How Tg effects epoxy performance once cured.

[smitacowper]

Please help me in understanding how tg effects epoxy performance once cured. I have seen many epoxies with tg of room temperature and below, so how they behave above their Tg.

 

[Compositepro]

At the glass transition temperature, Tg, polymers change from hard and brittle to soft and flexible and prone to creep. It is often highly desireable for adhesives to be flexible and be able to yield. The helps to distribute load more evenly over the bondline. The larger area carrying load more than makes up for the lower strength of the polymer above Tg. Tg is used to set service temperature limits for composite materials because yield is detrimental in polymer matrices. The polymer is what keeps fibers from buckling in compression.