Fiber Metal Laminates Research Articles

Strength and Ductility of Concrete Confined by Fiber Metal Laminate Composites

Strength and Ductility of Concrete Confined by Fiber Metal Laminate Composites

Research on the deformation law of ultra-thin fiber metal laminates under the synergistic effect of nano-reinforcement and scale effect

At present, titanium alloy/carbon fiber reinforced polymer (TA1/CFRP) laminates, representing the latest fourth generation of fiber metal laminates (FMLs), are predominantly applied in the field of aerospace. The miniaturization of traditional FMLs in thickness or plane size to the micron level for the study of structural properties of ultra-thin laminates will further expand the application of FMLs in the field of micro-devices. Given that carbon nanotubes have a strengthening mechanism in polymers. However, most existing studies have focused on the effect of carbon nanotubes on the properties of macro-scale FMLs, while the enhancement mechanism of the interfacial and mechanical properties of ultra-thin micro-scale FMLs has not been studied, leaving the mechanism still unclear. Based on this, this paper explores the interfacial deformation mode, damage fracture and performance enhancement mechanism of the ultra-thin TA1/CFRP laminates by comparing the parameters of tensile strength and elongation under quasi-static conditions and different process parameters of multi-walled carbon nanotubes content, test temperature, geometry size and grain size. Meanwhile, the correlation law between high-speed tension and quasi-static tension is determined, a 29.3 % increase in tensile strength as the strain rate rises from 0.001 s−1 to 100 s−1, yielding the basic deformation law of ultra-thin FMLs.

Performance Analysis of Helical Milling and Drilling Operations While Machining Carbon Fiber-Reinforced Aluminum Laminates

Being a difficult-to-cut material, Fiber Metal Laminates (FML) often pose challenges during conventional drilling and require judicious selection of machining parameters to ensure defect-free laminates that can serve reliably during their service lifetime. Helical milling is a promising technique for producing good-quality holes and is preferred over conventional drilling. The paper compares conventional drilling with the helical milling technique for producing holes in carbon fiber-reinforced aluminum laminates. The effect of machining parameters, such as cutting speed and axial feed, on the magnitude of cutting force and the machining temperature during conventional drilling as well as helical milling is studied. It was observed that the thrust force produced during machining reduces considerably during helical milling in comparison to conventional drilling at a constant axial feed rate. The highest machining temperature recorded for helical milling was much lower in comparison to the highest machining temperature measured during conventional drilling. The machining temperatures recorded during helical milling were well below the glass transition temperature of the epoxy used in carbon fiber prepreg, hence protecting the prepreg from thermal degradation during the hole-making process. The surface roughness of the holes produced by both techniques is measured, and the surface morphology of the drilled holes is analyzed using a scanning electron microscope. The surface roughness of the helical-milled holes was lower than that for holes produced by conventional drilling. Scanning electron microscope images provided insights into the interaction of the hole surface with the chips during the chip evacuation stage under different speeds and feed rates. The microhardness of the aluminum layers increased after processing holes using drilling and helical milling operations. The axial feed/axial pitch had minimal influence on the microhardness increase in comparison to the cutting speed.

On the bending behavior of hybrid fiber–metal laminates (HFMLs) based on aluminum and glass/Kevlar fibers reinforced epoxy

In this work, the mechanical behaviors under flexural loading of fiber–metal laminates (FMLs) comprised of an aluminum alloy reinforced with glass fibers (GFs) and Kevlar fibers (KFs) embedded in an epoxy composite are experimentally investigated. For this purpose, non-FMLs, FMLs, and hybrid FMLs (HFMLs) are tested and their results are compared in terms of the flexural strength and modulus, strain to failure, toughness, interlaminar shear strength (ILSS), and specific properties. Results show that the incorporation of GFs on the compression side and KFs on the tensile side improves the bending properties of the HFMLs compared to the KF-based FMLs, which enhances the laminates’ resistance to bending loads. The HFMLs exhibit improvements of 24%, and 5% in flexural strength and modulus, respectively, compared to the KF-based FMLs. Moreover, hybridization significantly improves strain to failure by up to 115% compared to the GF-based FMLs. Additionally, the ILSS analysis reveals improved values in FMLs compared to non-FML samples, when GF-based FMLs demonstrate higher ILSS than KF-based ones, which can be attributed to GFs’ stiffness and high-quality bonding with the aluminum sheets. HFMLs attain a 19% improvement in ILSS compared to the KF-based FMLs. The failure mechanism depends on the intrinsic features of the studied fibers, while the studied FMLs display better damage tolerance. In this context, the HFMLs present enhanced toughness, delamination resistance, and the ability to prevent crack propagation, positioning them as promising candidates for lightweight structural applications where a balance between strength, stiffness, and toughness is required.

