) glass fiber reinforced epoxy laminas with woven glass fiber reinforced polyester laminas in GLARE laminates on the tensile, bending and interlaminar fracture toughness of the laminate. Test results showed that the existence of woven glass fiber laminas increased the tensile strength with a decrease in corresponding strain, the flexure strength decreased significantly due to the existence of polyester instead of epoxy resin, and the mode I interlaminar fracture toughness increased. ABAQUS® software was used to simulate the tests, and ductile damage was employed to detect the failure of aluminum layers, the Hashin failure criteria to model the failure of composite layers in the laminate, and the cohesive surface interaction to capture delamination between layers. [ABSTRACT FROM AUTHOR]

Fiber metal laminates have been successfully applied in military aircrafts, armor vehicles and other modern engineering industries as protective structures due to their outstanding impact resistant properties. Prediction of the ballistic performance and investigation on the damage mechanism of the fiber metal laminates under general oblique impact conditions still remain a very challenging issue. In this study, a nonlinear dynamic finite element model in terms of continuum damage mechanics including intra- and inter-layer failure modes is presented. The accuracy of this model is validated with available experimental data. The damage and ballistic performance of two different structural fiber metal laminates subjected to high-velocity oblique impact by rigid hemispherical nose projectile with angles of 0°, 30°, 45° and 60° are studied. The numerical results show that the projectile deflects when the oblique impact occurs and the deflection angle decreases with increasing the impact velocity. The residual velocity of the projectile and the energy absorption of the target are related to the initial impact velocity and impact angle of the projectile. The proposed simulation approach offers a new proper reference for numerical investigations of common oblique impact problems in other fiber metal laminates. [ABSTRACT FROM AUTHOR]

Control of geometric dimension has been a major concern in the manufacturing process of fiber metal laminates (FMLs). In this paper, an analytical model has been proposed to predict the room-temperature shape of FMLs. Firstly, it is successful for using the proposed model to derive the process-induced stress due to the slipping behavior between the metal ply and the prepreg ply in the temperature rising phase. The slipping behavior between the metal ply and the prepreg ply was introduced by an interfacial shear stress which is applied to tailor the magnitude of interaction force. The analytical results show that the residual stresses in metal ply are almost constant along the metal thickness, while the distribution of residual stresses exhibits nonlinear characteristics through the thickness direction in the prepreg ply. Secondly, the proposed analytical solution based on the modification of the model presented by Dano and Hyer has been used to calculate the final curvature of FMLs by considering the process-induced stress developed both in the process of heating and cooling. The processing deformations results calculated by this model are good agreements with experimental data from the literature. [ABSTRACT FROM AUTHOR]

With the advancement of machine learning in leading technologies, it is perceived that machine learning is a new and effective alternative for the classic fatigue life prediction. This paper provides a regression tree ensemble‐based machine learning approach to predict the fatigue life of GLARE composites. In the model, mechanical, geometrical properties and fatigue loading stresses are selected as the training parameters (so‐called features), and the GLARE fatigue life is predicted as the output of the model. Experimental data of a total of 98 pieces of GLARE specimens with nine different layups are used for the training and validation of the machine learning model. Results show that the model can provide good fatigue life prediction accuracy and model stability. The most correlated, either positively or negatively, parameters to the fatigue life span are the stress developed in the aluminum layer, the maximum cyclic stress, alternating stress, and mean fatigue stress. [ABSTRACT FROM AUTHOR]

As primary structures and protective structures, fiber metal laminates (FMLs) in practical application are always in preload states before possible impact damage threats. In this work, a nonlinear finite element (FE) model is developed to study the impact damage scenario where tensile preloaded FMLs are impacted by a hemispherical nose projectile at high velocities. In the modeling, the intra-layer damage in aluminum sheets and composite laminates and the delamination between adjacent plies are entirely included. The FE model is verified with available experimental results in non-preload condition and then applied to predict the high velocity impact behavior in uniaxial and biaxial tensile preload cases. The ballistic performance and damage response of representative FMLs with different preloads and impact velocities are discussed and analyzed in detail. The numerical results and modeling strategy here provides applicable reference for preloaded impact issues in other FMLs. [ABSTRACT FROM AUTHOR]

