Bonding at high temperatures
For many industrial applications such as aerospace, transportation and electrical applications, it is essential to provide high-strength, almost permanent bonds, which can withstand continuous strain at high temperatures and for prolonged periods of time. To achieve this, structural adhesives are being developed since they have numerous manufacturing advantages over welding. Plastics, for example, cannot be welded, or fastened mechanically due to problems with stress and cracking. Lightweight metals such as magnesium and aluminium also suffer from distortion during welding. Four general types of cyanide adhesives were investigated. Specifically, two different commercial monomers, cyanate-epoxy combinations and rubber toughening. These varied in their chemical compositions and mechanical properties. When tested as adhesives on metal and composite surfaces, it was found that the resulting joint strength was retained over a wide range of temperatures. The materials also have low water uptake, which is essential for efficient long-term performance. By physically changing the adhesives, even stronger joints were produced, which increased the peel strength by a factor of at least three. The project also developed a method for more effective testing of strength. The Stringer Bonding Test (SBT) method, tests the strength of particular specimens, which are more representative of actual structures, rather than testing simple joints. The method gave reproducible, quantifiable results and with further development could be a useful test method for the future. Utilising this knowledge on increased adhesive bond strength, and a novel method for strength testing, new bonded materials can be developed for use in a wide range of applications.
