Thermal cracking

Thermal cracking is fracture caused by stresses generated as a material heats, cools, or develops temperature differences. It occurs when those stresses exceed the material’s capacity to relax or resist fracture.

Thermal stress: Stress produced when temperature changes cause a material to expand or contract unevenly or while constrained. It is the direct mechanical load that drives thermally induced fracture.
Elastic modulus: A measure of a material’s stiffness under elastic deformation. Stiffer materials generally develop greater stress when thermal expansion is constrained.
Thermal fatigue: Cracking and damage caused by repeated temperature fluctuations and their associated stresses. It is the cyclic form of thermal cracking in components exposed to repeated heating and cooling.
Stress corrosion cracking: Crack growth caused by the combined effects of tensile stress and a corrosive environment. It can occur alongside thermal stresses, but depends on chemical interaction with the environment.
Thermal shock: Rapid temperature change that creates steep thermal gradients and potentially damaging stresses in a material. Abrupt heating or cooling can make thermal stresses rise faster than a material can accommodate.
Fracture toughness: A material’s resistance to crack extension under a concentrated load. It sets how much crack-driving force a thermally stressed flaw can withstand.
Spalling: The flaking or breaking away of a material’s surface or near-surface layers. Thermal gradients can drive surface-parallel cracks that release fragments.
Hydrogen embrittlement: Loss of ductility and fracture resistance caused by hydrogen entering a material. It produces cracking through a chemical and microstructural mechanism rather than temperature stress alone.
Coefficient of thermal expansion: A measure of how much a material’s dimensions change with temperature. Expansion mismatch between regions or joined materials generates cracking stresses.
Fatigue: Progressive damage caused by repeated or fluctuating loads, often below a material’s static strength. Repeated temperature cycles can accumulate damage and extend cracks through thermal fatigue.

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