In this paper, an inverse method to identify the mechanical parameters of fiber metal laminates is proposed on the basis of the measured and calculated frequency response functions. The classical laminates theory, orthogonal polynomial method, and energy method are employed to characterize the theoretical modal of a fiber metal-laminated thin plate under pulse excitation. And, an iterative solution on the basis of frequency response functions and least square method is proposed to identify the mechanical parameters of fiber metal laminates, which conclude the elastic modulus, Poisson's ratios, and loss factors. As an example to demonstrate the feasibility of the developed inverse method, the experimental test of a TA2/TC 300 fiber metal-laminated thin plate is implemented to identify the mechanical parameters. Moreover, the influences of approximation points and calculation step sizes on the identification accuracy and efficiency are discussed. [ABSTRACT FROM AUTHOR]

This study focuses on vibration characteristics analysis of fiber metal laminated thin plate (FMLTP) with partial constraint layer damping (CLD) patches treatment. Firstly, the overall stress–strain relationships of the viscoelastic layer, the constraint layer and the covered FMLTP are deduced to establish the theoretical model. Then, the classical laminates theory, orthogonal polynomial method, complex modulus method and energy method are employed to solve the natural frequencies, modal shapes, vibration responses and modal damping ratios. As an example to demonstrate the feasibility of the developed model, the experimental test of TA2/TC500 laminated thin plate treated with different sizes and shapes of stainless steel/Zn-33 CLD patches is implemented. The calculated and measured results show a good consistency. Moreover, the influences of different CLD treating positions and shapes on the vibration characteristics of FMLTP are investigated here. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FMLs) are the hybrid composite materials that needed analysis for using them toward applications as rectangular plates subjected to uniformly distributed loads. Determination of first ply failure (FPF) loads is the focus of the present study. These loads are identified by the procedure developed on the basis classical laminate theory (CLT), and Tsai–Hill criterion is used to identify the failure load. The developed procedure was validated by applying it to the standard cases reported in the literature. The failure loads and deformation of FMLs are presented in the form of dimensionless parameters, and their variation was studied for width-to-length ratios. FMLs of GLARE and Ti-CFRP are studied based on their importance to research. [ABSTRACT FROM AUTHOR]

This paper aims to illustrate the effect of the impact damage on fatigue behavior of CF/PEEK-titanium hybrid laminates. To achieve this end, a fatigue life model was proposed to predict the S–N curves of the laminates at various initial impact energy levels and stress ratios based on the energy dissipation approach. The energy dissipation behavior of the laminates during fatigue loading under different experimental conditions was analyzed through a large amount of post-impact fatigue tests, and the correlation between the initial impact damage and the total fatigue dissipation energy was determined. The full-field axial strain distribution of the titanium layer on the impacted side of the laminate was characterized in terms of initial impact energy level and maximum stress using digital image correlation, and then the post-impact fatigue failure mechanism of CF/PEEK-Ti hybrid laminates was summarized. Finally, the validity of the proposed model was verified by fatigue tests under other conditions of stress ratio and impact energy level. It is worth mentioning that the proposed model is also applicable to other types of FMLs, and can accurately predict the residual fatigue life of laminates after impact with only one set of S–N curve data. [Display omitted] [ABSTRACT FROM AUTHOR]

