K_IC is a measure of a material's resistance to crack propagation. It quantifies the stress intensity at the tip of a crack when the crack begins to grow. A higher K_IC value indicates that a material can withstand greater stress before failing, making it crucial for assessing the durability of materials in engineering applications. This property is particularly important in fields like mechanical engineering and materials science, where understanding how materials behave under stress is essential. K_IC values help engineers select appropriate materials for structures, ensuring safety and reliability in products ranging from bridges to aircraft.