"纤维强化热固性" can be translated as "fiber-reinforced thermosetting" (when referring to materials like fiber-reinforced thermosetting plastics or composites).
If you want to be more specific about the material, you could say:
"Fiber-reinforced thermosetting plastic" (纤维强化热固性塑料)
"Fiber-reinforced thermosetting composite" (纤维强化热固性复合材料)
These terms are commonly used in engineering and materials science contexts.