• Effects of stacking sequences on the axial compressive performances of channel-section CFRP/Al laminate columns were analysed. • A concise calculation method was derived for axial compressive local buckling load of the channel-section CFRP/Al laminate columns. • Parametric analysis was conducted to investigate the structural influencing factors on the axial buckling load based on the proposed theoretical method. Open-section composite profiles are often used as columns in civil engineering structures. Their thin-walled nature makes these sections prone to buckling phenomena when loaded in compression. This paper presents a study on the axial compressive performances and failure behavior of channel-section CFRP/Al laminate columns with two different stacking sequences. Typical mechanical responses and failure characteristics were first explored through experiments. Then the damage propagation mechanisms of the two kinds of columns were further compared based on a three-dimensional progressive damage model. The results indicated that column with CFRP layers stacked on the exterior surfaces exhibited smaller delaminated areas compared with the ones with aluminum alloy layers stacked exteriorly, thus resulting in the higher load-bearing capacities. Finally, a concise theoretical calculation equation for buckling load was derived, based on which further structural parametric analysis were performed. [ABSTRACT FROM AUTHOR]

The surface treatment of metals has a great role on the adhesion of the metals to the polymers. There are various surface treatment methods for adhesive joint applications. However, the effect of the combination of surface treatment methods on the mechanical behavior of adhesive joints has not been extensively studied. In this study, the effects of applying a combination of surface treatments on the flexural and Charpy impact behavior of fiber metal laminates (FMLs) were investigated. The surface treatments included forest product laboratory etching (FPL), sulfuric acid anodizing (SAA), sandblasting, sandblasting + FPL and sandblasting + SAA. The FMLs were made from Al2024-T3, basalt fibers and epoxy. Scanning electron microscopy (SEM) was used to study the surface morphology of the Al2024-T3 laminates and fracture surface of the samples. Furthermore, the surface roughness of the Al2024-T3 sheets after different surface treatments were evaluated using profilometry. Results showed that the adhesion of Al2024-T3 to polymeric layers was significantly affected by various surface treatments. Results of bending tests indicated that the highest bending strength and strain to failure values were respectively achieved for the SAA and sandblast treated samples. On the other hand, although there was a slight improvement in the bending strength, the application of SAA or FPL etching after sandblasting caused a negative effect on the strain to failure value of the samples. However, impact test findings showed that the combination of FPL or SAA treatments after sandblasting rendered positive effects on the low-velocity impact behavior of the FMLs. [ABSTRACT FROM AUTHOR]

• Fracture modes partitioning for generally layered beams with hygrothermal effect. • Analytical solutions for the mode I and II fracture energies for various tests. • Residual thermal stresses effect on the fracture toughness of fiber metal laminates. • Analytical modeling of the contact problem in the end-notched flexure test. An analytical framework is presented to calculate the mode I and II components of the strain energy release rate (SERR) of a delamination between two generally layered sub-laminates, considering the residual hygrothermal stresses effect. First, the sub-laminates are modeled as Timoshenko beams, the crack tip is assumed rotationally flexible and the mode partitioning is based on the global method. Next, SERR and mode mixity are obtained for an arbitrarily loaded delaminated beam and reduced for some typical delamination fracture tests. An asymmetrically delaminated fiber metal laminate (FML) is analyzed under double cantilever beam (DCB) and end-notched flexure (ENF) configurations. For the ENF configuration, the inherent contact problem was analytically approached. We demonstrate that the thermal effect on the SERR and mode mixity of the FML, rather ignored so far in the literature, can be non-negligible. Finally, the analytical results are validated against numerical predictions using the finite element method. [ABSTRACT FROM AUTHOR]

The tensile behavior of fiber metal laminates consisting of layers of aluminum 2024-T3 alloy and glass fiber reinforced composites under high strain rate loading is investigated. Fiber metal laminates having four different layups, but all having the same total metal layer thickness, were fabricated using a combined hand lay-up cum vacuum bagging method. The fiber metal laminate specimens were loaded in high strain rate tension using a split Hopkinson tensile bar. The rate-dependent behavior of the glass fiber composite was also obtained as baseline data. The strain on the gage area of the specimen was measured directly using high-speed digital image correlation. Another high-speed camera was used to capture the sequence of damage by viewing the specimen edgewise. The results indicated that the strength of the fiber metal laminates increased at high strain rates primarily due to the rate-dependent behavior of the composite used. The response was also influenced by the distribution of the metallic layers in the fiber metal laminates. The failure in the case where the individual composite layers were separated by metallic layers was more progressive in nature. [ABSTRACT FROM AUTHOR]

