Fiber metal laminates (FMLs) comprised of metal alloy and composite materials have been extensively applied in a broad range of engineering structures in virtue of their outstanding functional characteristics and cost benefits. This paper provides a comprehensive review on the state-of-the-art of the impact characteristics of fiber metal laminates through experimental, numerical and analytical methods. First, influences of various internal and external factors/parameters on the impact responses and damage mechanisms of fiber metal laminates are discussed in detail for different impact conditions. Second, a range of numerical techniques are compared to evaluate their effectiveness for modeling the impact behavior of fiber metal laminates as reported in literature. Third, analytical models and associated engineering applications of fiber metal laminated structures are also discussed. Based upon the material constituents and manufacturing techniques, some feasible methods are suggested to enhance the impact resistance of FML materials. Finally, the concluding remarks and outlooks are provided for recommending the potential future studies on novel FML materials and structures.

On impact behavior of fiber metal laminate (FML) structures: A state-of-the-art review

In this study, experimental investigations are implemented to evaluate the effect of incorporation of graphene nanoplatelets (GNPs) on the low-velocity impact behavior of composites and fiber metal laminates (FMLs). The hand layup technique is employed to fabricate composite specimens and FML panels with 2/1 configuration. Impact response and damage patterns of unmodified and modified specimens subjected to various impact energy levels are compared. The results reveal that the incorporating 0.2 wt% of GNPs strengthens the impact resistance of FMLs so that the modified panels possess higher bending stiffness, peak load, energy absorption and SEA compared to the unreinforced ones. Visual inspections and SEM images exhibit that the inclusion of GNPs enhances the adhesion between resin/fibers as well as composite plies, thereby reducing damage area and increasing penetration threshold of FMLs. In addition, reinforcing composite panels considerably improves the impact behavior in comparison with the unmodified composites.

An experimental investigation on the effect of incorporating graphene nanoplatelets on the low-velocity impact behavior of fiber metal laminates

Fabrication processes of metal-fiber reinforced polymer hybrid components: a review

This research investigates the effects of the inclusion of graphene nanoplatelets (GNPs) on the buckling response of a set of novel three-dimensional fiber metal laminates (3D-FMLs) under a uniaxial compressive load. This special 3D-FML consists of a 3D fiberglass fabric (3DFGF)-epoxy composite hybridized with basalt-epoxy laminate with their resin containing different concentrations of GNPs (0.25, 0.5, and 1.0 wt%), sandwiched between stainless steel (SS) face-sheet with different thicknesses (0.3 mm and 0.48 mm). To further enhance the response of the 3D-FMLs, the cavities of their 3D fabric are filled with two-part low- and high-density liquid polyurethane foam. The main objective is to develop a lightweight and resilient hybrid material system with a competitive cost. In addition, the response of the 3D-FMLs is simulated numerically using LS-DYNA, a commercially available finite element (FE) software. The results produced by the FE models are in good agreement with those obtained experimentally. Moreover, a parametric numerical study is carried out to assess the influence of SS thicknesses and specimen gauge lengths on the buckling response of this hybrid system. The results indicate that a combination of high-density polyurethane foam with 0.25 wt% of GNP content produces the highest buckling capacity, cost-effectively. The microstructural analysis using the field emission scanning electron microscopy (FESEM) technique would also exhibit the distribution and agglomeration of GNPs within the core of 3D-FMLs.

Enhancement of buckling response of stainless steel-based 3D-fiber metal laminates reinforced with graphene nanoplatelets: Experimental and numerical assessments

Effect of graphene nanoplatelets on water absorption and impact resistance of fibre-metal laminates under varying environmental conditions

Investigation into effect of the graphene oxide addition on the mechanical properties of the fiber metal laminates

