In addition to thermal shock resistance defined by material fracture strength, models have also been defined within the fracture mechanics framework. Lu and Fleck produced criteria for thermal shock cracking based on fracture toughness controlled cracking. The models were based on thermal shock in ceramics (generally brittle materials). Assuming an infinite plate and mode I cracking, the crack was predicted to start from the edge for cold shock, but the center of the plate for hot shock. Cases were divided into perfect and poor heat transfer to further simplify the models.