Structural integration of electronic devices on composite - Study on the mechanical durability
Topic(s) : Multifunctional and smart composites
Co-authors :
Alois FRIEDBERGER (GERMANY), Andreas HELWIG , Wolfgang MACHUNZE (GERMANY), Patrice LEFEBURE , Caroline PETIOT (FRANCE)Abstract :
Sensor and electronic integration on composite enables real time monitoring of loads and structural properties of the composite, but also of environmental parameters such as temperature and pressure. The direct integration on composite structures without the need of conventional housings, connectors and cabling reduces weight, complexity and installation effort. Several publications over the past years show different approaches such as a) application of functionalized fibers, b) direct printing of electrical tracks and simple sensors on composite, c) integration of electronic devices on a polymer foil and its bonding to composite. We have been working on the latter approach because it is very versatile:Many sensors are available as miniaturized devices and electronic chips can be added for data pre-processing and communication.
Our research is addressing the question whether a functionalized foil - electronic devices embedded in a polymer foil - which is solely covered by a protective coating can be integrated on composite parts and can withstand harsh aeronautic conditions as on an aircraft wing or fuselage. Figure 1 shows our test structure: Typical electronic devices such as QFN (quad flat no-lead package), SMD (surface mounted device) or copper meanders as electrical resistors R have been integrated on a 100 µm thick TPU (thermoplastic polyurethane) foil and connected with copper tracks on that foil. A TPU layer was added for protection. These functionalized foils have been bonded to 4 mm thick M21E/IMA epoxy CFRP composite coupons using an adhesive film. Further variants have been produced with either a 0,4 mm thick GFRP epoxy fabric or a 0,1 mm thick copper foil above the functionalized electronic foil. Another configuration utilized a 1 mm thick EPDM rubber between composite and electronic foil.
During quasi static indentation, force was gradually increased at the coupon center (Fig 2). When the composite substrate failed at 11,5 kN, all electronics were still functional. Tests were repeated with dynamic impact of 60 J - an extremely large energy for typical composite structures. Impact directly on the electronic devices revealed that SMDs are more robust than the QFNs and that the EPDM layer reduces the impact resistance. Static pressure load tests represented a worker stepping e.g. on an aircraft wing corresponding to approx. 0,3 MPa - our samples did not fail until ~14 MPa. Cyclic four point bending for 100.000 cycles was done from ~5500 to 9900 µm/m strain and showed that EPDM increases the failure load by about 20 %. Also for cyclic tensile testing, there is some advantage of the EPDM. Taking all results into consideration, the GFRP layer is the preferred protection from a robustness and manufacturing point of view.
Our work revealed remarkable mechanical robustness of composite integrated functionalized electronic foils towards aeronautic loads and showed the feasibility of utilizing the approach for multifunctional structures.
Our research is addressing the question whether a functionalized foil - electronic devices embedded in a polymer foil - which is solely covered by a protective coating can be integrated on composite parts and can withstand harsh aeronautic conditions as on an aircraft wing or fuselage. Figure 1 shows our test structure: Typical electronic devices such as QFN (quad flat no-lead package), SMD (surface mounted device) or copper meanders as electrical resistors R have been integrated on a 100 µm thick TPU (thermoplastic polyurethane) foil and connected with copper tracks on that foil. A TPU layer was added for protection. These functionalized foils have been bonded to 4 mm thick M21E/IMA epoxy CFRP composite coupons using an adhesive film. Further variants have been produced with either a 0,4 mm thick GFRP epoxy fabric or a 0,1 mm thick copper foil above the functionalized electronic foil. Another configuration utilized a 1 mm thick EPDM rubber between composite and electronic foil.
During quasi static indentation, force was gradually increased at the coupon center (Fig 2). When the composite substrate failed at 11,5 kN, all electronics were still functional. Tests were repeated with dynamic impact of 60 J - an extremely large energy for typical composite structures. Impact directly on the electronic devices revealed that SMDs are more robust than the QFNs and that the EPDM layer reduces the impact resistance. Static pressure load tests represented a worker stepping e.g. on an aircraft wing corresponding to approx. 0,3 MPa - our samples did not fail until ~14 MPa. Cyclic four point bending for 100.000 cycles was done from ~5500 to 9900 µm/m strain and showed that EPDM increases the failure load by about 20 %. Also for cyclic tensile testing, there is some advantage of the EPDM. Taking all results into consideration, the GFRP layer is the preferred protection from a robustness and manufacturing point of view.
Our work revealed remarkable mechanical robustness of composite integrated functionalized electronic foils towards aeronautic loads and showed the feasibility of utilizing the approach for multifunctional structures.