Moisture effects on FM300 structural film adhesive: Stress relaxation, fracture toughness, and dynamic mechanical analysis

Abstract

ABSTRACT:The behavior of cured FM300 epoxy, a structural film adhesive, subjected to partial and full moisture saturation has been evaluated. Three separate but interrelated test methods were used: stress relaxation, fracture toughness, and dynamic mechanical testing. The mechanical response of the epoxy due to increasing moisture content was dependent on the testing method. In stress relaxation testing, the epoxy was plasticized when partially saturated with moisture, but it became more rigid when fully saturated. The plasticization-to-stiffening transition was not observed in the other two test methods. Fracture testing showed that the material toughness increased with increasing moisture concentration: plasticization effects were dominant. Similar changes in the loss modulus were found in dynamic mechanical analysis. We propose that the differences in behavior have been due to differences in load levels and loading rates used in these probing techniques. Stress relaxation testing, at a relatively lower load and loading rate, appeared to be more sensitive to the localized interactions between the absorbed water molecules and the crosslinked structure. Higher loads and loading rates tended to reveal the bulk effects of plasticization only. Nevertheless, there was also strong evidence from glass-transition temperature measurements that these moisture effects were mostly reversible.

Mode I fracture toughness of co-cured and secondary bonded composite joints

“…As expected, the mechanical properties are clearly dependent on the glass transition temperature. The stiffness is proportional to T g , as has been reported elsewhere [19], with the specimens representing the SB120 joint system (T g of 150 • C) being less compliant than those of the CC180 system (T g of 137 • C). The specimens representing the SB120 joint system also have the highest failure stress while the CC180 specimens have the highest strain at failure.…”

The Diffusion Coefficients of Different Types of Liquid Environments Into Binary Polymer Blend

“…Frequently, however, the Fickian model does not adequately represent the absorption process. Such cases are called non-Fickian, or anomalous diffusion [10].…”

Long-term creep behavior of self-reinforced PET composites

“…Calculation of shift factors assuming a constant value of the activation energy (E a ) was performed, which represented the only unknown parameter. Thus, the E a of the glass transition relaxation corresponds to the energy barrier that must be overcome to initiate the molecular motions causing the transition [36]. The magnitude of E a was calculated using the obtained frequency dependence of T g (the utilized method was described earlier in Section 3.1).…”