Effect of boundary conditions on the low‐velocity impact damage mechanism of fiber metal laminate

AbstractThe boundary condition is a very important factor when characterizing the impact performance of a material or a structure. However, its effect on fiber metal laminate (FML) has been rarely mentioned. In the present investigation, three levels of low‐velocity impact tests were conducted on the glass fiber reinforced aluminum laminate (Glare) under two different boundary conditions, one was that defined in ASTM D7136 and another one was self‐designed that has the same constraint area but different constraint degree. One basis of the experiments, finite element analyses were performed to gain a deeper understanding of the different damage mechanisms. With which another three boundary conditions were investigated for further considering the effect of constraint areas on both the impact and non‐impact sides, including that defined in another commonly used standard ASTM D5628 and two self‐designed cases. It was indicated that the boundary conditions influenced less the force and energy responses of Glare laminate, regardless of the impact damage levels, and hardly on the damage behavior as well when perforation was encountered. However, influences were obtained under lower and intermediate damage levels, and it was the constraint area on the rear side and constraint degree that played the dominant roles, respectively. The results achieved can provide suggestions for reasonably evaluating the low‐velocity impact performance of FML.Highlights Comparisons were made between the low‐velocity impact behavior of Glare laminates under five different boundary conditions. Boundary conditions influenced hardly on maximum impact force and energy absorbed ratio, but evidently on damage behavior. Constraint area and constraint degree governed damage mechanism under lower and intermediate impact energies, respectively. Influence of boundary conditions on damage behavior disappeared when the impact energy was enough to perforate Glare laminate.

The Effect of Self-Healing Microcapsules in Corrosion Testing on Magnesium AZ31 Alloy and Fibre Metal Laminates

Fibre metal laminates (FMLs) are the most interesting composite materials of the past decade. They possess the properties of both polymer composites and metallic alloys. However, there is a problem with corrosion when the outer layers are made of aluminium or magnesium. The electrochemical changes that occur during the corrosion process and the mechanisms associated with the corrosion phenomenon are still being investigated. Recently, self-healing phenomena have emerged as a useful approach to prevent corrosion. However, there is limited research on the combination of FMLs and self-healing layers. Therefore, the main purpose of this article is to evaluate the self-healing ability of a magnesium/PEO layer based on microcapsules in a corrosion environment. It was observed that the corrosion mechanism in magnesium alloys is very complex. However, the use of a barrier layer with PEO treatment and microcapsules yielded positive anti-corrosion results. The FML samples were subjected to a 6-week corrosion test, and the addition of microcapsules to the layers showed positive results. In contrast, the samples without microcapsules exhibited intergranular corrosion. In the future, comprehensive tests using self-healing microcapsules in FMLs could greatly enhance their anti-corrosion properties and improve the integrity of the structure.

Low-velocity impact of sandwich beams with fibre-metal laminate face-sheets considering local denting effect

Low-velocity impact of sandwich beams with fibre-metal laminate face-sheets considering local denting effect

Experimental investigation on the low-velocity impact responses of fibre metal laminates with various internal and external factors

This paper aims to investigate the low-velocity impact (LVI) failure mechanism of fibre metal laminates (FMLs), and systematically explore the effects of internal factors (layup sequence and laminate configuration) and external factors (impact energy and environmental temperature) on the LVI responses. The drop-weight impact tester was utilised to conduct LVI tests at -30 °C, 25 °C, and 80 °C on FML-2/1 and FML-3/2 laminates. These laminates were made of S-class high-strength glass fibre and 2024 aluminium-alloy sheet with unidirectional, angle-ply, cross-ply and quasi-isotropic layup sequences. The characteristic curves including contact force-time, contact force-deflection, absorbed energy-time, and strain-time near the dent on the impacted and non-impacted specimen surfaces were obtained respectively. Furthermore, the dent depth of the impacted surface of the FMLs was measured. FML's damage was detected by ultrasonic C-scan, and its longitudinal and transverse sections were scanned by X-ray computed tomography (CT). The findings suggest that the layup sequence has a significant effect on the LVI response of FML-2/1, but has no obvious influence on FML-3/2. Moreover, FML-3/2 exhibits greater impact resistance compared to FML-2/1. The severity of LVI damage increases with the increase of impact energy. Notably, compared to the cases at 25 °C, the LVI failure mechanisms of FMLs undergo significant changes at -30 °C. The elevated temperature of 80 °C significantly affects the LVI damage of FML-2/1, while it has no significant effect on FML-3/2.

