Time-dependent hygrothermomechanical properties of a structural adhesive.

摘要

This research determines the effect of hygro-thermal environment and strain rate on the tensile properties and develop a method to determine the long-term durability of structural adhesive FM300k.; Topics related to structural adhesives are reviewed, including development history, classification, application, and chemical structure. Most high performance structural adhesives are epoxies with viscoelastic behavior which is greatly affected by relative humidity (RH), temperature, and strain rate. Theories for modeling the viscoelastic materials are also investigated.; A testing system was developed with which the time-dependent hygro-thermo-mechanical properties of structural adhesives can be measured. This effort consists of building tensiometers and environmental chambers, controlling RH and temperature, preparing and conditioning specimens, applying displacements with a computer-controlled stepper motor, developing C++ and LabVIEW programs, and acquiring data automatically.; Tests performed in the present study include thermal expansion and moisture swelling, tensile creep and stress relaxation, monotonic tensile tests, and adiabatic cooling.; Tensile stress-strain curves are measured at different RHs (15%, 50% and 85%), temperature (–15°, 30° and 50°C) and strain rate (10-2, 10-4, 10-6 and 10 -8 s-1) to determine the effects of batch, loading method, environment, strain rate, and adhesive. Results from the five series of tests show very good correlation and indicate the excellent performance, high reliability, and reproducibility of the testing system developed in the present study.; Mathematical models of creep and stress relaxation are used to predict the long-term durability of structural adhesive FM 300k.; The concept of a master stress-strain curve for polymeric materials is introduced based on the results of the monotonic tensile tests. Using a master stress-strain curve, the long-term hygro-thermo-mechanical properties of structural adhesive FM300k can be predicted. An RH-temperature-strain rate equivalence is proposed which can be regarded as an extension and modification of time-temperature superposition principle.; A strain rate method of determining the yield stress of adhesive is developed that is more accurate than previous methods.