Research led by Georgia Tech physicist Itamar Kolvin has found that the presence of small imperfections or heterogeneities in materials can have a dual effect on their strength and resilience. While heterogeneities were historically believed to make materials stronger by creating an obstacle course for cracks, the new study shows that in some complex materials, heterogeneities can actually accelerate crack propagation and weaken the overall structure. The findings have implications for how engineers design and reinforce materials to optimize their toughness.