Role of stacking sequence, metal sheets, and nano particle on strength and toughness of FMLs

The effect of nano particle inclusion and the stacking sequence/metal volume fraction on the tensile strength and energy absorption properties of Fiber Metal Laminates (FML) is investigated. The FML structure is composed of lightweight thin sheets of aerospace grade aluminum alloy 7075 and unidirectional glass fiber composite sheets with Araldite LY5052 thermoset epoxy system as the matrix. The volume fraction of aluminum sheets in the FML structure was varied by increasing the number of aluminum sheets from 2 to maximum 4. In the second batch, the epoxy matrix is reinforced with of multi-walled carbon nano tubes and nano diamond particles together, each with 0.15 wt%. The purpose is to enhance the properties of the epoxy matrix to facilitate higher inter-laminate adhesion (FRP and aluminum). The results of the tensile testing show that with the increase of the metal volume fraction, the tensile strength as well energy absorbing capability (toughness) both are increased. The inclusion of the nano-reinforcements has increased the tensile strength and the toughness of the FML structure as compared to that of the FMLs without nano particles. The strength-to-weight ratio of FML structures is also increased after the inclusion of nano reinforced as desired for aerospace applications.

The effect of STF-Kevlar composite materials on the impact response of fibre metal laminates

Many studies have confirmed that composite laminates made of metal and fiber reinforced composites have an excellent performance, especially when subjected to impact and fatigue loading, while maintaining a low weight-to-strength ratio. This paper presents an investigation on the impact resistance of shear thickening fluid (STF)-Kevlar composites-based fibre metal laminates (FMLs) subject to low velocity projectile impact. Firstly, the different surface treatments of aluminium alloy were carried out to identify the best bonding strength between the aluminium and composite layers, with the effect of 30V-20min anodizing treatment being identified as the best one. Secondly, impact tests were conducted on pure Kevlar fabric and STF-Kevlar composite fabric to compare their load bearing capacity and energy absorption, showing the latter with more than doubled energy absorption. Subsequently, FMLs based on STF-Kevlar and pure Kevlar fabrics were subjected to low velocity projectile impact. It is found that the impact resistance of the STF-FMLs made with one layer of STF-Kevlar composite fabric is almost equivalent to that of the FMLs made with two layers of pure Kevlar fabric. STF-Kevlar fabric, as a reinforcing material, has a significant contribution to the enhancement of the energy absorption of STF-FMLs.

Automated Porosity Characterization for Aluminum Die Casting Materials Using X-ray Radiography, Synthetic X-ray Data Augmentation by Simulation, and Machine Learning.

Detection and characterization of hidden defects, impurities, and damages in homogeneous materials like aluminum die casting materials, as well as composite materials like Fiber-Metal Laminates (FML), is still a challenge. This work discusses methods and challenges in data-driven modeling of automated damage and defect detectors using measured X-ray single- and multi-projection images. Three main issues are identified: Data and feature variance, data feature labeling (for supervised machine learning), and the missing ground truth. It will be shown that simulation of synthetic measuring data can deliver a ground truth dataset and accurate labeling for data-driven modeling, but it cannot be used directly to predict defects in manufacturing processes. Noise has a significant impact on the feature detection and will be discussed. Data-driven feature detectors are implemented with semantic pixel Convolutional Neural Networks. Experimental data are measured with different devices: A low-quality and low-cost (Low-Q) X-ray radiography, a typical industrial mid-quality X-ray radiography and Computed Tomography (CT) system, and a state-of-the-art high-quality μ-CT device. The goals of this work are the training of robust and generalized data-driven ML feature detectors with synthetic data only and the transition from CT to single-projection radiography imaging and analysis. Although, as the title implies, the primary task is pore characterization in aluminum high-pressure die-cast materials, but the methods and results are not limited to this use case.

