Aluminum Laminates Research Articles

New Advances and Future Possibilities in Forming Technology of Hybrid Metal–Polymer Composites Used in Aerospace Applications

Fibre metal laminates, hybrid composite materials built up from interlaced layers of thin metals and fibre reinforced adhesives, are future-proof materials used in the production of passenger aircraft, yachts, sailplanes, racing cars, and sports equipment. The most commercially available fibre–metal laminates are carbon reinforced aluminium laminates, aramid reinforced aluminium laminates, and glass reinforced aluminium laminates. This review emphasises the developing technologies for forming hybrid metal–polymer composites (HMPC). New advances and future possibilities in the forming technology for this group of materials is discussed. A brief classification of the currently available types of FMLs and details of their methods of fabrication are also presented. Particular emphasis was placed on the methods of shaping FMLs using plastic working techniques, i.e., incremental sheet forming, shot peening forming, press brake bending, electro-magnetic forming, hydroforming, and stamping. Current progress and the future directions of research on HMPCs are summarised and presented.

Wide Scale Characterization and Modeling of the Vibration and Damping Behavior of CFRP-Elastomer-Metal Laminates\u2014Comparison and Discussion of Different Test Setups

The investigated hybrid carbon fiber reinforced plastics-elastomer-metal laminates (HyCEML) offer the potential of tailored structural materials with adaptable damping properties. Conventional fiber metal laminates, like glass laminate aluminum reinforced epoxy are already widely spread in the aviation industry owing to their outstanding fatigue behavior. By integrating an elastomeric interlayer, the glass fibers can be substituted by carbon fibers and damping properties of these laminates can be adjusted. The viscoelastic interlayer dissipates energy within the laminate by inducing shear strain during bending, which is commonly known as constrained layer damping. The aim of this paper is the description of the vibration and damping behavior of HyCEML over a wide temperature and frequency range by using different test methods. Dynamic mechanical analysis is used for the individual polymeric constituents and coupon specimens and modal analysis is used with different specimen geometries up to a component sized panel. In addition, analytical and numerical approaches complement the experiments and lead to a deeper understanding of the vibration and damping behavior. Owing to the high damping, already at frequencies of 5 kHz only running waves can be detected for the investigated panel size. The discussion of different test methods helps to identify material and wavelength dependent effects, but also possible adverse effects of certain methods.

Microstructure and Mechanical Properties of Al-Mg-Si Similar Alloy Laminates Produced by Accumulative Roll Bonding.

As the applications of heterogeneous materials expand, aluminum laminates of similar materials have attracted much attention due to their greater bonding strength and easier recycling. In this work, an alloy design strategy was developed based on accumulative roll bonding (ARB) to produce laminates from similar materials. Twin roll casting (TRC) sheets of the same composition but different cooling rates were used as the starting materials, and they were roll bonded up to three cycles at varying temperatures. EBSD showed that the two TRC sheets deformed in distinct ways during ARB processes at 300 °C. Major recrystallizations were significant after the first cycle on the thin sheet and after the third cycle on the thick sheet. The sheets were subject to subsequent aging for better mechanical properties. TEM observations showed that the size and distribution of nano-precipitations were different between the two sheet sides. These nano-precipitations were found to significantly promote precipitation strengthening, and such a promotive effect was referred to as hetero-deformation induced (HDI) strengthening. Our work provides a new promising method to prepare laminated heterogeneous materials with similar alloy TRC sheets.

Interlaminar shear strength (ILSS) characterization of fiber metal laminates (FMLs) manufactured through VARTM process

The aircraft industry is always seeking materials with excellent mechanical properties and good strength to weight ratio. Fiber metal laminates (FMLs) are the emerging class of hybrid composite materials consisting of fiber-reinforced polymers (FRP) plies and metal sheets. Aircraft parts are subjected to different types of mechanical loading during operation. Combining the properties of FRPs and metals provides excellent resistance to impact as well as improves the fatigue performance of the aircraft. In this study, aluminum 7075-T6 sheets were used to fabricate FMLs with varying fiber reinforcements. These sheets were treated with different surface and chemical treatment processes. The short beam shear test is utilized in this work that gives practical information on interlaminar shear strength (ILSS) and it can also be employed in real design applications. The results indicated that the ILSS of carbon fiber reinforced aluminum laminates (CARALL) was higher than glass-reinforced aluminum laminates (GLARE) and aramid-reinforced aluminum laminates (ARALL) at all displacement rates. The reason for the higher ILSS of CARALL is due to the stifness of carbon fiber and the strong adhesion of carbon with aluminum metal. However, ILSS for all three types of FMLs did not change significantly which shows that it is independent of displacement rates.

