That is exactly how material scientists study the grain structure and crack propagation. If the crack joint is too small, it acts as a lever. This is why you fi

That is exactly how material scientists study the grain structure and crack propagation. If the crack joint is too small, it acts as a lever. This is why you fillet and chamfer a joint in a designed part, but the concept works down to the molecular level. The holes you are talking about are points of stress relief, without them, the crack can continue to travel through the material, amplifying the forces. Fiberglass isn't strong because the material is special, it is stronger because the imperfections in it have been removed due to surface tension self organizing the impurities away (that would form cracks) during the remelt. The polymer structure in the linked article is not unlike a fiberglass+epoxy composite.