Abrasive waterjet cutting of r‐GO infused magnesium fiber metal laminates: Experimental investigations and optimization through gorilla troops algorithm

AbstractLaminated metal‐composite structures, known as fiber metal laminates (FMLs), are modern lightweight materials extensively utilized in diverse industries such as aerospace and automotive manufacturing. These materials offer enhanced impact and fatigue resistance, making them invaluable for various applications. However, machining FMLs poses a challenge due to the occurrence of delamination and heterogenous in nature during conventional methods. Therefore, this study aims to investigate the quality characteristics such as kerf width, surface roughness and kerf taper of Magnesium based FMLs processed with an unconventional machining process namely abrasive water jet cutting (AWJC). These FMLs comprise alternately stacked kevlar/carbon fibers adhesively bonded with epoxy resin matrix filled with varying wt% of reduced graphene oxide (r‐GO), combined with AZ31B alloy sheet as the skin material. AWJC experiments were performed by varying the process parameters including waterjet pressure (275–325 MPa), stand‐off distance (2.5–3.5 mm), and cutting speed (600–800 mm/min) based on the box–behnken experimental design. The findings from the statistical analysis underscore the significant influences of stand‐off distance and waterjet pressure on kerf characteristics, while the inclusion of r‐GO is observed to notably affect the surface quality. In pursuit of enhancing cut quality, a multi‐response optimization was conducted employing the Gorilla Troops Optimization (GTO) algorithm. Comparative analysis with established metaheuristics like the gray wolf algorithm, dragonfly algorithm, and harmony search algorithm reveals GTO's superior performance across various metrics, including rapid convergence, diversity, and spacing values. Further, the cutting‐induced damages such as matrix plowing, fiber‐metal debonding and composite delamination were observed through microstructure analysis.Highlights Magnesium (AZ31B) fiber metal laminate comprising with various wt% of reduced graphene oxide was fabricated. Abrasive waterjet cutting of FMLs were performed based on box–behnken design experimental approach. Statistical analysis and influence of process parameters on the kerf width, surface roughness and kerf taper were investigated. Multi‐response optimization was carried out using metaheuristic‐based gorilla troops algorithm.

Dynamic wetting performance and resin-flow behavior of two-level selective laser-etched metal surface in resin transfer moulding process of fiber-metal laminates

ABSTRACT In selective laser etching for the interfacial strengthening of Fiber Metal Laminates (FMLs), the wettability of customized structured features significantly affects their overall mechanical properties. For two-level features, their complicated geometry makes the evaluation of wettability difficult, which introduces challenges to feature design. In this study, a sandwich FMLs comprising an AA2024-O metal skin and a plain-woven carbon-fiber fabric core is investigated. Three types of two-level feature interfaces are designed and introduced into the FMLs structure. To understand the effect of two-level features on the resin flow and dynamic wetting progress in resin transfer molding, two-phase flow Computational Fluid Dynamics numerical models coupled with porous media and level-set numerical methods are built. The feasibility of the numerical simulation in the qualitative analysis was verified by comparing the results with those of the testing porosity values from X-ray scanning. In addition, the mechanisms of pore formation and transportation are revealed. These results indicate that the deeper groove structure in the etched features plays an important role in discharging residual air and determining the transformation of pores to reduce porosity. The permeability orientations of the porous media and surface structure both have significant impacts on the flow behavior and formation of pores.

Very high cycle fatigue assessment of thermoplastic-based hybrid fiber metal laminate by using a high-frequency resonant testing system

The prolonged fatigue lifetime of fiber metal laminates (FML) compared to monolithic metals is a key aspect for safety-relevant components, where detailed knowledge about the fatigue properties up to the very high cycle fatigue (VHCF) regime is necessary. For thermoplastic-based FMLs, offering formability, recyclability, and mass production due to short consolidation cycle times, this knowledge needs to be established.In this study, FML containing AA6082 sheets and unidirectional glass and carbon fiber-reinforced polyamide 6 was investigated. Fatigue tests up to max. 109 cycles were conducted on a servo-hydraulic and a high-frequency resonant fatigue testing system with frequencies of 10 Hz and 1,000 Hz. Frequency-induced self-heating was evaluated and limited using air-cooling to maintain the matrix properties. Fatigue progress was monitored through high-speed optical deformation analysis.Compared to HCF loads, VHCF loads lead to reduced crack and delamination occurrence. Changes in microstructure are dominated by singular crack initiation and propagation within the aluminum. The FML’s S-N curve shows a significant flattening from the HCF to the VHCF regime, simplifying the predictability of the fatigue life. By using post-stretching, the VHCF strength can be increased by over 60 %, making this thermoplastic-based FML a considerable competitor in the field of FML.

