Statistical methods play a central role during the design and assessment of vehicle components with respect to durability and reliability.

Usage Variability and Loading Statistics

Statistical methods play a central role during the design and assessment of vehicle components with respect to durability and reliability.

The entire process starts with the description and modeling of the usage variability, which arises due to the combination of different mission profiles or driver behaviour and the varying environmental conditions in different regions of the world. For instance, the mixture of applications for a tractor of a certain class such as plowing or transport varies from customer to customer as well as the regional conditions such as topography, size of fields etc. Accordingly, the loads of the machines or vehicles vary considerably and a proper statistical modeling is required including factor models, ANOVA-type methods, handling high variances etc.

Durability
© Photo ITWM

Durability

The next step is to derive reference loads which are used within the development process and fundamental for release tests. Measured data is analysed and extrapolated to a given design life based on the classification of factor models (which type of load cases are relevant) and the application of usage models (how often do these load cases occur in a certain customer group). High quantiles of the corresponding distributions are used to define the reference loads.

That process was, among others, executed in a common project with Volkswagen Nutzfahrzeuge and reported during the VDI conference Commercial Vehicles 2015 in Eindhoven. Some of the applied methods, e.g. extending the evaluation of measured data using geo-referenced information and the statistical analysis based on factor models, were presented in more detail during the DVM-conference of the AK Betriebsfestigkeit 2016 in Steyr.

For demonstrating the required reliability of a component based on release tests, safety factors are introduced to cope with the remaining uncertainty due to lack of knowledge in the extreme tails of the load and strength distributions. In addition, statistical reasoning is needed for estimating how many specimens have to be tested in order to prove a certain reliability with a certain confidence.

The department MDF develops and applies methods for supporting the sketched process with focus on the vehicle industry including construction and agricultural machinery. However, other applications such as wind turbines or railway industry are also covered. Most of the methods are applicable within the assessment of energy efficiency or fuel consumption as well.

References

  • Weyh, T., Speckert, M., Opalinski, A., Wagner, M.: Planung einer Messkampagne durch Osteuropa mittels der Fraunhofer Software VMC („Virtual Measurement Campaign“), VDI-Bericht: Nutzfahrzeuge 2015 Commercial Vehicles 2015 Truck, Bus, Van, Trailer, VDI-Berichte/VDI-Tagungsbände 2247, Vol. Bericht 2247 2015.
  • Speckert, M.; K., D.; Lübke, M.; Halfmann, T.: Automatisierte und um GEO-Daten angereicherte Auswertung von Messdaten zur Herleitung von Beanspruchungsverteilungen, DVM Bericht 143, 2016.

 

Application Fields

Load Data Analysis, Loading Statistics and Operation Optimization

Load data on system or component level are usually represented as time signals. This applies to field data and rig loads as well as for numerical simulation. The analysis process starts with the detection and correction of irregularities due to possible problems in the measurement process. Often, spikes, drifts or offsets need to be corrected.

Geo-referenced Analysis and Virtual Measurement Campaign (VMC®)

Since several years, the department MDF at Fraunhofer ITWM is investigating the analysis of geo-referenced data to support and improve the derivation of design loads as well as the assessment of energy efficiency by statistical reasoning. The approach is mainly motivated by the desire to understand usage variability and the resulting scatter in loads or fuel consumption and to provide methods for making use of that information within vehicle development.

U·Sim – Assessment of Customer Usage Profiles

The software U·Sim simulates durability loads representing a vehicle’s entire design life (“virtual customers”) based on selective measurements on public roads. The key to the solution is to separate between (a) the exploration of the different operating states by appropriate measurements and (b) the recombination of these states based on usage models.

Example Projects

 

Optimal Track Mixing

During the validation of vehicles or components proving grounds are often used to generate well defined and repeatable loads within the vehicle. 

 

Simulation of Customer Loads for Control Units under Thermic Loading

Electronic components in vehicles, like control units, are affected by various different loadings, e.g. due to temperature changes, long stay at high temperature or simultaneous influence of temperature and humidity.

 

Load Data Analysis and Simulation for Excavator Development

In order to align their product development better with customer demands and make the whole design process more efficient, VOLVO CE has recently made a considerable investment into state-of-the-art methods for virtual product development (VPD).