China FAW Co., Ltd. R&D Center is the largest research, development, test and inspection facility for the automotive industry in China, and is a key technology center for both OEM FAW Group Corporation and the Chinese government. The company focuses on product innovation while developing commercial vehicles, such as passenger cars, minivans, buses and trucks, as well as automotive components. Engineering expertise covers the entire vehicle development cycle.
Durability strongly influences perceived vehicle quality. It is more than a crucial selling point. Customers take it for granted that their cars will survive for approximately 300,000 kilometers, or their trucks will withstand a rough operational environment. But trends in the automotive industry to launch more vehicle variants, as well as minimize weight in view of fuel economy demands, challenge engineers to deliver robust, high-quality vehicles ontime and at an attractive price. So-called “design by experience” leads to recurrent prototype testing and very long and expensive development cycles. Therefore, automotive original equipment manufacturers (OEMs) and their research centers look for new durability engineering technologies, including simulation that frontloads design decisions and delivers better performance from the first prototype.
Crucial to successful fatigue life predictions is defining correct road loads and understanding how they affect individual vehicle components. Calculating those analytically is challenging, especially with the presence of active suspension systems. Measurement data is usually either only partially available, or not at all during the concept phase. Over the years, multibody simulation has been advanced as reliable technology to accurately calculate road loads. Several methodologies exist to handle different levels of model complexity and available measured data.
Siemens Digital Industries Software has developed a full computer-aided engineering (CAE) approach, called the “digital test track,” as well as a combined test and CAE approach. The latter, included in motion software from the Simcenter portfolio, is based on time waveform replication (TWR), originally a test technology for exact re-creation of measured field data on a laboratory shaker system. This process helped China FAW Co., Ltd. R&D Center substantially cut the development time of a recent commercial truck.
The Center is the biggest research, development, test and inspection facility for the automotive industry in China. This key technology center for both OEM FAW Group Corporation and the Chinese government focuses on product innovation while developing commercial vehicles, such as passenger cars, minivans, buses and trucks, as well as on automotive components. Its engineering expertise covers the entire vehicle development cycle, from styling and design, to simulating and testing several functional performance aspects, to computer-aided manufacturing (CAM). To implement a more efficient and reliable durability engineering approach, specialists from the Center decided to collaborate with experts from Simcenter Engineering and Consulting and afterwards deployed a complete, integrated software solution.
“We had issues with damage in components, such as the fracture of critical parts in the front or on local areas of the body,” says Xin Yan, CAE engineer in the Body Department of the Center, specializing in cabin development for commercial trucks. “We used to design the cabin based on static analysis and using our experience. But in this way, we often had fatigue damage while testing the prototypes. That meant that we had to modify the structure recurrently, which lengthened the development cycle. Thanks to our collaboration with Siemens Digital Industries Software, we could investigate the problem of fatigue cracking, and we could deploy a simulation process that allowed us to accurately describe road loads and optimize the structure for durability. The driver’s cabin prototype of the first commercial truck we developed using Simcenter solutions immediately met the durability requirements during the first test.”
The employed TWR-based approach offers engineers a pragmatic way to include test track measurements in simulation for the road load prediction, starting from any type and number of tested data. The process replicates a laboratory vehicle road load test using an unconstrained multibody model and the experimental data as boundary condition, and yields back-calculated equivalent drive signals through an iterative control technique. By computing these drive signals for the wheel centers, motion software from the Simcenter portfolio avoids the need to model complex elements, such as dedicated tire models, digitized roads and driver models, which usually takes a lot of time. The simulation corresponds to a durability test rig. The motion simulation solution from the Simcenter portfolio features a powerful and accurate solver and dedicated modeling functionalities such as flexible bodies, as well as active suspension components with their controls through co-simulation with Simcenter Amesim™ software. The software calculates the individual component loads for further use in a simulation with durability software from the Simcenter portfolio.
“The implementation of this new process started through collaboration with Simcenter Engineering and Consulting experts,” says Xin Yan. “We did measurements on the track for road load data acquisition. The enormous amount of data resulting from this campaign was processed in Simcenter Tecware to get the load data for simulation.” This software package helps engineers efficiently validate and understand gigabytes of raw mobile testing data. The data signals are consolidated by various operations, such as removing anomalies, filtering, deriving new channels based on mathematical operations and many more. In this way, the data is ready for further use in simulation. Simcenter Tecware allows subtracting durability-specific content and contains a wide range of dedicated data interpretation methods to help efficiently qualify and quantify the load data durability potential. The data can be readily imported into motion simulation solution from the Simcenter portfolio.
In the next step, the engineers built a multibody model of the commercial truck, including the cabin and the mounting system. “The motion simulation solution from Simcenter portfolio is very user friendly,” says Xin Yan. “Moreover, we received very good training and daily help from the local support team. With their help, we can easily build the multibody model and calculate the drive signals, and in the next step the component fatigue loads.” The Center’s engineers were impressed by the performance and the capabilities of TWR module in the motion software. “The twist road event we wanted to replicate is a difficult case, because the low-frequency behavior is very dominant, and that can complicate convergence in a time-domain iterative process,” says Xin Yan. “But the powerful algorithm in the software can handle this very well. On top of that, our model was very detailed and could even include an accurate physical description of the air springs between cabin and suspension thanks to co-simulation with Simcenter Amesim.”
By combining the calculated component fatigue loads with material curves, cyclic fatigue parameters and stress results based on finite element analysis (FEA), durability simulation solution from the Simcenter portfolio can accurately determine critical fatigue areas and assess the expected fatigue life. “The software has very specific modeling features for spot welds and seam welds, which are typically areas sensitive to fatigue,” says Xin Yan. “And, by using dedicated postprocessing functions, we can quickly identify and solve problems.” The entire process can be parametric, allowing experimentation with multiple design options and structural optimization. Xin Yan explains, “We especially appreciated the integration of the entire process chain. That makes this solution very effective. When designing the commercial truck, the prototype of the driver cabin immediately passed the 8,000 kilometer durability test. Using the same process, we have also solved some other problems. We found the solution for fatigue cracking of the front part that belongs to an off-road vehicle, and for fatigue damage in mounting systems.”
An extra and critical advantage of this TWR-based durability engineering process is that the drive signals calculated can be recovered for a different vehicle development process because these loads are invariant. This is very useful in the early design stages of a new vehicle, when no prototype is available, hence no testing can be done. It allows frontloading durability engineering to the very early phases of the development process. “It is part of our intent to completely break with our former procedures and to make this approach the standard one in our company,” says Xin Yan. “In that context, we want to set up a load spectrum for common use. This will be used as a reference for all research and development activities in the field of fatigue analysis, and will drastically reduce the time we spend on data acquisition in the future.”
FAW engineers plan to further deploy the simulation-based fatigue analysis process and explore more capabilities. “In the Chinese automotive industry, we are a pioneer in this area, and we want to keep this leading position,” says Xin Yan. “In practice, that means that we will start investigating fatigue problems in non-metal materials and optimizing the fatigue life of shock absorption systems. We want to achieve the highest possible precision, because reliable durability simulation helps us control the length of the development cycle. That enables us to bring our products earlier to the market than our competition.”
Successful projects have proven him correct. “Thanks to the use of Simcenter solutions from Siemens Digital Industries Software, we cut costs during the development of the commercial truck by 20 million rmb,” says Xin Yan. He concludes, “The new durability engineering process brought us two awards. We won second prize in the ‘China Award of Science and Technology – Automotive Industry’ contest, and first prize in the ‘FAW Group Technology Innovation Prize’ contest.”