Abstract Fiber metal laminates (FMLs) have been widely used in many high-tech industries as protective structures because of their excellent impact resistance. The damage constitutive model that accurately characterizes the complex damage modes and failure processes of FMLs is the base to study the ballistic impact problems by numerical simulation. In this paper, a nonlinear finite element model based on continuum damage mechanics is established to investigate the damage modes and failure mechanisms of carbon fiber reinforced aluminum laminates (CRALLs) under high velocity impact. Johnson-Cook material model and a 3D rate-dependent constitutive model are applied to identify the in-plane damage in aluminum and fiber composite layers respectively; cohesive elements governed by bilinear traction-separation constitutive model are implemented to simulate the inter-laminar delamination induced by impact. The ballistic performance and damage characteristics of CRALLs under high velocity impact by projectiles with different shapes are studied in detail. The obtained numerical results correlate well with the available experimental data thus validates the proposed finite element model, which also provides an appropriate reference for numerical studies of high velocity impact issues in other FMLs. [ABSTRACT FROM AUTHOR]

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In the one-step manufacturing process for fiber metal laminate parts, the so-called in situ hybridization process, the fabrics are interacting with metal blanks. During deep drawing, the liquid matrix is injected between the metal sheets through the woven fiber layers. The metal blanks can be in contact with dry or with infiltrated fibers. The formability of the blanks is influenced by the variation of the starting time of injection. The reason for that is that, due to high contact forces, the fibers are able to deform the metal surface locally, so that movement and the strain of the blanks is inhibited. To investigate the influence of different fibers on the formability of metals, Nakazima tests are performed. In these tests, two metal blanks are formed with an interlayer of fibers. The results are compared with the formability of two blanks without any interlayer. It is shown that in with fibers between sheets, the formability decreases compared to the formability of two metal blanks without interlayers. Based on a simplified numerical model for different types of fibers, the interactions of the fibers with the metal blank are analyzed. It could be shown that the friction due to contact has more influence than the friction due to the form fit caused by the imprints. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A new overall damage model is proposed to predict the induced damage of FML. • A sensitivity analysis indicates that ε cr,nm has the most effect on the FML damage. • CPU time reduced by 4 times using the present model compared with layered model. • Reasonable agreement between the present model and the experiment was obtained. Abstract Fiber Metal Laminates (FMLs) are hybrid composites made of interlacing layers of thin metal and fiber reinforced layers. In this work, a new overall damage model is developed to estimate the damage of FML considering the influence of stress triaxiality. The parameters of the damage model were determined using tensile test and iterative FE optimization for each sub-layer. Moreover, the stiffness degradation test was carried out to validate the proposed model for FML plain specimen. Additionally, notched FML specimens were used to simulate the material behavior under more complicated states of stress by implementing the proposed damage model in MSC MARC commercial FE code. A reasonable agreement was obtained between the FE and the experimental results for plain and notched FML specimens. The results indicated that the proposed model not only predicts the strong nonlinear behavior of plain and notched specimens, but also can estimate the failure strain with sufficient accuracy. [ABSTRACT FROM AUTHOR]

