LMS Supports Ford Otosan in Developing Accelerated Durability Testing Cycles
Executing extensive field tests to validate the durability performance of a vehicle is very expensive and time-consuming. This pressures OEMs to develop compressed testing cycles and to efficiently reproduce equivalent laboratory tests. In addition, durability engineers have to gain a precise understanding of the loads that the vehicle will undergo during its lifetime to guarantee valid fatigue performance testing. Ford Otosan and LMS engineers developed a compressed durability testing cycle for Ford Otosan’s new Cargo truck. LMS engineers performed dedicated data collection, applied extensive load data processing techniques and developed a 6- to 8-week test track sequence and 4-week accelerated rig test scenario that matched the fatigue damage generated by 1.2 million km of road driving.
Ford Otosan is a joint venture between Ford and Koc Group with each company holding a 41% share and the remaining 18% share publicly held. The joint venture has headquarters in Kocaeli and employs over 7,300 people in engineering, manufacturing, sales and marketing, and parts distribution. Last year, the company sold 137,631 vehicles and generated revenues of 1.817 billion euros. The new Cargo model was introduced last year and its popularity has helped the company increase its market share of the heavy truck market from 16.4% to 22%. Ford Otosan is in Turkish market with a wide range of vehicles; A class Ford Ka to 40 tonner Ford Cargo The Cargo Cabin is produced at a new plant in Kocaeli and assembled at Inönü Plant.Meeting 1.2 million km durability requirement
One of the critical pre-launch requirements for the Ford Otosan Cargo was passing a structural durability test equivalent to driving 1.2 million kilometers on Turkish roads without experiencing any cracks in critical suspension, frame, and cab systems. Even if the truck were to be driven at 1000 km per day, it would take nearly three years to complete this test in road driving road. Ford Otosan decided to involve an external engineering partner to establish an accelerated proving ground test scenario that matches the fatigue damage that the truck experiences throughout its lifetime. Ford Otosan selected LMS for its capabilities and experience in durability field-testing, load data analysis, and test schedule development for virtual simulation and durability track and rig testing. Compressing the time histories
Ford Otosan provided a predecessor truck that had been modified to closely match the newly model. Ford Otosan collaborated with LMS to map out a route through Turkey that represented the typical usage of the vehicle. Mapping out these data collection scenarios represents a critical step in the overall process, since the collected data will form the basis for loading scenarios that represent a large spectrum of driver profiles and road types. LMS engineers instrumented the vehicle with strain gages to estimate 3D forces at all cab mounting positions, and accelerometers on each hub and the cab mounts. They measured the wheel to chassis vertical movement at each wheel and the cab motion in three axes at the mounts, for a total of about 50 channels. The selection of channels was critical in order to instrument the vehicle to record all the relevant load information. LMS engineer collected data driving over 5,000 km and consolidated the resulting time histories using LMS TecWare load data processing software to eliminate spikes, drifts, sensor failures and other anomalies.
LMS engineers used the same software to conduct rainflow data analysis by counting pairs of reversals of loads or accelerations, which indicate material fatigue damage. They displayed the results in a rain flow matrix format that showed how often events of particular amplitudes occur and extrapolated the data to estimate the damage generated by road testing over the full 1.2 million kilometers. This extrapolation was based on Ford Otosan’s targeted weighting mix of 60% highway, 30% local roads, and 10% city driving. The goal was to achieve the full 1.2 million kilometers without any cracks in the major components of the vehicle.
Since one of the objectives of the project consisted of defining an accelerated schedule for proving ground testing, LMS engineers had to create a reference database of rainflow matrices for the proving ground. After the field tests in Turkey, the test vehicle was shipped to Belgium where LMS engineers re-instrumented the vehicle exactly the same way as in the road tests and ran it on the Ford proving ground in Lommel, Belgium. They collected road load data for each of the test surfaces on the proving ground and then converted the time histories to rainflow matrices using the methods described above. At this point, LMS engineers had created the two reference databases consisting of rainflow matrices, one representing Turkish roads and the other the test track.
Defining the test sequence
The next phase aimed at calculating the optimal mix of test track sequences and events that match the 1.2 million km target. For example, these analyses might determine that 200 passes on the Belgian blocks, 70 potholes and 50 off-road circuits are required. The LMS TecWare Test Schedule Definition software enables the LMS project engineers to set specific objectives for the load sequences, such as minimizing the time required to perform the tests or achieving the best correlation regardless of the time involved.
LMS TecWare took each of the channels of load information into account to ensure that the damage content is equivalent for each channel between the test track and road load matrices over the entire period of the test. Another constraint was to ensure that, for example, the early part of the test track sequence doesn’t overstress one particular area and cause a premature failure that in the road load sequence would not be seen until the end of the test.
Throughout the overall project, LMS engineers developed load sequences that achieved a time reduction of a factor of 100, while keeping a sufficient correlation to the target. As a net result Ford Otosan was able to perform the complete test sequence in less than eight weeks of proving ground testing.
Running accelerated testing
Having closed the test schedule preparation job, LMS and Ford Otosan continued their joint project into running the defined test series on the track and assessing the vehicle’s fatigue resistance. The vehicle was inspected at regular intervals to see if any cracks had appeared. LMS engineers documented each failure with a description and photographs and provided them to Ford Otosan engineers who used them to improve the design to fix the problems and build a new prototype. After several build and test cycles, Ford Otosan had modified the design to the point that it passed the test track sequence without any failures.
In parallel, LMS engineers also used the proving ground test schedule to create a sequence to test the truck cabin on a 4-poster durability test rig. Testing the cabin on such a durability rig makes it possible to optimize its fatigue performance before proving ground testing, since the physical prototype of the truck cabin becomes available before the full-vehicle prototype.
Testing the cab on a rig also is faster because it eliminates the downtime experienced on the test track, such as for making repairs to secondary systems not covered by the test. In this project, the cabin test took under four weeks, about half the time required for the proving ground test cycle.
Reliable fatigue testing
Accurate load scenarios for durability engineering are critical to reliable durability assessments. Any inaccuracies may result in either unnecessary cost and weight associated with over-dimensioning the structure or the risk of customers experiencing failures. On this project, LMS engineers developed a target durability test track sequence that accurately replicated the excitation of the actual road in one-hundredth of the time that would have been required for road testing.
LMS engineers performed the complete test preparation cycle for Ford Otosan, from preparing the data collection tests, instrumenting the vehicle, performing tests on both local roads and the test track, processing the road load histories to meet the customer’s durability objective, up until developing test sequences for both the track and rig. The resulting proving ground and rig testing scenarios accurately replicated the excitation of the actual road in one-hundredth of the time that would have been required for road testing.