Structural integrity, fuel efficiency, and reduced emission of greenhouse gases are the topmost priorities of the modern-day aerospace and automobile industries. Fiber-metal laminates (FMLs) can reduce most of these concerns by reducing a significant amount of weight without compromising structural reliability. Although this material was invented a few decades ago, large scale production, especially the forming process of small and complex-shaped products, has not matured yet. The necessity of manual processing makes it more cost-intensive and time-consuming. The forming difficulty comes with the limited elongation of the fiber layers compared to the metallic layers. As a result, the conventional approaches to form FMLs parts are not very suitable. In this paper, an investigation has been conducted to improve the drawability of FMLs sheets in deep drawing of cylindrical cups, made of semi-cured Glare material. A variable blank holder force (VBHF) method was proposed, which means the variation of the friction force of the holder and the laminate on contact surfaces, as a function of the position of outer flange edge. Fracture and wrinkling limits have been determined, and a BHF control trajectory has been presented to improve the forming quality, increase the drawing depth, and eliminate defects. Both experimental and numerical results from the VBHF were compared with constant BHF results. It is evident that the proposed VBHF scheme helps to improve the drawing quality compared to the conventional constant BHF. As a result, this method can enhance the production rate as well.

Experimental and numerical investigation of fiber metal laminate forming behavior using a variable blank holder force

Demand for lightweight materials with structural integrity is necessary due to the increased global concern about air pollution and excessive fuel consumption. Fiber metal laminates (FMLs) have the potential to find the perfect balance between weight reduction and structural reliability, which includes improved damage tolerance. However, the fiber used in FMLs has limited elongation, and existing forming approaches are not qualified enough to produce small and deep laminate components, especially for mass production. In this research paper, an investigation has been carried out to understand the laminate system’s failure mode, eliminate defects, and improve drawability. A comparative study has been carried out for producing small parts made of GLARE (glass laminated-reinforced epoxy) material, using the conventional cured laminate and non-cured laminate with a hot-pressing method. The effect of these two methods on the GLARE forming behavior has been discussed. The numerical and experimental results of the new approach were compared with the conventional method. Results exhibit the positive effect of this approach on the quality of the formed cups and depth. Finally, this investigation can enhance the FMLs, and GLARE part applications compared to the conventional methods.

A comparative study on the GLARE stamp forming behavior using cured and non-cured preparation followed by hot-pressing

Even though fiber metal laminates (FMLs) were developed many years ago, existing forming approaches are not well qualified to produce intricate and small thin geometry. There are great difficulties in the deep drawing procedure, even for low forming depth. These difficulties are mainly related to the fiber layers limited elongation compared to the metals, and the process parameter selection during the deep drawing, which needs to be chosen very carefully. This research presents a numerical and experimental study on the influence of the hydroforming process parameters on FML hemispherical dome. The Aluminum 2024-T3 and prepreg glass fiber were used to produce the FML blanks. The parameters covered in this investigation were cavity pressure (CP), blank holder force (BHF), die entrance radius (DR), blank holder gap (BHG), and punch speed (PS). Taguchi’s design of experiments determined the effects of the input parameters on wrinkling and thinning. Results indicated that the BHG has the most significant impact on thinning and wrinkling. Optimization was conducted, and the optimum selected process parameter values were 80 kN for BHF, 15 MPa for CP, 8 mm for DR, 1.1 mm for BHG, and 30 mm/min for PS. Results revealed that FML cups formed by the optimized parameters could improve the utilization of the FMLs in mass production.

An Analysis of Process Parameters in the Hydroforming of a Hemispherical Dome Made of Fiber Metal Laminate

Controlling the material flow under the blank holder in hydroforming is a delicate point that can be controlled by the blank holder force (BHF), cavity pressure (CP) and the blank holder gap (BHG). BHG is one of the effective parameters to control the material flow. A numerical and experimental approach studied the impact of the BHG on the Hydromechanical Deep Drawing (HDD) of a hemispherical cup made with 2/1 Glare sheets, including another two factors, CP and BHF. BHGs with different thickness was used in the experiments to form Glare Laminate. Simulation and experiment illustrate that an optimized value of these parameters has a good effect on the forming quality and depth of the final product. Finally, an appropriate value of the BHG is projected and the explanations of the failure modes are discussed.

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Shahrukh Khan

Papers

Investigation into effect of the graphene oxide addition on the mechanical properties of the fiber metal laminates

Experimental and numerical investigation of fiber metal laminate forming behavior using a variable blank holder force

A comparative study on the GLARE stamp forming behavior using cured and non-cured preparation followed by hot-pressing

An Analysis of Process Parameters in the Hydroforming of a Hemispherical Dome Made of Fiber Metal Laminate

Process Control Improvement in Deep Drawing of Hemispherical Cups Made of GLARE Material