Recycling of aluminum from fibre metal laminates
Recycling of aluminum alloy scrap obtained from delaminated fibre metal laminates (FMLs) was studied through high temperature refining in the presence of a salt flux. The aluminum alloy scrap contains approximately mass fraction w(Cu) = 4.4%, w(Mg) = 1.1% and w(Mn) = 0.6% (2024 aluminum alloy). The main objective of this research is to obtain a high metal yield, while maintaining its original alloy compositions. The work focuses on the metal yield and quality of recycled Al alloy under different refining conditions. The NaCl-KCl salt system was selected as the major components of flux in the Al alloy recycling. Two different flux compositions were employed at NaCl to KCl mass ratios of 44:56 and 70:30 respectively, based on either the eutectic composition, or the European preference. Different additives were introduced into the NaCl-KCl system to study the effect of flux component on recycling result. Although burning and oxidation loss of the alloying elements during re-melting and refining take place as the drawbacks of conventional refining process, the problems can be solved to a large extent by using an appropriate salt flux. Experimental results indicate that Mg in the alloy gets lost when adding cryolite in the NaCl-KCl salt system, though the metal yield can reach as high as 98%. However, by adding w(MgF2) = 5% into the NaCl-KCl salt system (instead of using cryolite) all alloying elements were well controlled to its original composition with a metal yield of almost 98%.
Development of a Firefighting Agent Application Test Protocol for Aircraft Fuselage Composites, Phase I—GLARE
A research effort is underway to develop a standardized test method to determine the amount of firefighting agent needed to extinguish fires involving aircraft built with advanced composite materials. These tests focus on evaluating the behavior of GLAss-REinforced aluminum laminate (GLARE) when exposed to a simulated aviation fuel-fed pool fire. This test is a continuation of previous carbon fiber-reinforced plastic fire tests reported in DOT/FAA/TC-12/6, “Development of a Firefighting Agent Application Test Protocol for Aircraft Fuselage Composites, Phase I—Carbon Fiber.” This series of tests assessed the fire behavior of GLARE samples that are representative of aircraft skin applications. These tests focused on determining (1) if the temperature transfers through the sample, (2) if burnthrough or post-exposure burning occurs, (3) if a smoldering condition exists after fire exposure, (4) the amount of time it takes for the sample to naturally cool below 300°F (149°C) after the fire source is removed, and (5) if there are any physical indicators that would help firefighters determine if the sample has cooled sufficiently to prevent re-ignition. The Federal Aviation Administration NextGen Burner was used as the fire source. It generates temperatures just over 1800°F (990°C), which are similar to that of an aviation fuel-fed pool fire. Twelve tests were conducted using GLARE 3-5/4-0.3, with a total thickness of 2.5 mm (0.098 in.). Nine of these tests used a 12- by 18-inch sample positioned flat, with the face of the sample in front of the fire source. The remaining three tests used the same size sample cut into four equal pieces layered 0.75 inch apart and set with the edges of the long side facing the fire source. The samples were subjected to different fire exposure times. Temperature measurements and infrared images were collected during the tests. The nine flat panel tests measured the temperature on both sides of the sample, and the temperature measured on the back of the sample was less than half of the burner side temperature. Burnthrough did not occur during any of these tests. In each test, the outer layer of aluminum that faced the burner melted away, but the glass layers below remained mostly intact. There was some amount of post-exposure flame in all tests performed. Despite the exposure duration, the post-exposure flame lasted approximately 1 minute. The recorded times for the flat panel test samples to cool below 300°F (149°C) were not consistent. However, for the layered tests, the recorded times were consistent with an average time of 11 minutes 36 seconds. There were no visual indications that the samples had cooled below 300°F (149°C).
Fatigue and Damage Tolerance of Glare
Methods have been developed to describe the fatigue initiation and propagation mechanisms in flat panels as well as mechanically fastened joints and to determine the residual strength of large flat panels. Glare shows excellent crack growth characteristics due to the mechanism of delamination and fibre bridging. The fatigue insensitive fibres restrain the crack opening and transfer load over the crack in the metal layers. During the initiation phase fibre bridging does not occur and the behaviour is dominated by the metal initiation properties. Mechanically fastened joints introduce additional effects such as secondary bending, load transfer and aspects related to the fastener installation. The residual strength of Glare is dependent on the amount of broken fibres and the delamination size and can be described with the R-curve approach.The impact resistance of Glare is related to the aluminium and glass/epoxy properties and is significantly higher than the impact resistance of monolithic aluminium. The same has been proven for fire resistance. Depending on the Glare grade and thickness, the outer aluminium layer will melt away, whereas the other layers will remain intact due to carbonisation of the glass/epoxy layers and delamination of the laminate. The air in the delaminations will act as insulation, keeping the temperatures at the non-exposed side relatively low.