Abstract The deformation behavior of novel fiber metal laminates based on aluminum-lithium alloy (NFMLs) after shot peen forming was investigated to further reveal their deformation mechanism and seek a desired forming method. AZB425 ceramic balls were used to sharp the NFMLs strips with various shot peening intensity and coverage. Furthermore, arc height of the laminates was measured to describe the deformation behavior. The X-ray and layer removal methods were adopted to reveal the distribution characteristics of residual stress. The results indicated that the forming curvature of 165.24 mm was achieved for 3/2 cross-ply NFMLs. Plastic deformation was produced only in the shot peened metal layer, while elastic deformation in other fiber and metal layers. Comparing with metal materials, NFMLs possessed similar deformation rules following the variation of shot peening intensity and coverage. However, the laminates were inclined to deform perpendicular to fiber direction. Besides, shot peening significantly changed the residual stress state of NFMLs. The distribution of residual stress for shot peened NFMLs was obtained qualitatively in this study. The relaxation behavior of complicated residual stress was negligible even after 1000 times thermal impact from 100 °C to 0 °C. [ABSTRACT FROM AUTHOR]

Abstract In this study, the micro-arc oxidation (MAO) processes in different electrolyte composition ratio were carried out on magnesium alloy sheets and then the carbon fiber reinforced polymer (CFRP)/magnesium alloys laminates were manufactured by using a cure process. The Mode I (peel) interlaminar strength was measured to systematically investigate the effects of the electrolyte concentration on interfacial bonding strength and failure mode of CFRP/Mg laminates in consideration of surface microstructures and roughness. The results show that with the increase of KOH in electrolytes solutions, the Mode I (peel) strength of FMLs performs sharply decreasing due to the decrease of roughness in local regions and the emergence of interspace between magnesium and epoxy. In addition, with the rise of KF in electrolytes solutions, the Mode I (peel) strength of FMLs declines rapidly on account of the sharply weakening of electro-chemical reactions, which causes the decrease of surface roughness. The specimen exhibits the optimal Mode I interlaminar strength of 2.04 N/mm when the KOH and KF concentration is 7.28 g/L and 2.9 g/L, respectively. [ABSTRACT FROM AUTHOR]

Hybrid composite materials, which combine two or more types of fiber in a single matrix, have currently drawn the interest of researchers. This research investigates the tensile and impact properties of hybrid kenaf/glass reinforced metal laminates (FMLs) with different fiber orientations and stacking configurations. FMLs were formed by sandwiching the annealed aluminum 5052 sheets to the composite laminates using hot press molding compression technique. The tensile test was performed at a quasi‐static rate of 2 mm/min with reference to ASTM E8 whereas Charpy impact test was conducted using impact pendulum tester according to ASTM E23. Results showed that improvement in tensile and impact strength was observed in hybrid FMLs compared to kenaf fiber reinforced FMLs. Fiber orientation of ±45° reduced the tensile strength but increased the impact strength of FMLs in comparison with fiber orientation of 0°/90°. Overall, hybrid FMLs incorporated with a fiber stacking sequence of glass/kenaf/glass showed superior characteristic in tensile and impact performance. [ABSTRACT FROM AUTHOR]

• The high-velocity hail impact onto CARALL is investigated in experiment and finite element method. • Different hail impact schemes including velocity, laminate ply scheme and angle are carried out. • The effects of different hail impact schemes on damage evolution and energy absorption efficiency of CARALL are revealed. The experiment and finite element method (FEM) simulation of high-velocity hail impact on carbon fiber reinforced aluminum alloy laminates (CARALL) were carried out in this paper. CARALL were prepared via an autoclave process after surface anodizing. The properties of the specimens were verified by mechanical properties testing. The light gas gun was employed to conduct the hail impact tests with different impact velocities, impact angles and ply sequences. The surface damage, displacement of the impact center and deformation depth in different test schemes were compared. The FEM model of the high-velocity impact of hail on CARALL was established using ABAQUS/Explicit. The strain-rate dependent model was adopted for hail while the Johnson-Cook damage constitutive model was adopted for the aluminum alloy layer. The 3D Hashin criterion damage model based on fracture energy was applied for the CFRP layer via the VUMAT subroutine. The cohesive element was inserted between the laminates to investigate the interlaminar damage. The accuracy of FEM was verified by comparing with the results obtained by tests. Combined with the energy absorption and internal damage mechanism, the effects of different parameters on the hail impact resistance of CARALL were studied. [ABSTRACT FROM AUTHOR]

