Ford is accelerating and improving the durability engineering process by using LMS TecWare to optimize the use of load data in every step of the durability engineering process. Formerly, TecWare entered the process at the physical prototype stage, where it was used on test rigs to optimize the durability scenarios developed from road load test data. More recently, LMS TecWare has been applied to speed up the virtual durability-engineering loop at Ford, optimizing full-vehicle multibody simulation. LMS TecWare also plays a role at the critical point between the durability sign-off and the final vehicle sign-off, when last minute optimization for NVH or other performance attributes calls for a change to the design.
More accurate and realistic load scenarios for test-based engineering
The unique TecWare technology extracts only the most relevant information out of long time history data sets. It trims the load history to a minimum by scripting the durability scenarios using only those events that are strictly relevant to design targets. Ford can go even further, TecWare also eliminates the data about surfaces that are non-damaging and builds scenarios only around the damaging events. TecWare can judge an event’s damage content based on a number of variants of the same event - such as driving through a pothole. Typically, 2 out of 10 variants can be selected as being representative of the type of damage that would be incurred. These data selection techniques keep schedules as short as possible, using Ford’s test time more efficiently, and optimizing the expensive test hours on the test rigs.
LMS TecWare not only reduces the test schedules and scenarios, it dramatically increases the accuracy of the scenarios, and therefore the “real life” relevance of the tests performed on the rig and in virtual simulations. To deliver this critical heightened accuracy, LMS TecWare implements multi-axial rainflow-counting. This technique goes beyond the typical uni-axial methods and takes into account the phase relationships that exist between the vertical, lateral and longitudinal spindle loads. This phase information needs to be represented in the load scenario in order for it to be fully realistic. It is therefore critical that the phase information is kept even when the original load scenario is drastically reduced in time. Without the phase information, the derivative test schedules could lead to over-testing, or much worse, dangerous under-testing of the prototype on the test rig.
Test-based load scenario definition for simulations
Ford is progressively including more numerical models in the design process to simulate the effect of design variations on the durability of the full vehicle. These virtual simulations save precious time in the development process, and economize on expensive prototype testing on the rigs or the track.
Although durability simulation on the level of single components is straight-forward, virtual durability assessment on the level of the full vehicle is not so evident. You need complex, full-vehicle multibody simulation models to accurately predict the load interfaces between the numerous components. These models are difficult to make, and the simulation calculations are long - taking into account realistic durability load time histories.
To solve this calculation bottleneck, Ford applied the same TecWare capabilities that they used to prepare their test load schedules. They trim the time histories to suit the durability target of the simulation.
Virtual durability simulation relies just as heavily on the accuracy of the loading data as does a physical test. The only difference is that the loading data are applied to FE-models for numerical life prediction. Therefore, TecWare’s multi-axial rainflow-counting is also used here to make sure that the dramatically reduced durability scenarios still fully represent real life conditions, and to prevent over- or under testing of the virtual model.
Decision support for late design changes
Although late design changes after the durability sign-off of the prototype should be avoided altogether, in reality they still happen due to unpredictable NVH or Handling issues. In late prototype stages, the vehicle is severely tested to make sure that the targets in other key attribute areas such as the handling of the vehicle, the interior sound quality and overall vibration comfort are met. Very often, small design changes are applied to optimize these attributes on the level of bushing characteristics or the stiffness of roll bars, to optimize NVH or Handling performance.
For each of these late design changes, durability engineers must decide whether their final “go-ahead” is still valid. Considering that at this point the development process is already closing in on the actual launch of the vehicle, doing additional testing is not really an option. A new virtual simulation loop – could take a couple of weeks – even with the load scenarios optimized with LMS TecWare. So, even doing a new virtual signoff could delay the launch of the vehicle. Omitting virtual durability validation could be very unsafe and create a huge risk of expensive product recalls.
Ford uses TecWare as a decision support tool to resolve the dilemma. After a quick test with the newly adapted prototype on the test track, Ford engineers do a quick comparison of key damage information taken before and after the late design change. The spindle load data measured with wheel force transducers before and after a late design change are rendered as load influence spheres in LMS TecWare. Side by side comparisons in TecWare of the load influence spheres show at a glance whether the durability loading has changed its damage content significantly enough to warrant a repeat of the simulations. Again, the phase information between the different load channels is considered at all times. Through these visual comparison techniques, LMS TecWare enables the engineers at Ford to see if the changes in loads due to a design change are great enough to warrant more durability simulations or even indicate the need for a new physical prototype test. Ford reported that by using the LMS TecWare tool to assess the need for repeating the full validation process, they have been able to reduce their time-consuming full-vehicle durability virtual simulations, and to avoid very time consuming and expensive physical validation testing.