The Effect of Load Steps and Initial Crack Length on Stress Distribution of Fiber Metal Laminates

Fiber Metal Laminates (FMLs) are advanced composite materials composed of alternating layers of fiber-reinforced composites and metal sheets, offering a unique blend of high strength, stiffness, and fatigue resistance. Understanding the behavior of FMLs under different loading conditions, particularly in the presence of initial cracks, is crucial for predicting their structural integrity and performance. This study investigates the effect of initial crack length and load steps on the stress distribution within FML structures through numerical simulation. A glass fiber-reinforced epoxy (GFRE) composite is constituted by glass fibers in off-axis directions of 0o/90o. The crack length of 3 mm, 6 mm, 9 mm, and 12 mm is initially defined on the side of fiber metal laminates. The tensile load was gradually applied to the laminates for five different ratios. The ratios are defined by dividing the tensile load with the area of the laminates which is then called stress ratio. The results show that the greater the initial crack length and load step ratio, the greater the stress around the crack tip. The stress distribution in each layer of the laminates shows different characteristics between tensile and compressive. This will affect the crack propagation behavior of the laminates. Moreover, the findings also provide valuable insights for optimizing FML design, improving damage tolerance, and extending service life in diverse engineering applications.

Spring‐back of Al/CF/PEEK parts during one‐step hot stamping forming using a CAE chain considering all process steps

AbstractSpring‐back is a forming defect in thermoplastic fiber‐metal‐laminate (FML) structures that is influenced by all steps of the forming process. Here, we propose a complete CAE chain to predict spring‐back in a FML parts during one‐step hot stamping by fully considering the material properties, latent heat, thermal mismatch, and modulus mismatch during forming and cooling. Then, constitutive models of the aluminum sheet, a visco‐hyperelastic constitutive model, and an elastic model of the UD CF/PEEK prepregs during hot‐stamping and cooling are introduced to describe the deformation behavior. A Coulombic friction model, latent heat model, and contact resistance model are also proposed to describe the interfacial flow, heat generation, and thermal conductivity. The proposed models and CAE chain are validated by the experimentally determined punching force, geometric shape, temperature, and spring‐back angle. The S‐shaped feature of the FML greatly increases the spring‐back of the FML specimens, and lower punching speeds and higher forming temperatures decreases the S‐shaped feature, thereby reducing the spring‐back angle.Highlights A complete CAE chain was proposed to predict spring‐back in a FML curved beam. A new visco‐hyperelastic constitutive model of the CF/PEEK was applied. The latent heat and thermal mismatch were considered in cooling simulation. The S‐shaped feature of the FML greatly increases the spring‐back. The thermal mismatch increased the S‐shaped feature of the FML.

Adhesion strength and mechanical properties of nanoclay modified hybrid kevlar/jute‐epoxy fiber metal laminate

Adhesion strength and mechanical properties of nanoclay modified hybrid kevlar/jute‐epoxy fiber metal laminate

Study on static load performance of FMLs based on ultra-thin stainless-steel foils and cross-ply thin CFRP

