High Temperature Failure Analysis

Creep occurs under load at high temperature.  Boilers, gas turbine engines, and ovens are some of the systems that have components that experience creep.  An understanding of high temperature materials behavior is beneficial in evaluating failures in these types of systems.

Failures involving creep are usually easy to identify due to the deformation that occurs. Failures may appear ductile or brittle. Cracking may be either transgranular or intergranular.  While creep testing is done at constant temperature and constant load actual components may experience damage at various temperatures and loading conditions.

Creep of Metals

High temperature progressive deformation of a material at constant stress is called creep.  High temperature is a relative term that is dependent on the materials being evaluated. In a creep test a constant load is applied to a tensile specimen maintained at a constant temperature.  Strain is then measured over a period of time.

Stress Rupture

Stress rupture testing is similar to creep testing except that the stresses used are higher than in a creep test.  Stress rupture testing is always done until failure of the material.   Once a designer knows the materials will creep and has accounted for this deformation a primary goal is to avoid failure of the component. Stress rupture tests are used to determine the time to cause failure.