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

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 long-term effects thermal cycling tests are performed up to 36000 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.