This paper primarily investigates the effects of chemically grafted modified carbon fibers on the bonding properties of fiber metal laminates (FMLs). Relative elemental content on the carbon fibers’ surface was performed via X-ray photoelectron spectroscopy (XPS). Scanning electron microscopy (SEM) was utilized to observe the material microstructure. The effect of chemically grafted carbon fibers on the bond strengths of FMLs was experimentally investigated through lap joint testing. The carbon nanotubes (CNTs) grafting concentration and curing conditions of the samples were also investigated. The test results demonstrate that grafting concentrations of 0.1, 0.2, and 0.3 mg/mL CNT solution increased the bond strength of the cured samples under vacuum conditions by 63.51%, 87.16%, and 71.56%, respectively. In addition, the bond strengths of vacuum-cured samples were also increased.

This article presents selected aspects of an interlaminar shear strength and failure analysis of hybrid fiber metal laminates (FMLs) consisting of alternating layers of a 2024-T3 aluminium alloy and carbon fiber reinforced polymer. Particular attention is paid to the properties of the hybrid FMLs with an additional interlayer of glass composite at the metal-composite interface. The influence of hygrothermal conditioning, the interlaminar shear strength (short beam shear test), and the failure mode were investigated and discussed. It was found that fiber metal laminates can be classified as a material with significantly less adsorption than in the case of conventional composites. Introducing an additional layer of glass composite at the metal-composite interface and hygrothermal conditioning influence the decrease in the interlaminar shear strength. The major forms of damage to the laminates are delaminations in the layer of the carbon composite, at the metal-composite interface, and delaminations between the layers of glass and carbon composites.

This paper investigates the eccentric low-velocity impact of Fiber metal laminates (FMLs) subjected to spherical projectile using a unified Zig-Zag plate theory. The presented zig-zag plate theory enforces transverse shear stress continuity through the thickness and can be reduced to conventional plate theories using appropriate shape function. The governing equations and suitable boundary conditions are obtained using the principle of minimum total potenital energy. Runge-Kutta method is employed to solve initial value problem resulted by the method of Ritz. The present model is validated by comparison and good agreement between its results and those of reports in open literature. Influence of various specifications of impact phenomenon such as laminate thickness, projectile radius, projectile velocity, in-plane load and eccentricity parameter is examined on deflection and contact force time history. The obtained results indicate that continuity of transverse shear stress is required to achieve accurate contact force even for moderately thin FMLs. [ABSTRACT FROM AUTHOR]

Abstract The effect of the distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their projectiles impact response is studied using high speed 3D digital image correlation technique (DIC). The FMLs consisting of aluminum alloy 2024-T3 sheets of thicknesses 0.3 mm, 0.4 mm, and 0.6 mm and glass fiber reinforced epoxy layers (two layers with each of 0° and 90°) were prepared by the hand layup process followed by vacuum bagging. The metallic layers are placed at different locations through the thickness of four different layups while keeping the total metal layer thickness constant. The hemispherical and conical nose projectiles of the same mass are impacted normal to the FMLs plate using nitrogen gas gun. The performance of the FMLs is evaluated using different parameters such as the deformation history, residual deformation and also the surface and internal damages. FML 4/3–0.3 in which the two adjacent composite layers with different fiber orientations separating by an aluminum layer exhibited the highest deformation with hemispherical projectile impact for the same impact energy level. The deformation was found to be lower and nearly same for the other three FMLs. This observation is also noticed in the case of drop weight impact (low velocity impact). The FML 2/1–0.6 in which the composite layers were stacked together exhibited a comparatively higher lateral spread of delamination and interlayer opening with hemispherical projectile impact when compared to FML 4/3–0.3, indicating that the lateral spread of damage within the FML can be decreased by distributing the aluminum layers in the FML. This is also observed in the case of drop weight impact. Highlights • The projectiles impact response of aluminum based fiber metal laminates (FMLs) has been investigated using high speed 3D digital image correlation technique. • Internal damages are identified by slicing the specimen. • Effect of meal layer distribution through the thickness of FMLs on the projectiles impact response of FMLs is brought out. • Damage pattern is affected by distributing the aluminum layers through the thickness with more extent of damage exhibited by projectiles impact. • Hemispherical projectile impact imparts more collateral damage to that of conical projectile. [ABSTRACT FROM AUTHOR]

