In this thesis, studies on failure strength were performed in accordance with the design parameters for the two types of carbon/BMI-Nomex Sandwich Joints.
First of all, An experimental study has been conducted to investigate the effects of elevated temperature and humidity on the strength and failure mode of carbon/BMI-Nomex composite sandwich joints. Pull-out and shear tests were performed with respect to three different humidity conditions (dry, pre-saturation, and full saturation) and five different temperature conditions (-55, 24, 82, 177, and 204°C). All the tested specimens were cross-sectioned and investigated in detail to study the relation between failure load and mode. In the pull-out loading tests, while the ultimate failure modes were diverse in accordance with the environmental conditions, the first damage mode of the joints was always core shear buckling. In tests of the joints under shear loading, bearing failure of the upper face by the insert flange and insert separation from the potting mass commonly occurred as the main failure modes in every environmental conditions. The pull-out and shear strengths of the sandwich joints at the coldest temperature (-55°C) in a dry condition always showed the highest values among all conditions. Incontrast, the lowest strength was observed at an elevated temperature (177°C) in a fully saturated humid condition. The results reveal that the combined effects of high temperature and moisture should be carefully considered in the design of carbon/BMI-Nomex sandwich joint.
In the case of potting sandwich joints, an extensive parametric test was conducted to investigate the hygrothermal effects on the failure of the carbon/BMI-Nomex sandwich joints with different core heights and densities. Pull-out tests were performed for two different humidity conditions (dry and saturation) and three different temperature environments (24, 82, and 177°C). Two different honeycomb core densities (32 and 64 kg/m3) and three different core heights (9.5, 15, and 25.4mm) were also examined. The test results showed that the core shear buckling was commonly observed in all specimens except for the joint with the core density of 64kg/m3. After core shear buckling, however, the joints carried additional loads over the buckling loads and then finally failed in the bottom face. The joint with 32kg/m3 core density had an ultimate failure loadw hich was 35% lower than that of the joint with 64kg/m3 core density. However, there was no effect of core height on the ultimate load. The ultimate load at the elevated temperature (177°C) and wet conditions were 24.5% higher than that at room temperature.