JEC COMPOSITES MAGAZINE - Issue #51 - September 2009 - 57

withstand the high loads and flexing of longer blades. They also need to display high fatigue resistance in order to ensure long service life, preferably without weight penalty. Fig. 4: Example of wind blade construction showing adhesive bonds. Table: Main features: toughened composite assembly adhesive. Fig. 5: Fatigue testing using dynamic mechanical analysis (at 1 Hz and 23°C). Epoxy assembly adhesive Temperature resistance (Tg, °C) Density (g/cm3) Flexural modulus (MPa) Flexural elongation (%) Single-lap shear strength on laminate (MPa) Crack initiation resistance Bend notch K1C(MPa√m) Crack propagation resistance Bend notch G1C (J/m2) 73 1.20 3,600 4.6 26 Nanoparticle toughened adhesive 75 1.05 3,100 5.7 28 Replacing aerospace film adhesives Until now, structural bonding in aerospace applications has almost exclusively used heat-curing film adhesives. Such film adhesives meet the stringent requirements of the aerospace industry in terms of high strength and toughness, high temperature resistance and long-term durability. Film adhesive curing requires temperatures in the 120-180°C range and pressures up to 7 bars. Consequently, cure must be carried out in an autoclave, which significantly increases costs and production times. In addition, the high curing temperature and pressure can lead to stresses in the finished components. The need for higher production rates in aircraft manufacturing has demanded revolutionary changes in both manufacturing and repair processes for structural parts. The main requirements are faster throughput, reduced labour and equipment costs, and reduced energy consumption. Ease of use, good storage stability, and low curing temperature and pressure are also highly desirable to eliminate the need for the rigorous clean room conditions and autoclave curing of film adhesives. Huntsman is a partner of the ABiTAS EU programme (Advanced Bonding Technologies for Aircraft Structures), which aims at developing a novel process chain for paste adhesive bonding of components contributing to both short-term (-20%) and longterm (-50%) cost reductions following the ACARE recommendations. Within this programme, Huntsman has developed a 2-component epoxy-based adhesive that can compete with the toughness of structural film adhesives by employing nanoparticle technology. The dispersed nanophase provides toughness and impact performance without sacrificing high-temperature resistance and hot/wet performance. Figures 6 and 7 show the lap shear strength (EN 2243-1) and roller peel strength (EN 2243-2) on aluminium 2024T3 of three epoxy-amine based, 2-component adhesives. Two of them – Araldite® 420 A/B (ASNA 4125, issB) and Epibond® 1590 A/B (AIMS 10-07-002) – are aerospace-qualified commercial 1.3 2.4 375 1,625 Research has been carried out by Huntsman Advanced Materials to enhance the toughness and fatigue resistance of epoxy adhesives and composites using molecular self-assembly to induce the formation of an organic nanoparticle phase. The nanoparticles formed during the phase separation of the copolymers used have been found to dramatically increase both crack resistance and crack propagation compared with similar non-toughened epoxy systems. When testing such an adhesive system, low shrinkage and exotherm are found, even when cured in thick sections. Furthermore, organic nanoparticles have a much lower density than mineral or fibre reinforcements, reducing the overall density and leading to considerable weight savings for the finished part. Fatigue testing shows the breakdown of the adhesive after repeated mechanical loading. Results for the nanoparticle adhesive show a nearly five times higher deformation rate before damage is initiated and the adhesive starts to fail. This translates into a substantial improvement of fatigue resistance, meaning that parts will withstand greater deformation (flexing) and last longer in service. No51 September 2009 / jec composites magazine 57

JEC COMPOSITES MAGAZINE - Issue #51 - September 2009

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #51 - September 2009