Review 2021 - FEMFAT LAB​​​​​​​​​​​​​​

Design of powertrain mounting bracket is always a challenge in achieving good NVH characteristics and durability with less weight. For this activity engine mount load is necessary to optimize the weight to meet durability and NVH targets. This paper introduces a new method to calculate engine mount loads from chassis accelerations. The method starts by measuring chassis acceleration near engine mount location, then reproducing the same chassis acceleration in Multi Axis Shaker Table (MAST), and finally extracting the load in engine mount using testing (using load cell). 

The MAST test actuator displacement input is imported into ADAMS and engine mount loads are extracted. The extracted loads are correlated with physical test results. The correlation includes load time history and peak-to-peak load range. It is recommended to implement this method in early vehicle design phases.

Implementing engine mount bracket weight optimization is desirable in early design stages.  To avoid MAST testing and then MAST simulation based on road load data, FEMFAT virtual iteration and MSC.ADAMS integration helps us to integrate the road load data into MAST input data. It is a promising methodology to facilitate data-driven design decisions to be made at early stages of the vehicle development cycle.

In this speak, the analysis process of the the durability of the cab is introduced with the airspring suspension cab of a commercial vehicle as an example, mainly including road load spectrum acquisition at proving ground, equivalent load cases, load spectrum signal processing, multi-body dynamics model establishment, virtual iteration and model improvement, fatigue load extraction, fatigue durability calculation. At last, comparison of simulation life and test value at fatigue crack. Therefore, the reliability of load extraction and fatigue calculation is verified.

Development of structural strength and durability, data processing and analysis, development of Bush performance load spectrum, virtual iterative decomposition of vehicle load, research and application of equivalent road shape in load prediciion development, etc.

In order to improve the endurance performance of the pickup truck, the fatigue life analysis of the truck frame was carried out by the virtual iteration technology. The load iteration and output were completed by FEMFAT_LAB software. The fatigue life analysis was completed by the nominal stress method in FEMFAT software, and the simulation results were benchmarked with the vehicle road durability test results to form a closed cycle of simulation analysis.

The CAE is now a well-known and required steps in vehicle development. The virtualization is growing, and more and more focus is made to get more accurate load definitions at earlier design stages. This is to avoid the mistakes and redesign loop at hardware stage. For calculation of the durability of the vehicle body and suspension components usually some simpler forces are used at early stage. Here the Full MBD vehicle model is used and run in different road and load operating conditions. The Pseudo Damage and total damage evaluation is used to calculate the total damage and then the real damage has been calculated to compare if the prediction is good. A good coloration of Pseudo Damage has been observed between calculated damage and Pseudo Damage. This leads to a much shorter simulation and enable a better lifetime evaluation at early design stage.

​​​​​​​Accurate input of fatigue load is the key of structural fatigue durability evaluation.In order to accurately evaluate the fatigue endurance performance of the front axle of a commercial vehicle, the road spectrum of the test field was collected by using a six-component dynamometer and an acceleration sensor. The rigid-flexible coupling dynamics model of the vehicle was established, and the corresponding response channels were set in the multi-body model according to the actual placement of the sensors. Then Femfat Lab software was used to carry out virtual iteration on each strengthened road surface in the test site to extract the load at the front bridge attachment point.The results show that the iterative signals and the measured signals have good consistency in the time domain under various road conditions, and the damage recurrence ratio is between 0.5 and 2.The value of the load history is within the normal range, and the fatigue load extracted is used for life analysis, and the result is in line with the expectation.

Because of the large motor torque and rapid response of electric vehicles, the mount force is generally large. Therefore, it is necessary to pay more attention to its durability during the mount development process. The mount rubber is difficult to verify the durability due to its super-elastic properties. At present, the durability of mount bushes is mainly verified by test methods, because most of the mount bushing parts tests are based on the GM load cases and related classic load cases, the correlation with the vehicle verification condition is poor, so in previous projects, there were many cases of the bush that passed the component verification, but cracked in the vehicle durability road test, Therefore, there is an urgent need for a set of effective mount verification conditions to fully verify the mount bush in the early stage In this example, the mount load is solved by the virtual iterative method, based on the measured signal of the mount road spectrum, and the iterated load is used in the mount component test, thus effectively identify and avoid risks in the early stage of the project, and avoid failure problems such as cracking of the mount bushing in the later vehicle durability test.