Fracture toughness is a material property that measures a material's ability to resist crack propagation when subjected to stress. It is an important factor in engineering and materials science, as it helps predict how materials will behave under load, especially in critical applications like aerospace and civil engineering. The fracture toughness is typically expressed in terms of stress intensity factor, denoted as K_IC. Higher values indicate that a material can withstand greater stress before a crack grows, making it essential for selecting materials in structures that must endure harsh conditions or heavy loads.