"纤维强化热固性" can be translated as "fiber-reinforced thermosetting" (referring to materials like fiber-reinforced thermosetting plastics or composites).
If you want to be more specific about the material type, you could say:
Fiber-reinforced thermosetting plastics (纤维强化热固性塑料)
Fiber-reinforced thermosetting composites (纤维强化热固性复合材料)
The choice depends on the context in which it is used.