Comparison of Tensile Strength and Fracture Toughness of Co-Bonded and Cold-Bonded Carbon Fiber Laminate-Aluminum Adhesive Joints.

The purpose of this work is to compare the co-bonding vs. cold-bonding route on the adhesive joint performance of a CFRP (Carbon Fiber Reinforced Polymer) laminate–aluminum connection. In particular, the overlap shear, tensile strength and Mode I and Mode II fracture toughness will be evaluated. The adhesives for co-bonding and cold-bonding are, respectively, a thermosetting modified epoxy, unsupported structural film and a two-component epoxy adhesive, chosen as representative of applications in the high-performance/race car field. The emerging trend is that, in tensile e Mode I fracture tests, the failure path is predominantly in the composite. Mode II fracture tests instead resulted in a cohesive fracture, meaning that, under pure shear loading, the weakest link may not be the composite. The lap-shear tests are placed midway (cohesive failure for co-bonding and composite delamination for cold-bonding, respectively), probably due to the different peel stress values related to the different adhesive Young’s modulus. The exploitation of the full capacity of the adhesive joint, hence the possibility of highlighting better, different performances of co-bonding vs. cold-bonding, would require consistent improvement of the out-of-plane strength of the CFRP laminate and/or to someway redistribute the peel stress on the bondline.

Medium‐term absorption kinetics and thermal stability analysis of hybrid fiber metal laminate and experimental investigations on its physical and tensile properties

AbstractFiber metal laminates (FML) are promising material candidates in several applications such as aerospace, marine, and construction industries due to their high strength, impact resistance, corrosion resistance, and fatigue properties. However, these materials have a negative impact on the environment due to their higher carbon footprint. This problem could be overcome by hybridizing carbon material with natural biodegradable materials. It is assumed that the higher moisture absorption and lower thermal properties of such materials may affect the long‐term stability of the FML. Hence, an attempt is made in this work to evaluate their stability potential by investigating the influence of the addition of natural jute fiber in carbon reinforced aluminum laminate (CARALL) on FML and report their physical effect of stacking sequence on dynamic, mechanical, and thermal properties. In addition, the medium‐term absorption kinetics of jute fiber hybridized CARALL, that is, carbon‐jute reinforced aluminum laminate (CAJRALL) were performed. The results show that the tensile load bearing capacity of all the immersed laminates decreases at the end of 2 weeks of immersion. Further, CAJRALL was found to possess moderate thermal stability by yielding fewer thermal residues on burning. Finally, the outcome of dynamic mechanical analysis of the hybridized FML reveals that they are capable of storing relatively higher elastic and viscous energies under dynamic conditions with increased damping capability when compared to CARALL. From this study, it is worth to point out that hybridization of CARALL with jute fiber plays a pivotal role in improving environmental friendliness with a lower impact on the overall material properties.

Experimental and analytical assessment of the hypervelocity impact damage of GLAss fiber REinforced aluminum

This article addresses the response of GLAss fiber REinforced aluminum to hypervelocity impacts of micrometeoroid analogs at impact velocities of 7 km/s and beyond. In relation, the damage modes of different GLAss fiber REinforced aluminum configurations have been exemplified. The GLAss fiber REinforced aluminum configurations comprised six to twelve variably thick aluminum layers and up to four plies of glass fiber reinforced epoxy per composite laminate. Hypervelocity impact experiments have been conducted with the help of a two-stage light-gas gun, wherein aluminum- and stainless steel projectiles were launched at velocities up to 7.15 km/s. Visual inspection of the damage area suggested the dissipation of impact energy in elastic-plastic deformation, petalling, delamination, debonding, tensile failure of fibers, and pyrolysis of epoxy. A prevailing damage mode was not apparent albeit. The quasi-isotropic ply orientation of S2-glass/FM94-epoxy laminates promoted the interference of shock- and rarefaction waves and suppressed the damage area of GLAss fiber REinforced aluminum. To discriminate between the impact performance of different GLAss fiber REinforced aluminum configurations, the energy dissipated in different damage modes of GLAss fiber REinforced aluminum has been assessed quantitatively. In terms of normalized energy, the cross-ply GLAss fiber REinforced aluminum dissipated higher energy in petal formation than in other primary damage modes. The normalized petalling energy was found to decline with the increase of impact energy. The outcomes of this study will help to optimize the GLAss fiber REinforced aluminum laminate, which will be employed as a bumper shield to prevent the fatal damage and the unzipping of a spacecraft pressure bulkhead.