The ultra-thin stainless steel/CFRP laminates overcome the limitations in application due to the weight drawbacks of conventional thick cold-rolled stainless steel. By laminating these two high-performance materials, it allows enhanced design flexibility and exceptional formability, rendering them highly promising in various industries such as automotive structures, shipbuilding, and electronics. The existing research on steel/CFRP laminates primarily revolves around locally reinforcing CFRP with cold-rolled plates of typical thickness (≥1 mm). Nonetheless, there remains a dearth of investigations examining the mechanical properties of laminates with varying metal thicknesses under the same volume fraction, particularly for ultra-thin stainless steel below 0.1 mm in thickness. In this study, to investigate the influence of micron-scale thickness ultra-thin stainless-steel foils on the performance of fiber metal laminates (FMLs), the laminates were manufactured and characterized using stainless-steel foils with thicknesses of either 0.05 mm or 0.025 mm. The tension and bearing properties of cross-ply thin CFRP (30 g/m2) laminates were examined both with and without the incorporation of ultra-thin stainless-steel foils. The findings confirmed that a substantial improvement in tensile strength of up to 35 % when ultra-thin stainless-steel foils were incorporated, accompanied by a remarkable increase in modulus by 65 %. Furthermore, the addition of stainless-steel foils to CFRP composites shifted their failure mode from brittle failure to progressive damage during three-point bending tests. Notably, utilizing 0.025 mm thick stainless-steel foils not only enhanced the strength and modulus but also mitigated post-yield stiffness loss compared to FMLs incorporating 0.05 mm thick stainless-steel foils for cross-ply thin CFRP laminates. Further researches revealed that ultra-thin stainless-steel foils with a thickness of 0.025 mm exhibited improved compatibility for deformation with cross-ply thin CFRP as evidenced by both tensile and bending damage behavior.

Enhancing carbon fiber reinforced aluminum laminates with cellulose paper interlayers: experimental characterization of tensile, flexural, and interlaminar fracture toughness

ABSTRACT The mechanical properties of fiber metal laminates (FML) are influenced by several various factors. Interface adhesion plays a particularly crucial role in interlaminar strength. Enhancing the interlaminar strength of carbon fiber reinforced aluminum laminate (CARALL) composites present a persistent challenge due to inherent weaknesses between metal and composite elements. Therefore, this study focuses on improving the interlaminar performance of CARALL composites by introducing cellulose paper interlayer at the metal/composite interface. The cellulose paper interlayer offers the advantage of being cost-effective and sustainable. Cellulose paper-interleaved CARALL composites were fabricated by vacuum bagging method and exhibited noteworthy improvements in mechanical properties. Comparative analysis with pristine samples revealed substantial enhancements, including a 15% increase in tensile strength, a remarkable 42% improvement in flexural strength, and a significant enhancement in mode-I fracture toughness by 65%. Furthermore, the cellulose paper interleaving played a crucial role in stabilizing fracture formation at the fiber-matrix interface, with mode II fracture toughness witnessing a 3% increase. Visual examination revealed the underlying toughening processes occurring in the interfacial area. This innovative approach of interleaving laminated composites with cellulose paper emerges as a sustainable and effective strategy, demonstrating the potential to fortify and toughen the interlaminar zones of CARALL composites.

Evaluation of mechanical properties and Fick’s diffusion behaviour of aluminum-DMEM reinforced with hemp/bamboo/basalt woven fiber metal laminates (WFML) under different stacking sequences

This work examines the mechanical properties and structural aspects of Al-Hybrid fibre metal laminates (HFMLs) reinforced with fibres from basalt, hemp, and bamboo, including commercial-grade Al6061 alloy mesh (Al-DMEM). Compression moulding of sustainable fibres into various stacking configurations, such as BAlB, BHAlHB, and BBbAlBbB, was required for fabrication. Using cutting-edge methods like SEM and EDX for microstructure investigation, extensive testing was carried out, including tensile, flexural, impact, interlaminar shear, hardness, and water absorption tests. Basalt/Bamboo/Aluminum/Basalt (BBbAlBbB) was the FML configuration with the best mechanical parameters, showing Vickers hardness (24.23 MPa), tensile strength (44.537 MPa), flexural strength (218.24 MPa), and impact resistance (2.01 J) (59.982 HV). In addition, BAlB showed 83.9 % Vickers hardness, 41.7 % flexural strength, and 90.4 % tensile strength of BBbAlBbB samples. BHAlHB displayed 92.9 % of the flexural strength, 65.3 % of the tensile strength, and 93.7 % of the Vickers hardness of BBbAlBbB. Bamboo is hydrophobic by nature, so adding bamboo fibres to BBbAlBbB significantly boosted its resistance to moisture. This study highlights the potential of hybrid FMLs as high-performance, eco friendly materials that are particularly well-suited for applications in interior and exterior panels for micro-mobility (E-vehicles), with AL-DMEM reinforcement offering significant benefits like improved fibre bonding and structural integrity.