Experimental Investigation on the Low Velocity Impact Response of Fibre Foam Metal Laminates

The combination of fibre metal laminates (FML) and sandwich structures can significantly increase the performance under impact of FMLs. The goal of this work was to create a material that will combine the superior properties of FMLs and foam sandwich structures in terms of the impact resistance and simultaneously have lower density and fewer disadvantages related to the manufacturing. An extensive impact testing campaign has been done using conventional fibre metal laminates (carbon- and glass-based) and in the proposed fibre foam metal laminates to assess and compare their behaviour. The main difference was observed in the energy absorption mechanisms. The dominant failure mechanism for fibre foam laminates is the formation of delaminations and matrix cracks while in the conventional fibre metal laminate the main failure mode is fibre cracking due to high local stress concentrations. The reduction in the fibre cracking leads to a better after-impact resistance of this type of structure improving the safety of the structures manufactured with these materialsThis research was financed in the framework of the project Lublin University of Technology–Regional Excellence Initiative, funded by the Polish Ministry of Science and Higher Education, grant number 030/RID/2018/19

The Durability of an Organic–Inorganic Sol–Gel Interlayer in Al-GFRP-CFRP Laminates in a Saline Environment

The aim of the study was to assess the selected properties of a hybrid organic–inorganic silane sol–gel coating (HSG) used in hybrid fiber metal laminates (FML) in a corrosion environment. The HSG coating on the aluminum alloy was produced using 3M™ AC130-2 formulation consisting of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (zirconium(IV) propoxide) (TPOZ). Laminates consisted of aluminum alloy AA2024-T3 sheets, with carbon fiber reinforced polymers (CFRPs) and a glass fiber reinforced metal–composite structure (GFRP). Potentiodynamic and polarization curve and impedance (EIS) tests were carried out on HSG at ambient temperatures after 1 h and 150 h of soaking. Neutral 0.5 M NaCl and 0.8 M NaCl solutions were used for open circuit potential (OCP) and potentiodynamic tests, and 0.5 NaCl was used for the EIS test. A neutral salt spray (NSS) test was applied to laminates with a 12 week exposure period. The results obtained revealed that the HSG coating did not provide sufficient protection against corrosion of the aluminum alloy in direct contact with an aggressive environment but was effective as an interlayer. Local aluminum sheet perforation did not lead to delamination at the metal–composite interface regardless of the type or configuration of the composite. This confirms the durability of HSG used in FMLs

The Correlation of LVI Parameters and CAI Behaviour in Aluminium-Based FML

An experimental analysis of mechanical behaviour for aluminium-based fibre metal laminates under compression after impact was conducted. Damage initiation and propagation were evaluated for critical state and force thresholds. Parametrization of laminates was done to compare their damage tolerance. Relatively low-energy impact had a marginal effect on fibre metal laminates compressive strength. Aluminium–glass laminate was more damage-resistant than one reinforced with carbon fibres (6% vs. 17% of compressive strength loss); however, aluminium–carbon laminate presented greater energy dissipation ability (around 30%). Significant damage propagation before the critical load was found (up to 100 times the initial damaged area). Damage propagation for assumed load thresholds was minor in comparison to the initial damage size. Metal plastic strain and delaminations are dominant failure modes for compression after impact

The Effect of Layer Thicknesses in Hybrid Titanium–Carbon Laminates on Low-Velocity Impact Response

The purpose of the work was the effect of metal volume fraction of fiber metal laminates on damage after dynamic loads based upon the example of innovative hybrid titanium–carbon composite laminates. The subject of the study was metal–fiber hybrid titanium–carbon composite laminates. Four types of hybrid titanium–carbon laminates were designed with various metal volume fraction coefficient but constant thickness. Based on the results, it can be stated that changes in the metal volume fraction coefficient in the range of 0.375–0.6 in constant thickness titanium–carbon composite laminates do not significantly affect their resistance to impacts in the energy range of 5–45 J. It was concluded that there were no significant differences in maximum force values, total contact time, and damage range. Some tendency towards a reduction in the energy accumulation capacity was observed with an increase in thickness of the metal part in relation to the total thickness of the laminate, especially in the lower impact energy range. This can result in the lower bending stiffness of laminates with lower metal content and potential elastic strain of the composite part before the initiation of the fiber damage process

Non-destructive testing investigation of gaps in thin Glare laminates

The manufacturing of Fibre Metal Laminates, consisting of alternating layers of pre-preg fibre and metal is complex, and defects can be introduced during manufacturing. The automation of the manufacturing steps is vital for future Glare production, and specific defects have to be considered. Among them, gaps between pre-preg plies represent a potential risk for the mechanical performances of the laminate. In this paper/research, non-destructive testing based on ultrasonic inspections are performed on Glare with pre-preg gaps in order to extend and improve the current state of the art to different pre-preg gap widths, depths, and lay-ups. Firstly, gaps were introduced in Glare specimens. Then, a conventional C-scan ultrasonic inspection is performed. In order to overcome the current limitations of a top or planar view of the laminates, the evaluation of the depth of the gaps in the laminates is performed by means of phased array ultrasonic testing. Finally, images of the laminate cross-section have been collected in order to provide a meaningful evidence of the ultrasonic-based analysis. Results from different Glare and gap widths and depths show the accuracy of the proposed investigation which is able to provide a detailed assessment of the gap occurrences also for very thin laminates.Aerospace Manufacturing Technologie

The mechanical effects of kissing bonding defects in hybrid metal-composite laminates

Fibre metal laminates (FML) are hybrid materials perspective for wind-turbine, containers and marine objects, besides the aerospace industry. During the manufacturing process some faults can occur and can be hazardous for the reliability of FML structures. One of the most critical defects are kissing bonding due to their lack of detectability and strength compared to traditional delamination defect. The quantitative explanation were under consideration, such as loads effects; material properties; prediction of response; fracture analysis. The purpose of this work is the evaluation the impact of this type of defect on the part in-plane and the out-of-plane mechanical properties. It was presented that even responsive NDT methods are not able to detects the kissing bonding defect in FML components. Simultaneously, the kissing bonding impact on mechanical properties in FML is significant. In the case of FMLs with the orientation of the fibre perpendicular to the peel direction there is one failure pattern which is interlayer fracture. Whereas in the case of FMLs with the direction of the fibres longitudinal to the peel direction two failure patterns occur which is interlayer fracture and translaminar fibre crack. Depending on the kissing bonding area width the interlayer fracture in the composite can be observed until kissing bonding defect area and then transmission of the crack to the metal/composite interface through the fibres. In the case of low extension of poor adhesion area, the two parallel interlaminar cracking can be seen, one at the metal/composite interface in poor adhesion area, the second continuous in the composite layer.Aerospace Manufacturing Technologie