An experimental and numerical investigation on low velocity impact response of GLAREs

Glass fiber aluminum laminates (GLAREs) are a type of fiber metal laminates (FMLs) that are widely used in the aviation industry. The present article aimed to carry out the numerical and experimental study of the damage mechanism initiation and development in the FMLs subject to low velocity impact. In the experimental part, the drop weight impact test was conducted at four energy levels of 8, 11.5, 15, and 18.5 J on the GLARE laminates. The first crack in the aluminum layer was observed at 18.5 J in the lower aluminum layer. In the numerical simulation, the user-material subroutine VUMAT, including the three-dimensional Hashin damage initiation criterion and the modified progressive damage evolution model, was coded and implemented in the ABAQUS/Explicit finite element package to predict damage initiation and development. The numerical simulations were validated by the experimental results in terms of force–time, force–displacement, and absorbed energy-time curves. The optical microscopy (OM) and scanning electron microscopy (SEM) images of the specimen cross-section were produced to detect the FML damage pattern. The numericalsimulation andexperimentalresults showed to be in good agreement.

Numerical optimization of process parameters of water chestnut flour incorporated corn‐based extrudates: Characterizing physicochemical, nutraceutical, and storage stability of the developed product

The present research was undertaken to optimize process conditions for development of water chestnut incorporated corn-based extrudates. The independent extrusion variables—feed composition, feed moisture, screw speed and barrel temperature were studied to determine their influence on dependent variables-specific mechanical energy, expansion index, bulk density, water solubility index, water absorption index, hardness, and color. All system and product responses were significantly (p < .05) influenced by independent variables. The regression models fitted to experimental design showed high coefficient of determination (R2 ≥ 0.99). The optimum conditions for development of extrudates obtained by numerical optimization were corn flour : water chestnut flour (60:40), feed moisture (14%), barrel temperature (170°C), and screw speed (300 rpm). Moisture, protein, and fat contents of extrudates developed using optimum conditions were significantly (p < .05) lower than corn and water chestnut. Storage studies revealed safe storage of extrudates packed in aluminum laminates up to 120 days under ambient conditions without compromising much of its qualities. Practical applications Water chestnut possesses excellent therapeutic potential owing to the presence of bioactive compounds including glycosides, phytosterols, flavonoids, and tannins, which may help in alleviating various diseases. Besides, water chestnut has low glycemic index; thus, the developed products prepared from it may be suitable for diabetics. Extruded products have better consumer acceptability in terms of shelf life and organoleptic characteristics. Therefore, the extruded products developed from nutritionally rich water chestnut would be a better alternative to already available extruded snacks in food industry. It can open up a new horizon in the field of extrusion products.

Evaluation of mechanical properties of novel GLARE laminates filled with nanoclay

AbstractIn this research work, we have investigated the effect of nanoclay fillers in the epoxy adhesive on improving the interfacial adhesion and the mechanical properties of glass‐reinforced aluminum laminates. The laminates were prepared with a varying weight percentage of nanoclay fillers (i.e., 3, 4, and 5 wt%) in the epoxy resin using the hand lay‐up method. During the tensile test, the laminate's anisotropic nature was investigated using the samples cut in different orientations to the rolling direction (i.e., 0, 45, and 90°). The flexural, lap shear, and impact tests were conducted as per ASTM standards. After each test, the failure mechanisms of laminates were studied using the scanning electron microscope. The results showed that 3 wt% of nanoclay added in the epoxy enhanced the laminates' overall mechanical properties than other composites. The fiber metal laminates (FML) containing the nano clay more than 3 wt% showed deterioration in the mechanical property due to the improper distribution of nanoclay in the epoxy matrix. The FML's mechanical properties with nano clay filler were compared with other fillers' performance in the previous studies. It was found that the mechanical properties of FML with nano clay filler were more significant than others.

