부산대학교 도서관

Thermal expansion differences between electrical insulation materials and other components are important engineering considerations for long-term use. Thermal expansion is traditionally measured with constant thermal heating rates. This study shows that modulated heating rates provide much more accurate and detailed information for insulation with a significant viscoelastic component. Our choice of characterization technique is Modulated Thermal Mechanical Analysis (mTMA). Temperature modulation allows separation of reversible and non-reversible linear expansion. The slope of the reversible dimension change with temperature gives the true thermal expansion coefficient. Garolite, a commercial epoxy-fiberglass laminate, was measured perpendicular to the woven fiberglass layers. Three samples were aged with different environments for comparison with the as-received composite sample. Density was measured using pycnometry.The non-reversible expansion was found to be greater than the reversible expansion for all samples over the temperature range examined. The slope of the reversible dimension change is highly dependent on the aged condition. Densities for all aged samples were less than the as-received sample, suggesting structural relaxation from the high-pressure forming process. The authors recommend characterizing thermal expansion using mTMA and separating out the reversible dimension change as a function of temperature for all insulation samples with a viscoelastic component.