Effect of Thermal Cycling and Aging on Heated Fiber Metal Laminates and Glass‐Fiber Epoxy Composites

Abstract

By integrating heater elements in Fiber Metal Laminates, such as GLARE, the material has a promising potential as de-or anti-icing system in aircraft structures. Application of this so called "heated GLARE" material will however result in increase and (up to ten fold) more frequent temperature loading compares to the regular flight conditions. To investigate the longterm effects thermal cycling tests are performed up to 36 000 cycles in three different temperature ranges. Both heated GLARE and FM906 glass-fiber epoxy samples have been thermal cycled using an in-house developed thermal cycling setup. Heating is performed in two different ways, from the outside using Peltier elements and from the inside using integrated heater elements. In addition, continuous heating tests are performed to further examine the effect of aging and internal stress relaxation. FM906 glass-fiber epoxy samples cycled by external heating show an increase in interlaminar shear strength (ILSS) as a result of physical aging, whereas internal heating shows a decrease. Most GLARE samples cycled by internal heating shows an increase in ILSS. The continuous heating tests on heated GLARE confirm that aging and internal stress relief have counteracting effect on the ILSS. The temperature level determines, which effect is most dominant.

Effect of thermal cycling heated Fibre Metal Laminates under static load

“…The temperature range in the thermal cycling tests was chosen from -20 to 50 • C. The typical thermal cycles for the heated GLARE 5-2/1-0.3 samples are shown in Figure 5. Thermal cycling tests in this temperature range showed the largest decrease in ILSS in previous research [2,3]. In this range the negative effect of internal stress relief on the ILSS is not counteracted by the positive ageing effect on the glass-fibre epoxy as present at higher temperatures.…”

“…Therefore, both the mechanical and the thermal loading have a cyclic nature and can lead amongst others to fatigue damage [21]. Moreover, the elevated temperatures in case of anti-and de-icing are expected to cause physical ageing of the epoxy [2,22]. Damage on the leading edge can also be caused by impact, for example due to bird strike, and more gradually due to moisture ingress during the lifetime of the structure.…”

“…In previously reported research the effect of thermal cycling and moisture on heated GLARE has been examined separately and in combination with each other [1,2,3]. The effect of additional static loading was however not yet considered in these investigations.…”

New Materials and Processes for Transport Applications: Going Hybrid and Beyond

“…In the present case, heating elements are integrated in aluminum–glass fiber type FMLs for aerospace applications to provide deicing capabilities. The effect of increased thermal cycling on mechanical properties caused by an introduction of such systems is studied experimentally and evaluated on the basis of changes of interlaminar shear strength …”

Creep behaviour of FM906 glass-fibre epoxy as used in heated fibre metal laminates

“…The elevated temperatures during icing conditions are expected to accelerate physical ageing of the epoxy too. 8,9 Creep in FMLs For FMLs, the literature on creep is limited. Creep research has been performed by Pindera on ARALL (aramid fibre reinforced aluminium) at 121 C and mechanical stress levels between 207 and 345 MPa.…”