Nanoparticles enhanced interfaces of Glass fiber laminate aluminum reinforced epoxy (GLARE) fiber metal laminates

AbstractFiber metal laminates (FMLs) based on unidirectional glass fabric and aluminum alloy 7075‐T6 sheet bonded with 5052 epoxy, were prepared by vacuum molding followed by hand layup method. Interface of metal‐adhesive was improved by a series of surface treatments of aluminum sheets, which increased the surface roughness (Ra) of aluminum from 227 to 1067 nm. Matrix was modified by incorporation of graphene nanosheets (GNs) and nanodiamonds (NDs). In‐order to optimize the quantity of nano‐reinforcements three different proportions were used, that is, 0.5, 1, and 1.5 wt%, inclusive of equal proportions of GNs and NDs. For comparison, pristine epoxy based FMLs were also fabricated. Synergetic effect of GNs and NDs improved the tensile strength by 25%, inter laminar shear strength (ILSS) 46%, and fracture toughness 70%, by combination of GNs and NDs up to 0.5 wt%. Surface roughness test and water drop contact angle test were performed to evaluate the surface roughness of aluminum, while the microscopic analysis was conducted to observe the fracture behavior of FMLs. Finite element method (FEM) for numerical validation of experimental results was also performed. From the results, it was concluded that combination of aluminum surface treatment and matrix modification improved the overall performance of FMLs.

Effect of face sheet on the flexural and tensile characteristics in GLARE laminates

ABSTRACT The present study is carried out to study Glass Fibre Reinforced Aluminium Laminate (GLARE) structures and to evaluate their flexural and tensile properties. The GLARE specimens were fabricated using hand layup with vacuum bag moulding process wherein the aluminium sheets and E-Glass fibre woven mats of fixed thickness are bonded together by application of epoxy resins. Three different thicknesses of aluminium alloy (0.2 mm, 0.3 mm and 0.4 mm) Al-2024 T3 are used for the purpose of the study. The aluminium sheets are stacked together by application of epoxy resin between the sheets and are cured under a compression moulding machine under constant pressure. The overall thickness of the specimen is maintained constant for 2 mm. The samples were subjected to a three-point bending and tensile test as per ASTM D790 and ASTM D3039 standards, respectively, to evaluate their mechanical properties. The results indicate that the tensile strength of the composites is maximum for the specimen with aluminium 2024 T3 face sheet with a minimum thickness of 0.2 mm; however, with the increase in the thickness, the tensile strength is found to be decreasing.

Indentation Creep Response and Rupture Mechanisms in GLARE: Experimental and Statistical Evaluation

Abstract Fiber metal laminates (FMLs) are structural materials that play a vital role in the aviation sector, in which they are exposed to cyclic long-term loading. This article investigates creep response and rupture mechanisms of glass laminate aluminum reinforced epoxy (GLARE) FMLs based on microindentation creep testing. Specimens were manufactured by compression molding, and experiments were conducted under different test parameters, namely, aluminum surface treatment (in terms of surface roughness), creep chamber temperature, indentation load, and run time. In addition, rupture mechanisms were analyzed using scanning electron microscopy. The individual interaction of control parameters on creep strain and mass loss response was studied using Taguchi method. Among the studied factors, specimen condition and creep chamber temperature predominantly control creep rupture, whereas load and time were less important, as confirmed by statistical predictions using linear regression.

