DAF Benefits from Research Project FATYNAMICS
DAF trucks, part of the PACCAR Group of companies, is based in Eindhoven in the Netherlands and produces around 25,000 trucks a year, primarily for the European market. In addition to the routine vehicle designs for medium and heavy road transport, DAF also actively seeks out and fulfils the needs of specialist markets – for example, vehicles that carry flowers from Holland to other parts of Europe.
Having many variants causes a challenge for the design department: each vehicle must be tuned to minimize weight in order to compete with other manufacturers on payload and consequently transport efficiency – yet the vehicle must meet design life targets of over 1.2 million kilometers. Since 20% of the design effort is spent on durability engineering, being able to get the process faster and more reliable was one reason why DAF joined the international research project, FATYNAMICS.
Design to Meet Customer Needs
European road patterns are variable and the laws for trucks are different in each country: permissible axle loads for instance. This leads to many design variants to be developed for different markets and applications. Furthermore,more severe circumstances due to the growing communication with Eastern Europe make accurate customer assessment more difficult. Traditionally, DAF estimated design loads resulting from road surface roughness by combining local knowledge about pavement types with a reference photograph album. This would lead to an expression of vehicle service loads in terms of mileage traveled on a number of reference road surfaces. Back in Eindhoven, this data could be related to so many kilometers (typically 8000) of pave on the DAF test track or a test-rig equivalent. In effect, a million miles of customer usage can typically be simulated in a week. The effort of tailoring a design to actual customer usage rather than the use of a design ‘cookbook’ leads to lighter and better-engineered designs. But how accurate was the existing process, could it be improved, and what factors are important anyway?
FATigue dYNAMICS - FATYNAMICS
Due to the relatively large size of trucks on the one hand and the relatively slender build of the truck chassis on the other, the fatigue life of truck components is largely determined by the structural resonances of the chassis. For this reason, and due to strong requirements for reliability and safety, truck manufacturers and their suppliers spend a lot of time and money optimizing and verifying the fatigue life of new truck designs. An additional complication for truck development is the wide range of circumstances, such as varying loads and road conditions,and the large number of variants within a product line (wheel bases, engines, cabin dimensions, number of axles) affecting the dynamic
behavior and consequent durability of trucks. The FATYNAMICS project aimed at improving the design process by developing and implementing new methods for testing and analysis. Improving the accuracy of both numerical and experimental simulations was an important aspect, but considerable emphasis was also placed on reducing the time, cost and effort required for fatigue assessment in the modern truck development process.
In the context of a European-funded BRITE EURAM framework, LMS, DAF, Renault Vehicules Industriels (RVI), Monroe, Phoenix, and the University of Leuven worked on the FATYNAMICS project for three years.
It involved five areas of interest:
- to design a load analysis system allowing incorporation of durability
experience from previous and similar designs. As a direct consequence of
the FATYNAMICS project, LMS TecWare Durability Data Management product Revision 2.10 now incorporates these features.
- to develop and implement methods and tools to efficiently optimize
structures for durability early in the design process, using purely numerical or hybrid numerical/ experimental structural models of the truck and representative load histories. As illustrated in a previous LMS Newsletter, LMS FALANCS with modal super-position was used to successfully optimize a dashboard support for RVI. LMS Gateway and LMS OPTIMUS were used in this context to correlate and update some of the numerical models of DAF.
- to develop tools for the design of accelerated endurance tests on test
tracks or test rigs that are equivalent to normal service life fatigue, using
numerical durability analysis methods. These tools also needed to feed time-compressed loads back into the numerical analysis tools. LMS CombiTrack was extended to allow this and was used to develop test scenarios for Monroe’s cabin shock absorbers.
- to implement methods to derive truck-independent drive signals for a fatigue test on vehicle vibration test rigs (road simulators) to accommodate the truck industry specific problem of multiple variants.
- to tightly link all elements into a concurrent engineering approach for
durability optimization of trucks.
During the FATYNAMICS project DAF bought LMS CombiTrack to synthesize a test schedule that must be reproduced on the test track. CombiTrack eliminates any guesswork by calculating the optimum mix of basic test track sections that match the target. It will automatically determine, for example, that 3 passes of Belgian block, 6 pot-holes and 2 off-road circuits are required. Frequency information can be controlled as well. This is important for tests on complete truck sub-assemblies and suspensions – or for full vehicle and spindle-coupled systems.
CombiTrack not only allows us to improve customer correlation of defined test profiles, but to also explain where the difference lies and what needs to be changed or added to the test scenario. “CombiTrack does the job really well,” said Senior Test Engineer Simon De Cock. “We’re happy with the user interface, it does what we want very quickly. We are much more specific about where errors lie. Over-testing for certain components will remain inevitable. However, for these components, over-testing has been reduced now to a factor of two or three at the most.”
Finally, in order to optimize the vibrational and fatigue behavior of a new truck design consisting of an existing truck frame and a new engine, the LMS FRF-Based1Substructuring (FBS) product was used to1develop a hybrid model consisting of1numerical models of the engine and engine suspension and an experimental (FRF) model of an existing chassis.
“FATYNAMICS” was very successful,” according to Henk Voets, Manager of the CAE department at DAF. “We’ve developed new technologies, validated them in real-life conditions, and we’re beginning to deploy them in our development process.” DAF has been able to save process time. The design loads are much more aligned to the 95 percentile customer, resulting already in a 165kg weight reduction for the recently introduced new DAF CF series.