In aviation industries, most of the stiffened structural components are manufactured by forming and laminating process. Combination of several conventional manufacturing processes is required in modern industries in hybrid laminate production. Fiber metal laminates undergo various joining process during assembly of aero-structures. Among them, forming and drilling are often required during assembly. Understanding the significance of various process parameters enables quality production and assembly of fiber metal laminates structures. Many researchers explored the cause and effect of few parameters and mechanisms which significantly alter the quality of form and drill. This review describes the progress in forming and drilling of fiber metal laminates for aerospace applications. Especially towards the process parameters, defects and their causes along with the preferred solutions recommended by the researcher society in forming and drilling processes. Numerous factors have controlled the quality of forming and drilling processes. Due to the machining parameters, different failure modes will occur in different layup of the laminates. To overcome the failures in machining/forming of fiber metal laminates, choosing the optimum parameter for the selection based procedure is needed to improve quality of fiber metal laminates. [ABSTRACT FROM AUTHOR]

During the manufacturing process of fiber metal laminates (FMLs), incompatible residual strain leads to the problem of slippage interaction at the interface between the metal layer and the fiber layer. An analytical model and finite element (FE) model considering slippage effect are established to obtain the cured shape and deformation of cross-ply [Al/0/90/Al] FMLs. Both analytical and FE results are in good agreement with experimental results. The predicted models proposed in this paper can accurately and effectively calculate the equilibrium configurations of FMLs at room-temperature. In order to reveal the curing deformation characteristics of FMLs, the influence laws of geometry dimensions and metal ply thickness on the cured stable shapes are obtained by using the prediction models for the square and rectangular laminates. [ABSTRACT FROM AUTHOR]

In this paper, the new analytical prediction models were proposed for assessment of static strength and fatigue life of Fiber Metal Laminates (FMLs). The proposed static model combines composites mechanical linear-elastic behavior with non-linear elastoplastic behavior of metals, including curing stresses in laminae. Based on determined internal stress distribution through the thickness of the laminate, the fatigue life of FML is modeled at the lamina level, based on S-N mother curves of monolithic materials. The new criterion for prediction of residual fatigue life period in FMLs was proposed. Theoretical work was experimentally validated with good convergence of results. [ABSTRACT FROM AUTHOR]

The feasibility on shot-peen forming of the novel fiber metal laminates based on aluminum-lithium alloys (NFMLs) was investigated to seek a desired forming method. The failure behavior of shot-peened NFMLs was then examined using C-scan ultrasonic testing and scanning electron microscopy (SEM). The changes in surface roughness and formed curvature were also analyzed. The unique deformation behavior of the laminates comparing with monolithic materials was revealed. The results indicated that NFMLs were feasible to manufacture by shot-peen forming. High shot-peening intensity and large ball sizes caused serious plastic deformation in shot-peened surface with evident stress variation at the metal/fiber interface. This led to interface delamination and fiber breakage. Moreover, increased but quite uniform surface roughness was obtained for the shot-peened laminates. Large-size ball was found beneficial for improving the surface quality when achieving the same shot-peening intensity. Also, the ball type and size significantly affected the formed curvature of NFMLs due to the complex effects of fiber layers on the formation behavior. Overall, the AZB425 ball was found more beneficial in improving the surface quality and formed curvatures. The minimal curvature radius reached approximately 200 mm within the investigated processes. [ABSTRACT FROM AUTHOR]