Multichannel Real-Time Electronics Platform for the Estimation of the Error in Impact Localization with Different Piezoelectric Sensor Densities

The work presents a structural health monitoring (SHM) electronic system with real-time acquisition and processing for the determination of impact location in laminate. The novelty of this work is the quantitative evaluation of impact location errors using the Lamb wave guided mode S0, captured and processed in real-time by up to eight piezoelectric sensors. The differential time of arrival is used to minimize an error function for the position estimation. The impact energy is correlated to the amplitudes of the antisymmetric (A0) mode and the electronic design is described to avoid saturation for signal acquisition. The same electronic system is designed to acquire symmetric (S0) low level signals by adequate gain, bandwidth, and signal-to-noise ratio. Such signals propagate into a 1.4 mm thick aluminum laminate at the group velocity of 5150 m/s with frequency components above 270 kHz, and can be discriminated from the A0 mode to calculate accurately the differential arrival time. The results show that the localization error stabilizes at a value comparable with the wavelength of the S0 mode by increasing the number of sensors up to six, and then remains constant at up to eight sensors. This suggests that a compromise can be found between sensor density and localization error.

Effects of Thermal Residual Stresses on Tensile and Interlaminar Shear Behaviors of GLARE Laminates

The residual stresses caused by curing, forming and machining process significantly affect the mechanical behaviors of composite materials, especially for super hybrid structure like GLARE (glass fiber reinforced aluminum laminates). In this work, the curing thermal residual stresses characteristics of GLARE and corresponding effects on tensile and interlaminar shear behaviors were investigated. Firstly, the characteristics of residual stresses were described by a finite element (FE) model and verified by layer removal method. Then, thermal residual stresses were incorporated into FE mechanical behavior prediction models in the form of predefined field to analyze the effects on tensile and interlaminar shear behaviors. The corresponding simulation conclusions were consistent with the experimental observations. The results indicated that there were about 40 MPa tensile residual stress in aluminum layers and 70 MPa compressive residual stress in GFRP (glass fiber reinforced polymer) layers of GLARE. Residual stresses had obvious reduction effect on the yield strength of GLARE, and the prediction accuracy was hence improved by 9%. Moreover, the failure mode of tensile tests was hardly affected by the residual stresses, but the tensile strength and the initial damage loads were reduced slightly. In interlaminar shear tests, the peak load and initial damage load were reduced by the residual stresses in the adhesive layers of GLARE, and the interlaminar shear strength was slightly influenced. An edge failure mode caused by edge effect was observed during the propagation of the delamination cracks, which was verified by interlaminar shear finite element models and SEM (scanning electron microscope) images.

Effect of coupling agent quantity on composite interface structure and properties of fiber metal laminates

AbstractEpoxy silane coupling agent A‐187 and amine silane coupling agent A‐1387 were used to modify the interface of carbon‐reinforced aluminum laminates (CARE), respectively. The effects of the type and content of coupling agent on the microstructure and mechanical properties of CARE were investigated. Results show that with the increase in the content of two coupling agents, the wettability first increases and then decreases. When the mass fraction of the two coupling agents is 1%, good wetting property is obtained, and the interlaminar shear and flexural strengths of the CARE plate are the best. Compared with epoxy coupling agent A‐187, amine coupling agent A‐1387 had better wettability to aluminum alloy surface and highly contributed to the improvement of interface structure and properties, which then increased the interlaminar shear and flexural strengths by 19.1% and 8.9%, respectively.

Experimental and numerical analysis of anti-icing a GLARE laminate

Abstract This study aimed at developing a numerical model to estimate the power consumption of a GLAss fiber REinforced aluminum-based electro-thermal ice protection system for anti-icing. The GLAss fiber REinforced aluminum laminate was embedded with recurred S-shaped copper meshes thermally energized by a surface power density. The model determined the influence of a forced convective heat loss and copper-mesh dimension on anti-icing. As a test case, the numerical model addressed the anti-icing performance of a GLAss fiber REinforced aluminum 5A-3/2 laminate at a sub-freezing ambient temperature of 267.95 K. The model demanded a surface power density of 13.03 kW/m2 in order to keep the temperature of the outer aluminum-skin at 285.44 K, which was clearly beyond the water freezing point. The numerically predicted power consumption for anti-icing was in excellent agreement with that from the experiment. The experiment was conducted in a miniature icing wind tunnel by incorporating the comparable icing condition of the numerical analysis. In the experiment, an infrared thermography camera determined the spatio-temporal temperature history of the outer aluminum skin in contact with the free-stream. The infrared thermography camera measurements of surface temperature collapsed in close proximity to that from the numerical analysis. The outcomes of this study will consolidate the confidence of aircraft manufacturers on the proposed anti-icing system.

