Stress Rupture Testing

Definition:

Stress rupture testing is a high-temperature mechanical test used to determine the time to failure of a material under constant stress. It is similar to a creep test but focuses on the material's rupture life rather than long-term deformation.

Test Procedure:

Specimen Preparation
- A standard metal specimen (dog-bone or cylindrical shape) is prepared.
Applying Constant Stress & Temperature
- A constant tensile load is applied.
- The test is conducted at elevated temperatures

(typically 40–80% of the melting point).

Monitoring Time to Rupture
- The test runs until the material fractures.
- Time to rupture is recorded.
Plotting Rupture Data
- Results are plotted as stress vs. rupture time to predict long-term material performance.
- Higher stress or temperature reduces rupture life.

Applications of Stress Rupture Testing

Gas turbines & jet engines – Ensuring material durability under extreme conditions.
Power plants – Testing boiler tubes, steam pipes, and turbine blades.
Aerospace components high-temperature alloys.
Automotive industry exhaust manifolds and turbochargers.

Stress Rupture Test Graph

The typical stress rupture graph is a log-log plot of stress vs. time to rupture. Here’s how to interpret it:

Graph Axes:

X-Axis (Log Scale): Time to rupture (in hours or minutes).
Y-Axis (Log Scale): Applied stress (MPa or psi).

Key Characteristics:

Slope of the Curve:
- A steeper slope indicates that a small increase in stress significantly reduces rupture life.
- A gentle slope suggests better long-term durability.
Effect of Temperature:
- Higher temperatures shift the curve downward, meaning the material fails sooner.
- Multiple curves can be plotted for different temperatures to predict long-term performance.
Extrapolation for Design:
- Engineers use this graph to estimate how long a material can last under specific conditions.
- Helps in selecting materials for turbines, boilers, and jet engines.

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