Fiber metal laminates are commonly used materials in industrial applications due to low density and excellent mechanical properties such as impact resistance. In this study, the effect of shape memory alloy wires on the impact properties of fiber metal laminates is evaluated and discussed. The volume fraction of wires and the pre-strain of wires were selected as the variables of the experiments. The samples were fabricated using hand lay-up method and their behavior was evaluated under high-velocity impact test. Based on the results, a significant change in the amount of absorbed energy was obtained using embedded wires. However, with increasing the volume fraction of wires, the absorbed energy decreases due to the discontinuity in mechanical properties of the specimens. On the other hand, applying pre-strain leads to residual stresses in samples. The observed residual stress in specimens with four embedded wires and 2% pre-strain level shows the most absorbed energy. [ABSTRACT FROM AUTHOR]

The effect of distribution of aluminum layer through the thickness of fiber metal laminates (FMLs) on their low velocity impact response was studied. The FMLs were prepared using aluminum 2024-T3 layers (0.3, 0.4, 0.6 mm thickness) and glass fiber reinforced epoxy (two layers of 0° and 90° each) through hand layup followed by vacuum bagging. The four different layups considered had metallic layers placed at different locations through the thickness while maintaining the total metal layer thickness constant. The FMLs were subjected to low-velocity impact using a drop weight testing machine. The performance of FMLs was evaluated using different parameters such as maximum force, energy absorbed, damage degree, dent depth and maximum deflection. Among the four FMLs, it was observed that the FML 2/1–0.6 in which the composite layers were stacked together had lower levels of cracking and deformation and recorded the highest force for the same impact energy level, whereas the FML 4/3–0.3 in which two adjacent composite layers having different fiber orientations were separated by metallic layer recorded the lowest force and maximum cracking and deformation. The lateral spread of delamination and interlayer opening was comparatively greater for 2/1–0.6 when compared to 4/3–0.3, indicating that distributing the aluminum layers in the FML can decrease the lateral spread of damage within the FML. [ABSTRACT FROM AUTHOR]

The possibility of galvanic corrosion typically prohibits the pairing of carbon fiber and aluminum in a fiber metal laminate (FML). In this study, the authors describe a new type of FML comprised of alternating layers of bulk metallic glass (BMG) and carbon fiber reinforced polymer (CFRP) composite. The authors compare the galvanic coupling and mechanical behavior of an Al‐based FML and a BMG‐CFRP FML. Results show that when paired with CFRPs, BMG exhibits far less galvanic corrosion than aluminum paired with CFRP. In fact, the corrosion between BMG and CFRP is similar in magnitude to the corrosion between aluminum and glass fiber, the two constituent materials of GLARE, the most widely used FML. While interlaminar shear strength and flexural strength are similar for both FML types, the tensile strength and modulus of BMG‐based FMLs are greater than those of Al‐based FMLs. [ABSTRACT FROM AUTHOR]

Fiber metal laminates (FML) have receive much interest in the aviation sector due to their high strength-to-weight ratio and durability. In aerospace structures, drilling is one of the primary processes to enable permanent joining of multiple structural members, and dimensional stability of a material during machining is a key factor in materials selection. In the present manuscript, an attempt is made to achieve a flawless drilling through investigation of different drill bit geometries in glass fiber epoxy/aluminum stacked laminates (GLARE). More specifically, the effect of the margin of the drill-bit is extensively analyzed through various characterization techniques. Thrust force measurement and its relationship with the delamination is one of the highlights of the investigation that supports tool selection. Vibrational analysis is used to control the quality and advancement of the drill bit during drilling. The results support the use of margin free drill bits to machine laminates, which removes stacked glass fibers and produce precise cylindrical drill inside the volume with high surface finish and less delamination. [ABSTRACT FROM AUTHOR]