Understanding the Effect of Halloysite Nanotubes Addition Upon the Mechanical Properties of Glass Fiber Aluminum Laminate

The influence of different wt. % of halloysite nanotubes (HNTs) on the mechanical properties of glass laminate aluminum reinforced epoxy (GLARE) was explored. GLARE (3/2) with quasi-isotropic lay-up, [Al/[(0°/90°)/(45°/−45°)]s/Al/[(0°/90°)/(45°/−45°)]s/Al] filled with 0, 0.25, 0.5, 1, 2 and 3 wt. % of HNTs was fabricated using hand lay-up followed by compression molding. Tensile, flexural, in-plane shear, interlaminar shear, bearing and impact tests were conducted. Results revealed that the maximum effect on the studied mechanical properties was obtained at 1 wt. % of HNTs. Further increase in HNTs wt. % reduces the trend. The tensile, flexural, in-plane shear and interlaminar shear properties of GLARE filled with 3 wt. % of HNTs were lower compared with original GLARE. But the bearing strength and impact strength are still higher. To examine the fracture mechanism, scanning electron microscope (SEM) images were taken. Field emission scanning electron microscope (FE-SEM) and energy-dispersive X-ray spectroscopy (EDX) were used to show the chemical composition of the studied samples.

Damage analysis of carbon fiber reinforced aluminum laminate under short beam and single edge notch beam bend test

In the present study, the carbon fiber aluminum laminates were fabricated in two configurations Al/0°/Al/0°/Al/0°/Al/0°/Al, Al/0°/Al/90°/Al/90°/Al/0°/Al (represented as Carall 1, Carall 2 respectively) after different surface modifications employed to AA2024-T3 sheets. The influence of surface modification on interlaminar shear strength (ILSS) was investigated by short beam shear (SBS) test for each configuration with different span to depth ratio. The Caralls fabricated by abrasion of 220 grit size paper show maximum apparent ILSS than other surface modifications due to the better mechanical interlocking at the interface. The measured apparent ILSS is about 35% higher than only anodized treatment. The finite element (FE) simulation reveals in both laminates the failure is initiated by inter laminar delamination near the mid span of the laminate. The position of the crack in Carall 1 is at the innermost interface however in Carall 2 at the outermost interface. In the later stage of SBS tests multiple delamination followed by matrix cracking leads to final separation of the laminate layers. Further, the full field strain in the neighbourhood of notch during single edge notch beam bend (SENB) test was evaluated using the digital image correlation technique supported by FE simulation. Carall 1 treated with 220 grit paper shows 46% more plane strain fracture toughness than AA2024-T3 and about 10% improvement than anodized treatment attributed to crack bridging and improved inter laminar strength. The improvement of toughness significantly reduces for Carall 2 and maximum 13% improvement is noticed for Carall 2 treated with 220 grit papers for improved inter laminar strength.

Short-beam shear fatigue life assessment of thermally cycled carbon–aluminium laminates with protective glass interlayers

Fibre metal laminates (FMLs) are attractive construction materials, especially for use in aerospace and transport facilities. Throughout their service life, thin-walled structures made of FMLs are exposed to static and dynamic loads, as well as corrosion and the unfavourable influence of environmental conditions. The paper presents an experimental analysis of the combined mechanical and environmental long-term behaviour of carbon-based fibre metal laminates and their variants with protective glass layers. The Al alloy/CFRP and Al alloy/GFRP/CFRP laminates in a 3/2 configuration were used. The tested laminates were subjected to 1500 thermal cycles with a temperature range of 130 °C. The static and fatigue interlaminar shear strengths were tested before and after thermal conditioning. It was shown that the stable stiffness reduction in the tested laminates was observed with increasing fatigue cycles, due to the progressive fatigue damage accumulation. The thermally cycled laminates feature slightly smoother stiffness loss, while a more rapid decrease was observed in thermally untreated laminates. Moreover, the fatigue life of the tested laminates subjected to thermal cycling revealed nine times fewer fatigue cycles of laminates with glass protectors after thermal cycles in comparison to the laminates not subjected to thermal cycling.