What is Stress Rupture Test?
Stress rupture test is a type of mechanical test used to measure the strength and performance of materials under long-term stress.
This type of test can be used to evaluate how certain materials react when exposed to extreme temperatures, static stresses, or cyclic stresses over a given period of time.
It is often used by engineers and scientists in order to gain an understanding of the behavior of specific materials when subjected to these types of conditions.
A stress rupture test, though similar to a creep test, is carried out up to the failure of the material. Higher loads are used in the stress rupture test than in the creep test, so creep rates are higher.
Creep Test vs Stress Rupture Test
Generally, a creep test is performed at low stresses so as to avoid tertiary creep. Creep tests are frequently conducted for periods of 2000 h and often up to 14,000 h.
In the creep test, the total strain is often less than 0.5 percent, but in the stress rupture test, the total strain may be up to 50 percent.
Simple strain-measuring devices such as dial gauges can be used for this purpose. The higher stresses and creep rates in the stress rupture test cause structural changes in the metals at shorter times, and the stress rupture test can be completed in 1000 h. It is particularly used to determine the high-temperature creep strength of new alloys for jet engine applications.
The basic information obtained from the stress rupture test is the time to cause failure at a given stress under constant temperature. The elongation and reduction in the area at fracture are also determined.
If stress is plotted against the rupture time on a log-log scale, a straight line is usually obtained as shown in Figure 5.25. The changes in the slope of the stress rupture line are due to structural changes occurring in the metals, such as transgranular to intergranular fracture, oxidation, recrystallization and grain growth.
The principal deformation processes at elevated temperatures are slip, subgrain boundaries and grain boundary sliding. High-temperature deformation is characterized by extreme inhomogeneity. A number of secondary processes have been observed in metals at elevated temperatures, such as multiple slip, formation of coarse slip bands, fold formation at grain boundaries and grain boundary migration.
Stress Rupture Test Procedure
The following outlines the steps for performing a stress rupture test according to ASTM E139-11 standards.
The first step is specimen preparation. The test specimen for the stress rupture test is similar to the tensile test specimen.
For welded samples, it can be transverse or all weld specimen.
The set-up for this type of test typically includes an environmental chamber with a variable temperature range and pressure capabilities, depending on the desired testing parameters. The sample being tested will be enclosed in the chamber along with instrumentation that monitors its performance over time.
A representative sample of the component must be cut according to a strict specification and then machined into its final shape before being subjected to chemical cleaning and heat treatment processes.
After these processes are complete, the sample is ready for testing. Next, the sample must be placed in an appropriate test fixture and tensioned using a calibrated force transducer while it undergoes elevated temperatures up to 600°C (1100°F).
What is stress rupture strength?
Stress rupture strength is a measure of structural integrity used for many engineering materials. It indicates the material’s ability to withstand long-term stresses or loads without failure.
Stress rupture strength is determined by subjecting a sample of the material to a fixed stress level and recording its behavior over time. This test can help identify a material’s fatigue limit, which is the maximum stress it can undergo during cyclic loading before a fracture occurs.
Understanding how different materials behave under prolonged stress enables engineers to make informed decisions when selecting appropriate products for specific applications.
Factors such as temperature, moisture levels, and surface condition must be taken into consideration when evaluating stress rupture strength in order to accurately assess its performance capability in real-world scenarios.
A full evaluation of the material’s properties should be conducted prior to its use in any application where safety or reliability is an issue.