The integration of untethered, multi-stimuli responsive actuation into soft microrobotic devices is a goal in the development of “smart” materials. This manuscript reports on a dual-stimuli responsive bilayer actuator consisting of a light responsive liquid crystal network (LCN) and a magnetic responsive polydimethylsiloxane (PDMS) composite. This design is of facile fabrication with ample design freedom, using no additional adhesion layers. Untethered control of the bilayer permits motions including bending and rotation, steered individually or in synchronization. Through a systematic study the direct impact of the PDMS layer was elucidated on the light triggered rate of actuation and maximum deformation amplitude of the LCN film. The alignment (homeotropic or planar) of the LCN has a profound effect on the resulting bilayer actuation. It is demonstrated, both experimentally and theoretically, that the rates of sample heating and actuation are directly correlated and highlight the critical role of the PDMS as a heat sink. The maximum amplitude of displacement of the bilayer is tied to the stiffness, being inversely correlated to the PDMS thickness to the third power. These results give insights and provide straightforward design rules to fabricate bilayer actuators with programmed multi-responsive properties.

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An innovative deicing system for aircraft leading edges has been developed which integrates heater elements into fibre metal laminates. Such an electrical system can lead to weight reductions and more efficient performances compared to conventional bleed air systems. However, the combination of thermal and mechanical loadings also raises new questions on the durability of such a structure, in particular due to the repeated heating to elevated temperature. The linear viscoelastic creep behaviour, including the effects of temperature and ageing, is therefore investigated for manufactured FM906 glass-fibre epoxy composite as used in heated GLARE. A master curve is derived based on the time–temperature and time–age superposition. The effect of physical ageing during loading is included in a long-term creep prediction.

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Heated GLARE, a Fibre Metal Laminate with an integrated heater element, has a promising potential as de- or anti-icing system in aircraft structures. To investigate the long-term durability of heated GLARE previously reported thermal cycling tests up to 12,000 cycles are extended up to 144,000 cycles and moisture conditioning is included. Similar testing up to 72,000 cycles is performed on FM906 glass-fibre epoxy laminates with an integrated heater element to study the influence of the aluminium layers in GLARE. In all test results the initial decrease in interlaminar shear values from 0 to about 10,000 thermal cycles is followed by a recovery phase and a resumed decline after roughly 60,000 cycles. The decrease in ILSS is expected to be caused by internal stress relief which is counteracted by the positive effect of physical ageing due to elevated temperature exposure. Thermal cycling of conditioned samples generally resulted in slightly larger decreases in interlaminar shear strength for both heated GLARE and heated FM906 glass-fibre epoxy laminates.

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Heated GLARE, a Fibre Metal Laminate with an integrated heater element, has been developed for de- or anti-icing systems in aircraft structures. Besides cyclic thermal loading these structures are also subjected to mechanical loading. To investigate the effect of static loading in addition to thermal cycling a series of tests have been performed on heated GLARE using a specifically designed mechanical load fixture and thermal cycling setup. Three different tensile stress levels, 150, 200 and 300 MPa, were used in combination with up to 36,000 thermal cycles between −20 and 50 °C. The effect of the combined thermo-mechanical loading was investigated by testing the interlaminar shear properties of each sample after thermal cycling. Thermal cycling under a 150 MPa static load showed much less reduction or even increase in strength compared to previously reported test results for thermal cycling only. This effect was not found for thermal cycling under the 200 and 300 MPa static load cases. On the contrary, in these cases more reduction in strength was found compared to test results after thermal cycling without static load.@en

Carbon fibre thermoplastic composites can be induction welded thanks to the electrical conductive nature of carbon fibre. Due to a locally contrained current flow more heat is generated at the edges of the composites. To counteract this so called edge effect a highly conductive material is attached to the edge to create an electrical bypass. The effect of a thin copper bypass has been assessed by performing induction heating experiments on single and double carbon fibre PPS composite coupons. The induction parameters where chosen such that without a bypass the edge would locally reach the melting temperature. The results clearly show the ability of the copper bypass to reduce the edge effect and prevent overheating at the edge.@en

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.

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Fibre metal laminates with integrated heater elements have a promising potential as de- or anti-icing systems in aircraft structures. The alternating metal and composite lay-up in fibre metal laminates seems ideal for the development of a multifunctional skin with embedded heater elements. However, the long term durability needs to be carefully examined.

A unique thermal cycling setup has been designed and built to investigate the effects of thermal cycling on the material properties of GLARE (glass fibre reinforced aluminium). Peltier elements were used to provide external heating and external cooling by inverting the direction of the electrical current. With the same setup, heated GLARE samples can be internally heated using the integrated heater elements and externally cooled using the Peltier elements.

Glass-fibre epoxy composite, GLARE, and heated GLARE samples have been thermal cycled for 4000, 8000 and 12,000 cycles with temperature differences of 120 °C. The interlaminar shear strength (ILSS) increased by 6.9% after 8000 cycles for the glass-fibre epoxy composite material compared to the non-cycled samples. The GLARE samples showed a maximum ILSS increase of 4.2% after 12,000 cycles. However, the heated GLARE samples showed a continuous decrease of the ILSS with a maximum decrease of 7.8% after 12,000 cycles.@en

Nowadays, the application of glass-fibre composites in light-weight structures is growing. Although mechanical characterizations of those structures are commonly performed in testing, chemical changes of materials under stresses have not yet been well documented. In the present work coupon tests and Hyperspectral Imaging (HSI) have been used to categorise possible chemical changes of glass-fibre reinforced polymers (GFRP) which are currently used in the aircraft industry. HSI is a hybrid technique that combines spectroscopy with imaging. It is able to detect chemical degradation of surfaces and has already been successfully applied in a wide range of fields including astronomy, remote sensing, cultural heritage and medical sciences. GFRP specimens were exposed to two different thermal loading conditions. One thermal loading condition was a continuous thermal exposure at 120°C for 24h, 48 h and 96h, i.e. ageing at a constant temperature. The other thermal loading condition was thermal cycling with three different numbers of cycles (4000, 8000, 12000) and two temperature ranges (0°C to 120°C and -25°C to 95°C). The effects of both conditions were measured using both HSI and interlaminar shear (ILSS) tests. No significant changes of the physical properties of the thermally cycled GFRP specimens were detected using interlaminar shear strength tests and optical microscopy. However, when using HIS, differences of the surface conditions were detected. The results showed that the different thermal loading conditions could be successfully clustered in different colours, using the HSI linear unmixing technique. Each different thermal loading condition showed a different chemical degradation level on its surface which was indicated using different colours. @en