**Background**

In industry management of risk and uncertainty are a priority because the decisions made directly affect profitability.

Probabilistic analysis gives businesses a decision-making edge since it allows risks and opportunities to be visualized in an intuitive way. There are many applications:

- Calculation of project returns and determination of project strategy
- Fitness for service assessments and risk based inspection relating to fatigue and fracture
- Quantification of manufacturing variability and determination of process requirements
- Modelling and analysis in the fields of solids, heat transfer and fluid mechanics.

See below for an example of how probabilistic analysis is used to predict the fatigue resistance of structures.

**Fatigue Assessment**

Most mechanical failures are caused by fatigue and many of the factors that contribute to fatigue failure are both variable and uncertain, such as load level, loading frequency and a material’s fatigue resistance.

Because of this, probabilistic analysis is very well suited to fatigue problems. Some advantages with probabilistic fatigue analysis are:

- They can be used to remove unnecessary conservatism from assessments. You can properly predict the effects that different uncertain variables have on the probability of fatigue cracking, rather than being forced to make a series of conservative assumptions. This saves money since you’ll spend less time focussed on imaginary fatigue problems and more time improving your business.
- Its not that much work (really!). After all the trouble of defining loads, finding material fatigue properties and performing stress analyses, the actual probabilistic fatigue assessment is quick. All you need is the right toolbox.
- They help you plan for the future. You can identify regions that might require design improvement and/or inspection, and even survey possibilities coupled to lifetime extensions and/or performance upgrades.

**So how does probabilistic fatigue assessment work?**

We can provide you with a toolbox that makes probabilistic fatigue assessment simple and convenient. The approach we use consists of the following steps:

- Create a stress range spectrum (pdf). This is based on known load cases and the results from stress analysis.
- Define fatigue resistance, consisting of an everyday fatigue curve plus a stochastic parameter which describes the variability in fatigue resistance.
- Define an acceptable risk for fatigue cracking, based on guidance from relevant standards.
- Perform the probabilistic fatigue assessment and obtain the probability of fatigue cracking as a function of time. The fatigue life is the time it takes to reach the acceptable risk for fatigue cracking.