This trend illustrates the complexity of determining the relative importance of h on the fracture mechanics results. This arises because the thermal stresses are a strong function of the thermal gradient. The K1C curves start at 200 ksi when the temperature is at its initial value and transitions to approximately 35 ksi after the cooldown. The transition time is shifted by more than 10 minutes for the range of h values considered. K1C is a measure of the fracture toughness, which is a function of the temperature of the material.
Lower temperatures result in a lower fracture toughness.
K ratio . When the K ratio is greater than one, the assumed crack is predicted to grow. The K ratio accounts for all of the thermal effects in a single parameter. The K ratio plot in Figure 4 illustrates how variations in h can affect the fracture mechanics. From 0 to about 100 minutes, the K ratio is larger for larger values of h.