STRUCTURAL PERFORMANCE OF GLASS VINYLESTER COMPOSITES AT ELEVATED-TEMPERATURES/

Organic polymer matrix based fiber reinforced composite materials unde rgo viscoelastic transitions followed by reversible and irreversible t hermal damage when exposed to evaluated temperature due to shipboard f ires. To determine the limits of composite structural performance at e levated temperatures. Dynamic Mechanical Thermal Analysis (DMTA) was p erformed. In the first step, glass reinforced vinylester composite pan els were isothermally aged and tested in DMTA for storage (E') and los s (E'') moduli for a period of eight hours at 77, 150, 200, 250, 300, 400, 500, and 600 degrees F (25, 66, 93, 121, 149, 204, 260, 316 degre es C) respectively. Data show that E' decreases at subsequently increa sing temperatures until 200 degrees F. A significant drop in E' takes place between 200 and 250 degrees F followed by a catastrophic drop be tween 250 and 300 degrees F. Thus, 206 degrees F represents the upper threshold of operating temperature for unprotected glass reinforced vi nylester load bearing composite structures. In the second step, all sa mples, previously isothermally aged at various temperatures, were cool ed to room temperature and retested. Data show that samples previously isothermally aged up to 150 degrees F for a period of eight hours, an d subsequently cooled to room temperature, do not exhibit thermal dama ge and recover all of their original structural performance. Beyond 15 0 degrees F and up to 406 degrees F, the glass/vinylester samples begi n to exhibit thermal damage. However, load bearing structures exposed to these temperatures up to 400 degrees F still retain up to 70 percen t of original flexible properties. Beyond 400 degrees F, the glass/vin ylesters samples suffer significant thermal damage and begin to lose l oad bearing viability as a composite structure. This can be further ob served in dynamic scans for loss factor (tan delta) obtained from DMTA testing of previously isothermally aged samples. At temperatures of i sothermally aging beyond 400 degrees F, vinylester resin exhibits chem ical breakdown as evidenced by the loss of matrix resin viscoelasticit y. These scans show that vinylester resin is no longer capable of tran sferring the load to the fiber. As such, load bearing structures expos ed to isothermal aging for a period of eight hours at temperatures abo ve 400 degrees F may necessitate significant damage repair or even rep lacement of composite load bearing structure.