1. Miner's rule is used to predict the expected time to failure in fatigue:

• Write down the mathematical expression for Miner's rule.
• A component was tested in the laboratory to determine its fatigue life. The test results were as follows:

Stress level (x 10⁸N/m²) 6.8 8.0 10.0

Mean cycles to failure (x 10⁵) 12.7 4.2 0.6

The component will be used in service with these stress levels occurring in the following proportions, respectively:

Proportion of cycles 0.5 0.3 0.2

What will be the expected time to failure in service, if the stress cycle rate is 1000 per hour?

• Comment on the factors that would influence the accuracy of this prediction.