Creep tests are carried out on alloy samples to ascertain their physical properties at standard operating temperatures. Simply put, a sample is heated to a stable temperature (dependent on the material) above 300°C. In order to exert a longitudinal force on the alloy’s grain structure, a stress is then applied to the sample. The sample is sustained in this state until it either ruptures or the test ends. During this test, the data is monitored closely and recorded to understand the stability of the temperatures, sample extension and loading.
How are Creep Test Furnaces Used?
It is critical to have a continuously strict control over the temperature throughout the whole sample. The standard uniformity tolerance is 0.2 centigrade. Many creep test furnaces need to use extremely accurate control devices which have three zones of heating. These creep tests can run for months or even years and as such it is crucial that control systems are manufactured to withstand power failures and have abort strategies meaning tests can continue following interruptions.
Laboratories which are specifically designed for creep testing can have hundreds of creep test furnaces which are simultaneously testing different samples.
Creep takes place in three stages: Primary/stage one, secondary/stage two, and tertiary/ stage three. Primary creep takes place at the start of the tests when the creep is briefly at an unsteady state. Resistance to creep builds up until the secondary creep stage is reached and the creep becomes steady.
In the tertiary creep stage, the creep rate slowly accelerates as the cross-sectional area of the specimen diminishes as a result of necking or when internal voiding decreases the area of the specimen that is effective. If the creep is not stopped in stage three, the specimen will fracture.
Constant load creep testing applies a constant load. A weight is hung from the back of a machine and the force does not alter, no matter how much the specimen stretches. This is the type of creep testing which is most frequently used.
Constant stress creep testing is when a sample stretches and the cross section becomes narrower, the load amount is reduced to keep the force across the cross sectional area consistent. This is achieved by changing the level at the top of the machine as the sample stretches.
What are Creep Test Furnaces Used For?
Creep test furnaces are instrumental in the formation of creep rates which are used for the evaluation of boiler materials, gas turbines, jet engines, ovens and any other applications which need to use high temperature under load. Understanding the behavior of metals under high temperature is critical in the design of systems which are resistant to failure.
Creep Test Furnaces from Deltech