How do you manage and mitigate the risks of creep and fatigue failures in safety-critical systems?

1 What is creep and fatigue?

Creep and fatigue are both time-dependent phenomena that depend on the material properties, the applied stress, the temperature, and the environment. Creep is the slow and continuous deformation of a material under a constant stress, usually at high temperatures. Fatigue is the progressive and localized damage of a material under cyclic or fluctuating stress, usually at low or moderate temperatures. Both creep and fatigue can reduce the strength and stiffness of a material, and lead to cracks, fractures, and failures.

2 How to identify creep and fatigue failure modes?

One of the first steps in managing and mitigating the risks of creep and fatigue failures is to identify the potential failure modes in your system. This can be done by performing a failure mode and effects analysis (FMEA), which is a systematic method to evaluate the causes, effects, and likelihood of failures in a system. FMEA can help you prioritize the critical components and conditions that are most susceptible to creep and fatigue, and establish the failure criteria and detection methods.

3 How to model creep and fatigue behavior?

Once you have identified the creep and fatigue failure modes in your system, you need to model their behavior using appropriate methods and tools. Depending on the complexity and accuracy required, you can use empirical, analytical, or numerical models to predict the creep and fatigue life of a component. Empirical models are based on experimental data and empirical equations, such as the Larson-Miller parameter for creep and the S-N curve for fatigue. Analytical models are based on theoretical principles and analytical solutions, such as the Kachanov-Rabotnov model for creep and the Paris law for fatigue. Numerical models are based on computational methods and software, such as the finite element method (FEM) for creep and fatigue.

4 How to design against creep and fatigue?

In order to manage and mitigate the risks of creep and fatigue failures, it is important to design your system to avoid or reduce these failure modes. This can be accomplished by selecting a material that has the appropriate creep and fatigue properties, resistance to environmental effects, and compatibility with other materials. Additionally, reducing the stress level and concentration in the component, controlling the temperature and thermal gradients, minimizing the stress cycles and fluctuations, and adding safety factors are all recommended design principles and guidelines. These strategies can help ensure that your system is optimally designed to reduce or avoid creep and fatigue failures.

5 How to test for creep and fatigue?

In addition to modeling and designing your system against creep and fatigue, you also need to test your system to verify its performance and reliability under realistic or accelerated conditions. Testing can help you validate your models, evaluate your design choices, and detect any defects or anomalies in your system. Testing can be done at different levels, such as material, component, or system level, using different methods and equipment, such as tensile, compression, torsion, or bending tests, strain gauges, extensometers, or acoustic emission sensors.

6 How to monitor and maintain creep and fatigue?

The final step in managing and mitigating the risks of creep and fatigue failures is to monitor and maintain your system throughout its service life. Monitoring can help you measure and record the actual stress, strain, temperature, and damage in your system, using sensors, data loggers, or wireless networks. Maintenance can help you repair or replace any damaged or degraded components, using inspection, non-destructive testing, or preventive maintenance techniques. Monitoring and maintenance can help you extend the life of your system, prevent catastrophic failures, and ensure safety and quality standards.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?