aining unit coated with continuous graphite fiber or woven graphite fabric or graphite unidirectional tape impregnated with a polyamide-imide of the following structure: ##STR6## and units of: ##STR7## wherein the free carboxyl groups are ortho to one amide group, Z is a trivalent benzene ring or lower-alkyl-substituted trivalent benzene ring, R1 and R2 are the same or are different and are divale