Component fatigue

In materials technology, fatigue refers to a reduction in strength due to an alternating mechanical load. The loads acting in this context can be of the most varied nature. A fatigue failure is often encountered due to a cyclical application of force with strong peaks when changing direction. But other environmental conditions such as temperature or a corrosive atmosphere can also trigger a sudden yielding of the material.

Predictions are not always easy

Damage caused by a creeping fatigue process can be particularly treacherous, as many visual inspection procedures are not suitable for detecting the advancing damage. For this reason, serious accidents occur time and again as a result of component fatigue, despite regular inspection.

Preventive measures

Constructive prevention

Often, attempts are made to counter possible fatigue phenomena constructively through high safety margins. With known application scenarios and proven procedures, this constructive prevention is also a tried and tested method.

Early pointer exchange

In the case of less expensive components that are at risk of damage, but whose damage effect is within a tolerable acceptance range, a suitable safety factor can also be included in the maintenance interval. As a rule, the affected components should be easily accessible in the course of regular maintenance work.

Additional active and passive protective devices

If the damage effect is not acceptable and both a shortening of the replacement interval and a design change are out of the question, additional active or passive protective devices must be provided. These then have the task of reducing the effects in the failure scenario. However, it is not always ensured that they fulfil the intended purpose, since not all causal relationships were known at the time of design or a chain of unfortunate circumstances was not foreseen. If the result is, for example, machine damage because the process ran differently than predicted in the CAM software, there is at least only the question of monetary liability.

Condition monitoring & predictive maintenance strategies

In the case of high-quality assemblies and products that could cause high downtime costs, an attempt is made to detect possible deviations from the target condition (so-called anomalies) at an early stage by continuously recording condition data. In the best case, sufficient empirical values have even been collected in the past to be able to forecast the damage model into the future. If deviations can be detected but not reliably predicted, this is referred to as condition-monitoring or, in other cases, predictive maintenance.

Selection of suitable procedures

The first step is to determine the borderline cases by means of a suitable risk analysis in order to delimit the decision space for optimisation alternatives. Once the safety-critical areas have been identified and risk minimisation measures have been defined, a large field of possible measures remains. Here, economic and quality-oriented criteria, as well as the desired customer relationship, are to be used as decisive decision parameters. The determination of the spare parts structure alone often holds great potential for optimisation, because it is not so much the technical concerns but the customer's acceptance threshold that plays a role in this regard. If the fatigue fracture does not pose a safety risk, the determination of the maintenance and service strategy is a multivariate optimisation problem and by no means a trivial gut decision.

In principle, we therefore recommend separating safety and economic considerations with regard to the maintenance strategy.